Physical Results of Research Drilling in 

Thermal Areas of Yellowstone National 

Park, Wyoming 

By D. E. WHITE, R. 0. FOURNIER, L. J. P. MUFFLER, 

and A. H. TRUESDELL 

GEOLOGICAL SURVEY PROFES SIONAL PAPER 892 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1975 

10 Jllll ~,~ 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Physical results of research drilling in thermal areas of Yellowstone National Park, Wyoming. 

(Geological Survey Professional Paper 892) 

Bibliography: p. 69. 

Supt. of Docs. No.: I 19.16:892 

1. Geothermal resources-Yellowstone National Park. 2. Boring-Yellowstone National Park. I. White, Donald Edward, 1914- II. Series: 

United States. Geological Survey. Professional Paper 892. 

GB1025.W8P49 553 74-28233 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-02602 
CONTENTS 

Page 

Abstract 1 

Introduction______ _____ _______ _______ ____________________ ___ 1 

Scientific objectives ------------------------------------ 2 

Scope of this report ------------------------------------ 3 

History of the program______________ _____ ___ ___ _________ 3 

Drilling equipment and procedures _____ ____ ____ __ ____ ___ 3 

Scientific data acquisition ------------------------------ 7 

Definition of terms________ _____________ ____ ___ ___ _______ 9 

Acknowledgments _ _ _ _ _ _ ____ ___ _ _ _ __ ____ _ _ _ _ ___ _ _ __ _ _ _ _ _ 11 

Upper Basin and Upper Firehole River __ ___________________ _ 11 

Y-1 (Black Sand Basin) drill hole _____ __ ___ _____ _____ ____ 11 

Y-7 (Biscuit Basin I) drill hole _______ _____ ____ ___ _______ 15 

Y-8 (Biscuit Basin II) drill hole ________ _____ ________ _____ 17 

Horizontal "self-sealing" and circulation pattern 

between Y-8 and Y-7 drill holes ______________________ 22 

Carnegie I drill hole, Myriad Group ____ _____ ____ __ _______ 22 

Y-6 (Lone Star) drill hole, Upper Firehole River __ ___ ____ _ 25 

Lower and Midway Basins ---------------------------------- 28 

Y-2 (Firehole Lake) drill hole _______ ________________ ___ 28 

Page 

Lower and Midway Basins-Continued 

Y-3 (Ojo Caliente) drill hole -------------------------,---- 34 

Y-4 (Nez Perce) drill hole ------ ------------------------ 38 

Y-13 (Porcupine Hills) drill hole ______ _______________ ___ 41 

Correlation of data from Y-4 and Y-13 drill holes ___ _____ 45 

Y-5 (Rabbit Creek) drill hole---------------------------- 48 

Norris Basin _____ ______ __ -'-- ____________________ ____ _____ - 49 

Y-9 (Norris I) drill hole - --------------------- ---------- 49 

Y-12 (Norris II) drill hole ------------------------------ 54 

Carnegie II (Norris) drill hole ____________ ______ _____ ___ 57 

Summary of subsurface relations, Norris Basin, and 

changes induced by the drill holes ___ ______ ____ ________ 61 

Mammoth Hot Springs ____ ___ __________ _______ ____________ ___ 63 

Y-10 (Mammoth Terrace) drill hole ___________ ________ __ _ 63 

Mud Volcano area ------------------------------------------ 65 

Y-11 (Sulphur Cauldron) drill hole ---- ~--------- ------ -- 65 

Conclusions ________ _____ ________ ___ __ ________ _______ __ _ --- 68 

References cited _______ ___ __ ____________ __ _________________ - 69 

ILLUSTRATIONS 

Page 

FIGURE 1. Map of Yellowstone National Park, showing major geothermal areas and sites of research drill holes _~ -----~ ---- --------- 3 

2. Photographs of truck-mounted diamond-bit coring equipment used in Yellowstone Nation~;~.J Park- ~---,-------- ----- ---- 3 

3. Photograph of valve, return water "tee," and stuffing box, ,.Y-2 drill hole, Firehole Lake __________ ---,.------------------ 4 

4. Photographs showing eruptions from drill rods _________ ________________ ___________________________________ _____ __ _ -- 6 

5. Photograph of Y -8 drill hole after completion __________ ___________ __________________________________ _________ ______ - 7 

6. Graph showing recovery of bottom-hole temperature in Y-1 (Black Sand) drill hole when depth was 100ft --------------- 8 

7. Photographs of apparatus used to measure tetnpGratures at Y-1 drill hole as drilling progressed ---------------------- - 9 

8. Graph showing temperatures and other data, Y-1 drill hole, Upper Geyser Basin ______ __________ ---------------- ----- 14 

9. Diagram showing preferred explanation for differences in gage pressure recorded in Y-1 drill hole and its redrilled 

lower segment, Y -1x _ __ _ __ ___ _ __ __ _ _ ___ ___ __ _ _ _ _ __ __ __ _ _ _ __ ___ _ _ _ __ ____ _ _ _ ___ __ _ _ _ __ ___ __ _ _ _ _ _ _ _ __ _ __ _ _ _ _ _ __ __ 15 

10. Graph showing temperatures and other data from y..:..7 (Biscuit Basin I) drill hole, Upper Basin ____ -- -- ---- ------ ---- 17 

11. Graph showing temperatures and other data from Y-8 (Biscuit Basin II) drill hole, Upper Geyser Basin ______________ _,.__ 19 

12. Graph showing in-hole temperature and pressure, Y-8 drill hole after completion, with other reference.c1,1rves · --------- 20 

13. Section through Y-7 and Y-8 drill holes, showing pressures, temperature contours, and deduced self-sealing by deposition of hydrothermal minerals in originally permeable ground -----------------------------------------------,.--.. 21 

14-24. Graphs showing: 

14. Temperatures and other data from Carnegie I drill hole, Myriad Group, Upper Basin ---'-",-- --------------------- ~4 

15. Temperatures and other data, Y-6 (Lone Star) drill hole, Upper Firehole River --------------------------------- 26 

16. In-hole temperatures and pressures of Y-6 drill hole after completion ---- --------------------------- ---------- 27 

17. Temperatures and other data, Y--2 (Firehole Lake) drill hole, Lower Basin -------------------------------,---.;--- 29 

18. In-hole pressures of Y-2 drill hole after completion, compared with other data ------------ --------------------- 33 

19. Temperatures and other data, Y-3 (Ojo Caliente) drill hole, Lower Basin _________________ ___ ____ ____ ___________ 36 

20. In-hole temperatures and pressures of Y-3 drill hole after completion ------------------------------------------ 37 

21. Temperatures and other data, Y-4 (Nez Perce) drill hole, Lower Basin -------- --------------------------------- 39 

22. In-hole temperatures and pressures of Y-4 drill hole after completion, compared with other data ________________ _ 40 

23. Temperatures and other data, Y-13 (Porcupine Hills) drill hole, Lower Basin ______________ ____ _________________ 43 

24. In-hole temperatures and pressures of Y- 13 drill hole compared with reference curves ____ __ ____ ___ ____________ 44 

25. Section through Y-13 and Y-4 drill holes, Lower Basin, showing initial temperature contours, wellhead water pressures, and some hypothesized relationships _ ___ _____ _ _ _ __ _ _ _ _ ___ _ _ _ _ _ _ ___ _ _ _ _ _ _ __ _ _ ___ _ _ _ _ _ __ _ __ _ _ _ _ _ _ _ ___ _ _ _ _ __ 4 7 

26-31. Graphs showing: 

26. Temperatures and other data, Y-5 (Rabbit Creek) drill hole, Midway-Lower Basin ___________ ____ _______ _______ _ 50 

27. Temperatures and other data, Y-9 (Norris I) drill hole, Norris Basin ___ _________________________ _________ ______ 52 

III 
IV CONTENTS 

FIGURES 26-31. Graphs showing-Continued 

Page 

53 

56 

58 

60 

28. In-hole pressures ofY-9 drill hole compared with other referenCe curves__________________ -------------------

29. Temperatures and other data. Y-12 (Norris ID drill hole, Norris Basin-----------------------------------------

30. In-hole temperatures and pressures of Y -12 drill hole after coljlpletion, compared with other data---------------

31. Temperatures and other data, Carnegie IT drill hole, Norris Ba8in ---------------------------------------------

32. Vertical section through Norris Basin drill holes Y-9, Carnegie IT, and Y-12, showing bedrock, measured bottom-hole 

temperatures, and inferred temperature contours ---------------,------------------------------------------------

33. Graph showing temperatUres and other data. Y-10 (Mammoth Terrace) drill hole -------------------------------------

62 

64 

34. Graph showing 67 temperatures and other data, Y-11 (Sulphur Cauldron) drill hole, Mud Volcano area -------------------

TABLE 1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

15. 

16. 

17. 

TABLES 

Page 

Casing diameter, bit diameter, and core diameter used in Yellowstone drill holes -------------------------------- -4 

Temperatures, pressures, and other observations from Y-1 (Black Sand) drill hole, Upper Basin, Yellowstone National 

Park ---------------------------------------------------------------------------------------------------- 12 

Summary of physical data of all research drill holes in Yellowstone National Park ________________________________ 13 

Temperatures, water levels, and other observations from Y-7 (Biscuit Basin D drill hole, Upper Basin------------- 16 

Temperatures, pressures, and other observations from Y-8 (Biscuit Basin ID drill hole, Upper Basin ________________ 18 

Temperatures, pressures, and other observations, Carnegie I drill hole, Myriad Group, Upper Basin (reported by 

Fenner, 1936 ---------------------------------------------------------------------------------- ~~~------- 23 

Temperatures, pressures, and other observations from Y-6 (Lone Star) drill hole of the Upper Firehole River ______ 25 

Temperatures, pressures, and other observations from Y-2 (Firehole Lake) drill hole, Lower Basin ---------------- 30 

Temperatures, pressures, and other observations from Y-3 (Ojo Caliente) drill hole, Lower Basin ------------------ 35 

Temperatures, pressures, and other observations from Y-4 (Nez Perce Creek) drill hole, Lower Basin· ---- -------- 38 

Temperatures, pressures, and other observations from Y-13 (Porcupine Hills) drill hole, Lower Basin ------------ 42 

Temperatures, pressures, and other observations from Y-5 (Rabbit Creek) drill hole, Midway-Lower Basin -------- 49 

Temperatures, pressures, and other observations from Y-9 (Norris D drill hole, Norris Basin---------------------- 51 

Temperatures, pressures, and other observations from Y-12 (Norris ID drill hole, Norris Basin -------------------- 55 

Temperatures, pressures, and other data from Carnegie II drill hole, Norris Basin -------------------------------- 59 

Temperatures, pressures, and other observations from Y-10 (Mammoth Terrace) drill hole ------------------------ 63 

Temperatures, pressures, and other observations from Y-11 (Sulphur Cauldron) drill hole, Mud Volcano Group ---- 66 

CONVERSION FACTORS 

[English units of measurement are used in this report. em:ept fur temperature, because all tables and figures were prepared and all drill mres were ID8I'ked and cataloged in these units) 

Length.: 1 inch = 2.54 centimetres 

1 fuot = 0.3048 metres 

1 mile = 1.61 kilometres 

Tempemture: OC = 5/9 (°F - 32) 

°F = 1.8 (OC) + 32 

Pressure: llb/in2 (psi)= 0.06895 bar 

= 0.06805 atm 

= 0.07031 kglcm2 

All pressures are absolute, with 11.1 psi (0. 78 kglcm2) added to gage pressures, even though actual ground-level air pressures range from 

11.5 psi at the Mammoth {Y-10) hole to 11.0 psi at the Mud Volcano {Y-11} hole. 
PHYSICAL RESULTS OF RESEARCH DRILLING 

IN THERMAL AREAS-OF 

YELLOWSTONE NATIONAL PARK, WYOMING 

By D. E. WHITE, R. 0. FouRNIER, L. J. P. MuFFLER, and A. H. TRUESDELL 

ABSTRAGr 

The shallow parts of geothermal systems are important for the 

understanding of total systems, but commercial geothermal drilling 

has focused almost entirely on target depths of 2,000 ft and more. 

Previous drilling of the shallow parts of geothermal systems, primarily for research purposes, is known to have been conducted only in 

Yellowstone in 1929-30 and Steamboat Springs. Nevada in 1950--51. 

Yellowstone National Park contains a magnificent display of thermal 

features. unequalled elsewhere in the world, and thus the area is ideal 

for research drilling of natural hydmthennal systems essentially 

undisturbed by human activity. 

'l1rirteen research holes were drilled in the principal thermal areas 

of Yellowstone National Park in 1967-68. Depths of the holes ranged 

from 215 ft to 1,088 ft, and the total drilled footage was 6,802 ft. 

Bottom-hole temperatures were measured as drilling progressed. 

We conclude that most temperatures measured at the then-existing 

bottom after 8 hr of drilling and 16 hr for recovery are within 2"C of 

original ground temperatures prior to drilling. The drilled bottom is 

least affected by circulation of drill water and its temperature thus 

recovers the fastest. 

Most holes show a near-surface zone ofless than 100ft to more than 

250 ft characterized by a large rather linear conductive thermal 

gradient. Many rocks in this zone were initially highly permeable but 

lost most of their permeability because of hydrothermal alteration 

and deposition of silica and silicate minerals. This upper zone is 

bounded downward by the first aquifer in which significant convective 

flow occurs. 

Other aquifers of convective flow normally occur at greater depths. 

Temperatures there are generally close to the reference boilingtemperature curve, which is a computed curve that assumes a 

water-filled column up to the ground surface, with every point just at 

boiling (thus involving continuous variation in density of water with 

temperature). 

In each hole located in or near centers of upflow, the maximum 

temperature was measured at maximUm depth. Holes drilled on the 

borders ofupflowing systems showed lower gradients and, commonly, 

temperature reversals. The highest temperature, 237 .50C, was recorded at the bottom of our deepest hole, 1,088 ft, in Norris Basin. 

Most of our holes were drilled to depths close to 500 ft, with typical 

maximum temperatures near 2000C. 

With increasing depth, every hole showed an increase in static 

water level, generally rising from the initial water table a few feet 

below ground to 100ft or more above ground. The vertical water 

pressure gradients in all holes except one exceeded 110 percent of 

hydrostatic and ranged as high as 147 percent of hydrostatic in one 

hole in the Lower Geyser Basin. These extreme pressure gradients, 

not generally recognized in other geothermal areas, permit temperatures to exceed the simple boiling-temperature curve at depth, but all 

temperatures are at or below boiling for water at the existing pressures. In our shallow holes, we could not distinguish between true 

artesian pressure and thennoartesian pressure resulting from heating of water, with consequent the:rmal expansion. Thennoartesian 

pressure clearly is involved, but normal artesian pressure is not 

excluded. 

Two holes in Upper~ two in Lower Basin, and three (including 

one drilled by the Carn.egie Institution) in Norris Basin are close 

enough to each other to justify two-dimensional analysis of temperatures. pressures, and convective flow. In each of the three sets, one 

hole was in or near a centerofupfiow, and one was on the border of the 

same general system. 

The very high temperature and pressure gradients account for the 

rapidly increasing drilling difficulties encountered at increasing 

depth, and probably also help to explain why major geysers are more 

abundant in Yellowstone than in other geothermal systems of the 

world. 

In-hole measurement of pressures and temperatures after completion of each hole shows that the aquifer of highest static water level 

generally becomes dominant over the pressures and temperatures of 

all other aquifers in the uncased part. H casing is bottomed in perm.eable rocks, the influence of a deep aquifer can extend up into cased 

levels of flow of fluids up through the permeable rocks. 

Other relationships indicate the complex changes that can occur 

locally in a geothermal system as a result of drilling, with oonsequent 

"'short-circuiting' of natural aquifers. These include: (1) as gas accumulates in the hole and the water level is depressed, generally to 

the first uncased aquifer, wellhead shut-in pressures rise; (2) with 

time, the temperature of any drilled level may increase or decrease, 

depending on local hydrologic influences; decreases of asmuchas22"C 

(Y -3) and increases of as much as about 150"C (top ofY - 9) have been 

noted; (3) even with the precautions we took at the time, postdrilling 

analysis of our data indicates that four of our drill holes affected 

nearby springs, generally converting them temporarily into geysers. 

Our conclusions from Yellowstone indicate that physical relations 

in many commercially explored geothermal reservoirs are not as 

uniform as routine postdrilling measurements have indicated. 

INTRODUCTION 

Although there has been considerable drilling for 

geothermal energy throughout the world (Koenig, 

1970, 1973), the data available from shallow parts of 

thermal systems are sparse and generally unreliable, 

particularly in the cases of older or wildcat drilling. 

Modern development practice involves much data acquisition, testing, and evaluation, but few measurements are made in the shallow parts of geothermal 

systems. The expense of drilling deep, large-diameter 

holes dictates that the contractor drill round-the-clock 

in an effort to make as much footage as possible. Downtime for testing or for allowing the well to come to 

1 
2 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

thermal equilibrium is expensive and is normally 

avoided until the drill penetrates the target reservoir, 

commonly at -3,000 to -9,000 ft. In addition, the use of 

drilling muds delays thermal recovery, distorts the 

thermal regime, and contaminates the natural fluids. 

Coring in shallow parts of geothermal systems is particularly rare and even at production depths is sporadic, 

due to the high cost of pulling rods to replace the normal 

bit with a coring bit. 

Aside from measurements in the natural vents of 

springs and geysers, the shallow parts of geothermal 

systems have been investigated in detail at only a few 

places in the world. Many of the relevant data come 

from the investigations in Yellowstone National Park 

in 192~30 by the Carnegie Institution (Fenner, 1936) 

and from the investigations of the U.S. Geological Survey at Steamboat Springs, Nevada, in 1950-51 (Vvhite, 

1968). 

The shallow parts of geothermal systems are very 

important in the overall understanding of geothermal 

systems, because at these depths temperatures change 

abruptly, fluid compositions change through rock-water 

interactions and mineral precipitation, steam and other 

gases separate from water, two-phase fluid flow occurs, 

and the geothermal fluids interact with the normal hydrologic regime. In addition, many prospecting techniques, including geochemistry and thermal-gradient 

surveys, depend on knowing the properties of the shallow part of geothermal systems. Accordingly, our drilling program was designed to focus on the shallow parts 

of geothermal systems, and to compare the various 

geological and geochemical situations represented by 

Yellowstone hydrothermal activity. 

Yellowstone National Park is particularly suitable 

for research drilling in the shallow parts of geothermal 

systems. The Park contains the world's most extensive 

display of hot springs, geysers, fumaroles, and mud 

pots. Yet, owing to the area's preservation, the surface 

thermal features have not been destroyed by man's activities. Furthermore, there have been no efforts to produce fluids for commercial use, so the thermal features 

have been spared the destruction that followed geothermal exploration and development at Beowawe, 

Nevada, and at Broadlands and Wairakei, New Zealand. Yellowstone remains nearly undisturbed and is 

thus uniquely valuable for the study of hydrothermal 

phenomena in their natural state. 

These factors were clearly recognized by Arthur L. 

Day and E. T. Allen of the Carnegie Institution of 

Washington, and the first research drill holes in thermal areas were drilled by the Carnegie Institution in 

1929 and 1930 under the direction of Clarence N. Fenner. In addition to the published report (Fenner, 1936) 

we have Fenner's original field notes, and selected core 

samples from the two Carnegie Institution holes (one in 

Upper Geyser Basin, one in Norris Geyser Basin) have 

been transferred to the U.S. Geological Survey. In this 

report 'Ye attempt to reinterpret the data from the Carnegie drill holes in light of our drilling some 37 years 

later. The fact that our interpretations do not always 

agree with Fenner's does not detract from the 

significance of Fenner's accomplishment. 

The National Aeronautics and Space Administration's interest in remote-sensing techniques led it to 

select Yellowstone as a test area for the correlation of 

remote-sensing ·data with surface and subsurface phenomena. Under NASA funding and with the close cooperation of the National Park Service, the Geological 

Survey conducted extensive geologic investigations in 

the Park. In addition to the drilling, maps were made 

of thermal features and deposits, hydrothermally altered rock from the drill holes was studied (Honda and 

Muffler, 1970; Muffler and Bargar, 1974), and hydrothermal fluids, both from hot springs and from drill 

holes, were sampled and analyzed. Investigations by 

other Survey personnel included studies of Pleistocene 

volcanism (Christiansen and Blank, 1972), surficial deposits (U.S. Geol. Survey, 1972b), Eocene volcanism 

(Smedes and Prostka, 1972), pre-Tertiary stratigraphy 

(Ruppel, 1973), and geophysics. A summary geologic 

map of Yellowstone Park (U.S. Geol. Survey, 1972a) is 

available, and a general review of the geologic history of 

the Park has been published (Keefer, 1972). 

SCIENTIFIC OBJECTIVES 

The drilling program in Yellowstone was designed to 

provide the following: 

1. The best possible estimates of original ground temperatures and temperatures within the holes after 

drilling was completed. 

2. Data on wellhead pressures (or water levels) for calculations of down-hole pressures. 

3. Continuous cores to determine the stratigraphic sequence, and subsequent mineralogical and chemical analyses leading to a description of rock-water 

interactions in hot-spring systems. 

4. Continuing access to the drill holes to allow intermittent sampling of fluids, measurement of temperatures and in-hole pressures, and testing of 

geophysical logging devices. 

As the drilling program progressed, the limitations of 

our wellhead pressure data became clear. The data were 

neither as reliable nor as accurate as we would have 

liked, and furthermore, no down-hole pressure measurements were made during the drilling program. 

Equipment for measuring down-hole pressures was 

constructed after completion of the drilling (Fournier 

and Truesdell, 1971) and was used to determine the 
INTRODUCTION 3 

postdrilling pressure profiles discussed in this paper. 

SCOPE OF THIS REPORT 

This report emphasizes the measurement and interpretation of temperature and pressure data. The petrology of the drill core is published elsewhere (Honda and 

Muffler, 1970; Bargar and others, 1973). The chemical 

analyses and interpretations will appear in a separate 

paper of this series. 

HISTORY OF THE PROGRAM 

Sites for the drill holes were selected in 1966 with the 

cooperation of John M. Good, Chief Naturalist of Yellowstone National Park. A mixture of scientific and 

practical considerations was weighed in selecting sites. 

The drill holes were to be distributed to include the 

major hot-spring areas and principal types of activity 

(figure 1). We also wished to locate drill holes near 

major zones of fluid upflow, yet not where they might 

damage any well-known thermal feature. We could not 

drill near active hot springs for stability reasons, so we 

sought places where relatively cool, stable ground was 

adjacent to a zone of major upflow or, better yet, between 

closely spaced areas of prominent activity. 

The drilling contract was let in early 1967. Drilling 

began on April18, 1967, and continued throughout the 

summer and fall until November 1. Drilling was resumed on May 15, 1968, and was terminated on ~uly13 . 

Temperature and pressure measurements have been 

made in succeeding years in holes not plugged or 

blocked. Y -1 was plugged and abandoned immediately 

after drilling. Y-2, Y-3, Y-9, and Y-11 were plugged in 

1969. 

DRILLING EQUIPMENT AND PROCEDURES 

Safety was important at all sites. From experience at 

Steamboat Springs and elsewhere (White, 1968) we 

thought that rnost geothermal wells could be kept under 

control by maintaining cold water in the well, because a 

colun1n of col~ water is considerably heavier than an 

equivalent column of hot water (White, 1968, fig. 29). 

VIe found that at Yellowstone, however, pressures at 

depth were high enough for static water levels to rise far 

above the ground surface. Such high pressures, combined with high subsurface temperatures, establish a 

high potential for eruption of hot fluids. In order to 

minimize this possibility we sought sites elevated above 

local hot springs. Such locations gave us a greater head 

of cold water to counterbalance the high water pressures at depth, and usually provided good unaltered 

ground in which we could cement our near-surface casing. 

Drilling was done with a truck-mounted diamond-bit 

drilling rig (fig. 2) equipped with wire line for withdrawing cores through the rods without pulling out the whole 

Mammoth 

Hot Springs 

Norris 

Geyser ¥-12 

Basin C-ll 

Y-9 

0 

0 5 10 KILOMETRES 

YELLOWSTONE 

LAKE 

FIGURE 1-Map of Yellowstone National Park showing major geothermal areas and sites of research drill 'holes. U.S. Geological 

Survey holes are numbered Y-1 to Y-13 in order of drilling; holes 

drilled by the Carnegie Institution of Washington in 1929-30 are 

designated asC--I and G--IL 

FIGURE 2.-Truck-mounted diamond-bit coring equipment used in 

Yellowstone National Park. Y-2, Firehole Lake, Lower Geyser 

Basin. 

drill string. This capability allowed nearly continuous 

coring, greatly increased the efficiency of drilling operations, and facilitated down-hole temperature measurements. 

Water, generally pumped from nearby streams, was 

'I used as the circulating fluid. Storage tanks of 1,000-gal 

capacity at each drill site provided a reserve water supply in the event the pump failed. Drilling mud was not 
4 PHYSICAL RESUL~ DRILLING IN THERMAL .AREA.a YELLOWSTONE NATIONAL PARK 

used, in order to avoid contamination of the core, to 

avoid sealing off pores and fractures, and to allow collection of clean fluid samples. In addition, mud would have 

significantly delayed thermal recovery after stopping 

circulation, hampering efforts to obtain temperature 

data Furthermore, use of mud would have delayed the 

drilling operation and increased the expense, both for 

the mud itself and for a cooling system for the hot 

(300C-900C) return fluid.1 

The main difference between holes drilled at Yellowstone and those drilled at Steamboat Springs was that 

at Yellowstone subsurface water pressure in most holes 

was high enough for static water levels as much as 

about 220 ft above ground surface. Immediately after 

circulation stops, water level may drop below ground 

level, and may rise to ground level as the water expands 

upon heating. Such a column of water, if everywhere 

just at boiling for existing pressures, is metastable. H 

undisturbed the water level remains constant, but if 

disturbed by boiling or injection of gas, the water level 

rises, the hole starts to overflow, and a steam-water 

eruption begins. 

In the Yel.owstone drilling, wellhead water pressures 

ranged up to about 90 psig (pounds per square inch 

gage), far more than needed to cause a drill hole to 

overflow and burst into eruption. Accordingly, on every 

hole we attached a 4-inch valve as soon as the surface 

pipe (5 %,. O.D.) was set. The valve, with suitable reducers, was transferred to narrower casings as these were 

emplaced. Mounted on top of the valve (fig. 3) was a 

~, for return water and then a stuffing box, which 

consisted of two opposed hard-rubber cylinders. The 

inner end of each cylinder was shaped to fit around the 

drill rods. The rubber cylinders could be forced against 

the rods by manually operated cranks, thus controlling 

leakage around the drill rods. 

Rotation of the drill rods abraded the valve seats, 

causing the valves to leak. Accordingly, an old 4-inch 

valve was used during drilling and was replaced with a 

new 3-inch valve after completion of e&ch hole. Replacement was accomplished by inserting a packer 

through the 4-inch valve and expanding the packer 

against the casingjust below ground surface. The 4-inch 

valve could then be removed and slipped up over the 

packer rod, and the 3-inch valve emplaced. In Y -13 the 

packer, designed for NX casing (table 1), could not be 

forced through the erupting column into the hole, either 

because the BX casing was too close to the ground surface or because the pressure was too high for the rubber 

•Drilling mud was used 0111:e at Y- 2 in an attempt to prevent eruption &om the rods as the 

upper partofthe driB string was pulled from the well after shearing the driB string at depth. 

'l1le mud (a mixture of bentonite and Hamid) was not hea"Y enough to prevent a violent 

emption that spread the mud over a large area around the drill site. Drillers were scalded by 

the sticky, hot mud.. In this .espect,. mud is mwe dangerous than water; one can be splasbed 

with hot or even boiling water with little efl'ed,. because of rapid evaponttive cooling and 

water"slowYiscosity. Mud, however, retains beat and adhenstoftesh. causing painful hwns. 

FicUBl!: 3.-Photograph of valve (V). return water "'tee" (T). and stuffing box (8). Y-2. Firehole Lake. 

TABLK I.-Casing diameter, bit diameter, and core diameter, in 

ind&es, used in Yellowstone drillholes 

Size designation Casing Bit Core diameter 

O.D. ID. Set.O.D. Std. Wire 

line 

4x5% ------ 5.495 4 

NC ---- 4..500 4.026 3.875 ?ill .. 2nm 

NX ---- 3..500 3.000 ~980 21-&. P ia 

BX ---- ~875 2..3'15 2360 15/a Pit& 

AX ---- ~250 1.906 1.890 Ph& Ph& 

Example-NX bit passes through NX casing and driDs a hole that aa:epts BX casing. 

expanding unit. Cement was forced into the top part of 

the hole, and, after it set, the 4-inch valve was replaced 

with a 3-inch valve: the cement was then drilled out. 

Our drilling would have been seriously affected by an 

uncontained eruption outside of any casing in the hole.2 

An eruption inside the rods or casing can be controlled, 

although not without excitement and some danger. But 

'"This is essentially what happened at the Norris drill bole lC--moa-theCanlegielnstitution 

in 1930(Fenner.1936, p. 286). The situation there was remedied by pumping5tonsofc:ement 

down the casing and out into the fonnation! 
INTRODUCTION 5 

leakage of hot fluids at high pressure outside the casing 

would have been very difficult to control. To preclude 

such an accident, we started each hole with a 4" x 5~" 

bit and set and cemented NC casing (table 1), generally 

to a depth of 20 ft. We then drilled with an NC:bit to a 

nominal depth of 100ft, where we set and cemented NX 

casing. Except for the initial string in the open hole, 

cement was forced at pressures up to 400 psig dc)wn the 

·casing and up the annulus. Cement also was pumped 

through the return valve and down the annulus. Ordinary portland cement was used; it sets very quickly at 

the temperatures of the geothermal systems. Additional casing (BX) and cementing were required at 

-415 feet in Y-2, -530 feet in Y-12, and -227 feet in 

Y-13. AX casing was required at -451 feet in Y-2. 

During drilling, cold water was pumped down inside 

the drill rods and returned, usually heated to as much as 

80-85°C, up the annulus between the rods and casing 

and out a 2~-inch pipe mounted between the valve and 

the stuffing box (fig. 3). Unless there was a major influx 

of hot water at depth, the return fluid did not boil and 

drilling was straightforward. 

Pulling core or adding a length of drill rod, however, 

posed more significant problems. In the absence of high 

fluid pressures, core was pulled by raising the rods 

about 10ft off the bottom, unscrewing the quill from the 

uppermost drill rod, backing the kelly off of the drill 

string, and lowering the "picker" down the water-filled 

drill rods until it latched to the inner core barrel. The 

picker and inner core barrel were then pulled up 

through the rods, and an empty core barrel was dropped 

down the drill string. With high wellhead pressures (or 

even with just. an unstable column of water that boiled 

near the surface if the core barrel was withdrawn 

rapidly), water gushed from the open drill string, 

changing quickly to a steam-water eruption that could 

forcibly drive out the inner core barrel, picker, and wire 

line. This was prevented by inserting the wire line 

through a cap before attaching the picker. The cap is 

threaded for attachment to the drill pipe and also fixed 

with a swiveled water inlet so. that cold water can be 

pumped down the rods as the picker and core are pulled 

up. A 2-foot-long rubber sleeve around the wire line 

between the picker and the cap prevents the picker from 

being jarred against the cap and dropping the core. 

When the picker reaches the top of the drill string, the 

cap is unscrewed, the picker and core barrel quickly 

withdrawn, and a new core barrel dropped down the 

hole.3 During this time cold water may gush.from the 

pipe. As soon as the second core barrel disappears down 

the drill string, a new rod is maneuvered over the drill 

3'Jhe mds should contain water when the new core bane) isdroppecl On Y-11 we made the 

mistake of dropping the core barrel into a drill striog full of steam. The core barrel belled out 

and damaged the bit when it hit, bcing us to pull the whole string. 

string and screwed into place. Since the new rod is 

suspended by a blank plug, the whole string can then be 

lowered into the hole. The blank plug is then unscrewed 

and, as water discharges from the rods, the kelly is 

repositioned over the rods, and the quill joined to the 

rods. Water is then forced into the rods at considerable 

pressure to insure that the inner core barrel locks in 

place.4 

Alternatively, one can add the length of drill rod 

before pulling the core, and then lower the whole drill 

string so that the bit rests on the bottom of the hole. In 

this position, flow of hot water into the bit is restricted, 

thus reducing the chance of eruption during the critical 

few seconds when the picker and core are being extracted and the new inner core barrel dropped down the 

rods. 

In several of the hotter holes, the water in the drill 

rods was heated so rapidly after circulation ceased that 

an eruption occurred almost immediately after removal 

of the quill. In the first seven drill holes we merely tried 

to keep eruptions from occurring, but during the drilling ofY -8 we installed a check valve in the upper part of 

the inner core barrel. This allowed cooling water to go 

down but blocked flow of hot water back up the rods, 

restricting the eruption to the water in the rods. Such 

eruptions, although initially spectacular, ended quickly 

when the water in the drill string was exhausted (fig. 4). 

The picker could then be lowered and the core withdrawn. 

Under extreme pressures, our method of withdrawing 

cores consisted oflowering the picker into an extra 20-ft 

length of drill rod, attaching the swivel cap and water 

hose to the upper end of this drill rod, and hoisting the 

rod to the top of the mast. The quill was then moved off 

the drill string, the rods allowed to erupt dry, and an 

open valve attached to the drill string. The 20-foot 

length of drill rod was then attached to the valve, and 

the picker was lowered as cold water was pumped down 

the rods. After capture of the core barrel, the picker was 

withdrawn into the 20-foot length of drill rod, the valve 

closed, the rod removed, and the core barrel extracted. 

The new core barrel could be inserted by resting it on 

the closed gate valve, attaching a 10-foot length of drill 

rod to the valve and over the core barrel, attaching the 

swivel cap to the top of the drill :rod, and simultaneously 

pumping water and opening the gate valve to let the 

barrel drop. At times, the barrel had to be forced down 

the hole by water pressure from the pump. Once the 

barrel was locked, the rods were again allowed to erupt 

dry, the valve was removed, and the quill attached. 

All these techniques became increasingly arduous 

4 Jftbe barrel is not securely locked. an enlptioaoftheftuid in the drill string may upel the 

inner core baneL AtY-11 tor-example. the inoew' barrel (with5 ft of cme)wasDCJt.locbd when 

the rods erupted; the core barrel sbotoutofthe rods. careeaed oft' the mast. and landed in the 

woods 50 feet a_y_ 
6 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

FIGURE 4.-Eruptions from drill rods. A, Initial discharge from Y-4 

drill hole on July 22, 1967, when static water level was about 190ft 

above ground level. When the fittings were disconnected, cool drill 

water was first discharged. B, Initial explosive eruption of watersteam mixture from open drill pipe in Y-5 (Rabbit Creek) drill hole, 

August 20, 1967. The "bursting" .effect results from flashing of 

superheated water erupted to atmospheric pressure at and just 

above the top of the drill pipe. The eruption phase typically follows 

a brief interval of quiet overflow such as shown in A and passes 

rapidly into the near-vertical ejection of steam: and water, such as 

shown in C. C, Eruption of water and steam above the top of the drill 

tower, Y-9 drill hole, Norris Basin. 
INTRODUCTION 7. 

and dangerous· at wellhead pressures over 50 psig and 

particularly in highly permeable rocks such as at Y-13. 

In several holes (Y-9, Y-11, Y-13) we approached a 

point where any failure of equipment, human error, or 

even delay in action would have resulted in an eruption 

controllable only with great difficulty. In each case we 

terminated drilling while we were still in control. 

Upon completing each hole, a 3-inch valve was 

mounted on the casing, and an inconspicuous concrete 

box was built around the valve by the National Park 

Service (fig. 5). The valve was locked in a closed position 

by a chain and padlock, and a steel lid on the concrete 

box was also locked. This arrangement allowed periodic 

access to the holes for tern perature and pressure measurements and for fluid sampling, but prevented tampering or vandalism. 

Several holes (Y~2, Y-3, Y-9 and Y-11) displayed 

FIGURE 5.-Typicalarrangement at wellhead after completion, showing valve mo-q:I?-ted at top of casing, concrete box (with steel lid) 

around the wellhead, and the gear used to introduce temperaturemeasu~ing equipment into the completed well. Y-8 drill hole, 

Upper Basin. 

increasing wellhead corrosion and leakage with time 

and were plugged with cement in 1969. Y-10 al~o developed a bad leak from a defective nipple below the 

valve. In June 1968 we successfully replaced the nipple 

and valve by the use of a packer. 

SCIENTIFIC DATA ACQUISITIO~ 

The primary data needed for interpreting the dynamics of a geothermal system in its undisturbed state are 

the original predrilling distributions of temperature· 

and pressure. Know ledge of these parameters in three 

dimensions would be ideal, but is clearly financially and 

logistically impossible. In most areas ofYellowstone we 

had to be satisfied with a single hole in each hot-spring 

area, and thus with a one-dimensional analysis. In 

three areas, however, hoies were close enough together 

to allow two-dimensional analysis (Y-7 and Y -8 in 

Upper Basin; Y-4 and Y-13 in Lower Basin, and Y-9, 

C-1 and Y-12 in Norris Basin). 

The mere act of drilling the hole distorts the temperature _and pressure regimes to an uncertain extent. Circulation of drilling water cools the rock adjacent to the 

hole. The uncased length ofhole .serves as an easy flow 

path (a ((short circuit") between aquifers of differing 

wellhead pressures, causing distortions of temperature 

and pressure. The hole _rv.a,y also develop small convection cells, and any separate gas phase ac_c-umulates in 

the upper cased _portion of the hole .. All of these effects 

result in a temperature profile unlike that in the1original ground. L : u .. 

Although drilling does disturb the ,previous regime, 

the initial distortion is minimal at the bottom of the 

hole. Drill fluid .has generally not been in contact with 

rock at the bottom. for more than a few minutes, and 

thus has lowered the temperature only slightly, and 

only immediately adjac€nt to the hole. In regai_ning 

temperaturertatthe bo-ttom, heat is conducted both· vertically upward·,: and :radially inwar~, rather than just 

radially. Accor,dingly, rock temperatures at the ·hole 

bottom are lowered the least and rebound the fastestto 

a state not much different from the original gr.ound· 

temperature. To obtain a depth profile consisting of a 

series of bottom-hole temperatures, we drilled no more 

than 8 hours per day, let the drill hole stand overnight, 

and 1 measured the bottom-hole temperature immediately befgre drillt~g started the next day.. The h,ole 

·was ne;:1rly always free of cuttings and slough to the 

depth reported by the drillers, as shown by the agreement between drilled and probed depths. In zones of 

rapid penetration, we limited the footage drilled per day 

to .o.btain a. sufficiently close spac~ng_ of data points .. ,. 

An, example of the recovery o(bottom-hole tempera:-

ture is shown in figure .6. Temperatures recover rapidly. 

during the first 6 to 8 hr after circulation ceases. Afte.r 
.g PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

en 144 ::> 

§ 140 

w 136 0 

en 132 w 

w 128 a: 

(!) 

w 

0 

~ 

u.i 

a: 

::> 

~ a: 

w 

Q.. 

::::E 

w 

1-

0 2 4 6 8 10 12 14 16 18 20 

TIME, IN HOURS 

FIGURE 6.-Recovery of bottom-hole temperature after circulation of 

drilling fluid was stopped in Y -1 (Black Sand) drill hole when depth · 

was-100ft. 

16 hr the temperature has nearly recovered to that of 

the original ground. NoPmally we did not attempt to 

determine a recovery curve such as figure 6, but at 

nearly every shutdown of a day or more, measurements 

were made at longer intervals for comparison with our 

normal overnight shutdown of approximately 16 hr. 

These comparisons indicated that recovery over 16 hr 

was generally within 1 o or 2°C of the maximum eventually observed. With more time, temperatures either remained constant or fluctuated a degree or so, due probably to convective disturbances in the drill hole. 

Bottom-hole temperatures were measured using maximum-recording mercury thermometers rather than 

thermistors, thermocouples, or other devices. This 

choice was determined primarily by considerations of 

reliability. Our experience with electrical temperaturemeasuring devices was that they worked for only a few 

trips in and out of a high-temperature hole before failure either of insulation or of potting compound. Furthermore, with the large local temperature contrasts, 

we did not require great precision, and we needed only 

a single reliable bottom-hole temperature at each 

depth, rather than a continuous profile. The m~ximumrecording thermometers proved to be an effective compromise between accuracy and reliability. 

· Individuai thermometers selected for use must have a 

tight restriction between bulb and temperature scale; a 

loose restriction increases the probability of mercury 

being jarred down during withdrawal of the thermometer. At most depths two measurements were made, with 

different thermometers. In the tables for individual 

holes, the thermometer number is shown, permitting 

comparison of differences between thermometers, a~d 

also reproducibility using the same thermometer at different times. In the field, the thermometer was cooled to 

about 20°C before reading; the thermometers must not 

be read while still hot. 

Thermometers were standardized in the laboratory, 

and those with large positive or negative corrections 

were rej~cted. Pressure corrections were also obtained 

experim~ntally but were found to be small for the ~ype 

most co~monly used. Significant pressure correctiOns 

were applied, however, to the thermometers used at 

temperatures much above 200°C, as discussed for Y-12 

drill hole. 

Obviously, a simple maximum thermometer provides 

accurate bottom-hole temperatures only where the 

temperature at the bottom is hotter than at all other 

points in the hole. This was the case in most of our 

Yellowstone holes. But in some (for example, Y-5, Y-8, 

and Y-10), temperatures appeared to level off with 

depth. To determine accurate bottom-hole temp~ratures in these holes, the thermometer was placed 1n a 

capped metal pipe filled with dry asbestos. The thermometer was lowered to the bottom as quickly as possible (usually less than a minute), left at the bottom for at 

least 30 minutes, and then raised quickly. Measurements made with various times over 15 minutes gave 

consistent results. The thermal lag in the iron case plus 

the insulating properties of the asbestos allowed the 

thermometer to measure the bottom-hole temperature, 

rather than the temperature at some higher level. 

The means by which the maximum thermometer was 

lowered into the well is illustrated in figure 7. Normally 

the pressure chamber (a short length of pipe) was 

mounted on the drill rods, but with suitable fittings it 

could equally well be mounted on the main valve or the 

stuffing box (if the rods were out of the hole for any 

reason). Advantages of taking the measurements 

through the drill rods were fewer round trips for the 

drill string and eliminating the chance of jarring the 

thermometer on a rock lip in the hole wall or on the 

bottom of the casing.5 Upon finishing a day's drilling, 

the drillers would suspend the rods 10 or 20 ft off the 

hole bottom, tighten the stuffing box to prevent much 

leakage, and attach a valve to the top length of rod. 

Temperature profiles measured after a hole was completed were usually obtained with thermistors, which 

were generally satisfactory at low temperatures, but. 

they commonly failed after short intervals near or 

above 200°C. We are now (1973) hopeful that thermistor 

cable and insulation problems have been solved for 

temperatures somewhat above 200°C. Silicone grease 

forced into the thermistor cage with a grease gun has 

proved to be much more reliable than the solid potting 

compound formerly used. 

When the thermistor gear was inoperative, temperature profiles were made with successive runs with a 

maximum thermometer-a tedious exercise. 

s Although the thermometer could be jarred when being raised through the bit, norm~lly we 

knew about how far the bit was above the bottom of the hole, and thus could ratse the 

thermometer very slowly through the bit. 
INTRODUCTION 9 

FIGURE 7 .-Apparatus used to measure temperatures at Y -1 drill hole 

as drilling progressed. A, Stainless steel wire on a reel (lower left, on 

drilling platform); wire extends over an aluminum sheave, through 

a threaded plug, and is attached to lead weight. A maximumreading mercury thermometer screws into the bottom of the lead 

weight, thus permitting emplacement ofthermometer as close as 

possible to drilled bottom. The four-inch pipe upon which the sheave 

is mounted constitutes a pressure chamber, which extends below 

the drilling platform. The pipe is fastened either to the main valve 

Fluid pressures of the natural environment are more 

difficult to measure than temperatures, and in retrospect, we are aware that our Yellowstone procedures 

were not ideal. Pressures were measured only at the 

wellhead before completion of each hole. Wellhead pressure is mainly responsive to the aquifer of highest head 

in the hole, provided that permeability in this aquifer is 

also high; this aquifer is normally not specified by the 

data and need not be near the bottom of the hole. Wellhead pressure also reflects the density of the fluid in the 

hole, which in turn is a function of temperature distribution and the amount of entrained vapor. If a gas 

capis present within the casing, the measured pressure 

will be too high depending on the height of the gas cap. 

In most cases the gas cap bled off as a thermometer or 

other instrument was lowered into a drill hole, with a 

proportional drop in measured pressure to a steady level 

when water rather than gas began to leak from around 

the wire that suspended the instrument. 

Pressure profiles were made after a hole was completed using equipment devised by Fournier and Truesdell (1971). A long flexible stainless-steel tube is inserted into the hole and maintained full of nitrogen 

from a gas cylinder. At any given depth the pressure 

outside the tube is balanced by the pressure of inert gas 

in the tube. Pressure is accurately measured with a 

pressure gage mounted between the tube and the gas 

cylinder. 

Recovery of cores was an important objective of the 

drilling operation. After retrieval of the core barrel 

(fig. 3) or to a valve on the uppermost of the drill rods in the hole. B, 

Detail of the sheave, lead weight, and thermometer. The sheave 

rotates a counter (opposite side, not shown). The threaded cap 

through which the stainless steel wire runs is pierced here by a 

simple hole. In later versions, as in fig. 5, the cap was modified by 

the addition of a Teflon insert around the wire. The insert could be 

screwed further into the cap, compressing packing material against 

the wire, thus minimizing or eliminating leakage when the valve 

below the pressure chamber was opened for in-hole measurements. 

from the drill string, the core was carefully extracted, 

the pieces arranged in correct orientation and sequence 

in a core tray, and each piece immediately marked with 

an arrow pointing in the original ((up" direction. The 

core was then marked and labeled at each foot before 

being transferred to cardboard core boxes. The core ·was 

described and logged at the drill site. A representative 

sample of about 20 percent of the core was selected for 

detailed laboratory study in Menlo Park, Calif. The 

remainder was stored in government facilities. 

Fluid sampling was conducted several times for each 

accessible well. Wellhead samples were collected immediately upon well completion, even though they were 

generally much contaminated by drill water. At intervals of months or years thereafter, additional samples 

were collected, both at the wellhead and at depth, using 

a down-hole sampler designed by Fournier and 

Morgenstern (1971). This sampler allows the fluid at 

depth to be sampled in situ and raised to the surface 

without loss by boiling or exsolution of gas. 

DEFINITION OF TERMS 

Fluid pressure.-Total fluid pressure observed at any 

specified point of measurement, most commonly at the 

wellhead; does not distinguish between liquid and vapor. Either psia (pounds per square inch absolute) or 

psig (pounds per square inch gage) is specified in this 

report. 

Water table,-The free-standing level of water in porous ground that communicates directly to the atmos-
10 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL J;ARK 

phere; in fine-grained or dense fractured material, the 

level that water attains in an open hole or in a wide 

fracture. Thus, effects of surface tension and the capillary fringe are minimized. All depths below ground 

surface are shown as negative, thus permitting water 

levels above ground (and positive pressures) to be 

shown as positive values. 

Static water level.-The level that water attains in an 

open hole under steady-state conditions with no change 

in subsurface temperature or proportion of vapor to 

liquid; in actual practice, a ~~static water level" may 

involve competing effects from two or more aquifers, 

and probably no part of the system being measured is 

strictly static. With increasing depth in a geothermal 

system, the static water level generally rises up to and 

then above the ground surface. High positive levels are 

generally not measured directly but are computed from 

positive wellhead water pressures; for convenience in 

this report, a single factor of 1 psi = 2.4 ft of water is 

used, but where greater precision is required, the factor 

depends on the vertical distribution of temperatures 

and densities of water and vapor in the part of the 

system being measured. 

Well head fluid pressure .-Observed gage pressure 

(psig) at the wellhead. In practice, generally measured! 

to 5 ft above ground, with difference from ground-level 

pressures neglected in this report. Does not discriminate between liquid and vapor pressure. 

Wellhead water pressure .-Observed gage pressure 

(psig) at the wellhead with the hole filled with liquid 

water; the latter qualification generally can not be 

confirmed but is assumed valid if water without vapor 

bubbles leaks from valves or other fittings (exsolution of 

vapor bubbles from liquid after leakage does not invalidate the assumption). 

Gas-accumulation effects.-The vapor pressures of all 

gases, including H2 0, are commonly high enough for 

vapor to separate from liquid at the top of a capped hole, 

depressing the water level until a steady state is attained; as the water level is depressed below gage level, 

the wellhead pressure increases, by the rough conversion factor 1 psi = 2.4 ft of water. 

Reference boiling-temperature curve.-The variation 

of temperature with depth in many vigorous, hightemperature geothermal systems can be approximated 

by the reference boiling-temperature curve for pure 

water. This curve, calculated from laboratory experimental data for pure water (Keenan and others, 1969), 

is based on the following relationships: (1) the boiling 

temperature of water increases with pressure, and 

(2) the increase in pressure with depth is due to the 

weight of the overlying water. 

Calculations such as those of White (1968, p. C56), 

Haas (1971), and Manuel Nathenson (written commun., 

1973) assume a column of water, the top of which is at 

ground level (for Yellowstone, about 7,500 ft, equivalent to a boiling temperature of 92.4°C, and temperatures everywhere just at boiling, considering the weight 

of overlying water. The reference boiling-temperature 

curve takes into account the differences in density of 

water with increasing temperature. Points that plot to 

the left of the curve are characterized by water. Points 

that plot to the right of the curve (where the assumptions are valid) are characterized by steam. Points that 

plot on the curve are characterized by the coexistence of 

steam and water, but with so little dispersed vapor that 

density is that of the liquid. Other reference curves, not 

considered here, have been calculated for different altitudes, salinities, cold columns to point of boiling, and 

lithostatic pressures (White, 1968; Haas, 1971). 

Throughout this paper drill-hole measurements are 

compared with this boiling-temperature curve. In actual fac;t, no single curve is appropriate for all situations 

because the temperature of formation of a vapor phase 

at a given depth depends on (a) the salt content of the 

fluid (increased salinity raises temperature of boiling, 

but this effect is negligible for Yellowstone waters), (b) 

the dissolved gas content (increased gas content lowers 

temperature of vapor formation), (c) the proportion of 

dispersed vapor in the column, (d) the surface altitude, 

(e) the depth of the water table, and (f) the artesian or 

thermoartesian pressure (to be defined). With a water 

table below ground surface, the boiling-temperature 

curve should be lowered an equivalent distance. A static 

water level above ground, on the other hand, requires 

that reference curve be raised by an equivalent distance. 

Obviously, no single reference curve can apply to all 

geothermal wells in the same area, or even to a single 

well at different depths because aquifers differ in gas 

content, static water levels, and salinity. Accordingly, 

our standard reference, the boiling-temperature curve, 

assumes pure water, everywhere just at boiling at the 

prevailing pressures, and with a free surface at ground 

level. This curve is useful for reference purposes and 

does not specify whether vapor is present at the depth of 

each measured temperature. Discrepancies are particularly important with respect to gas content, static water 

levels above ground, and actual temperatures and densities of overlying water that differ from those assumed 

for the reference curve. 

Reference boiling-pressure curve.-The pressure 

curve equivalent to . the boiling-temperature curve. 

Changes in boiling pressure with depth are nearly 

linear. 

Equivalent depth.-The measured depth corrected for 

the static water level. Use of equivalent depth rather 

·than measured depth allows all measured temperatures 
UPPER BASIN AND UPPER F'IREHOLE RIVER 11 

to be compared to a single reference boilingtemperature .curve. For positive static water levels, 

equivalent depth is greater than measured depth; for 

negative static water levels, equivalent depth is less 

than measured depth. 

Water overpressure.-A qualitative term referring to 

water pressures in excess of the reference boilingpressure curve; also used quantitatively with in-hole 

pressure measurements at specific depths. 

Eruption.-Many drill holes discharge water and 

steam just like an erupting geyser (White, 1968), especially if static water levels are above ground surface. 

Opening a valve or disconnecting a drill tool lowers 

pressure at the wellhead and throughout the hole, causing water to flow from the hole. The temperature of 

discharge may be low at first, but it then rises, eventually exceeding the boiling point at existing atmospheric 

pressure. Part of the water ((flashes" into steam as pressure decreases in the hole. The violence of an eruption 

depends on initial temperature, wellhead water pressure, and permeability of rocks penetrated by the drill 

hole. 

T hermoartesian pressure .-Effects in a hydrothermal 

system similar to artesian pressure in nonthermal sys-:-

tems, and caused by thermal expansion of water and 

consequent decrease in density with increasing temperature. The term ((thermo-artesian" pressure was 

first used by Studt (1958, p. 707); such pressure may be 

superposed on artesian pressure. In Yellowstone both 

kinds of artesian pressure are probably present. 

Self-sealing .-Outflow channels of hydrothermal systems ofhigh temperature tend to decrease in permeability due to deposition of minerals in open spaces. Deposition results from decreases in temperature and pressure 

upward, and reactions of fluids and wallrock. Silica 

minerals (quartz, chalcedony, cristobalite, and opal), 

zeolites, and calcite are especially common deposits in 

outflow channels (White and others, 1956; Honda and 

Muffler, 1970). 

Water pressure g radient.-(1 ) Vertical pressure gradient, as measured by changes in static water level with 

depth in a drill hole. In Yellowstone, static water levels 

normally increase with depth; that is, the water pressure gradient is positive upward and can be expressed 

as the fraction by which the hydrostatic gradient is 

exceeded. (2) Horizontal pressure gradient is measured 

by comparing static water levels in two or more holes 

when drilled bottoms are at approximately the same 

altitude. The difference in static water levels divided by 

the distance between the holes provides the horizontal 

gradient. 

ACKNOWLEDGMENTS 

Our hydrothermal studies in Yellowstone could not 

have been conducted without the strong support of the 

National Park Ser vice. We are indebted to former 

Superintendent J. S. McLaughlin and Superintendent 

J. K. Anderson; to Dale N uss and Lynn Williamson, 

former and present West District Rangers; and to J. M. 

Good and W. W. Dunmire, Chief Naturalists during and 

soon after completion of our drilling program. John 

Douglas and John Stockert, former and present West 

District Naturalists, and Dr. George Marler, retired 

geyser specialist, have all provided invaluable support 

for these nontraditional and at times hazardous research activities. 

The drilling contractor throughout the program was 

Sprague and Henwood, Inc. We wish here to express our 

appreciation to Sprague and Henwood and their personnel for unstinting cooperation in this research effort. 

Many aspects of the Yellowstone drilling were new to us 

and to the contractor. The success of the drilling experinlent was due in large measure to the contractor's 

cooperation and the skill, diligence, and willingness of 

the- drilling personnel to adapt to new situations and to 

devise new methods. 

We thank our many colleagues of the U.S. Geological 

Survey for their cooperation, interest, and advice, 

specifically Terry E. C Keith, Keith Bargar, Mike 

Thompson, Reba Fournier, and James Mattinson. R. L. 

Christiansen, Frank Olmsted, Manuel Nathenson, and 

W. H. Diment have been especially helpful in providing 

data and critical reviews of this report. N athenson has 

checked many of our calculations and has provided 

temperature-profile data from Y-7 and Y-13, using 

thermistor and thermocouple gear that he assembled. 

UPPER BASIN AND UPPER FIREHOLE RIVER 

Y-1 (BLACK SAND BASIN) drill hole 

SITE SELECTION 

Y -1 was our first research drilling into Yell owstone hot-spring systems. The site selected was in 

Black Sand Basin, a subdivision of Upper Geyser Basin 

1.2 mi west of Old Faithful Geyser; the site is also 

about 0.9 mi west-northwest of Carnegie I drill hole 

and 62ft lower in altitude. It was chosen in part because 

of accessibility via a snowplowed secondary road, and in 

part because we anticipated relatively favorable conditions for introducing our contractor and crew to the 

problems of drilling in hot-spring areas. The specific site 

is not presently recognizable from surface evidence; it is 

4 7 ft S. 75° E. of Whistle Geyser, and 5.5 ft below the 

crest of Whistle's cone. 

PHYSICAL MEASUREMENTS 

Data from Y-1 are summarized in table 2, and summary data on altitudes, depths, maximum temperatures, pressures, and other data from this hole and all 

other Yellowstone drill holes are shown in table 3. 

Temperatures considered to be the most significant are 
12 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

TABLE 2.-Temperatures,pressures, and other observations from Y-1 (Black Sand) drill hole, Upper Basin, Yellowstone National Park 

Date and time Observation Temp, Thermometer Static water Wellhead 

1967 depth, ft 1 OCI No. level, ft' 2 pressure, Comments 

psig1 

4/18 1015 6.2 (17) (-4.8) 5 min shutdown. 1325 18.5 -4.9 1 hr shutdown, then drilled at -21 ft. 1540 20.5 (37.5) 1 hr after 4-in. casing set and cemented to -21 ft. 1650 19.8 (76.2) 2 hr after; temperatures may be too high from setting of cement? 1920 15.5 (65.0) 5 hr after. 4/19 0730 12.8 48.6 17 hr after (cement in hole; probably best of shallow temperatures). 1030 22.5 -2.0 - 10 min shutdown; good water level? 1130 30.5 -1.8 - 10 min shutdown; good water level? 1220 35 (83) 1

/ , hr after circulation. 1 

1410 60 (-3.1) 1645 79.7 (103) (-2.7) 1 hr after drilling to -80 ft. 

4/20 0735 79.6 125.9 15 -1.4 Drilled to -100 ft at 1125. 1930 99.3 (129.1) 15 (-1.7) 8 hr after circulation. 4/21 0720 99.3 gu} 134.1 15 -0.7 100ft of 3-in. casing set and cemented 1030. 14 1445 43.4 (84) In cemented hole. 4/22 0800 43'h 97.0 In cemented hole. Drilled out cement, then to -185 ft. at 1540. Lost circulation 

4/23 0921 183.4 ~~~:~} 

drill water -178 to -182 ft; with no discharge or wellhead pressure evident. 

158.1 4 (+15 ,) l 17 ~2 hr after circulation. 183.5 7 ~2 

1835 183.5 ~g~ § } 159.0 4 (+ 17 1

12) 7V.. 27 hr after circulation. 

7 71

12 4/24 0726 182.8 !58.6 ) 4 17 7 38 hr after circulation. Then drilled to-215ft at 1315; first eruption from hole when 182.9 159.2 159.2 7 core barrel removed (see text). 159.3 4 7V2 159.7 7 4/25 0727 214.6 169.6 4 (+74) 31 31 psig wellhead water pressure. Thermometer No. 7 lost in hole; 14'h hr after circulation. 4/26 0738 214.6 ·t +g:~} 170.7 4 (+71) 29'h 38 hr after circulation. In effort to control water flow, hole filled with cement but 

8 30~2 bottom probably not sealed. 4/27 24 After pumping cold water in hole for 40 min. Redrilled hole diverged from cement at about -115 ft. Drilled on to -130 ft with positive tressures and discharge at 

0716 i!~:~} 

depths below about -110 ft, contrasting with first dri ling 4/22. 4/28 g~ ~} 128.4 146.8 4 2 Wellhead pressure. Then drilled to -180 ft, cemented in new attempt to control 0731 8 8 flow. 1333 169.0 (96.4) 14 38 min after circulation. 1348 168.75 (103.2 ) 14 6~2 53 min after circulation. 1455 - 156 (123.9) 14 2 hr after circulation. 4/29 0725 152.8 155.0 4 On cemented bottom, no pressure obtained. Then drilled to -194 ft: still discharging so cement not effective. 4/30 0937 t~g :~ } 190.7 ~~g:~} 163.7 4 (+30) 13 Pressure above 4/23-24 at -183 ft even though very permeable from - 183 to 0951 4 12.5 -191ft. 5/1 0734 190.7 ~~g:~} 163.4 4 (+33 V2l 17 Slight temperature decrease from 4/30? 40 hr after circulation. Then drilled to 0747 189.7 8 14 -211 ft at 1130. 1130 Erupted trying to get back into hole; more gas than previously 1415 Decided to terminate drilling. · 1545 50 Pressure much above 4/25-26. Why? (see text). 1600 60 Pressure still rising steadily. Decided to cement hole. 

'Data in boldface considered most reliable; data in parentheses, least reliable. 2Relatlve to ground surface; positive levels calculated from wellhead pressures considered to be water pressures least affected by vapor. 

plotted versus depth in figure 8; most but not all of these 

are probably close to original ground temperature. 

The measured bottom-hole temperatures (fig. 8, curve 

B) intersect the reference boiling-temperature curve 

(A) at -128ft and exceed the curve at all greater depths. 

The rather regular increase in temperature with depth 

is interrupted at -183 ft, where the temperature is 

about 4 oc lower than expected. From -17 8 to -182 ft no 

drill water returned to the surface, and the core recovered from this zone is highly permeable sandstone and 

vuggy conglomerate. The break in temperature gradient may be due to intersection of a local channel of 

relatively cool water, but is more likely to be explained 

by local convective circulation within the permeable 

zone. 

The water table was first identified 4.8 ft below 

ground. As the hole was deepened the static water level 

in the hole changed in response to changing subsurface 

pressure conditions, rising to ground level when the 

hole was about 100 ft deep. With continued deepening, 

positive wellhead fluid pressures were measured, with 

pressure rising to 6V2 psig at-183ft and 31 psig at -215 

ft; corresponding static water levels are + 15¥2 ft and 

+ 7 4 ft. These pressures are interpreted to be wellhead 

water pressures, that is, we conclude that etther a separate vapor phase was not present in the hole, or vapor 

had minimal effects. 

Curve C of figure 8 shows equivalent depths corrected 

for differences in static water-levels, all adjusted to 

ground level by amounts shown in column 6 of table 2. 

Temperatures at equivalent depths of curve C nowhere 

exceed the reference boiling-point curve (A) and are 

generally 1 o to 5°C below it. This departure is probably 

related to the effect of dissolved gases in lowering the 

temperature of vapor formation; a partial pressure of 

other gases of 5 to 10 psi can explain these differences. 

The effects of gases are considered in more detail in 

holes for which more complete data were obtained. 

ERUPTION PROBLEMS 

Previous drilling experience at Steamboat Springs, 

Nevada, where wellhead fluid pressures were generally 

low, had suggested that eruption tendencies ofthe Yellowstone test holes could be controlled by cold drilling 

water, a stuffing box around the drill rods, and a valve 

on the casing. We had not anticipated that wellhead 
TABLE 3.-Summary of physical data of all research drill holes in Yellowstone National Park 

Maximum pressures 

Altitude Altitude Casing depths Maximum Depth of --- Depth of hole Total .. ~!f~c~" in ft measured water Altitude in ft., Rise in 

depth, of of below ground temp., oc table of water when water static Near-bottom Wellhead Wellhead surface, "bedrock," water fluid water fluid ft ft ftl ftl and below table level first level, ft depth, ft ground, ft to surface pressure, pressure, pressure, 4-in 3-in BX AX psi a psig psig 

u~;: ~~£~--- ~----- 215 7,294 211~ 7,082 21 100 170.71.::.215 4":9 : 7,289 :...·roo 79 (3) .. ~ ~ -30? ·· >So · 

Y-7 -------------- 242 7,266 173 7,093 21 102 143.1 -235 5.0 7,261 242 -3 (3) Ll.3 0 Y-8 -------------- 503 7,272 181 7,091 20 93 169.8 -342 3.1 7,269 -25 -95 231 -35 86 Camktie I __ ____ 406 7,356 220 7,136 544 180 @-406 2-1 -7,355 (3) ? (3) 57 Lower idway Basin 

Y-2 -------------- 516 7,372 104 7,268 29 128 408 '450 203~-516 3.5 7,369 -83 -103 6233 -42 214 Y-3 -------------- 514 -7,195 138~ -7,057 32 90 200 196.0 -494 -8? -7,187 - 75? -60 217(?) -20? 72 Y-4 -------------- 691 -7,205 0.4 - 7,205 21 120 195.8 -689 17.8 -7,187 -80 -207 366 79 96 

Y-5 -------------- 538 -7,228 32 -7,196 32 102 170 -248 8.1 -7,220 -65 100 260 @-528' 38 84 Y-13 ------------ 465 -7,220 61 -7,159 21 72 227 203.4 -465 3.5 -7,216 62 -219 226 @-460' -90? 180 

Up-r-~ =-i~~~~~ --- --- 500 -7,640 69~ -7,570 50 118 180.8 @-499 3.2 -7,637 -170 53 228 21? 76 Mud Volcano 

Y-11 ------------ 347 7,709 64 7,645 . 20 90 191.4 @-347 7.5 7,702 -190? ? -188? ? 170 Norris Basin 

Y-9 -------------- 813 7,584 4 7,580 21 100 195.7 ~-813 28.8 7,555 -230 -150? 357 -50 140 Y-12 ------------ 1,088 7,538 0 7,538 21 110 530 237.5 -1,088 17.9 7,520 -505 -138 425 @-1,079' -50? 50 Camegie II __ ____ 265 7,519 0 7,519 ? 60? 205 @-246~ - 15? -7,504 -70? ? (3) (3) 297~ 

Mammoth 

Y-10 125 psia ------------ 370 6,742 253~ 6,488 22 86 -73 >50ft 11.8 6,730 1-70 -110 -39 78 to bottom @-192' 

1

"Bedrock" is the uppermost lava or ash flow of each hole. 4Psig equivalent of depth of water level below surface. 2Rise in static water level/total depth; difference between ground and water level 5Depths and diameters of casing not specified. ignored. 6

233 psia at - 488 ft; point B of figure 18 suggests bottom-hole pressure of at least 254 3Not measured. psia at -516ft. 

Vertical 

pressure 

gradient2 

0.3'7· .01 

.19 

? 

.20 

.12 

.30 

.19 

.47 

.11 

? 

.18 

.13 

? 

.30 

~ ~ 

t:rj 

~ 

tx1 

> 00 

·z 

~ t:l 

c::: 

~ ~ 

~ 

~ :I: 

0 

~ 

~ 

ti3 

~ 

...... 

Cr\j 
14 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS,.Y.ELLOWSTONE NATIONAL PARK . 

CASING RECORD TEMPERATURE, IN DEGREES CELSIUS CONDENSED 

LOG 

0 20 40 60 80 

0 

of 4-in. 

casing 

100 100ft 

of 3-in. 

casing 

100 

8 

1 

120 140 

~ ' . 

' ' . 

160 180 290 

Obsidian-rich 

sediments, 

generally 

zeolitized 

and cemented 

220 

Curve C. ', 

Equivalent depths, corrected for ', .. 27,38 } Lost circulation 

200 

TD 

215 

fw 

w 

u.. 

~ 300 

I 

fQ_ 

w 

0 

400 

500 

EXPLANATION 

0 Bottom-hole temperature- 16 hr 

after circulation ceased 

88 Bottom-hole temperature, indicating 

hours after circulation ceased 

1 Equivalent depth, corrected for differences 

in static water level for comparison 

with curve A 

differences in static water levels ' , " 

'40 .. 

38 

Reference-boiling-temperature 

curve for pure water, assuming 

water table at ground surface 

and at altitude of- 7,500 ft 

Biscuit Basin 

rhyolite flow 

FIGURE B.-Temperatures and other data, Y-1 (Black Sand) drill hole, Upper Geyser Basin. 

water pressures at Yellowstone would be so much 

higher than at Steamboat Springs. Eruption tendencies 

ofY-1 first became evident near-180ft but were easily 

controlled to -209 ft where the core barrel was retrieved from within the drill rods without difficulty. But 

when the core barrel was withdrawn from-215ft, cool 

drill water gushed from the rods in response to the high 

wellhead water pressures. The drillers did not have the 

time or sufficient experience with potentially erupting 

wells to maneuver the drill chuck back over and into .the 

rods in order to control the hole. Within a few seconds 

the top cool water was followed by a mixture of boiling 

water and steam, and the well surged into violent 

eruption-a shattering experience for all of us! The 

eruption had the ((bursting" characteristics of many 

geysers of high temperature and abundant water supply (White, 1967, p. 661). Boiling water and steam covered the drilling platform and concealed the control 

levers used for maneuvering the drill chuck. 

The eruption continued unchecked, with some. decrease in bursting but little decrease · in discharge. 

Clearly, the permeable rock in the uncased hole below 

-100ft could deliver ample thermal water to continue 

the eruption indefinitely. After about 30 minutes, however, visibility improved enough for the driller to maneuever the drill chuck_ into the erupting column and 

down into the drill rods. The chuck was then screwed to 

the rods, cold water was pumped into the hole, and the 

eruption was terminated. 

Three subsequent eruptions occurred during withdrawal of the drill rods from the hole, in spite of intermittent pumping of cold water. A maximum wellhead 

water pressure of31 psig was measured on April25; this 

is equivalent to a static water level about 74 ft above 

ground surface. This was our introduction to the high 

. wellhead fluid pressures that were later found in all but 

1 of the 13 Yellowstone drill holes. 

In order to increase · the density of water in the hole 

and thereby decrease the wellhead pressure, on April26 

cold water was pumped down the hole for 40 minutes. 

By this procedure the wellhead pressure was decreased 

from its previous ~30 psig, but only to 24 psig. High 
UPPER BASIN AND UPPER FIREHOLE RIVER 15 

wellhead pressures were clearly to be a continuing prohlem. We then tried to lower formation permeability by 

pumping 10 sacks of cement into the hole, using a maximum pumping pressure of550 psig. We had expected to 

redrill the cement in the old hole, but found that it was 

harder than the adjacent porous hydrothermally altered rock (Honda apd Muffler, 1970); deflection started 

to occur near-105ft, and was in new ground with no 

cement in core below-115ft. The new hole (called Y-1x 

for comparison) exhibited high pressure by discharging 

water when core was retrieved from -115 ft and the 

rate of discharge increased irregularly at successively 

greater depths. It was particularly high from -170 to 

-180ft, so cement was again pumped into the hole in an 

effort to plug the most permeable rock. Drilling continued without new problems until -211 ft, when 

another eruption took place through the rods. Although 

about as violent as the eruption of April 24, this new 

eruption was quickly controlled by moving the drill 

chuck over and down onto the rods. 

After withdrawing the rods, we reluctantly concluded 

that cement had not reduced permeability enough for 

drilling to continue safely. We decided to move the rig to 

another site, planning to return to Y-1 after we had 

developed more skill and better equipment for combating the high pressures. 

The drillers were dismantling the rig for moving to a 

new site when a pressure gage was put on the hole. To 

our surprise, wellhead fluid pressure was already 50 

psig or nearly 20 psi above the previously observed 

maximum. During the next 15 minutes pressure rose 

steadily to 60 psig with no signs of stabilizing. This was 

yet another problem not anticipated from previous experience. The drill crew was about to quit for the day; 

should we let the hole rest overnight, with the possibility of a continuing rise in pressure, perhaps exceeding 

the 125 psi rating of the valve? We decided to fill the 

hole with cement. 

During later drilling with improved equipment and 

more experience, we found that somewhat higher pressures could be controlled safely, and we then regretted 

our decision to cement Y-1. This not only prevented 

deepening the hole and collecting fluids from depth, but 

also prevented observations aimed at understanding 

the high pressures in Y -1x. 

The terminating eruption at-211ft in Y-1x differed 

from the terminating eruption at-215ft in Y-1 in that, 

even with cold water just pumped into the hole, Y-1x 

surged almost instantly into eruption. The explosive 

discharge of Y-1x suggested that so much gas was entrained in the water in the drill rods that the average 

density and physical behavior were very different from 

that of Y-1 at the same depth. 

Observations on subsequent Yellowstone drill holes 

30 pounds per 

square inch (gage) 

60 pounds per 

square inch (gage) 

Weight of 

water column 

= 30 psi 

pressure at 

Y-1 211 tt-about 

120 psig 

Gas (water 

vapor 

condensing) 

~ Water level 

forced down 

as uncondensed 

gases accumulate 

FIGURE 9.-Preferred explanation for differences in gage pressure 

recorded in Y-1 drill hole and its redrilled lower segment, Y-lx 

(here shown for simplicity as a separate hole). 

support our conclusion that the main difference in behavior between Y-1 and Y-1x ~as due to the greater 

content of gases in the fluids ofY-1x. The high wellhead 

pressures measured just before Y -1x was cemented 

were almost certainly caused by accumulation of gases 

beneath the valve, with a resultant depression of the 

water level in the hole, as illustrated by figure 9. The 

rising water near the center ofupflow may have already 

started to form vapor bubbles at depths and temperatures considerably greater than those of Y -1. We assume in figure 9 that Y-1x intersected such a channel of 

upflowing water and vapor,just missed by Y-1. Another 

explanation assumes that the lower part ofY-1 was not 

filled with cement and that the ((short-circuit" provided 

by the open hole permitted rapid flow of water from near 

or below -215 ft to higher levels. This hotter water 

when tapped by Y-1x would boil more vigorously and 

produce more gas than the water in Y-1 (see later discussion of Norris Basin holes). 

Y-7 (BISCUIT BASIN I) DRILL HOLE 

SITE SELECTION 

Two drill holes, Fenner's Carnegie I and our own Y-1, 

had explored the southern part of the Upper Basin, 

but the subsurface relationships were still not ade-
16 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

quately known. A site near the north end of the basin 

was selected as the best available for providing more 

data. The site is just north of the loop road at the north 

end of the Biscuit Basin parking area. 

PHYSICAL MEASUREMENTS 

The physical data from Y-7 are summarized in table 

4; temperatures and other pertinent data are shown in 

figure 10. Drilling was so trouble-free and rapid that 

only a few measurements were obtained (figure 10, 

curve B). Decreases in thermal gradient probably occurred just below the water table and also somewhere 

near -60 ft at the top of a permeable zone in which 

circulation was lost. All temperatures are far below the 

reference boiling-point curve (A of figure 10). 

Water-level measurements (table 4) are also 

significant. The water table was first identified at about 

5 ft below ground, at an altitude almost identical with 

that of the Firehole River north and northwest of the 

hole. The water level declined to about 6ft below ground 

when the drilled depth was near -60 ft, probably because of cooling by drill water with consequent increase 

in density of water in the hole relative to predrilling 

densities. The water level then rose to 3.8 ft below 

ground when the hole was first drilled to -242ft. The 

relatively low temperatures and the absence of static 

water levels above ground surface are marked contrasts 

with all other research holes in Yellowstone, and indicate that Y -7 is outside the main zone of upflowing hot 

water. Thus, drilling was terminated at -242 ft. 

POSTDRILLING MEASUREMENTS 

A thermistor temperature series was obtained from 

the surface to -110 ft, 11 days after Y-7 was completed 

(fig. 10, curve C), and a second series with a longer cable 

was measured to the bottom in June 1968, 9 months 

after completion (curve D). A third series obtained on 

September 4, 1969, was similar to but slightly lower 

than curveD, as was a fourth series on September 23, 

1971, ana a fifth series on September 16, 1973 (by M. 

N athenson). Seasonal fluctuations in water levels seem 

to occur, with highest levels during spring runoff(table 

4). These may be accompanied by slight fluctuations in 

temperature in Y-8 with higher temperatures in the 

spring and somewhat lower temperatures in the fall. 

This possibility has not yet been confirmed (by measuring a spring temperature profile) since curve D was 

obtained. 

After initial temperature recovery, the static water 

level averaged about 3ft below ground, or ~2ft above 

the water table (- 5 ft). This represents an upward hydraulic gradient of about 2 ft over 240ft or ~0.008 (table 

3); this is equivalent to a positive fluid pressure at the 

water table of about 0.83 psi from the bottom zone. 

Temperatures continued to rise for some weeks after 

drilling ceased. This may be due to further recovery of 

temperature after cooling by drill water, but a more 

likely explanation, based on the water-level data and 

experience with other Yellowstone drill holes, is that 

hot water flowing slowly up the hole and into permeable 

ground heated the ground slightly above predrilling 

temperatures, with consequent slight rise in the average static water levels. 

This slow increase in bottom-hole temperature over 

a long period of time is unique in our Yellowstone drill 

holes and indicates that drilling resulted in increased 

flow from surrounding hotter ground. This is a mild 

example of the pronounced changes to be described in 

Norris Basin drill holes. 

Each serie~ o~thermistor readings shows a relatively 

TABLE 4.-Temperatures, water levels, and other observations from Y -7 (Biscuit Basin 1) drill hole, Upper Basin 

Date and time Observation Temp. Thermometer 

1967 depth, ftl col No. 

9/6 1410 10.0 (20.5) 

1420 10.0 (20 .8) 

1505 (13) (22) 

1545 (17.6) (26.5) 

917 0900 8 34 

1510 44.0 (41.5) 

9/8 0800 62.0 86.0 

- 0815 (25.0) (50.0) 

9/9 0840 (65.4) (77.8) 

1455 

9/10 1030 g6:n 170.8 iii ~} 111.9 4 

1045 8 

9/11 0800 170.7 116.7 8 

9/12 1105 240.1 140.9 8 

9/13 0843 239.6 141.8 8 

9/22 

6/13/68 1140 231 142.3 

9/4/69 235 141.7 

143.1 13 & 14 

9/23/71 237.1 142.2 143.4 12 

9/16173 141.6 

'Data in boldface considered most reliable; data in parentheses, least reliable. 

Static 

water 

level, ft 1 

- 4.9 

- 5.0 

- 4.9 - 4.8 

- 4.4 

- 5.7 

- 6.4 

-3.7 

- 3.35 

- 3.80 

- 3.37 -3.05 - 1.3 

- 2.88 

- 2.42 

- 2.64 

Comments 

Drilled depth 11ft; after shutdown of 10 min; a minimum temperature; lost circulation 

1{}..-11 ft. After 20 min shutdown; probably best indication of water table. 

Then drilled to -21 ft at 1615; cased and cemented. In cemented hole. With drilling, intermittent lost circulation. 25 min after drilling to - 52 ft; hole caving; drilled to - 67 ft at 1630. 

Hole caved to 58 ft; 4 ft into fill. Much above bottom. Then drilled to - 102 ft at 1300, cased (3") and cemented. Lost 

circulation - 65 to - 102 ft. In cemented hole, much cooled by drill water. Lost circulation 148-167 ft; uncemented sand and gravel from - 162 to - 172ft? Drilled 

to -172 ft, 1350. 20 hr after circulation; note rise in water level with heating. 

41 hr after circulation; good core recovery below - 192 ft; drilled to -242ft; - 1230, 

hole terminated. - 22 hr after circulation. 

44 hr after circulation. Thermistor temperatures to -110 ft; see fig. 10, curve C. 

Thermistor temperatures to bottom, fig. 10, curve D. Thermistor series not shown on fig. 10; nearly identical to curve C to - 56 ft, then 

slightly below curve D to bottom. Thermistor series, not shown on fig. 10. 

Thermistor series measured by M. Nathenson, not shown on fig. 10; similar to curveD but slightly lower from - 30 to - 160 ft. 
UPPER BASIN AND UPPER FIREHOLE RIVER 17 

CASING RECORD TEMPERATURE, IN DEGREES CELSIUS 

CONDENSED 

LOG 

0 20 

0 

of 4-in. 

casing 

100 102ft 

of 3-in. 

casing 

200 

TO 1--

w 242 w 

LL 

~ 

I 300 

1--

Cl... 

w 

0 

400 

500 

Curve C. 

Thermistor series Sept. 22, 1967, 

11 days after completion 

Curve B. 

Bottom-hole temperatures 

as drilling progressed 

EXPLANATION 

0 Bottom-hole temperature - 16 hr 

after circulation ceased 

41 8 Bottom-hole temperature, indicating 

time after circulation ceased 

(hours, unless specified) 

.- Thermistor temperatures in completed hole 

Curve D. 

} 

Silt, sand, 

Lost circulation and gravel, 

partly 

altered and 

cemented 

} Lost circulation 

173ft ---------j 

Pumiceous flow 

breccia, Biscuit 

Basin lava flow 

Thermistor series June 13, 1968, 

9 months after completion 

Curve A. 

Reference boiling-temperature 

curve for pure water, assuming 

water table at ground surface 

and at altitude of -7,500 ft 

FIGURE 10.-Temperatures and other data from Y-7 (Biscuit Basin I) drill hole, Upper Basin. 

low gradient in the permeable zones from about -60 to 

-100ft and -150 to -170ft, where circulation losses 

were noted during drilling. Local convective circulation 

is likely to occur in each permeable zone, which would 

tend to equalize temperatures and result in low thermal 

gradients. The hole was cased and cemented to -102ft, 

which is near but probably not below the bottom of the 

thickest permeable zone. Permeability of rocks adjacent 

to the casing was high enough, however, for hot water 

from below to flow up around the casing, thus causing 

higher temperatures within the casing. This increase in 

upflow was indicated at least as high as -55ft, perhaps 

with some influence to -30 ft. 

Some convection also occurs within the NX casing, 

tending to raise temperatures in the upper part. Positive evidence for convection was identified by Manuel 

Nathenson on September 16, 1973, using a thermocouple and a portable strip-chart recorder. Fluctuations of 

as much as 1.5°C occurred in 10 minutes, and temperatures in individual eddies changed as much as ~ 1 oc. 

Y-8 (BISCUIT BASIN II) DRILL HOLE 

SITE SELECTION 

Temperatures and pressures in Y-7 were relatively 

low compared with other holes already drilled elsewhere in Yellowstone National Park. However, the 

chemical compositions of water from nearby springs 

suggested that subsurface temperatures in the immediate area were at least as high ( ~200°C), as found in 

previous holes. Accordingly, a second drill site was 

selected in Biscuit Basin about 425ft south ofY-7 and 6 

ft higher. The site is within a cluster of discharging 

springs, 48 ft northwest of a small geyser informally 

called ((Rusty" (Marler, 1973, p. 25). 

PHYSICAL MEASUREMENTS AS DRILLING PROGRESSED 

The physical data from Y-8 are summarized in table 

5; temperatures, the casing record, and a condensed log 

of the rocks are shown in figure 11. Some data on temperatures and depth of the water table were obtained 
18 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

close to the surface, but no reliable temperatures were 

obtained from 6.4 to 163 ft in depth because of the 

combined effects of casing, cementing, and rapid drilling. 

The water table was first identified at about -3 ft 

when the hole was 5¥2 ft deep. The hole started to discharge at a drilled depth of28 ft when the drill stem was 

opened for core recovery, so a static water level above 

ground was first noted at this depth or a little higher. 

The wellhead water pressure was 8 psig at-163ft and 

then rose abruptly to ~29 psig at -181 ft, where the 

first strong eruption tendencies were recognized. 

A zone of high permeability (indicated by partial loss 

of drill water) was noted from about -150 to -172 ft, 

evidently nearly isolated by partial self-sealing from a 

deeper permeable zone of much higher wellhead water 

pressure below-180ft. This deeper aquifer is near the 

upper contact of a flow breccia of the Biscuit Basin flow 

(R. L. Christiansen, written commun., 1974). Temperatures increased only slightly with greater depth, reaching a measured maximum at -261 ft, and then decreased slightly to the bottom of the hole. 

POSTDRILLING MEASUREMENTS 

Measurements made in June 1968 and October 1969 

indicate that since drilling was completed, hot water 

under high pressure has been flowing up the hole into 

the permeable sediments of lower water pressure, at 

least up to the bottom of the · casing at -93 ft. Consequently, temperatures and pressures at depths of less 

than - i80 ft have increased significantly. 

Curv~s C and D of figure 11 cannot represent original 

ground temperatures. For example at -163 ft, where 

wellhead water pressure was ~8 psig (table 5), the predrilling ground temperature might have been as high as 

158°C, or 5°C above the observed temperature and 4°C 

above the reference boiling-point curve; this is the maximum temperature consistent with the observed wellhead water pressure. The postdrilling temperature of 

about 167oC at the same depth must be accompanied by 

a wellhead water pressure of at least 33 psig. Wellhead 

fluid pressures (largely if not all water) of about 35 psig 

(table 5) were observed during the month after completion of the hole. Vapor bubbles in the liquid, separating 

in part because of the partial pressures of other gases 

and thereby decreasing average density, may account 

for the discrepancy of about 2 psi in pressure at the 

wellhead. Predrilling overpressures below -180ft were 

probably higher than 35 psig. 

Downhole pressure measurements were made in 

1969 and 1971 (fig. 12). In Y-8, after the hole was 

capped for a sufficient time, the water level was disTABLE 5.-Temperatures, pressures, and other observations from Y-8 (}3iscuit Basin II) drill hole, Upper Basin 

Date and time Observation Temp. Thermometer Static Wellhead Comments 1967 depth, ft 1 oct water pressure, No. level, ft 1 2 psig1 

9/12 1525 2 Vz (-2.3) Drilled depth 3Vz ft; drilled on to - 7\t., ft at 1545. 

1605 5.5 (17) (- 1.4?) 9/13 0800 5.5 51 1fl - 3.15 Temperature at sand level; few gas bubbles. 

0815 6.4 72 Thermometer 9 in. into sand. 

1325 17.5 -1.75 Drilled to -· 20 ft at 1425, cased (4 in.) and cemented. 

9/14 0825 8.3 (64) (- 1.0) On cement; much cooling by lost d.rill water. o . 

1050 28 > 84 Above Hole discharged 6 gpm at-28ft; discharge temperature 84 C. Dnll water 

ground muddied spring 50 ft to southeast, and Rusty Geyser less active. Dnlled to - 93 ft at 1545; set casing (3 in.) and cemented. 

9/15 1000 11.7 (72) On cement. Drilled to - 163 ft at 1540. Rusty active again. 

9/16 0820 162.9 153.1 8 (+ 19) 8 Only partial drill water return from - 163 to - 173 ft. 

1205 181 (+70) 29 Pressure increased near - 180ft. Drilled to -211 ft at 1440. 

1530 211 166.0 8 29 \fo, - 1 hr after circulation. 

9/1 7 1315 211 168.1 8 (+74) 31 Approximate wellhead water pressure 22 hr after circulation. 

9/18 0758 211 167.9 8 30\fo, 40 hr after circulation. Well first erupted 0915; Drilled to - 261 ft at 

1530. 

1600 28 \fo, 

9/19 0800 - 261 i~~:§ } 169.6 4 (+ 74) 31 Drill rods dropped 2 ft at - 320 ft; soft, or a cavity. Drilled to -342 ft at 

- 261 8 1520. 

9/20 0755 341.6 169.8 8 (+78) 32'h Thermometer not insulated. Drill rods fell 1 ft at - 371 ft; cavity? Drilled to - 423 ft at 1600. 

9/21 0806 423.6 169.1 } 169.3 4 (+79) 33 Wellhead water pressure. Thermometer not insulated so temperature 

0821 423.6 169.4 8 33 reversal? Drilled to -503 ft at 1520. 

9/22 1235 500.6 166.4 } 166.9 4 (+80) 33Vz Thermometer insulated for first time; note slight temperature reversal. 

1420 167.3 8 34 

10/17 500.7 (169.0) 9 (+84 ) 72 to 35 Not insulated. Bottom pressure 235±3 psig. 

10/22 499.7 (+84) 35 Top pressure (after %as bled om. Bottom pressure 22 psig (probably low due to leaking check valve at bottom of tube). 

6/12/68 (275) (167.8) (+98) 84 to 41 Pressure decreased as gas bled off. Thermistor temperatures (curve C, 

494 166.0 fig . 11). 

9/15/69 498 Bottom pressure 230 ± 0.5 psig. 

10/4/69 86 to 47 Maximum-thermometer series, curveD, fig. 11, to check thermistor series of 6/12/68; maximum temperature (uninsulated), 169.6°C; probably 

near - 250 ft 1 gal. water during series. 

5/28171 (+95) 39.5±0.5 

499 Bottom pressure 230 ± 0.5 psig. 

9/23171 496 165.5 (+89) 78 to 37 

494 Bottom pressure 230 ± 0.5 psig. 

9/27171 496 (+89) 78 to 37 Bottom pressure 231 ± 0.5 psig 

'Data in boldface considered most reliable ; data in parentheses, least reliable. . . 2Relative to ground surface; positive levels in parentheses, calculated from wellhead pressures considered least affected by vapor; assumed factor of2.4 IS somewhat h1gh. 
UPPER BASIN AND UPPER FIREHOLE RIVER 19 

CASING RECORD TEMPERATURE. IN DEGREES CELSIUS 

CONDENSED 

LOG 

0 

0 

100 

20 40 60 80 100 

I ----- r-r--~----l(.pS::::J:==:::::::r:r.r====r-=-,_-=::::::c2oft 

Curve C. 

Thermistor series 

June 12, 1968 

Curve B. 

140 160 180 200 220 

-~-~---,-~,---'--~s~ft~--~~==c=~ 

Curve D. 

"""--- / Maximum-thermometer series 

:"X:----,_, ~ct. 4, 1969 

~ 

~ Sand and 

gravel, 

cemented 

Bottom-hole temperatures 

as drilling progressed 

} Lost circulation 

181 ft ---------------1 

200 

fw 

w 

u._ 

~ 300 - I -

fCl.. 

w 

0 

400 

500 

600 

EXPLAN ATION 

0 Bottom-hole temperature - 16 hr 

after circulation ceased 

40 8 Bottom-hole temperature, indicating 

hours after circulation ceased 

~ Thermistor temperature series in 

completed hole 

1 Equivalent depth corrected for 

differences in static water 

level for comparison with 

curve A 

X Maximum-thermometer measurements, 

Oct. 4, 1969 

Curve A. 

Reference boiling-temperature 

curve for pure water, with 

water level at ground surface 

Flow breccia 

206ft \ of Biscuit 

Basin flow 

Pumiceous 

tuff of 

Biscuit 

Basin 

rhyolite 

flow 

FIGURE H.- Temperatures and other data from Y-8 (Biscuit Basin II) drill hole, Upper Geyser Basin. 

placed to a depth of about 96ft. The pressure and temperature measurements of figure 12 were made after 

the accumulated gas had been bled from the well. Gas 

accumulated in Y-8 so rapidly that, during the measurements, a small amount of leakage was allowed to 

insure a maximum content of water in the hole. The 

linear array of pressure data indicates nearly complete 

success in this effort. 

The upper part of the postdrilling temperature profile 

(curve D) can be interpreted as reflecting a combination 

of convection, adiabatic boiling, and conduction. The 

inflection point at about -180 ft probably is due to the 

influx of gas-bearing water from the aquifer at -181ft. 

From this point to about -130 ft the approximate congruence of curve D with the reference boilingtemperature curve (B) suggests that boiling is occurring. From -95 to-20ft, linear gradients suggest cooling by conduction through the NX casing. The much 

lower but still linear gradient from -- 20ft to the surface 

may reflect the greater mass of highly conductive iron 

in the double strings of casing there. If adiabatic boiling 

is assumed in the zone from -130 to - 180 ft, pressure 

readings can be compared with the boiling pressures for 

pure water at corresponding depths and temperatures, 

determined from steam tables (curve E, fig. 12). The 

calculated pressures are all at least 8 psi below the 

measured pressures; the discrepency is most reasonably 

explained by the partial pressures of other gases. When 

a vapor phase is present, the measured pressure is equal 

to the partial pressure of water vapor plus the sum of the 

partial pressures of all other gases. If we assume that 

the proportion of vapor in the column was so low that 

average density was not decreased significantly, the 

partial pressure of all other gases (mainly carbon dioxide) is calculated to be about 8 psi or 0.54 atm. This 

assumption is supported by the fact that curves A and C 

of fig. 12 are nearly parallel, and both are slightly concave downward as they should be. Curve G, a nearsurface modification of pressure curve C, indicates the 

assumed effects of gas accumulation after a shutdown 

time long enough for the water level in the hole to be 

depressed to the bottom of the casing. 
20 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

EVIDENCE FOR NEAR-S URFACE SELF-SEALING 

IN Y -8 DRILL HOLE 

Pressures observed at the surface or calculated from 

water levels are shown in figure 13 relative to drill-hole 

depth at the time of each measurement. Wellhead water 

pressures clearly increase greatly downward, especially 

between depths of -163 and-181ft (near 7,100-ft altitude). A major decrease in permeability with time in 

Iw 

w 

LL 

~ 

I 

Ia.. 

w 

0 

CASING RECORD 

0 

TEMPERATURE, IN DEGREES CELSIUS, AND 

PRESSURE, IN POUNDS PER SQUARE INCH (ABSOLUTE) 

260 Or--.~-.------.-~~----~------~~.---~-.---,--~--.---,---.--.---.--,---,---~-.---.---,--, 

40 

80 

120 

160 

200 

240 

280 

320 

360 

400 

440 

480 

4-in 

casing 

3-in. 

casing 

TD 

503 

"\ i 

\.+ t'curve G. 

~ I Assumed near-

~ : surface pressure 

"'\ 1 with water dis-

'ffi.: placed by vapor 

"\--.Curve C. 

Curve A. 

\ 

\ 

\ 

\ 

\ 

\ 

Reference boilingpressure curve 

~ ~easu ed pressures ; 

"'-~est fit of all data 

~ Curve B. 

Curve E. 

Calculated boiling 

pressures for 

temperatures measured 

on Sept. 23, 1971 

EXPLANATION 

Measured temperature 

X Sept. 23, 1971 

Measured pressure 

8 Sept. 15, 1969 

0 May 28, 1971 

+ May 28, 1971 

'\'\ Reference boiling-

~ratum curve 

" ' \ 

(while venting-5 gpm) 

0 Sept. 23, 1971 

8 Sept. 27, 1971 

Curve D. 

Measured temperatures, 

Sept. 23, 1971 

\ 

\ 

\ 

\ 

\ 

\ 

~ \ 

X \ 

X \ 

t---Curve F. 

\ Calculating boiling 

\ temperatures for 

\ measured pressures 

\ 

\ 

\ 

\ 

\ 

' \G ~ 

\~ \ 

X 

~G 

~G 

\ 

FIGURE 12.- In-hole temperature and pressure, Y-8 drill hole after completion, with other reference curves. 
UPPER BASIN AND UPPER FIREHOLE RIVER 21 

response to hydrothermal activity is required to explain 

these pressure differences. The sediments are now well 

cemented and probably date from the late Early 

Pinedale glacial stage less than 25,000 years ago. The 

original stream sediments were mainly coarse grained 

and sufficiently well sorted to have had high porosities 

and permeabilities. However, only about a gallon per 

minute of water was discharging from the spring 50ft 

south of the drill hole (fig. 13), and probably no more 

than 20 gpm in total was discharging from all springs 

within 200ft of the drill hole. Obviously, in spite of the 

high vertical water pressure gradient from -180 ft to 

the surface, only a little water can actually flow upward. 

The only reasonable explanation is that originally high 

SOUTH 

Nearby 

7300' 

7200' 

6900' 

6800' 

0 100 

0 25 

permeabilities have decreased greatly in response to 

deposition of hydrothermal minerals in pore spaces and 

fractures. Petrographic and X-ray study of the cores 

from this hole (Terry E. C. Keith, written commun., 

1973) indicates abundant hydrothermal quartz, chalcedony, analcime, and calcite throughout most of the 

hole, especially within the 10-ft interval from -170 to 

-180 ft, where the pressure gradient is highest. Subordinate montmorillonite, celadonite, and mordenite also 

occur. The drill hole evidently provides an effective 

hydraulic ((short-circuit" across this self-sealed zone. 

The large increase in upflow in response to this shortcircuit explains the major differences between curves B 

and C of figure 11. The increase in upfiow also resulted 

Water table 

Sand and gravel 

(originally highly permeable) 

Flow breccia 

(originally permeable) 

NORTH 

-- ~----?-- -------

-1 .6 (Sept. 12, 1967) 

-0.5 (June 13, 1968) Pumiceous tuff 

(originally permeable?) 

200 FEET 

50 METRES 

6700'L_ _____________________________________________________________________________________________ 

EXPLANATION 

33 Wellhead water pressure, 

in pounds per square inch 

(gage), as drilling progressed 

- 2.4 Water level below ground 

expressed as negative 

wellhead water pressure 

--60"- Contour, showing inferred 

ground temperature, in 

degrees celsius 

Direction and qualitative 

rate of flow of thermal 

water 

Decreased permeability 

due to deposition of 

hydrothermal minerals 

FIGURE 13.-Section through Y-7 and Y-8 drill holes, showing pressures, temperature contours, and deduced self-sealing by deposition of 

hydrothermal minerals in originally permeable ground. 
22 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

in much greater pressures at all depths above -180ft; 

and the high initial temperature of the upflowing water 

( ~ 169°C) eventually raised all shallow temperatures. 

The in-hole fluid pressures measured in 1969 to 1971 

(curve C, fig. 12) all indicate wellhead water pressures 

significantly above the ~30 psig measured when the 

hole was being drilled through the zone of maximum 

temperature near -120 ft. The wellhead pressures 

measured as drilling progressed were generally slightly 

low because of the cooling effects of drilling water, but 

the measurements of September 16-18, 1967, suggest 

rapid recovery from this effect, at least near-211ft. In 

contrast, postdrilling in-hole pressures may be higher 

than original pressure because of extensive upflow and 

heating with consequent expansion of water in the hole 

at all levels above -181ft. The natural fluid pressure at 

about -181 ft before disturbance by the drill hole cannot be determined from our data but was probably about 

32 psi above curve A of figure 12, rising perhaps to 35 psi 

at the bottom of the hole. 

HORIZONTAL "SELF-SEALING" AND CIRCULATION 

PATTERN BETWEEN Y-8 AND Y-7 DRILL HOLES 

As discussed above, the increasing wellhead fluid 

pressures with depth in Y-8 are related to self-sealing 

by hydrothermal minerals. The original sediments, as 

displayed in the cores, contain no strata likely to have 

been initially fine grained and low enough in permeability to account for the observed vertical pressure differences. Equally strong evidence for horizontal selfsealing by hydrothern1al alteration and mineral deposition is the contrasts in wellhead water pressure that 

exist between Y-8 and Y-7 at equivalent depths. 

Many Individual beds were originally well-sorted 

permeable steam sands and gravels, and original hydraulic gradients must have been exceedingly low when 

hot water first started to flow through these sediments. 

The water table as identified in Y -8 and Y-7 differs in 

altitude by about 8ft (table 3), sloping downward to the 

north at a gradient of 0.019. In contrast, the present 

horizontal hydraulic gradient in sediments near -170 

ft in both holes is now about 7 psi per 100ft (32 psi less 

~2 psi for difference in altitude, table 3, divided by 425 

ft), or about 0.17. For comparison, the hydraulic gradient of the water table from Y-7 to the Firehole River is 

about 0.01. Pressure in Y-7 is clearly more closely related to a normal rate of increase with depth below a 

free:. standing water table than to the hydrothermal system tapped by Y -8. 

Horizontal temperature gradients per 100ft from Y-8 

to Y-7 are about 4°C at -50ft, 5°C at-100ft, 7%°C at 

-150ft, 8 %°C at-200ft, and 5°C at-250ft. Note that 

the calculated horizontal temperature gradients are 6 

to 12 times the vertical gradient for conductive lieat 

flow in !!normal" nongeothermal areas. All temperatures in Y-7 are much too low for a vapor phase to form. 

Temperatures are concluded to decrease for the most 

part from Y-8 to Y-7 because of slow northward flow of 

water through an imperfectly sealed zone, with upward 

conductive cooling of the water. 

Our interpretation of temperature contours and circulation patterns along a vertical section that includes 

Y-7 and Y-8 (fig. 13), involves the following concepts: 

1. Vertical or steeply dipping fractures probably control the upflowing water discharged from springs 

near Y-8; 

2. Temperature contours bulge upward on and near 

these upflowing channels. 

3. Except for such modifications, temperature contours from 60°C to 140°C are controlled by data 

from Y-7 and Y-8. 

4. Positions of the indicated 160° and 170oC contours 

are much less certain and are controlled entirely 

by data from Y -8. We are confident that 1 70°C does 

occur in or very close to Y-8 (169.6°C was measured at -261ft after 16% hr without circulation, 

so original ground temperatures probably exceeded 1 70°C). 

5. The slight reversal of temperature below-400ft in 

Y -8 is best interpreted as the intersection of the 

drill hole with the edge of a convecting cell that 

!!mushrooms" outward. Location of the center of 

the cell is not known, but subsurface temperatures 

of ~200oc are indicated from silica contents of 

springs to the west, south, and east of Y-8. 

6. The principal upflow is shown in figure 13 as occurring in zones of most extensive mineral deposition, 

which occurs in initially permeable walls of fractures as hot water escapes. Eventually the channels and their immediate walls are thoroughly 

sealed, and either new channels form or local flow 

declines and then ceases. 

CARNEGIE I DRILL HOLE, MYRIAD GROUP 

SITE SELECTION 

The Myriad springs, a rather inconspicuous group 

1,500 ft west of Old Faithful, were selected by Allen, 

Day, and Fenner of the Geophysical laboratory of the 

Carnegie Institution of Washington for their first research drill hole in Yellowstone in 1929, here called 

Carnegie I. Reasons for selection of this site were not 

specified, but a typical ((alkaline-water" area clearly 

was desired. Other factors evidently considered included proximity to Old Faithful, accessibility to housing, and a convenient supply of drill water, which was 

piped from Old Faithful Inn. The specific site is now 

marked with an inconspicuous concrete pad 100 ft 

northwest of Round Geyser and near the center of the 

Myriad Group. 
UPPER BASIN AND UPPER FIREHOLE RIVER 23 

PHYSICAL MEASUREMENTS AND INTERPRETATIONS 

Physical data from Fenner (1936) are summarized in 

table 6, supplemented by previously unpublished data 

from Fenner's field notes. The most significant temperatures are shqwn in figure 14. Obvious differences are 

evident between the temperature data of Carnegie I and 

corresponding data from our drill holes in Upper Basin 

and elsewhere. The measured temperatures in Carnegie I (fig. 14) are consistently below reference temperature curve A, in contrast to Y-1 (fig. 8), where all 

temperatures below -120 ft plot on or above the reference curve. The Carnegie I data suggest that G-I is 

comparable to Y-7 (fig. 10), which is in the border of a 

thermal system, rather than to Y-1 (fig. 8) or Y-8 (fig. 

11), which penetrate upfiowing systems. In fact, however, Carnegie I was sited near the center of the Myriad 

Group in which numerous steam vents, springs, and a 

few geysers are distributed throughout an area approximately 1,000 ft in diameter. Thus, we would expect 

Carnegie I to be even more centrally located in an 

upfiow system than either Y-1 or Y-8; conductive heat 

loss cannot in our opinion explain Carnegie I's characteristics. 

Thus, the data from Carnegie I need to be reexamined, utilizing our present knowledge of hydrothermal systems to determine whether the anomalies can 

somehow be reconciled. Although Fenner's published 

record contains no detailed data on drilling procedures 

or methods of measuring temperatures and pressures, 

his field notes indicate that Carnegie I was drilled using 

two shifts per day, in contrast to our single shift of 8 hr. 

The duration of each shift was not specified, but each is 

likely to have been at least 10 hr long, with continuous 

drilling probably from 8 a.m. of one day to 4 a.m. of the 

next. 

Until September 28, 1929, temperatures were measured at about 8 a.m., thus providing only 4 to perhaps 8 

hr for recovery from the cooling effects of previous drilling. On September 28, 1929, and generally thereafter, 

temperatures were measured during the day, at times 

only an hour or so after drilling had ceased. An armored 

thermometer was lJ.SUally lowered to within 1 or 2ft of 

the bottom of the hole. Some temperatures were measured soon after the hole had been opened and allowed to 

erupt. The decrease in confining pressure during eruption usually results in boiling and consequent cooling as 

heat is transferred to water from the rocks (table 6, 

series of Sept. 23, 1929), just as in an erupting geyser 

(White, 1967). Both the rate of drilling and rate of circulation of drill water were evidently much lower than in 

our holes. All these considerations other than rate of 

circulation should have resulted in measured temperatures relatively lower than ours. In figure 5, note that 

temperatures measured 4 to 7 hr after drilling, rather 

than our usual ~16 hr, would have been low by 6° to 

14°C (except in a high-pressure aquifer where original 

ground temperatures recover rapidly because of 

infiowing water). 

Fenner's pressure measurements cannot be compared 

directly with ours or evaluated with confidence in terms 

of wellhead water pressures and gas-accumulation effects; instead, they are clearly wellhead fluid pressures 

TABLE 6.-Temperature, pressures, and other observations, Carnegie I drill hole, Myriad Group, Upper Basin (reported by Fenner, 1936) 

Date and time' Drilled 

depth, ft. 

Sept. 14 1929 16 142 

19 0600 62 21 0800 95 23 0800 104.3 

24 0800 139 

25 0800 148 1700 26 0800 156 

27 0800 167 (2 168.3) 

28 0830 195 1400 205 

29 0800 220 

1445 226 30 0800 242 Oct. 1 1100 264 2 1500 292 

6 1400 313 7 1420 343 10 1010 379 

11 1610 406 

Aug. 29 1930 

'Largely from Fenner's original field notes. 

Temp. •c• 

125\12 

129 

(127 \12) 132 

145 

147 

(146) 

(146'hJ 155 

(141) 

159 \12 

164Y2 171 

175 

173 Y2 172 

180 

Wellhead fluid pressure, psig• 

13 

12 

(27\12) 

(27) 

25 

(30) 

32\12 

(3 7\12) 

(37) 

(37) 

27 \12 28 

(33) 

32\12 

(37) 

31 

(39) 

(42\12) 

42 Y.! (?J 43 

35 (?) 

49 

Comments' 

Drilling started; two shifts per day. Cased and cemented; depth of casing not stated, but evidently -42 ft where coring started. First steam, encountered suddenly. 

Chopping bit -97.7 to - 113.8 ft. (except "for a short time"J. 

After blowing for a few minutes. After blowing 3rd time. 

After blowing. 

After blowing. Drilled to -161.7 ft. first shift (2 ft more on 2d shift). Thermometer down after blowing. · Thermometer down after blowing (but may have hung up at - 121 ft.-not confirmed). Thermometer only to -121 ft.-hung up. Thermometer on drill rods, 2 ft. . off bottom (an hour or so after circulation ceased?). After blowing 20 min. Before blowing; thermometer only to -121 ft., jerking by steam? After blowing. 

(Time after circulation ceased not noted.) Before blowing; 40 psig after blowing, then to 42%, finally to 37 psig. After circulation? Pressure after blowing. Temperature after blowing, with thermometer 1'/• ft off bottom; pressure after blowing. At -300 ft, hole erupted for 1 hr but no effect on pools 50 to 75 ft away. After drilling; thermometer 1 Y.! ft off bottom. At -375 ft., hole erupted many hours, some slight surface effects; pool 50 ft. away became turbid. Thermometer to bottom on drill rods. Thermometer 1\12 ft off bottom several hours after circulation. Pressure 

before blowing; up to 57 psig after blowing. 

"Spring nearest drill hole now overflows and has overflowed since later stages of drilling; formerly rose and fell about 22 inches before drilling 

begun." 

2Data in parentheses considered less reliable. 
24 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

CASING RECORD 

0 20 40 60 

TEMPERATURE, IN DEGREES CELSIUS 

80 100 120 140 160 180 

CONDENSED 

LOG 

200 220 0,---~-=~==~~-----.---.---,---.---.-=~---,,---.-~.---.---,----.---.---.~-.---,----,--, 

----r--

Curve C. / ----- Approximate original ground -...;::· 

temperatures, assuming control Sand and 

gravel, 

cemented 

100 

200 

1-

UJ 

UJ 

LL 

~ 300 

::C 

1-

a. 

UJ 

0 

400 TD 

406 

500 

by water pressures as 

interpreted in text 

EXPLANATION 

0 Bottom-hole temperature as drilling 

progressed; differing times after 

circulation ceased 

X Calculated temperature from inferred 

water pressure 

Curve B. 

Temperatures and depths 

measured as drilling 

progressed 

Biscuit 

Basin 

rhyolitic 

obsidian 

flow 

FIGURE 14.-Temperatures and other data from Carnegie I drill hole, Myriad Group, Upper Basin (Fenner, 1936). 

in which effects of liquid and vapor cannot be distinguished. The pressure data of table 6 that are not enclosed in parentheses are most nearly comparable to our 

wellhead water pressures. If we assume equivalence, 

wellhead water pressures were about 12 psi near -100 

ft, 25 to 31 psi from about -140 to-240ft (and possibly 

deeper), and perhaps as much as 40 to 50 psi at depths 

below -250 ft. If the observed 49 psig of October 11, 

1929, was wellhead water pressure (which would have 

increased to 50 psig in a heated hole), and if the true 

bottom-hole temperature was directly related to this 

pressure, the original ground temperature may have 

been as high as 198°C rather than the observed 180°C. 

Curve C of figure 14 shows temperatures calculated 

from the most reliable pressure data of table 6. Each 

temperature thus calculated is likely to be a few degrees 

too high, but in our opinion curve C is much closer to 

original ground temperatures than curve B. Temperatures probably exceeded the reference boiling-point 

curve (A of fig. 14) at most or all depths below -62ft, 

where ~~steam" was first encountered (table 6). Fenner's 

indicated changes in temperature gradient near -140 

and -380ft probably have no significance. Additional 

evidence that subsurface temperatures in the Myriad 

system are at least as high as 205°C is based on silica 

content of 363 ppm in the spring nearest the drill hole 

(White and others, 1963), using the curves of Fournier 

and Rowe (1966). 

We emphasize here that the above comments are in 

no way either direct or implied criticism of Fenner or his 

drillers. On the contrary, we acknowledge our great 

indebtedness to these early pioneers. Carnegie I was the 

world's first research hole to be drilled into a highpressure hot-water system. Drilling equipment was 

primitive by present standards, and the effects of circulation of drill water and of induced eruption Cblowing") 

on bottom-hole temperatures were not yet understood. 

The principal previous drilling experience of the crew 

and of the Carnegie scientists had been in the vapordominated system ofThe Geysers, California (Allen and 

Day, 1927), where the most reliable temperatures and 

pressures were obtained after blowing (See White and 

others, 1971, for differences between hot-water and 

vapor-dominated systems.) 
UPPER BASIN AND UPPER FIREHOLE RIVER 25 

Fenner's previously unpublished comments on 

changes that occurred in nearby springs after the hole 

was completed (table 6) are similar to some of our observations. The increase in spring discharge probably resulted from ((short-circuiting" of aquifers by the drill 

hole, with consequent increase in upflow of hot water 

into spring vents. 

Y-6 (LONE STAR) DRILL HOLE, UPPER FIREHOLE RIVER 

SITE SELECTION 

Many hot springs of rather low discharge occur along 

and near the Upper Firehole River from 2 to 3% miles 

south of Old Faithful. The only named thermal feature 

of this group is Lone Star Geyser. Allen and Day (1935, 

p. 51) estimated a total hot-spring discharge of 0.06 

ft3/sec (25 gpm) from the area. An isolated drill site was 

needed for the last part of the 1967 summer tourist 

season; this isolation was provided by a locked gate on 

the service road to the Upper Firehole, half a mile 

southwest of Lone Star Geyser. The selected site was 

350 ft north of the footbridge of the Howard Eaton trail 

over the Upper Firehole, 7ft above river level, and 125 

ft northeast of the Firehole River, and thermal springs 

are absent. 

Our objectives were to obtain data on a rather inconspicuous hot spring group and to determine, if possible, 

its relation to the major Upper Geyser Basin 3 miles to 

the northwest. The altitude of the drill collar of Y -6 is 

about 7,640 ft; this is about 270 ft above Old Faithful's 

vent and 170 ft above Solitary Geyser, the highest 

thermal feature having a salinity similar to the other 

major springs of Upper Basin. 6 

PHYSICAL MEASUREMENTS AS DRILLING PROGRESSED 

The physical data of Y-6 are shown in table 7 and 

figures 15 and 16. Temperatures were relatively low in 

near-surface uncemented sands and gravels, probably 

because of southeastward flow of cold water through 

these sediments to the Firehole River. The water table 

was first identified at a depth of -3.2 ft, which is about 5 

ft above the mean level of the Firehole River 125ft to 

the southwest. 

Evidence for high wellhead water pressure was first 

noted at-172ft (table 7). From that depth to the bottom 

of the hole, most of our data indicate an almost constant 

6The Hillside Springs in the northwestern part of Upper Basin are more dilute than the 

geyser waters and are now depositing travertine rather than sinter; their highest altitude is 

nearly that of Solitary Geyser (7 ,4 70 ft), but old sinter from former springs in both the 

Hillside and Solitary areas occurs as high as 7,480 ft. 

TABLE 7 .-Temperatures, pressures, and other observations from Y -6 (Lone Star) drill hole of the Upper Fire hole River 

Date and time Observation Temp. Thermometer Static Wellhead 

1967 depth, ft 1 ocr No. water level, pressure, Comments 

fti 2 psig' 

8/17 1315 21.1 (17) Drilled to -50 ft at 1245; caving. 

1400 21.1 (15) Set 50 ft, 4-in. casing. Ceme_nted, 14 sacks cement. 

8/18 1000 22.0 20 On cement; drilled to -78ft at 1550. 

8/19 1630 51.4 28.8 -3.2 On 26V2-ft cave; temperature low from lost drill water. 

8/21 0740 51.3 33.9 Temperature probably close to original after 64 hr standing; drilled to -118 ft at 1425. 

-1500 93.2 (42.0) -3.1 Just after rods pulled; 25-ft cave; 3-in. casing set to -118 ft; cemented. 

8/22 0900 94.5 ~g.2 } 79.6 In cemented hole. Drilled to -182 ft at 1710 with first positive pressure 

94.5 noted at -172 ft. 

1750 182.5 103.8 14 (+4ll 17 v2 hr after circulation. 

1815 182.4 108.7 15 17 % hr after circulation. 

1822 182.4 111.6 14 161

4 1 hr after circulation. 

8/23 0740 182.5 129.1 } 128.8 4 37 to 18V2 Much gas at initial pressure. 

182.4 128.4 8 (+23) 18 to 934 Frothy water discharged at final pressure; drilled to -242 ft at 1715. 

8/24 0749 242.2 141.6 } 141.6 4 (+38) 16 to 16% 242.3 141.6 8 16% Then drilled to -302 ft at 1705. 8/25 0740 302.3 i!~:6 } 147.9 4 (+37) 15\">, 15V2 Leakage all water, no gas; all water pressure. 

302.3 8 16 Then drilled to -350 ft at 1530. 8/26 0833 349.7 } 349.8 (155.8 bumped) 4 (+ 36) 15 All water pressure. 0853 350.0 157.7 8 15 8/27 0804 349.6 160.0 8 (+38) 16 Leakage all water exsolving gas bubbles; all water pressure. -40 hr 

since circulation. 8/28 0737 349.5 i~8:~ } 160.1 4 (+38) 16 -64 hr since circulation. 0757 8 Then drilled to -383ft, 1600. 8/29 0737 382.9 } 382.9 (159.8 bumped?) 4 (+38) 16 to 161

/2 0755 382.9 161.7 8 16V2 Then drilled to -393 ft at 1430; quit for new bits. 

8/30 No morning measurements; drilled to -463 ft at 1725. 8/31 0736 463.3 i ~~:! } 173.9 4 12 down to 0 All gas at 12 psig, then to 0; no excess water pressure. 

0751 463.3 8 -15.4 Note depth to water in open drill rods. -20.7 Water level in drill rods after gas bled off outside rods; drilled to -500ft 

at 1530. 9/1 0902 499.7 } 499.6 i~g:~ } 179.3 4 (+40) 16V2 Note return of pressure, constant. 

0923 499.5 8 16V2 Hole terminated at -500 ft. 

9/2 0845 499.4 } 499.4 U6:g} 179.8 4 (+40) 16% Leakage, all water. 

499.3 8 16% 9/4 0942 499.0 180.7 8 (+41) 17 to 18% Leakage at first all water, exsolving gas, then water and gas as tempera9/5 0752 499.1 180.8 8 ture of discharge increased. 

(+41) 22 to 17 Pressure down, then up to 191

/2 psi. 10/16 1117 500 180.2 4 (+50?) 55 to 21 At first gas, then to all water exsolving gas. Bottom pressure 210 ± 5 psi; 

6/27/68 496 i~§:~ } overpressure -11 psi. 

179.7 12 (+55?) 26 to 23 Thermistor series; see figure 15. 

9/7/69 499 (+61?) 75 to 25V2 Bottom pressure 228 psia, 21 psi overpressure? 9/22171 494.2 179.2 12 (+50) 76 to 21 In-hole pressure and temperature series, with 227V2 psia recorded at 

-493ft. 

1 Data in boldface considered most reliable; data in parentheses least reliable. 2Relative to ground surface; positive levels in parentheses, calculated from wellhead pressures considered least affected by vapor; assumed factor of2.4 is somewhat high. 
26 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS; YELLOWSTONE NATIONAL PARK 

wellhead pressure of 16 psig. Fluid leaking from wellhead fittings during measurements was generally liquid water, commonly evolving a little gas only after 

leakage to atmospheric pressure. However, we observed 

puzzling pressure changes not recognized in other Yellowstone drill holes. At -182 ft on August 23 (table 7) 

after much leakage of gas and water, pressure fell to 9% 

psig, notably less than the 16 psig generally found elsewhere in the hole. On August 31 at a drilled depth of 

-463 ft, gage pressure fell to 0 as accumulated gas 

escaped. Surface fittings were removed, and depth to 

water inside the drill rods was then measured at -15.4 

ft; when gas was also bled from the space between drill 

rods and well casing, the water level inside the rods 

declined to -20.7 ft, or about 13ft below the level of the 

nearby Firehole River! By the next day, the well head 

water pressure was again near the normal16 psig that 

characterized most of the hole. 

Temperatures near the surface were about 90°C 

below the reference temperature curve (fig. 15, curves A 

and B). The difference between the two curves decreased rather regularly to about 17°C at the bottom of 

the hole. 

SUMMARY OF DRILLING PROBLEMS 

Y-6 was one of our easier drill holes to complete; fluid 

pressures and temperatures presented no problems that 

were n~t easily solved with the experience and drilling 

equipment available. The highest wellhead pressure 

observed during drilling was only 37 psig, and all pressures above about 20 psig were clearly caused by accumulating gas. Some minor drilling difficulty was encountered in penetrating the shallow glacial sands and 

gravels, which tended to cave in the open hole. 

POSTDRILLING MEASUREMENTS 

A thermistor temperature profile was obtained on 

June 27, 1968, nearly 10 months after completion ofthe 

hole (curve C, fig. 15), and a nearly identical second 

series was measured on September 22, 1971 (curveD, 

fig. 16), more than 3 years after completion. In-hole 

pressure measurements were made in September 1969, 

CASING RECORD TEMPERATURE, IN DEGREES CELSIUS 

CONDENSED 

LOG 

f--

w 

w 

lL 

~ 

I 

f--

a.. 

w 

0 

0 60 80 100 120 180 200 0~--~~~--~--~--~--~--~--~--~~~----~--~--.---.---,----.---,---,---,---,---,,--, 140 160 220 

100 

200 

300 

400 

500 

50ft 

of 4-in. 

casing Curve C. 

Thermistor temperatures obtained 

118 ft about 1 0 months after completion 

of 3-in. of the hole 

casing 

TD 

500 

EXPLANATION 

0 Bottom-hole temperature-16 hr after 

circulation ceased 

40& Bottom-hole temperature, indicating hours 

after circulation ceased 

-- Thermistor temperatures, June 27, 1968, 

-10 months after completion; "down" series 

X Temperatures on return to surface, 

June 27, 1968 

l Equivalent depth corrected for differences 

in static water level 

Reference boiling-temperature 

curve for pure water, assuming 

water table at ground surface 69.5 ft -----1 

and at altitude of-7,500 ft 

Curve B. 

Bottom-hole temperatures 

as drilling progressed 

Scaup 

Lake 

rhyolite 

flow 

FIGURE 15.-Temperatures and other data, Y-6 (Lone Star) drill hole, Upper Firehole River. 
UPPER BASIN AND UPPER FIREHOLE RIVER 27 

and again on September 1971, with results plotted in temperature curve A at all depths, indicating that heat 

is dissipated largely by conduction and by convection of 

water. Low-discharge nonboiling hot springs and sinter 

deposited by former springs occur from 175 to 300ft to 

the southwest, south, and southeast of the drill hole, but 

figure 16. 

INTERPRETATION OF DATA 

Temperatures measured as drilling progressed (curve 

B, fig. 15) are well below the reference boilingCASING RECORD 

0 

TEMPERATURE, IN DEGREES CELSIUS, AND 

PRESSURE, IN POUNDS PER SQUARE INCH (ABSOLUTE) 

0,-~~----~---------.--.---.--.~-.--.---~-.--~--~--.--.--~--~--.-~--~--~~.-~--~~ 

40 

4-in. 

casing 

80 

120 NX casing 

160 

200 

240 

1-

w 

w 280 lL 

~ 

:i 

1-

a.. 320 w 

0 

360 

400 

440 

480 

TD 

500 

520 

560 

600 

Curve B. 

Reference boilingpressure curve 

EXPLANATION 

Measured temperature 

8. Sept. 22, 1971 

G June 27, 1968 

Measured pressure 

0 Sept. 27, 1971 

\'.7 Sept. 7, 1969 

Curve A. 

Reference boilingtemperature curve 

Pressures measured 

\ept. 27, 1971 

\ 

\ 'B 

9 

FIGURE 16.-In-hole temperatures and pressures of Y-6 drill hole after completion. 
28 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

are absent to the north and west; the drill hole is on the gradient for 1% miles downstream from Y-6, so subsuredge of a convection system. The upflowing water of the face response to a base-level control anywhere along 

system, however, has· a temperature at least as high as this stretch cannot satisfy the demands imposed by our 

the 180°C measured in Y -6. These facts indicate that data. 

conduction of heat must be an important near-surface 

process in the area. Vertical conduction of heat, however, does not account for the general similarity between original ground temperatures (curve B) and the 

reference curve (A) of figure 15; the temperatures of 

curve B at depths near and below -200 ft occur nearly 

125ft below equivalent temperatures on curve A. The 

same puzzling relationship was observed in Y-4, which 

is also on the border of a convection system. This relationship in both holes may be best explained by boiling 

in the hottest upflow, with some water then being diverted horizontally and thell' downward on the borders 

of the systems in convective circulation. The springs 

south and southwest of Y -6 may indicate the center of 

an upflowing system, now much impeded by selfsealing. 

Thermistor temperatures (curve C of fig. 15) below 

-240 ft are nearly identical with the original ground 

temperatures, which are probably several degrees above 

curve B. Note that measurements, made ~ 16 hours 

after circulation ceased at -349.5 ft and-499ft, were 

only about 2°C below temperatures measured at the 

same depths after an additional 2 days or more without 

disturbance. Temperatures at depths above-200ft increased because of hot water flowing up the hole and out 

into ground below the 3--in. casing at -118ft. Most of 

the hot water probably flows into the hole near -240 ft 

· and out into adjacent rocks near and above -200 ft. 

Very little water seems to be supplied from depths 

below 240 ft, as indicated by lack of disturbance of 

predrilling ground temperatures below this depth. The 

nearly constant wellhead water pressures measured for 

depths below -200 ft are undoubtedly a key factor in 

accounting for this stability. 

What is the explanation for the unusual changes in 

pressure noted near -182ft and especially near -463 

ft, where wellhead pressure was 0 and water levels were 

then recorded as much as 13ft below the nearby Firehole River? Nearly all drill core from -350 to -410ft is 

remarkably fresh, with only a few hydrothermal veinlets, considerable iron oxide, and no pyrite. We suggest 

that these zones of anomalous fluid pressures are not 

controlled by the upflowing hot water of the system or 

by any relation to river level; the latter evidently is not 

the effective base level for all ground water of the area. 

Some parts of the thick Scaup Lake lava flow are isolated (by self-sealing?) from the high-pressure thermal 

upflow, but have permeable channels leading to lowlying ground of Upper Basin more than 2 miles to the 

northwest. The Upper Firehole River has a very low 

After completion of the hole, the wellhead water pressure remained nearly constant at 16V2 to 17 psig for at 

least 5 days. All pressure measurements made more 

than a month later indicate higher wellhead 

pressures-21 to 25 psig. This increase in pressure is 

largely if not entirely due to heating of the upper part of 

the hole, with consequent expansion of the water and 

increase in thermoartesian pressure. The down-hole 

pressure measurements indicate water pressure of 21 

to 23 psi above the reference boiling-pressure curve (B 

of fig. 16). 

All thermal features of Upper Geyser Basin and the 

Lone Star area could be fed by liquid water from a single 

large hydrothermal system characterized at depth by a 

common pressure regime. Under this model, high 

near-surface impedance to flow produced by self-sealing 

would allow some thermal water to discharge in the 

Lone Star area, some 270 feet above the floor of Upper 

Geyser Basin. The model requires that just below the 

self-sealed zone in Upper Geyser Basin, the sum of artesian and thermoartesian pressures would have to be 

greater than at a similar position in the Lone Star area. 

The difference would have to be at least equivalent to 

the hydrostatic difference between the two areas (270 

ft/2.4 ft/psi = 112 psi). Assuming that water overpressures in the Lone Star area do not exceed the measured 

17 psi, overpressures at depth under Upper Geyser 

Basin would have to be at least 129 psi. Such overpressures were not noted in our Upper Basin drill holes, but 

the holes (particularly Y-1) may not have been deep 

enough. Overpressures of at least 90 psi were found in 

the Lower Basin drill holes, however, so high overpressures are not precluded for Upper Basin. 

In summary, the data from Y-6 and from Upper 

Geyser Basin are compatible with the hypothesis of a 

single system but are inadequate to confirm it. Overpressures in Y -6 were only half those measured in 

Upper Geyser Basin and showed no tendency to increase with depth. In addition, the similarity in water 

chemistry between Upper Geyser Basin and the Lone 

Star area supports the model. We suspect that extreme 

overpressures do not occur at depth in the Lone Star 

area, and that this system may indeed be part of a 

system that is much larger than Upper Geyser Basin. 

LOWER AND MIDWAY BASINS 

Y-2 (FIREHOLE LAKE) DRILL HOLE 

SITE SELECTION 

Problems that developed during the drilling ofY-1 in 
LOWER AND MIDWAY BASINS 29 

CASING RECORD TEMPERATURE, IN DEGREES CELSIUS 

CONDENSED 

LOG 

100 

29ft 

of 4-in. 

casing 

20 40 60 80 

Curve B. 

160 200 220 

Sand, gravel, and 

pumice tuff, 

altered 

240 

128ft 

of 3-in. 

casing 

Bottom-hole data obtained 

as drilling progressed 

Elephant Back 

rhyolitic lava 

flow and 

related pyro200 

fUJ 

UJ 

LL 

~ 300 

EXPLANATION 

0 Bottom-hole temperature as drilling 

progressed, generally 16-22 hr 

after circulation ceased 

clastic rocks I 

~Curve C-2. I 

• I 

• I 

:i 

fa.. 40 6 Bottom-hole temperature, indicating hours 

after circulation ceased UJ 

0 

400 

:=-:: Thermistor temperature series 

in completed hole 

BX casing 

AX casing 

X Maximum-recording thermometer measurements 

Sept. 23, 1969 

Mallard Lake 

rhyolitic 

lava flow 

and related 

pyroclastic 

500 rocks 

TO 

516.5 

600 

1 Equivalent depth corrected for 

differences in static water 

level for comparison with 

curve A Curve A. 

Reference boiling-temperature 

curve for pure water, assuming 

water table at ground surface 

and at altitude of -7,500 ft 

FIGURE 17.-Temperatures and other data, Y-2 (Firehole Lake) drill hole, Lower Basin. 

Black Sand Basin of Upper Basin were related for the 

most part to wellhead pressures that were much higher 

than expected. Our second hole, Y-2, was selected 

partly in the hope of easier drilling under low-pressure 

conditions to provide us and the drill crew with more 

experience and time to devise new equipment for later 

more difficult holes that were expected. Firehole Lake, 

Hot Lake, and Steady Geyser of easternmost Lower 

Geyser Basin are characterized by waters of relatively 

low silica content (less than 200 ppm), suggesting a 

subsurface temperature of about 170°C (Four·nier and 

Rowe, 1966). High discharge rates (about 3,500 gpm for 

the group, according to Allen and Day, 1935, p. 53), 

spring temperatures mostly below surface boiling, and 

copious deposition of travertine (White, 1970) also indicated low subsurface temperatures and perhaps low 

pressures. 

On the other hand, we were also aware that extensive 

aprons of sinter from formerly active springs extend 

down to Hot Lake and Firehole Lake, isolated remnants 

of old sinter deposits occur on slopes of nearby hills at 

altitudes as much as 90ft above the Y-2 drill site, and 

active sinter-depositing springs high in sil~ca occur 

about 2,500 ft to the west in the Shelf-Pink Cone group. 

Old travertine, presumably deposited from springs 

similar to those of the present, also occurs as much as 28 

ft above the drill site. Thus, another objective in selecting this site was to clarify the unusual alternation between sinter and travertine in the Firehole Lake area. 

PHYSICAL MEASUREMENTS AS DRILLING PROGRESSED 

Physical data are shown in table 8 and figure 17 

(curve B). The near-surface data are not very satisfactory, largely because of restrictions imposed by casing 

and cementing. Bottom-hole temperatures evidently 

increase along a nearly linear conductive gradient from 

near -17 ft to about -130 ft. Fluid pressures were 

relatively low in the upper part of the hole. The water 

table was identified near -3.5 ft, and the first 

significant increase in static water level was near -83 

ft. Wellhead fluid pressure first became pronounced at 

-134 ft and increased irregularly to the bottom of the 

hole. Measured temperatures first exceeded reference 

curve A of figure 17 near -350 ft, but wellhead water 

pressures of about 15 psig prevented boiling from occurring above about -380ft in the natural system. 
30 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

At and below-380ft, most of the measured temperatures, when corrected for pressure and plotted at equivalent depth, are very close to reference curve .A; however, some natural exsolution of gas-enriched vapor was 

probably occurring near and below -380 feet before 

drilling. 

Puzzling combinations of temperature and wellhead 

pressure were found at depths of 406,426,451, and 458 

ft. At each of these depths the measured temperature 

was much lower than the general trend in the hole, but 

pressures were generally higher than elsewhere (table 

8); none of these pressures was clearly due to high wellhead water pressure except perhaps at-458ft. Most of 

these pressures were strongly influenced by the accumulation of gas in the hole. The temperature measured at -451ft is clearly not a significant indication of 

original ground temperature. The thermometer gear 

was lowered very slowly through separated sections of 

casing near -138 ft (May 28, 1967, table 8), where a 

slight downdrag on the gear seemed to occur. The same 

thermometer was again lowered and left on the bottom 

while a valve was opened slightly to permit some eruptive discharge. The observed temperature (167.8°C) was 

significantly above the previous measurement with the 

same thermometer (166.3°C). We conclude that reversed circulation was occurring in the hole before the 

first measurement; water was flowing up from the deep 

part of the hole outside the casing and was boiling as 

pressure decreased upward. At the casing break, vapor 

separated and accumulated in the top of the hole as the 

adiabatically cooled water flowed through the break 

and then back downward inside the casing. The slight 

eruptive discharge during the second temperature 

measurement caused some flow of water directly up the 

casing. Similar fluctuations in temperature, also interpreted as results of circulation reversal, were noted in 

TABLE B.-Temperatures, pressures, and other observations from Y -2 (Fire hole Lake) drill hole, Lower Basin 

Date and time Observation Temp. Thermometer Static water Wellhead 

1967 depth, ft 1 OCl No. level, pressure, Comments ft1 2 psig1 

May 3 1000 4.0 (40.5) Drill water intake 42°C. so temperature not significant. 1038 8.5 (41.5) - 3.3 11 ft drilled; lost circulation at -11 ft. 1110 10.8 (40) - 3.4 Then drilled to -16 ft. 1145 13 (43) - 3.4 10 min after circulation; on 3-ft fill; drilled to -21 ft. 1245 14.9 (53) - 3.5 20 min after circulation; on 6-ft fill. 1450 22.8 (58.9) - 3.45 29 ft drilled; 35 min after circulation. 1645 29.0 (46) Set 29 ft of 4-in. casing and cemented; into unset cement. 4 1330 52.5 (61.9) - 5.2 After drilling to -54ft; lost circulation at -51 ft. 1402 58. 1 (64) - 4.5 After drilling to -59 ft. 1625 76.8 (105.6) 8 After drilling to -78ft; 25 min after circulation. 1650 76.3 (106.1 ) 8 - 3.9 50 min after circulation. 0742 76.3 106.8} 8 No significant change in water level from -11 to-78ft; lost circulation at 77.4 107.9 107.3 4 -3.47 -51 ft. Thermometer emplaced below lead weight, increasing observa- 77.4 107.2 4 tion depth. Drilled to -83 ft. 0915 83 - 0.5 lncreasiny fluid pressure first becoming evident; some gas. 1005 88.7 (107.5) +3 After dril ing to -88 ft; water very gassy. 1135 96.9 (106.1) After drilling to -98 ft. . 1210 103 -6.45 After drilling to-103ft; lost positive pressure. Water levels 3Vz to 61

h ft 

¥~1~: Jri}J:dt~~~~~f~~t ;gg ~ -125 ft; lost circulation near -113 ft. 

1600 128 +9.8 No drill water return from -51 to-128ft. Then cased to-128ft, cemented from top and bottom but pressured (to 400 psi) only at top. 6 1050 17.1 80.4 ~~t~t 1ff::~i~~~f;Hro~.in casing; on cement; 19 hr after circulation. 1620 16.9 81.6 0945 16.9 82.2 42 hr after circulation. 1633 16.9 81.8 49 hr after circulation. 8 0757 16.9 81.8 64 hr after circulation; temperature considered very reliable even though in cemented hole. Drilled to -134 ft at 1534. 1645 134.3 132:9 8 (+20) 81-'l 70 min after circulation. 1700 134.4 133.3 8 (+19) · 8 85 min after circulation. 9 1000 134.4 134.4 8 5 Then drilled to -164 ft (reported) at - 1430; pressure and discharge increased. 1500 164.9 (132.5) 8 12V4 1515 164.0 (132.3) 4 (+29) 12V.. -1600 Cemented hole to replace leaky valve. 10 0752 128.1 133.9 } 133.7 8 On cement. 0807 128.1 133.6 4 No cement retained in hole from -141 to -164 ft (horizontally washed?). 1622 219.0 (151.6) 4 (+40) 16\-2 Drilled to -219 ft at 1515; 1 hr after circulation ceased. 11 0741 218.9 160.9 } 160.9 4 16\-2 All water overpressure. 0753 218.9 161.0 8 16\-2 Then drilled to -289 ft at 1615. 1632 286.2 (167.9) 4 17\-2 -Y.! hr after circulation ceased. 12 0730 285.5 171.7 } 172.1 4 (+44) 18\-2 0748 285.5 172.4 8 Then drilled to -309 ft at 1530; much gas; surging pressure. 1626 309.0 (167.9) 8 34 to 39 -1 hr after circulation ceased; valve leaking. 13 0902 308.8 174.3 } 174.8 4 (+34) 14 to 17 0917 308.8 175.3 8 14 to 23 No drilling May 13 or 14. 14 0927 307.8 (171.8; bumped?) 4 (+29) 12 to 19 0954 307.8 173.3(?) 8 141

/z Temperature lower than May 13 and 15? 15 0847 307.4 174.4 } 174.5 4 131

4 to 16 Valve leaking so hole cemented; removed leaking valves and found 174.7 8 15 adapter cracked. 16 Replaced adaptor and valve; drilled to -339ft at 1630 but new valve would not close; cemented again. 17 Removed valve-seats had rotated; installed another valve, drilled to -354 ft at -1400. 18 0733 350.0 } 349.9 181.4 } 181.9 4 (+34) 43 to 14 After escape of gas; 4 ft of caved reound. 0750 349.8 182.3 8 33 to 14% Gas accumulated rapidly, then bed off; drilled to -382 ft, when rods sheared off at -210 ft; all recovered. 

See footnotes on facing page. 
LOWER AND MIDWAY BASINS 31 

greater detail by White (1968, table 30, Sept. 12--13, 

1950) in drill hole GS-4 at Steamboat Springs, Nev. 

The relatively low temperatures recorded at -406 

and -426 ft c,an also be explained by reversed circulation. The measurement at -458 ft, however, is more 

difficult to explain. Shortly before this measurement, 

AX casing had been installed to -449 ft and was cemented under pressure at top and bottom, thus eliminating this particular reversed circulation. Reversed 

circulation could have occurred outside the BX casing, 

with conductive cooling of water inside the casing. 

An obvious alternative explanation is that one or two 

zones of real temperature reversal are related to 

inflowing water of lower temperature, similar to reversals recognized at Steamboat Springs (White, 1968, p. 

C51, C53). Sharp local reversals of this type are lacking 

in all other Yellowstone drill holes, and temperature 

profiles in the completed Y-2 hole failed to provide any 

suggestion of temperature reversals. The temperature 

of 192.2oC at -409 ft is so close to the projection of 

reliable data points of curve B above and below the 

questioned zones that real reversals seem unlikely. Because of the uncertainties, however, the predrilling 

ground temperatures from -380 to -480ft cannot be 

affirmed from available data, and alternative trends in 

temperature are shown in figure 17. 

SUMMARY OF DRILLING PROBLEMS 

Y-2 proved to be the most difficult hole to drill. In 

contrast to our hopes, high wellhead pressure first became evident at -134ft and was an increasingly serious 

problem with increasing depth, especially below -400 

ft. This greatly exacerbated other drilling problems, 

which included valves that did not seat properly, casing 

that was difficult to emplace and cement, and couplings 

and drill rods that failed. 

TABLE B.-Temperatures, pressures, and other observations from Y-2 (Firehole Lake) drill hole, Lower Basin -Continued 

Date and time Observation Temp. Thermometer Static water Wellhead level, pressure, Comments 1967 depth, ft' OCJ No. ftl 2 psig1 

May19 - 0800 379.4 186.8 } 187.3 4 15':4 to 13 Y2 187.8 8 (+31) 13 to 13% Then drilled to -408 ft; rods sheared off again at about -230 ft. 20-23 55 to 106 Fishing difficult because of high pressure and temperature; attempted 

24 -0800 use of heavy mud without success and finally recovered lost string. - 406 168.6 4 47 Some effect of gas accumulation on pressures and temperatures? BX casing 168.7 then set to - 408ft, forced in under pressure with bottom length plugged. 168.9 46 Cemented only at top, with cement forced between AX and BX casings, 

25 pressuring to 800 psig. Drilled out cement plugs in top and bottom lengths of casings. 26 409.4 192.3 } 192.2 8 30 to 15Y2 409.3 192.1 4 (+ 35) 14¥.. Steady pressure; wellhead water pressure? Drilled to -426ft at 1540. 27 0615 425.3 } 425.9 162.8 } 162.8 4 ? 80 to 64 Leakage of gas without water; gas accumulation effect. 426.5 162.8 8 76 Uncemented bottom of BX casing spun off at - 138 ft drilled through 

28 1400 - 451 166.3 4 76 separated casing to -451 ft at 1340. Slight down-pull on in-hole equipment below separation? Downfiowing 

- 451 167.8 4 water accounts for low temperature? 77 to 63 Temperature remeasured with hole discharging slightly at top in attempt 

29 to reverse circulation, resulting in higher bottom-hole temperature. 

Temperatures and pressures unreliable since 5/19, except for 5/26; decided 

31 to install AX casing. 

Preparing for AX casing. Slight leakage of gas outside all casings first noted; then increased. June 1 72 Temperature of dry gas leakage outside casing 93V2°C, but seemed stabilized. Installed 449 ft AX casing under pressure with cement plug in bottom length, and through separated BX. Cemented top and bottom (plug drilled out) until pressured. - 1600 (+91) 38 to 45 Drilled cement and new hole to -458ft at 1500; pressure after drilling. 0700 457.6 184.4 4 (+ 86) 37 to 36 Wellhead water pressure near 36 psig? -0730 457.6 181.8(?) 8 40 to 48 Cause of erratic temperature not known. Then drilled to-479ft at 1430. 1545 478.3 (176.0) 4 82 1 hr after circulation. 4 0950 479.2 (199.6) 4 58 First discharge all gas, then water and gas. 1027 479.1 201.1 8 68 to 78 Hole then erupted to flush out drill water. 0725 (+100) 42 Initial fluid only water; wellhead water pressure? 0740 479.0 

~gu} 202 .8 8 46 0755 8 55 Drilled to -506 ft at 1625. 6 0840 - 505¥.. 203.1 8 (+100) 42 to 46 Only water at first-water pressure? Erupted hole-water-steam changed to dry steam at l10°C and 8-12 psig. Drill rods vibrating and wearing 

516.5 rapidly; drilling terminated at - 516 ft, 1300. 0820 ~g~ 1 } 8 60 to 57 3 203.1 1 (200-500°F) 59 to 128 Hole erupted through Y2-in. vent; water and steam, changing to dry 

8 0828 516.3 ~8~:~ } ( +134?) 56 

steam, maximum_ 128 psig (vapor pressure of 174Y2°C). 

201¥.. 8 0850 8 58 to 60 Bottom temperature definitely less than on 6/7. 3 202 1 (200-500°F) 

July 28 1630 (443) 3(201 Y2) 3 (200-500°F) 130 to 100 High-temherature upflow from bottom? Pressure rise to 130 psig maxi- mum, t en down to 100, leaking water. Aug. 1 488 92 In-hole pressure 233 psia at - 488 ft, or about 30 psi of overpressure 

June 27, 1968 515 201.1 (+132? ) 55 up to 130 

relative to curve A, figure 18. Thermistor series, plotted on figure 17. Some leakage during measure- ments; see text for probable effect. Sept. 20, 1969 214 Initial wellhead pressure, with vapor in casing to about -449 ft. 

517 214 to 128 In-hole pressure 158 psig. 

Sept. 23, 1969 515 204.2 12 82 down to Hole degassed 9/22 and early 9/23 to insure maximum water in hole; 75, steady negligible leakage during series by maximum thermometer. Data points plotted on figure 17. After series, hole filled with 12 sacks cement, pressured to 200 psi. 

'Data in boldface considered most reliable, data in parentheses, least reliable. 2Relative to ground surface; positive levels in parentheses calculated from wellhead pressures considered to be water pressures least affected by vapor. 3 Pressure-corrected. 
32 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

The drill crew, contractor, and scientists had not yet 

devised equipment and procedures to correct equipment 

failures while controlling high-pressure fluids at all 

times. A new expensive type of high-pressure valve 

proved to have seats that rotated out of correct position 

because of friction from the drill rods (table 8, May 15 

comment). Because of the possibility of pollution, we 

were reluctant to use lubrication on drill rods; consequently, wear on the drill rods was excessive, and the 

rods sheared off twice in quick succession (May 18 and 

19). Fishing for the lost string was difficult, especially 

after the second loss when wellhead fluid pressures 

ranged from 55 to 106 psig. On May 24 BX casing with a 

wooden bottom plug was successfully emplaced; after 

drilling out the plug, the casing was hung in the hole 

but was not cemented at the bottom. With further drilling and friction of rotating rods on the top-cemented 

casing, a spinoff of most ofthe casing string occurred on 

May 27. AX casing was then emplaced through the 

separated section and was cemented at top and bottom 

under pressure; as we shall see, postcompletion measurements indicate that cement does not fill much of the 

space between the AX and BX casings at intermediate 

depths, or between the separated BX casing and the 

surrounding rocks. 

MEASUREMENTS IN COMPLETED HOLE 

AND INTERPRETATION 

Postdrilling temperature and in-hole pressure measurements are summarized in table 8 and figures 17 and 

18. These measurements were complicated by the fact 

that permeability around the open hole below the AX 

casing was so low that even slight discharge or leakage 

through our gear at the surface was only slowly replaced by new inflow. 

A series of thermistor temperature measurements 

made on June 27, 1968 (see table 8 and curves C-1 and 

G-2, fig. 17) demonstrates the drastic changes in temperature and wellhead pressure that occur where permeability is so low. Initial leakage from pipe fittings 

was nearly all liquid water (estimated as a few gallons 

in total), but wellhead pressure increased from 55 to 130 

psig during the series. Temperatures were first measured proceeding down the hole (fig. 17, curve G-1) and 

then, to check the effects of leakage and increasing 

pressure, temperatures were measured from-276ft up 

to the surface (curve G-2). Differences between the two 

curves raised questions about the magnitude of changes 

that presumably occurred immediately before and during the initial series; these questions could not be answered immediately because our thermistor soon failed. 

The thermistor gear was again inoperative when 

needed for Y-2 in 1969, but a few temperatures measured at selected depths by maximum thermometer on 

September 23 (indicated by X's on fig. 1 7) provided some 

confirmation for the qualitative reliability of curve G-1. 

An improved packing gland and revised procedures for 

securing the pressure chamber to the wellhead prevented leakage from the unthreaded joints and from 

around the thermometer cable, except for an estimated 

quarter gallon that escaped each time the thermometer 

was removed. Total leakage ofwater from the hole during the temperature series was estimated as less than 3 

gallons. Much accumulated gas had been discharged 

during the in-hole pressure measurements made 3 days 

earlier, and additional gas was discharged on September 22 and early in the morning of September 23. 

Accordingly, at the beginning of the maximum thermometer series about 2 hr later on the 23d, the hole was 

nearly filled with liquid water. Initial water level was 

about -17 feet, as estimated by changes in surface fluid 

pressure from 82 to 75 psig as the temperature series 

was made. Upflow into a cooler environment accounts 

for the modest decrease in temperature from 84 oc (first 

entry) to 67.5°C (final entry). 

Thus, the G-1 thermistor temperatures are concluded 

to be near but not identical to rock temperatures immediately adjacent to the hole on June 27, 1968, and 

thus are as much as 52oC higher (at -45 ft) than our 

best data for predrilling ground temperatures. We conclude that these large increases resulted from upflow of 

high-pressure water outside the imperfectly cemented 

AX and BX casings during the year after the hole was 

completed, and that the C-series of temperatures measured on June 27, 1968, cannot be close to original 

ground temperatures. This is clearly indicated by 

measurements near -77 ft, where a reliable temperature close to 107°C was obtained as drilling progressed; 

the water level at the time was about 8V2 ft below the 

ground surface. In contrast, the postdrilling temperature of about 150°C near the same depth demands a 

static water level at least 68 ft above ground level, 

equivalent to a wellhead water pressure of about 28 

psi g. 

Our best estimate of the maximum water pressure 

originally present in rocks penetrated by Y-2 is about 

40 psi above reference pressure curve A of figure 18. The 

wellhead pressure measured on June 5 and 6, 1967, 

with water at the top of the hole, was 42 psig. The 

in-hole temperature of 202.8°C measured on June 5, 

1967 (point A of fig. 18 at a drilled depth of 79 ft) 

demands a water-vapor pressure of 239 psia. This pressure is shown as point Bon figure 18. With respect to the 

reference boiling pressure curve, point B is overpressured by about 40 psi. 

The G-1 thermistor series of June 27, 1968, if accepted as approximating existing temperatures at the 

time in rocks adjacent to the hole, is interpreted as 

follows: 
0 

40 

80 

120 

160 

200 

240 

Iw 

w 280 u. 

~ 

IIa.. 

w 320 0 

360 

400 

440 

480 

520 

560 

600 

CASING RECORD 

0 20 40 60 

LOWER AND MIDWAY BASINS 

TEMPERATURE, IN DEGREES CELSIUS, AND 

PRESSURE, IN POUNDS PER SQUARE INCH (ABSOLUTE) 

80 100 

X 

Curve A. 

Reference boilingpressure curve 

120 

X 

X 

160 180 

\.---curve C. 

1 Pressures measured 

\ Sept. 20, 1969 

I 

I 

I 

I 

I 

I Curve B. 

200 

6 

I 

Reference boilingtemperature curve 

EXPLANATION 

X Bottom-hole temperature 

measured as drilling 

progressed 

Measured pressure 

0 Sept. 20, 1969 

8 Aug. 1 , 1967 

B 8 Vapor pressure calculated 

from measured temperature A 

I 

I 

I 

I 

I 

I 

I 

I 

I 

~ 

I 

I 

I 

I 

I 

I 

\ 

\ 

\ 

\ 

\ 

\ 

220 

FIGURE 18.-In-hole pressures of Y -2 drill hole after completion, compared with other data. 

33 

240 260 

The nearly constant but non vertical slope of the curve 

from about -230 ft to the bottom of the hole suggests 

that hot water is flowing up inside the BX casing and is 

boiling as pressure decreases upward. At the break in 

the BX casing near -230 ft, liquid and vapor separate. 

The liquid fraction flows down outside the casing to 

produce uniform temperature changes in all fluid fractions, reflected in the uniform slope and not evident in 
34 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

original bottom-hole temperatures as drilling progressed. Upflow above the bottom of the NX casing at 

-128 ft probably does not occur within the cemented 

hole but is more likely to occur in adjacent rocks up to 

the high-permeability zone oflost circulation from about 

-50 to -90ft. Wellhead water pressures in the latter 

zone are likely to have changed from about -1.4 psig 

(initial) to at least + 15 psig; the latter is required by 

the 148°C measured at -89 ft on September 23, 1969 

(fig. 17). 

The in-hole pressure measurements of September 20, 

1969 (fig. 18), when the hole was initially nearly filled 

with vapor at a wellhead pressure of 214 psig, demonstrate the effects of low permeability. Point B of figure 

18, calculated from a measured temperature, is at least 

40 psi above reference pressure curve A, but the bottomhole pressure of September 20 was only 158 psig, and 

the actual pressure gradient of curve C was much less 

than that of curve A. Evidently, the leakage of fluid 

from the hole before and during this series of measurements resulted in boiling, cooling, and transfer of heat 

from the rocks to the limited available water; the permeabilities of the rocks are so low that inflow into the hole 

was less than losses by leakage (not measured, but low). 

The significant physical changes induced by the drilling of this hole, with its faulty casing and cementing, 

were entirely unanticipated and, in fact, could not have 

been prevented after the AX casing was emplaced and 

cemented. The temperature changes also indicate that 

having casing in a hole does not guarantee original rock 

temperatures because short-circuited flow paths may 

occur outside the casing. The record ofY-2 is considered 

here in some detail because it provides dramatic evidence of the consequences of inadequate techniques in 

drilling high-pressure areas. 

A slight but detectable leakage of gas around the 

casing into our concrete box provided the basis forcementing and abandoning the hole on September 23, 

1969, even though further scientific study was desirable. The cementing stopped most but not quite all of the 

gas leakage, but the upflow of hot water at high pressures responsible for the leakage should eventually be,. 

come negligible through deposition of'silica, decreasing 

permeability by the self-sealing process. By July 1971 

the flow of gas had almost completely ceased. 

Y-3 (OJO CALIENTE) DRILL HOLE 

SITE SELECTION 

Major objectives of Y-3 were to clarify subsurface 

relations near the Pocket Basin hydrothermal explosion crater of late Pleistocene age (Muffler and others, 

1971) and to obtain general information on the stratigraphy and distribution of temperatures in . Lower 

Basin, the largest of Yellowstone's geyser basins. Y-3 

also was the closest permissible site to the western part 

of Lower Basin. The specific site was next to a parking 

area (since relocated) about 1,000 ft west of the Pocket 

Basin explosion crater and about 250 ft northwest of 

and 7 ft above the largest spring of the area, Ojo 

Caliente. 

PHYSICAL MEASUREMENTS AS DRILLING PROGRESSED 

Physical data from Y -3 are shown in table 9 and 

figures 19 and 20. Good data were not obtained in the 

shallow zone to -140 ft because drilling was rapid 

and was complicated by the setting of two strings of 

casings. Thereafter in this and in other holes we generally limited drilling to about 50 ft per day to insure a 

better record of temperatures and pressures. Our experience at Y-3·demonstrated that at least one good set 

of data, uncomplicated by the setting of casing and 

cementing, is essential at depths from about 20 to 90ft, 

and two sets of good data are very desirable. 

Temperatures in Y-3 increased so rapidly that the 

hole erupted from -90ft when only 32ft of 4-in. casing 

was in the hole. The temperature at -90 ft was not 

measured, but it was probably above reference temperature curve A, with a corresponding high wellhead 

water pressure to account for the high eruption potential. Temperatures from -90 to -140 ft cannot be deciphered with certainty from our data, but below -140 

ft they increased steadily to near the bottom of the hole 

(fig. 19, curve B). 

No reliable data concerning static water levels were 

obtained as drilling progressed, generally because gas 

accumulated rapidly in the casing. Wellhead water 

pressure of the aquifer near -100 ft is at least 6 psig 

(table 9, June 13, 1967). At greater depths, wellhead 

pressures during measurements of temperature commonly ranged from 30 to 40 psig, but at these pressures 

gas was always the dominant escaping fluid. A few 

measurements obtained when discharge from the gear 

was mostly water suggest that water overpressures 

were near 18 to 22 psig at depths of- 220 to -450ft, and 

then decreased to about 16 psig near the bottom of the 

hole. 

SUMMARY OF DRILLING PROBLEMS 

Because drilling from -32 to -90 ft was easy and fast, 

no temperatures were obtained and we had no warning 

of the very high temperature gradient and eruption 

potential. When eruption did occur from -90 ft, our 

planned NX casing was not yet in the hole, and the drill 

chuck was not large enough to accept pipe of such large 

diameter. With much difficulty the casing was manually forced down by winch into the erupting hole, and 

the drillers used gear for protection from the hot water. 

Fortunately, the first casing string to -32 ft proved to 

be well cemented and adequate. 
LOWER AND MIDWAY BASINS 35 

TABLE 9.-Temperatures, pressures, and other observations from Y -3 (Ojo Caliente) drill hole, Lower Basin 

Date and time Observation Temp. Thermometer Static water Wellhead Comments 1967 depth, ftl OCJ No. level, ft2 pressure, 

psig1 

618 1540 22.7 (23.5) (-1.3) Drilled to -32 ft at 1520; 20 min after circulation. Then cased to -32 ft, 

cemented. 6/9 0745 25.1 59.5 (-1.9) In cemented hole. No reliable water level data but best estimate -8 ft to 2000 79.4 131 4 -8? 26V2 depth of -70 ft, with some lost circulation. Drilled to -90 ft at 1430, 

132.4 when hole erupted; controlled with difficulty. 6/10 0730 79.1 } 132.4 4 35 to 32 After measurements, set 3-in. casing to -90 ft through erupting hole ; 79.5 132.3 8 cemented by 1330. 6/11 1400 17.1 (60 ) In cemented hole, but temperature still decreasing from eruption-see 6/12. 6/12 0745 17.1 54 42 hr after hole cemented; temperature probably good. Drilled out cement to -86 ft. 6/13 0800 (84.7) (93.3J On cement; why is temperature so low? Drilled to -135 ft at 1335. 1355 (127) (138.3) 4 (> 14) 6 Wellhead water pressure 10 min after circulation; hole not yet heated. 6/14 0740 124.6 i!&:6 } 4 36 to 38 Some gas accumulation; hole caving; attempted cementing, but only 2 V2 0755 124.6 140.1 8 39 sacks, not pressured. 1145 102.4 140.0 21 On cement 2 hr after circulation. Temperature at least 140°C. Drilled out cement; then to -144 ft at 1645. 6/15 0745 140.1 } 140.1 4 31 Much gas. Hole has caved 8 ft. Drilled to -184 ft at 1420. Started leaving 

0800 136.0 140.1 8 31 drill rods in hole overnight. 6/16 0738 184.6 153.3 } 153.3 4 30 to 31 Much gas. 0750 184.6 153.4 8 32 Then drilled to - 224ft at 1630. 6/17 0752 ~~g} 224.1 164.2 4 32 0807 (161.8) 8 32 ~~~ Jr~Iied to -256ft at 1530. 6/18 1032 (195.4) (160.0) 4 (+44) 22 to 18\.-2 Wellhead water pressure - 18 psi; - 60 ft off drilled bottom; caving. 

1041 (196.3) (160.0) Temperaiure unreliable. 8 19 2100 30 Gas and water. 

6/19 0740 (142.6) (151.1) 36 to 21 Upflow of hot water thru 113 ft of caved fill? 2045 264_7 172.2 4 (+45) 19 6 hr after drilling to -274 ft; wellhead water pressure; temperature 

6/20 0750 264 (162.8) fairly reliable. 4 62 to 42 Gas; thermometer snagged, temperatures less reliable than 6/19 p.m. 0755 264 (170.0) 8 38 to 37 Thermometer snagged. Drilled to -309 ft at 1600. 2105 ~gg } 307.7 176.7 } 177.0 4 44 to 39 Much gas; 5 hr after circulation. 2112 177.2 8 41 to 40 6/21 0745 307.7 176.7 } 177.0 4 52 to 44 Gas accumulation; cemented to -106 ft and drilled out, with open hole 0803 307.7 177.2 8 45 to 46 found below - 147ft. 6/22 0742 307.0 176.7 } 176.7 4 42 to 38 Then drilled to -354 ft at 1600; only - 1/s drill water returned during 0809 307.0 176.7 8 38 day. 2035 352.7 (180.0) 4 (+53) 26 to 22 -4 hr after circulation; thermometer snagged; some gas accumulation 

6/23 0734 352.2 185.6 so wellhead water pressure -22 psi. 8 38 to 36 Gas and water. Then drilled to -399 ft at 1525; about 30 percent of drill 

water returned. 6/24 0723 (141) (150.6) 4 57 Gas and water. Hole blocked at - 141 ft; drilled to -444 ft at 1435; low water return all day. 2122 441 193.3 } 193.3 4 71 to 22 Gas and water; 6 hr after circulation stopped. Wellhead water pressure 2138 440 193.3 8 (+53) 22 -22 psi? 6/25 0956 441 (191.1) 4 72 to 42 Gas and water. 1018 441 194.4 8 46to47 Gas and water; best temperature. 6/26 0739 438 (189.5i 4 56 to 38 Gas to gas and water. 0758 438 193.3 8 44 to 43 Gas; then drilled to -494 ft at 1545. 2113 494.7 (194 .5) 4 37 to 39 Gas and water -5 hr after circulation. 2132 196.0 8 39 Very gassy water. 6/27 0745 493.8 (193.4) 8 59 to 49 Gas and water; thermometer snagged. 493.7 195.6 8 58 to 51 Gas, no water out. Then drilled to -514 ft at 1445. 6/28 2110 125.6 (149.5) 4 56 Caved to -126 ft-Ojo Caliente started geyser eruptions. 7/16/68 BX casing hung in hole to -200 ft, tight below - 128 ft, to clear blockage and to terminate interference with Ojo Caliente. 7/19/68 514.9 173.4 14 (+38) 16 to 22 16 psi wellhead water pressure? Pressures then increase with slight leak- age during series. Data of curve C, fig. 19, measured with maximum thermometer (thermistor cable inoperative); temperatures below -277 

9/25/68 158.5 159.6 32 to 34 ft suggest reversed circulation. Thermistor series of temperature measurements. Data shown in curve E, 

9/17/69 512 35 to 40 fig. 20. Thermistor failed below -158.5 ft. Bottom-hole total pressure was 217 psia, indicating water overpressure of only about 6 psi, curve D, fig. 20. 9/23/69 512 189.6 12 41 to 29 Temperature series, maximum thermometer (see fig. 19, curve D); casing 

leaking below main valve so 11 Y, sacks cement pumped in hole. 

'Data in boldface considered most reliable; data in parentheses, least reliable. 2Relative to ground surface; positive levels in parentheses calculated from wellhead pressures considered least affected by vapor. 

Very permeable caving ground from-90ft to about 

-138ft continued to cause serious problems during the 

drilling of the hole (and throughout the next 2 years). 

With hindsight, we realized that BX casing should have 

been set to -150 ft in the initial drilling, but having 

been forced to case at-90ft, we were reluctant to case 

again so soon. Instead, we attempted, unsuccessfully, to 

control the caving by pumping cement down the hole 

into surrounding ground. 

After the hole was completed at-514ft and the drill 

rig was dismantled, caving prevented measurements at 

depths below -126 ft. Also, on the day after removal of 

the rig, Ojo Caliente, although having no previous record of geyser activity, started to erupt as a geyser. 

Almost certainly this change in activity was caused by 

flow of water and steam up Y -3 to the permeable zone 

from -90 to -138 ft, and then laterally to the hot 

spring. The cooling effect of drill water probably explains why Ojo Caliente did not erupt during the middle 

and late stages of drilling, but we had looked for specific 

evidence (such as turbidity) that drill water was entering the spring and failed to detect any. 

In the early summer of 1968, Y-3 site was reoccupied 

and BX casing was hung in the hole to a depth of-200 ft 

in order to clear the persistent blockage near -126 ft 

and to terminate or dampen any influence ofY-3 on Ojo _ 
36 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

Caliente. With difficulty the casing was forced down 

through the caving zone. Ojo Caliente is not known to 

have erupted as a geyser since this casing was emplaced. 

During the following year a leak developed between 

the BX casing and the main valve. In September 1969 

we applied a temporary clamp to shut off the leakage 

and then filled the hole with cement. 

POSTDRILLING MEASUREMENTS 

Postdrilling temperature and pressure measurements could be made in the lower part of Y -3 only after 

the BX casing was hung in 1968 to make the hole accessible. Our thermistor equipment failed on September 

25, 1968 (curve E, fig. 20) and was inoperative during 

most of 1969, so a detailed temperature profile was not 

obtained throughout the completed hole. However, two 

maximum-thermometer series were obtained; the 

series of July 19, 1968 was measured only 3 days after 

the BX casing was installed and is shown as curve C of 

figure 19 and C of figure 20; a second series measured 14 

months later is shown as curve D of figure 19. The 

thermistor series of September 25, 1968 (curve E, fig. 

20) tends to confirm the zone of nearly constant temperature suggested by the bottom-hole temperatures 

(curve B, fig. 19) at about -140 ft. The postdrilling 

maximum-thermometer series C and D of figure 19 are 

similar down to about -180 ft, but the spacing of data 

points is too wide to detect the zone near-140ft. Curve 

C (fig. 19) showed an unexpected decrease from original 

ground temperatures (curve B) at depths below about 

-260 ft, where measured temperatures were nearly 

identical (173.3°C, 173.4°C, 173.4°C) at three different 

depths. We suggest that cold water introduced into the 

hole just before the BX casing was installed may have 

cooled the hole enough to induce a downward flow of 

relatively dense (cooler) water from an aquifer near 

-260 ft (and overpressured by 18 to 22 psi) into an 

aquifer of lower overpressure (16 psig) but of initially 

higher temperature near the bottom of the hole. 

Significantly, the in-hole pressures measured on September 17, 1969 (table 9) indicated a bottom-hole water 

pressure of only 6 psig (fig. 20, curve D). Presumably the 

downflow in response to this pressure gradient conCASING RECORD TEMPERATURE, IN DEGREES CELSIUS CONDENSED 

LOG 

0 20 40 60 80 100 120 140 160 180 200 220 o.---.---.---.---.---~~-.---.---.---.--~.---.---.---.---.---.----,---.---.---.---,.---,--. 

fw 

w 

u_ 

100 

200 

~ 300 I -

f0.. 

w 

0 

400 

500 

32ft of 

4-in. 

casing 

90ft of 

3-in. 

casing 

BX casing hung 

in hole 12v2 months 

after completion 

TO 

514 

Curve B. 

Silt, sand, 

and gravel, 

hydrothermally 

altered 

138.5 ft - - - - - - - - - -

Bottom-hole temperatures 

as drilling progressed 

Nez Perce Creek 

rhyolitic lava 

flow 

EXPLANATION 

0 Bottom-hole temperature - 16 hr 

after circulation ceased 

Bottom-hole temperature, indicating hours 

after circulation ceased 

+ Temperature, maximum thermometer, 

July 19, 1968, 3 days after BX casing 

installed to -200 ft 

X Temperature, maximum thermometer, 

Sept. 23, 1969, 27 months after completion 

of hole and 15 months after BX casing 

installed 

1 Equivalent depth corrected for 

differences in static water level 

for comparison with curve A 

234 ft - --- - - --- -

Older 

~ 

I 

Curve C. 1 

July 19, 1968, 1 

3 days after I 

BX 

to-20~ 

ca~bn~ hung ~ 

\ 

Curve D. : \ 

Sept. 23, 1969, 1 \ 

27 months after 1 ~ 

drilling and 15 : I 

months after BX 1 I 

casing hung to ! I 

-200ft +I X 

Curve A. 

Reference boiling-temperature 

curve for pure water, assuming 

water table at ground surface, and 

at altitude of - 7,500 ft · 

unnamed 

lava flow 

FIGURE 19.-Temperatures and other data, Y-3 (Ojo Caliente) drill hole, Lower Basin. 
LOWER AND MIDWAY BASINS 37 

tinued for many days or weeks, being supplied by water 

near -260ft at a temperature near 173°C. 

but were not yet as high as predrilling ground temperatures (curve B, fig. 19). 

The hypothesized downflow, if real, decreased in rate 

with time. By September 1969 (curve D, fig. 19), temperatures near the bottom had increased significantly, 

Gas leaked from the hole before and during the inhole pressure measurements of curveD, figure 20. The 

low pressure gradient between -260 ft and the bottom 

0 

40 

80 

120 

160 

200 

240 

fUJ 280 UJ 

LL 

~ 

Ifa.. 320 UJ 

0 

360 

400 

440 

480 

520 

560 

CASING RECORD 

0 20 

4-in 

casing 

3-in 

casing 

BXcasing 

hung to 

200-ft depth 

TD 

514 

TEMPERATURE, IN DEGREES CELSIUS, AND 

PRESSURE, IN POUNDS PER SQUARE INCH (ABSOLUTE) 

80 100 

l0 0 

~ ---8" 

Pressures measured '\~Curve D. 

Sept. 17, 1969 

~ '\ 

Curve A. 

~ \ 

Reference boilingpressure curve 

~ \ 

i 

\ 

~ ' \ 

0 8 Curve E. 

~ Temperatures measured 

8 Sept. 25, 1968 

\ \ 

~ 0 'l 

0\~,\ . I '\' \ 0 B,\ 

fl 

\ 

0 

0 \\Curve C. 

Ju ly 19, 1968 

\, 

Temperatures measured 

I 

I 

I 

0 

\ ~ 

EXPLANATION 

Measured temperature 

0 As drilled 

0 July 19, 1968, maximum thermometer 

8 Sept. 25, 1968, thermistor 

Measured pressure 

1---8--i Sept. 17, 1969 

Bar indicates uncertainty 

imposed by fluctuating 

wellhead pressure 

\ 

~~ I 

\ I 

\B I \0 

~\ I 

I 

I 

I 

I 

0 

Curve B. 

Reference boilingtemperature curve 

FIGURE 20.-In-hole temperatures and pressures of Y-3 drill hole after completion. 

260 
38 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

of the casing at -200 ft clearly shows that vigorous 

boiling was occurring throughout the interval. Presumably at-200ft the steam either condensed or, more 

probably, was diverted outside the casing. Noncondensable gas filled approximately the upper 20 ft of the 

casing. During the measurements sudden changes in 

wellhead pressure of about 5 psig occurred, suggesting 

uneven flow in the system, probably from the zone near 

-260ft. 

Y-4 (NEZ PERCE) DRILL HOLE 

SITE SELECTION 

Y-4 was selected as the best accessible site on the 

bedrock margin of Lower Geyser Basin at an appreciable distance from prominent surface activity, in order 

to gain a better understanding of the borders of major 

geothermal systems. The site is in an abandoned gravel 

quarry where several feet of glacial gravels were removed many years ago and the underlying rhyolitic 

bedrock, the Nez Perce Creek flow, was exposed (R. L. 

Christiansen and J. D. Obradovich, written commun., 

1974; age ~140,000 yr). A service road with a locked 

gate provided the isolation we and National Park Service officials desired for our activities during the 1967 

mid-summer tourist season. The site is in a mature 

strand of lodgepole pines that show no evident effect 

from any thermal activity. The drill collar is about 30ft 

above Nez Perce Creek and 650ft N. 21 oW. of the nearest known thermal spring, which is on the north bank 

of the creek. This spring is an inconspicuous feature 

. with seeping discharge and a temperature of 44°C. 

A secondary objective was to clarify the subsurface 

volcanic stratigraphy, but the hole served only to demonstrate the great thickness and lack of internal structure of the Nez Perce Creek lava flow. 

PHYSICAL MEASUREMENTS AND INTERPRETATIONS 

Physical data obtained from Y-4 are shown in table 

10 and figures 21 and 22. The temperature gradient is 

linear to about -250ft, where the first significant fluid 

flow occurs in an iron-stained zone between -249 and 

-251 ft. Upward projection of this constant gradient 

TABLE 10.-Temperatures, pressures, and other observations from Y -4 (Nez Perce Creek) drill hole, Lower Basin 

Date and time Observation Temp. Static Wellhead Thermometer water level, pressure, Comments 1967 depth, ft1 oct No. ftl 2 psig1 

6/30 0930 Started drillii1, bedrock floor of old gravel quarry; drilled to -21 ft, installed an cemented 4-in casing. 

7/1 Drilled out cement, new hole to -55 ft at 1530. 

7/5 0800 49.7 29 - 17.8 After 3 Y2 days rest; then drilled to -95 ft at 1545. 

7/6 0800 (45) (26) - 18.0 Thermometer snagged on bit? Then drilled to - 121 ft at 1345; installed 

- 1400 f2i - 17.7 and cemented 120 ft NX casing, 8 sacks cement, not pressured. 

7/7 Drilled out cement; new hole to - 149 ft at 1525. 

7/8 0745 148.7 73.9 - 19.0 Then drilled to -204ft at 1515. 

7/9 1000 203.4 99.3 4 - 19.9 7/10 0748 203.8 (95.0) 18 - 19.8 Thermometer snagged near -175 ft coming out; could not get back down. Drilled to - 259Y2 ft at 1600. 

7/11 0735 ~~g:~ } 259.0 122.6 } 122.5 4 - 20.2 Then drilled to -304ft at 1545. 

0755 122.3 8 7/12 0714 ~8~ :g } 303.4 128.9 } 128.9 4 -20.5 Then drilled to - 351 ft at 1540; losing some drill water. 

0729 128.9 8 7113 0715 ~~8:~ } 350.5 143.6 } 143.6 4 - 21.9 Then drilled to -380 ft at 1540, with increasing loss of drill water. 

0731 143.6 8 7/14 0728 ~~~:~ } 379.6 149.0 } 149.0 4 -22.0 Then drilled to -424 ft at 1555, with almost no water return. 

0740 149.1 8 7/15 0718 423.4 159.9 } 160.0 4 -22.3 Then drilled to - 454 ft at 1440. 

0735 160.2 8 7/16 0917 451.2 166.8 } 166.8 4 - 21.9 

0933 166.9 8 7/17 0730 451.1 167.6 } 167.6 4 - 20.7 Note 1.2-ft rise in water level from heating of hole; then drilled to -514ft 

0749 167.7 8 at 1540 with - 15 percent water return. 

7/18 0730 513.2 172.0 } 172.2 4 - 21.9 Then drilled to -561 ft at 1545, with poor water return. 

0745 - 514 172.3 8 7/19 0715 ~~8:! } 560.4 179.9 } 180.2 4 -21.8 Then drilled to -597Yz ft at 1440, with fair water return. 

0732 180.4 8 7/20 0720 (579 7) (168.9) 4 - 20.1 Core barrel left in rods. 

0828 596 182.8 8 After core barrel removed. Then drilled to - 611 1'2 ft at 1445. 

7/21 0712 (177.8) 4 - 21.8 Bumped at drill bit; unreliable . 

0748 (608.1) (181.6) 4 Bumped, unreliable; then drilled to -641 ft at 1520. 

7/22 1005 640.8 188.4 8 -21.9 Temperature after core barrel retrieved. Then drilled to -691 ft; first positive pressure (and pyrite) near -680 ft. Pressure much greater 

downward. 

7/23 -1000 (141.5) (168.4) 4 (+190) 79lh All water pressure; hole blocked at -141.5 ft. Note effect of water flow up hole, increasing temperature at -141 ft about 96°C above original. 

7/24 0800 (141.5) (166.7) 4 (+189) 79 Hole still blocked. Hole then erupted and successfully cleared. Probably 

best indication of maximum over-pressure prior to drilling-79 psi. 

0906 690.5 195.6 4 80Y2 All water pressure. Drilling terminated. 7/25 1128 ~~~:~ } 689.1 i~~:f } 195.8 4 (+202) 84 All water, no gas. 

1155 8 84Y2 All water, no gas; top temperature 27°C. 

7/29 1400 690.0 193.9 4 (+208) 87 All water, no gas; note temperature decline. 

10/22 690.2 188.9(?) 11 (+216) 90 All water, no gas; bottom pressure 366±3 psia; calculated natural over- pressure at bottom 76 psi. 

6/14/68 1100 686 94 to 96 Thermistor temperature series, curve C, figure 21. 

7/9/69 690 (+216) 90 to 94 Bottom pressure 363 psia; calculated overpressure at bottom, 75 psi. 

9/17/69 688 (+216) 90 to 94 In-hole pressure series, curve E, figure 22. Bottom pressure 363 psia. 

Calculated overpressure at bottom 75 psi. 

5/24/70 685 93 to 94 In-hole pressure series, curve E, figure 22. Bottom pressure 363 psia. 

9/24/71 685 193 (+218) 91 to 94 In-hole thermistor and pressure series (curves C and E, fig. 22). Bottom 

194.2 12 pressure 361 psia. 

1Data in boldface considered most reliable; data in parentheses, least reliable. 2Relative to ground surface; positive levels in parentheses calculated from wellhead pressures considered to be least affected by vapor. 
LOWER AND MIDWAY BASINS 39 

through the dense homogeneous lava to the ground errors in measurement. A third segment, also of nearly 

surface suggests a mean annual surface temperature of constant gradient, extends from-450ft to the bottom of 

~6°C. the drill hole at -691 ft. 

A second segment of lower but nearly constant gradient extends from -250 to -450ft, with minor variations that are related either to very slight flow or to 

Fluid pressures were nearly constant to a depth of 

-650ft, with measured depths to water ranging from 

-17.8 to -22.3 ft(table 10). The tendency for the depth 

Iw 

w 

LL 

~ 

:i 

Ia.. 

w 

0 

CASING RECORD 

0 20 40 60 80 

TEMPERATURE, IN DEGREES CELSIUS 

100 120 140 160 180 200 

CONDENSED 

LOG 

220 o~~?,~--~--~--~--~--~--~--~--~~~--~--~--~-- ----.-~.---.---.---.---.---.----,--, 

21ft~, --------

100 

200 

300 

400 

500 

600 

700 

800 

900 

of 4-in . ''?, Curve C~----

casing Thermistor series -----...____ 

120ft 

of 3-in. 

casing 

TD 

691 

June 14, 1968, 101/z months ~ 

after hole completed 

Curve B. 

Bottom-hole temperatures 

obtained as drilling 

progressed 

EXPLANATION 

0 Bottom-hole temperature about 16 hr ' 

after circulation ceased 

40 8. Bottom-hole temperature, indicating hours 

(or other specified time) after circulation 

ceased 

-- Thermistor temperature series in completed hole 

l Equivalent depth, corrected for differences 

in static water level for comparison with 

curve A -

\ Curve D. V Reference boiling-

\ temperature curve 

\ 

corrected for 80 pounds 

--.._ \ per square inch (gage) 

------........_ of wellhead water 

............... \ pressure 

\ \ \\ 

~\ 

~ \ 

~ 

1 wk 

FIGURE 21.-Temperatures and other data, Y-4 (Nez Perce) drill hole, Lower Basin. 
40 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

to water to increase slightly as the drilled depth increased is mainly related to the cooling effects of drill 

water over an increasing depth range. Rocks high in the 

hole had been cooled by days or weeks of intermittent 

drilling, and in the absence ofupflow from hot aquifers, 

original ground temperatures did not recover rapidly. 

Note, for example, the rise in water level of1.2 feet from 

July 16 to 17 (table 10) while drilled depth remained 

constant and the bottom-hole temperature increased 

only 0.8°C. This rise in water level must have been due 

largely to thermal expansion of water at intermediate 

levels in the hole in response to conduction of heat from 

the walls. 

The first major change in fluid pressure became evident when the core barrel was retrieved from -681 ft 

and water rose for the first time above ground level. The 

actual change probably started to occur during the previous run near -679 ft, where the shallowest fresh 

CASING RECORD 

TEMPERATURE, IN DEGREES CELSIUS, AND 

PRESSURE, IN POUNDS PER SQUARE INCH (ABSOLUTE) 

0 200 300 400 o.-~.-~~=---..---,--~~-------.----~--,----.----.---,---.----.----.---.----.----.----.---, 

Curve G. 

. . " \ 

Calculated boiling pressures 

for pure water, from temperatures 

measured Sept. 24, 1971 

Curve E. 

Pressure series Sept. 17, 1969, 

May 24, 1970, and Sept. 24, 1971 

'\: 

\ 

:'\ :\ 

\ 

" \ 

\ 

'\ 

" \ 

\ 

\ 

\. 

" \ 

FIGURE 22.-In.-hole temperatures and pressures of Y-4 drill hole after completion, compared with other data. 
LOWER AND MIDWAY BASINS 41 

pyrite found in the hole occurs in fractures in drill cores. 

At -691 ft, nearly 80 psig was measured at the surface 

(table 10). The static water level had increased from 

about-22ft at-641ft to the equivalent of about+ 190 

ft at-691ft, and the hydraulic gradient through this 50 

ft interval averages 41Ji ft of water per foot of depth; 

between -671 and -691 ft the probable average gradient is close to 11 ft of water per foot of depth. Such 

hydraulic gradients are possible only in rocks of extremely low permeability. The temperature record provides no evidence for any predrilling upward flow of 

fluid from the high-pressure aquifer near-681ft. This 

aquifer obviously communicates with deeper levels of 

much higher pressure, but not with the surface. 

SUMMARY OF DRILLING PROBLEMS 

Y -4 was one of our easiest holes to drill. By July 1967 

the drill crew was experienced in handling many 

difficult problems, and satisfactory methods and 

equipment had been developed to drill into relatively 

high-pressure environments. However, the high pressures suddenly encountered near -680ft forced us to 

terminate drilling at -691 ft. At this depth the wellhead water pressure of about 78 psig was exceeded in 

only one other drillhole (Y-13). 

POSTDRILLING MEASUREMENTS 

Two series of temperature measurements were made 

in Y-4 using thermistor equipment. The first was on 

June 14, 1968, 101;2 months after completion of the hole 

(curve C, fig. 21) and the second on September 24, 1971 

(curve C, fig. 22). These curves clearly indicate that Y-4 

short-circuited the aquifers that it intersected. The hole 

allows hot water to flow from the high-pressure aquifer 

near -681 ft, then up and into aquifers of low initial 

pressure at intermediate and shallow depths, as indicated by loss of drill water during drilling. The upper 

part of the hole has been heated to temperatures above 

those of the original rocks. Also, in response to the 

upward decrease in hydrostatic pressure, the upflowing 

water at ~195°C starts to boil near -275 ft and continues to boil up to about -145ft. The change in gradient in curve C (fig. 22) near -148 ft suggests that 

high-temperature water is flowing out into a zone of 

fractures noted in drill cores from -138 to-149ft. The 

sllght irregularities in temperature below about -300 

ft shown in curve C, figure 21, and in curve C, figure 22, 

probably resulted from slow convective circulation of 

water in the hole during the measurements. 

Two months after completion of the hole, wellhead 

pressures increased from 79 psig to 91 psig (table 10). 

The fluid that leaked from the hole during all those 

measurements was liquid water with some vapor exsolving after leakage. The increase in wellhead pressure must have resulted from heating of the hole. 

In-hole pressure measurements clarify the actual 

conditions at depth. The pressures measured on September 24, 1971 (E of fig. 22) were used to calculate a 

boiling-temperature curve (D of fig. 22). This calculated 

curve has an average temperature of ~3°C above a 

parallel segment of temperature curve C (fig. 22), 

measured in the hole immediately before the pressure 

measurements. The parallelism indicates that a vapor 

phase was present from -260 to -140ft, but the temperature difference between the curves indicates vapor 

pressures of water that were significantly below the 

total pressure (that is, the water contained bubbles of 

exsolved gas). Curve G, figure 22, shows the partial 

pressures of water calculated at the measured temperatures in the interval -260 to -140 ft. This curve is 

almost exactly parallel to and about 13 psi lower than 

curve E (the measured pressures). Therefore, the sum of 

the partial pressures of gases other than steam was ~ 13 

psi or ~0.88 atm. 

Comparison of postdrilling in-hole pressure measurements (table 10 and curve E, fig. 22) and a calculated 

pressure curve appropriate for the predrilling subsurface temperatures at the Y-4 site (curve F, fig. 22), 

indicates 75 to 76 psi of water overpressure. This is very 

close to the 79 psig first measured at the wellhead after 

drilling. Later surface pressures measured when only 

liquid was leaking from the hole ranged from 80 to 

about 94 psig. All these higher wellhead fluid pressures 

resulted from heating of the hole at all levels about 

about -681 ft, probably with some effect from vapor 

bubbles in a slowly convecting ((boiling" segment near 

-200ft. 

Y-13 (PORCUPINE HILLS) DRILL HOLE 

SITE SELECTION 

Y-13, our final research drill hole, was planned for a 

depth of 500 ft. Our main objective was to obtain more 

information from the center of a hot upflow system. 

Yellowstone contains many geologically suitable sites, 

but nearly all were eliminated for one of three reasons: 

(1) no access by present road, (2) too close to major thermal features that might be irreparably changed, (3) too 

close to tourist traffic, involving possible danger and 

risk of accidents. For these reasons more of our previous 

drill holes were sited on the borders of upflow systems 

than we desired. For Y-13, however, we found a suitable 

site that was relatively isolated but accessible by a 

service and fishing road up the south side of Nez Perce 

Creek in northeastern Lower Geyser Basin. 

The Y-13 site is in a cluster of thermal springs of low 

discharge on a nearly horizontal terrace between the 

two western Porcupine Hills at an altitude about 45ft 

above Nez Perce Creek and 15 ft above the nearest drill 
42 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

hole, Y-4 (table 3). The hottest spring of the group was 

slightly superheated, with discharge of 1 to 2 gpm and 

located 70 ft northeast of Y-13; the drill site is on the 

slope of the sinter cone of this spring and 3 ft lower in 

altitude. Chemical data (Fournier and Truesdell, 1970) 

suggest that subsurface temperatures in the vicinity 

are slightly above 200°C, and that the ratio Cl/HC03 of 

springs near the drill site is the highest of Lower Basin, 

indicating a major upfl.ow zone. The lack of vigorous 

discharge from all springs of the group was assumed to 

result from extensive self-sealing of outlet channels. 

Wellhead water pressures of at least 33 psi were suggested by the existence of discharging springs and hot 

spring sinter of former springs at various places in Porcupine Hills at altitudes as 1nuch as 80ft above the drill 

site. 

PHYSICAL MEASUREMENTS 

Physical data from Y -13 are shown in table 11 and 

figures 23 and 24. The water table was identified at 

about -3% ft ( ~6% ft below the outlet of the 

TABLE H.-Temperatures, pressures, and other observations from Y-13 (Porcupine Hills) drill hole, Lower Basin 

Date and time Observation Temp. Thermometer Static water Wellhead 

pressure, Comments l968 depth, ft' oc• No. level, ft 1 2 

psig' 

6/25 1202 (-21.9) (<19) (-4.3) After drilling to -22ft; then set 4-in casing to -21ft. 1300 (21.9) (22.8) -3.5 45 min after circulation; then cemented; best shallow water level. 6/26 0810 15.7 52 (-5.5) On cement; then drilled to - 61 Yz ft at 1230. 1640 61.6 124.2 14? -0.1 4 hr after circulation. 6/27 0730 61.6 128.1 } 9 -0.3 Temperature on boiling point curve, so drilled to -72 ft at 0935; set 3-in. 129.2 . 128.9 11 casing to -72 ft, cemented bottom and top, securely. 129.2 12 6/28 -0730 37.8 87.3 (-0.2) On cement; note straight-line gradient, figure 23. Then drilled to -133 ft at 1600, with hole discharging below -117 ft. 6/29 0730 133.1 i~~:~ } 152.9 11 (+21) 9% Water pressure. Then drilled to -177 ft at 1545. 6/30 0850 - 177 ~~~:~ } 166.1 9 (+36) 17 to 15 Water pressure 15 psi? 

11 16 to 17 1930 (+50) 21 to 22 All water pressure? 7/1 -0730 - 177 i~~:~ } 166.5 9 27 to 28Yz Permeability high. Then drilled to -207ft at 1530. 

14 27 to 28Yz 7/2 0755 207.1 i~~:f } 166.2(?) 9 (+51) 21Yz Not insulated; water pressure? 

4 0815 207.1 161.4 13 21Yz Insulated; probably most reliable temperature but not certain. Then 

- 221 drilled to -227 ft at 1330; problems with caving. 7/3 0845 (169.8) (+72) 37 to 30 Water pressure? Thermistor -4oC low, failing? 

173.3} 12 Then set BX casing to -227 ft, cemented top and bottom after setting; 0930 223.5 173.7 173.7 12 41 to 38 drilled out to -210 ft at 1730. 174.0 9 7/5 0805 207.6 i~~:~} (160.2) 9 (9 to 14) On cemented bottom to check possible reversal of July 2; not conclusive. 

14 0820 (177.2) i~~:f} (1 56.7) 9 (13 to 17) 30 ft off cemented bottom to check 7/1 temperature; not conclusive. 14 0850 207.5 (154.4) (14 to 20) Thermistor check; temperature decreasing with leakage (1

/s gpm) as (152.0) pressure increasing; boiling from bottom in cemented hole. Then drilled to -293 ft at 1600. 1630 207 \"z (158.4) 14 (+60) 25 Water pressure (minimum). 7/6 0735 292.8 i~~:~ } 183.5 9 34 to 37 Then drilled to -347 ft at 1550. 14 7/7 0823 346.3 i~8:~ } 190.9 9 (+79) 35 to 33 Water pressure 33 psi? 14 7/8 0740 346.3 i~8 ~ } 190.8 9 40 to 41 Then drilled to -378 ft at 1445. 

14 (+91) 38 to 40 1555 378 42 to 64 Erupted through side pipe 30 min to determine pressure changes. 1625 (+77) 64 to 32 Pressure changes during 3 hr after closing valve. 7/9 0748 378.2 i~U} 193.8 9 (+89) 37 to 52 Water pressure 37 psi? 14 52 to 44 After decreasing leakage. Then drilled to -407 ft at 1520. 7/10 0740 408.8 i~+:~ } 197.5 9 (+96) 40 to 44 Water pressure 40 psi? Then drilled to -440ft at 1605. 14 7/11 0740 438.7 ~88:1 } 200.2 9 (+122) 51 to 54 Water pressure 51 psi? Then drilled to -465Yz ft at 1450 with increasing 14 problems from pressure. 1630 465 (+216) 90 Pressure 1 Yz hr after circulation ceased; may be best indication of natural 

1900 465 bottom-hole overpressure. 102 Pressure increased with slight leakage to 1900. 7/12 0700 465 118 to 120 Temperature not obtainable because main valve leaking. Decided to terminate drilling. Tried to change valves but packer not working. Pu~ed 1 sack cement into hole. 7/13 1400 464.8} 203 .7} 13 122 to 127 1 hr ter valve changed)and circulation ceased, but no circulation to 465.0 203.3 203.4 bottom of hole since 7/11? 1530 465.3 9 125 to 130 Temp. reference curve relationships demand at least 126 ft of water or 203.3 . 14 -53 psi overpressure at bottom. 7/15 0830 464.8 200.6 13 180 to 104 Initially all gas, then to all water. 7/16 0900 104 to 105 Thermistor series (curve C, fig. 23). 7/17 1150 465.3 197.1 14 178to102 Leakage all gas, changing to water; maximum thermometer series, not 

7/18 460 131 to 100 graphed. 

In-hole pressures; bottom pressure 226 psia, overpressure 34 psi? 

Bottom hole pressure 206 psia. 9/15/69 462 (+197) 163 to 82 Pressure change as gas bled off. 10/4/69 0940 (+199) 165 to 83 Maximum-thermometer series (fig. 23, curve D). 1200 464 198.0 } 12 (+180) 75 to 85 198.4 198.4 N-3 198.9 N-5 5/27/70 464 (+175) 154 to 73 In-hole pressure series (fig. 24, curves E and F). Bottom hole pressure 

5/29/70 455.7 (+173) 153 206 psia. 197.4 13 Maximum thermometer series (fig. 24, curve H). 9/25/71 464 198.5 148 to 72 In-hole pressure series (fig. 24, curve D) and maximum thermometer series 

464.5 (fig. 24, curve G). Bottom pressure 208 psia. 9/24173 197.8 12 >87 to Bottom-hole maximum thermometer. Thermistor series (fig. 24, curve I). 463.9 198.0 70 to 72 

'Data in boldface considered must reliable; data in parentheses, least reliable. 2Relative to ground surface; positive levels in parentheses calculated from wellhead pressures considered to be least affected by vapor. 
LOWER AND MIDWAY BASINS 43 

CASING RECORD 

0 --~====~,_--,- -.~~---,---. 

100 

21ft 

of 4-in. 

casing 

72ft 

of 3-in. 

casing 

Curve B. 

Bottom-hole temperatures as 

drilling progressed 

140 160 180 

CONDENSED 

LOG 

220 

Curve D. 

Maximum-thermometer series 

Oct. 4, 1969 

200 

fw 

227ft 

BX casing 

EXPLANATION 

0 Bottom-hole temperature about 

16 hr after circulation ceased 

w 

u.. 

~ 

::i' 300 

40 !;:::, Bottom-hole temperature, indicating hours 

(or other specified time) after circulation 

ceased 

fa.. 

w 

0 +-+Thermistor series, July 16, 1968 

(failure at -182 ft) 

400 

•-• Maximum-thermometer temperature series, 

Oct. 4, 1969 

X Near-surface check temperature of same series, 

Oct. 4, 1969 

TO 

465.5 

500 

1 Equivalent depth, corrected for 

differences in static water level 

for comparison with curve A 

FIGURE 23.-Temperatures and other data, Y-13 (Porcupine Hills) drill hole, Lower Basin. 

superheated pool to the northeast). The straight-line 

temperature gradient from near the water table to the 

base of the sediments near -61 ft seems to be a purely 

conductive gradient uncomplicated by convective disturbances. At greater depths temperatures increased 

rather regularly, generally plotting above the boilingtemperature curve (A of fig. 23). The only exception was 

near -207ft where a temperature reversal may have 

occurred, possibly related to penetration of a 

cooler tongue of water into the system. Several efforts to 

substantiate the suggested reversal were inconclusive 

(table 11, 7/2, 7/5). 

An increase in fluid pressures first became evident 

near-62ft and wellhead pressures increased regularly 

thereafter to about-180ft. Below the zone of uncertain 

physical characteristics near -207 ft noted above, pressures again increased rather regularly to about 40 psig 

at-409ft. At-465ft a wellhead pressure of ~90 psig 

was measured (7/11/68) when the drill rods were withdrawn from the bottom of the hole only 1 Y2 hr after 

circulation ceased; only liquid water was discharging at 

the top of the hole. This very high wellhead water pressure made it extremely difficult to control the hole while 

going in and out with the drill rods, so drilling was 

terminated. 

SUMMARY OF DRILLING PROBLEMS 

We avoided the mistake made at Y-3 where drilling 

progressed too rapidly through shallow, easily drilled 

ground of high eruption potential. Thus, our 3-in. casing 

was set only to -72ft-intentionally the shallowest of 

any of our holes. Perhaps we should have set casing at 

an even shallower depth, but we strongly desired a good 

anchor, and rhyolite was not penetrated until -61 ft. 

Our slight calculated risk fortunately paid off. 

Positive wellhead water pressures, as mentioned, 

first became evident at -62 ft and then increased 

rapidly with depth and rose higher above the reference 

pressure curve than in any other Yellowstone drill hole 

(table 3). In addition, the temperature of203.4°C measured at-465ft was higher than temperatures recorded 

in all drill holes with the single exception of Y-12 at 
44 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

depths below 700ft, with 237.5°C at -1,088 ft. Nevertheless, drilling progressed in Y-13 with no unsolved 

problems until very high fluid pressures were encountered near-465ft, which caused us to stop drilling. On 

the morning of July 12, 1968, the wellhead pressure was 

118 to 120 psig, with a mixture of water and steam 

leaking from the main valve. An effort was made to 

insert the packer for changing valves. For the first time, 

the packer failed to seal off the flow of hot fluids after its 

forced insertion through the main valve. Later inspection showed that 'the neoprene expanding unit was 

damaged, either from BX casing extending up too high 

within the NX casing, or because of the combined effects 

of high pressure and temperature. The drillers then 

pumped one sack of cement into the top of the hole so the 

valves could be changed. The change was successfully 

accomplished the following day after the cement had 

set. However, when the cement was drilled out, we 

found only one foot of solid cement below the new valve. 

A serious problem had been narrowly averted! The explanation for the inadequate quantity of cement is not 

known. 

CASING RECORD 

0 20 

0 ~ ~ 

u~eA ~ 9 4-

1n_. Reference bo1hng ' '-

casing pressures /~0 "-9: Cu~e F 

POSTDRILLING MEASUREMENTS AND INTERPRETATION 

Bottom-hole temperatures at approximately -465 ft 

were measured with a maximum-recording thermometer at times of about 48, 88, and 130 hr after the completion of Y-13 (table 11). On July 16, 1968, a thermistor 

series was run from the surface to -182 ft (C, fig 23), 

where the equipment failed. In the absence of reliable 

thermistor gear, temperature profiles were laboriously 

made with a maximum-recording thermometer on October 4, 1969 (D, fig. 23), May 29, 1970 (H, fig. 24), and 

September 25, 1971 (G, fig. 24). The first satisfactory 

thermistor temperature series was obtained on September 24, 1973 (table 11 and curve I, fig. 24). 

In-hole pressure measurements were made at the 

hole bottom on July 18, 1968, and on September 15, 

1969. In-hole pressure measurements at various depths 

were made on May 27, 1970, and on September 25, 1971 

(F, E, and D, fig. 24). 

All the in-hole pressure profiles show linear 

pressure-depth gradients at shallow depths. These gradients are parallel to the reference boiling-pressure 

TEMPERATURE, IN DEGREES CELSIUS 

40 60 80 100 120 140 160 180 200 220 

0-% .. ~~0 ~ .••••• 

--0 ·· .. 

0 ··..• Cu~eH . 

'--o~ 0/ Temperatures 

-k Cu~e E ~ '\. / Pressures 

3-ln. ~ Pressures 0 '\ May 27 1970· 

cas1ng "" ' May 27, 1970; ·'\'\ " \-] \ hole vent1ng ' ' 

~-~y 29, 1970 

------\\ 0 

100 

ti:i 200 w 

u. 

~ 

::C 

h: 

w 

0 

300 

400 

0 20 40 

~ no flow at '\0 9. - 5 gallons per 

, surface L?:,.\ ~mute "' :t-,, ~ ~,~\ . 

""" 0 '+""' \ -~ " ~ ~ 'f\'"'cu~e D. , Pressures 

~ \b Sept. 25, 1971 

' ~ ""* ' ~q 'i9. 

"'~\~ ~\\.0 lC\ \' 

Curve G. \ .. \ ~ Cu~e I. 

Temperatures S t ·. ~ 

25 1971 \ \ f \ Temperatures 

ep · • ·. \ 0 \ Sept. 24 1973 ... \ \ ' 

....... \§ \ 

·· .. "\'s 

Curve B.---------·.. \ I 

Reference boiling \... \\ 

temperatures .. 0 

\ I ": 0 

\ I ·~ 0 :_ I 

\ I ·~ 0 ~ 0 

\ \ 

V\ 0"' \B, "' ~ Cu~e C. 

vb~ '~ Minimum pressures 

:.. 0 

\I ~ 0 ~ necessary for temper-

'{'\ b ', atures measured as 

'il~b ~ drilling progressed 

v'f!Y ~ " ~ 

60 80 100 120 140 160 180 200 220 240 260 280 

PRESSURE, IN POUNDS PER SQUARE INCH (ABSOLUTE) 

\ ~ :._ I 

·~ 0 

:._G 

FIGURE 24.-ln-hole temperatures and pressures of Y-13 drill hole compared with reference curves. 
LOWER AND MIDWAY BASINS 45 

curve, but are displaced to the right because of water measured temperature of 203.4°C, with the higher 

overpressure. At greater depths, the pressure-depth temperatures being obscured by immediate postdrilling 

gradients are much too low for liquid water, indicating boiling and flow of water and steam up the hole. If the 90 

coexisting liquid and vapor. Boiling water and steam psig wellhead pressure measured on July 11, 1968 apfrom a zone near the bottom of the hole apparently flow . . proximates the original water overpressure at -465.5 

up and out into a relatively permeable zone of lower feet, the original rock temperature at this depth could 

pressure at the contact of two lava flows and near the have been as high as 211.5°C. If so, much heat had 

bottom of the BX casing at-227ft. The pressure-depth already been lost by boiling before the temperature of 

gradients suggest slight but significant boiling in the 203.4°C was measured on July 13. 

aquifer adjacent to the hole bottom, and such boiling The first satisfactory thermistor temperature profile 

was more extensive in 1970 than in 1971. In both years, in Y-13 was obtained on September 24, 1973 (table 11 

the extent ofboiling increased upward from about -400 and fig. 24, curve I). All temperatures obtained during 

to -250 ft. Most of the resulting vapor evidently flows and after October 1969 are in satisfactory agreement at 

out into the permeable zone at -227 ft, along with the depths below the BX casing at -227 ft, but puzzling 

water. A little vapor rises into the water within the BX disagreement had been found at higher levels. Differing 

casing and gradually dissolves upward as temperatures rates of upward leakage of fluids from the surface gear 

decrease. Consequently, the pressure-depth curves do had been considered as the major variable, but a comnot display sharp inflections at -227 ft but instead parison of curves G, H, and I of figure 24 demonstrates 

change smoothly into the linear pressure-depth gra- that data points of the earlier maximum-thermometer 

dients that characterize shallow depths. profiles were too widely spaced; the data points of curves 

The near-surface discrepancy between curves E and G and H, seemingly in major disagreement at depths of 

Don the one hand and curve F on the other is due to the about -50 to-175ft, actually agree closely with those 

differing amounts of water allowed to escape from the of curve I but the latter defined major changes in grasurface apparatus during the measurements. Curves D dient near -80 and-165ft. (These breaks in gradient 

and E were obtained with almost no leakage of fluids at were actually suggested in curves C and D of figure 16 

the surface but some gas had accumulated in the upper but were not considered significant.) 

40ft of the casing during curve E measurements. Curve All postdrilling temperatures indicate that a linear 

F, in contrast, was obtained while water and steam were temperature gradient extends from the bottom of the 

discharging from the surface apparatus at an estimated hole to about-175ft, or 50ft above the bottom of the BX 

rate of 5 gpm. This discharge resulted in decreasing casing. This gradient, as we have seen, results from 

pressures by 4 to 5 psi near the bottom of the hole, which upflow of coexisting liquid and vapor, with vapor inin turn decreased temperatures and increased the rate creasing upward as pressure decreases. U pflow outside 

of boiling as heat was transferred from the rocks to the an imperfectly cemented BX casing but within the 

fluids. Rock permeabilities in the lower 200ft of the hole drilled hole could explain the temperatures of curve I, 

are evidently low, thus accounting for the significant except for the abrupt decrease in temperature upward 

change in bottom-hole pressure in response to the esti- between -176 and -165 ft, which is unlikely to have 

mated discharge of only 5 gpm. been blocked by cement if the casing at greater· depth is 

The maximum bottom-hole temperature measured in imperfectly cemented. Instead, hot fluids are probably 

Y-13 was determined on July 13, 1968, only 48 hours flowing upward through adjacent permeable rocks to 

after drilling ceased. Bottom-hole temperatures then about-176ft; some fluid leaks through less permeable 

declined to 200.6°C after 88 hours, and 197.1 oc after 130 rocks from -176 to -165 ft, where resistance to flow 

hours. In other drill holes (e.g., Y-3), low postdrilling again decreases, but temperatures are lower. Within 

temperatures could be explained by circulation from a this zone, however, the upflow could be largely within 

shallow cool. zone at relatively high pressure as com- the drilled hole but outside the BX casing. The next 

pared to a deep hot zone with lower overpressure. Such higher break in thermal gradient is suspiciously close to 

an ·explanation is not possible for the Y-13 data, be- the bottom of the 3-in. casing at -72 ft, where good 

cause water overpressures increase rapidly downward. cementing would divert any upflowing fluid out into 

An alternative explanation is provided by the in-hole surrounding rocks. 

pressure data, discussed above, which require that heat CORRELATION OF DATA FROM y_4 AND y_ 13 DRILL HOLES 

be extracted from the rock bordering the drill hole, or 

from inflowing liquid if pressures are not high enough to Y-13 was very satisfactory in providing data from 

maintain a single liquid phase. near the center of an upflowing hydrothermal system. 

Original bottom-hole rock temperatures in Y-13 may Although this system is now relatively inconspicuous 

have been significantly higher than the maximum and low in total discharge, geologic evidence implies 
46 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

that it was large in the past-large enough to cement 

and hydrothermally alter great volumes of glacial deposits. The indicated decrease in discharge of this system over recent tens of thousands of years must be 

related, in major part, to self-sealing by hydrothermal 

minerals. 

Y-4 is about 2,200 ft northeast of and about 15 ft 

below Y-13 and is on the northern margin of the same 

general upflow system; temperatures are consistently 

much below boiling and in the upper 250 ft are controlled entirely by conductive heat flow. Relatively minor 

convective disturbances are evident in deeper parts of 

the hole, accounting for changes in thermal gradient 

near -250 and-450ft. A deep fracture zone containing 

water under high pressure ( ~76 psi above the reference 

pressure curve) had little effect on the thermal gradient, suggesting that this zone, if it was ever connected 

with the surface, has since been isolated by hydrothermal self-sealing. 

Y-4 and Y-13 drill holes thus provide a good opportunity for evaluating horizontal variations in physical 

characteristics between the center and margin of a convection system. The pertinent data are shown in figure 

25, greatly generalized between the two holes where 

subsurface data are lacking. 

The western ring-fracture zone of the Yellowstone 

caldera (Christiansen and Blank, 1973) probably occurs at depth under the section of figure 25 (but not 

shown), and this fracture zone has probably influenced 

all post-caldera structures and the distribution of lava 

flows. In the immediate area the lava flows are 

identified by Christiansen and Blank as the Nez Perce 

Creek flow, probably overlying the Elephant Back flow 

in Y-13 drill hole. The flow contact in figure 25 is 

hypothesized on this basis, with depths to the bottoms of 

the flows and identity of underlying rocks completely 

unknown. 

Figure 25 also shows our best estimates of original 

wellhead water pressures in the two holes, with 6 psi 

added to the data of Y-13 to compensate for its higher 

ground level of ~ 15 ft. Temperatures increase rather 

steadily in both holes. The temperature contours between the two holes of figure 25 are assumed to be 

generally convex upward because of convective upflow 

and discharge from the springs north and northeast of 

Y-13. 

The sands and gravels of the upper 60 ft of Y-13 

initially must have had very high permeabilities that 

have since decreased greatly because of deposition of 

hydrothermal minerals. The initial permeabilities of 

the underlying fractured rhyolite flows and flow breccias are less certain but were probably moderately high. 

Temperature differences between Y-13 and Y-4 are 

about 90°C at -100 ft (below ground surface, rather 

than strictly horizontal), 64°C at-200ft, 56°C at -300 

ft, 41 oc at-400ft, and 36°C at-500ft (projected under 

Y-13). The average horizontal temperature gradients 

at corresponding depths, assuming 2,200 ft between 

holes, are 4.1 °, 2.9°, 2.5°, 1.9°, and 1.6°C per 100ft. This 

regular pattern of decreasing gradients suggests that 

the gradient becomes slight at depths below 1,000 ft. 

Large horizontal contrasts in pressure also exist between the two holes. The shallow and intermediate 

depths provide no evidence of permeability high enough 

for any significant fluid communication. The massive, 

dense Nez Perce Creek lava flow, judging from cores and 

loss of drill water, had some initial fracture permeability, but the fractures have been effectively sealed from 

the deep high pressures by deposition of hydrothermal 

minerals. The highest measured horizontal pressure 

gradient between the two holes is at ~6,755 ft in altitude (the bottom of Y-13). Including the altitude correction of 6 psi, the pressure difference is 105 psi in a 

horizontal distance of 2,200 ft, or ~4.8 psi/100 ft. The 

equivalent hydraulic gradient is ·approximately 11¥2 ft 

per 100 ft (0.115). 

The temperature curves of Y-13 and Y"'--4 as drilling 

progressed are generally similar except that the Y -4 

curve is systematically offset to lower temperatures, the 

amount of offset ranging from 90°C at -100ft to 36°C at 

-500 ft. Is this similarity in curvature largely coincidental? 

Except at depths ofless than 60ft, the curve ofY-13 is 

controlled mainly by boiling, with excess heat of the 

rising water being utilized to form vapor. Control of 

temperature by vapor formation probably continues 

downward considerably below the drilled depth ofY-13; 

the silica content of its water (as much as 390 ppm) 

suggests a reservoir temperature possibly as high as 

229°C. A downward continuation of the deep thermal 

gradient ofY-13 to this temperature, assuming no additional increase in water overpressure, indicates that 

boiling may first start at a depth of about 700 ft. 

In contrast, boiling can play no direct part in controlling the temperatures of Y-4; the measured temperatures (curve B of fig. 21) are at least 10°C too low at all 

drilled depths to permit any vapor to form, and are 

probably at least 20°C too low at -690ft, considering 

the effect of overpressure. The major controls over 

temperature in the two holes therefore cannot be identical. Thus, subsurface boiling provides a major control on 

temperatures in Y-13, but conductive heat loss must 

become an increasingly important control as Y-4 is 

approached. 

Three lines of evidence suggest that the waters of the 

two drill holes are related and that a horizontal northward component of flow of water occurs deep in the 

system in the general area from Y -13 to Y -4. The 
LOWER AND MIDWAY BASINS 47 

SW 

7200 ' 

7000' 

6800' 

6600' Elephant 

Back 

flow t I 

Nez Perce 

Creek flow 

--- --~W~t~r-­

table 

.. ;> ... ~ 

.:· ~ J 

2ooo 

----------. ·:. ~ Self-sealed 

' ~ 

~ 

NE 

-----7-------

--- ;1_ "" ' -----l ···. · .. ·~upward 

6400' t ; 

10oFEETL 

100 FEET 

VERTICAL EXAGGERATION x 2 

? ------- ~ 

6200 '~----------------------------------------------------------~ 

EXPLANATION 

39 Wellhead water pressure, 

in pounds per square inch 

(gage) 

-7.5 Water level below ground 

expressed as negative 

pressure relative to surface 

-50°- Contour, showing inferred 

ground temperature, in 

degrees Celsius 

Direction and qualitative 

rate of flow of thermal 

water 

Decreased permeability 

due to deposition of 

hydrothermal minerals 

FIGURE 25.-Section through Y-13 and Y-4 drill holes, Lower Basin, showing initial temperature contours, wellhead water pressures 

(in psig, with water levels below surface as negative pressures) and some hypothesized relationships (6 psi added to original data 

from Y -13 to compensate for differences in ground level). 

chloride contents of waters from the two holes are almost identical (close to 260 ppm), and all analyzed 

springs in or near the intervening area have relatively 

uniform concentrations, ranging from 288 to 363 ppm. 

The spring waters of highest chloride content are in 

environments suggesting residual concentration by 

subsurface boiling or surface evaporation from large 

pools of low discharge. Thus all the waters of the area 

seem to be relatively homogeneous in chloride and from 

a common source. 

Mazor and Fournier (1973) have shown that the 

water from Y - 4 is unusual among sampled Yellowstone 

waters in its high retention of the noble gases; about 65 

to 85 percent of argon, neon, krypton and xenon are 

retained, assuming a common source of these gases 

from the atmosphere, equilibrating at low temperature 

in meteoric water recharging the hydrothermal system. 

Other sampled spring and drill-hole waters contained 

much less noble gases, probably because ofloss to vapor 

that formed as water rose and pressure decreased in the 

central part of each high-temperature system. The 

water of Y-4 could have lost only a little gas by deep 

boiling-but not directly below Y-4 because temperatures are too low for vapor to form, and no nearby dis-
48 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

charge of gases is evident. In contrast, some loss deep 

under the area of Y-13 seems more likely, followed by 

convective diversion (or flow with a horizontal component) to the northeast. Y-4's observed contents may be a 

little below those expected of atmospheric equilibration 

because some gas is lost by separation of vapor within 

the drill hole, or during or after the sample is collected. 

Another alternative is that meteoric recharge of 

these systems is largely from soil waters high in partial 

pressure of carbon dioxide and therefore relatively low 

in other atmospheric gases, by about 20 percent. 

A final indication of a deep horizontal flow involves 

the pressure gradients between the two holes. At the 

altitude of the bottom of Y-13, as we have seen, the 

pressure gradient toward Y-4 is ~4.8 psi per 100ft or a 

hydraulic gradient of0.115. Gradients at greater depths 

are less certain, but at the altitude of the bottom ofY-4 

(6,514 ft), the water.overpressure in Y-13 is probably at 

least 20 psi above that of Y-4, indicating a gradient of 

0.9 psi per 100ft. If the high rate of increase in water 

overpressure continues with depth in Y-13, the pressure gradient to the northeast must be even greater. 

Thus, temperatures in Y-4 seem to be influenced to a 

major extent by conductive heat loss. To the northeast, 

probably within or near the base of the Nez Perce Creek 

flow, the somewhat cooled, relatively dense water may 

circulate downward as part of a large convection cell 

that, in turn, is part of a more complex system. 

Y-5 (RABBIT CREEK) DRILL HOLE 

SITE SELECTION 

Y-5 was selected to provide data on subsurface conditions in the Midway (southern) part of Lower Geyser 

Basin. Grand Prismatic Pool (4,800 ft to the northwest), 

is the largest thermal pool in the Park, and Excelsior 

Geyser (700 ft northeast of Grand Prismatic) has the 

highest discharge of any single hot spring in the Park 

(about 3,000 gpm according to Allen and Day, 1935, p. 

268). The selected site is on the west edge of the nowabandoned Rabbit Creek garbage dump on a former 

service road with locked gate, isolating the site suitably 

from midsummer tourist traffic and tourist-related 

hazards (but not from grizzly bears!). 

All previous drill holes had encountered high wellhead water pressures that prevented deep penetration 

with our drilling equipment. We hoped that the large 

natural discharge from Excelsior and other nearby 

springs would have resulted in lower fluid pressures 

than in other systems of more restricted discharge, but 

this hope was not realized. This hole was especially 

valuable stratigraphically because it penetrated the 

only known occurrence of the Lava Creek Tuff within 

the western segment of the Yellowstone caldera. Lava 

Creek Tuff first occurs at the surprisingly shallow depth 

of 32 ft in Y-5. Careful search of Rabbit Creek and 

nearby areas failed to locate any outcrops of the tuff. 

PHYSICAL MEASUREMENTS AS DRILLING PROGRESSED 

Physical data from the hole are shown in table 12 and 

figure 26. Temperatures increased rapidly to about 

-100ft and then less rapidly to about-250ft where the 

maximum temperature of the hole, about 170°C, was 

measured. With deeper drilling, temperatures declined 

slightly to about 165°C at the total drilled depth of -538 

ft. 

Static water levels above ground surface first became 

evident at-66ft; wellhead water pressures increased to 

about 11¥2 psig at-211ft and then abruptly to ~39 psig 

at -248 ft. At greater depths, wellhead pressures seem 

to have decreased slightly (table 12) to 37 or 38 psig. 

The major hazard in the drilling of Y-5 was the 

grizzly bears feeding at the Rabbit Creek garbage dump 

300 ft to the east. The only actual damage was done by 

bears that chewed the plastic hoses carrying drill water 

from the creek. This problem was easily solved by moving the hose to a route less attractive to the bears. 

POSTDRILLING MEASUREMENTS 

A series of thermistor temperatures was obtained in 

the hole about 10 months after completion (fig. 25, curve 

C), showing a maximum of 167.8°C at -232 ft and 

confirming a slight temperature reversal downward to 

the bottom of the hole. Near-maximum temperatures 

also persisted upward to -160ft and temperatures then 

declined abruptly to the surface; boiling from about 

-120 to -140 ft (curves C and D) is indicated. 

The first reliable in-hole pressures were measured on 

October 22, 1967 (table 12). Other in-hole pressure 

measurements were made in July 1969, September 

1969, May 1970, and September 1971. The results (not 

illustrated) were all nearly identical and show a uniform increase in pressure with depth. An in-hole pressure at -240ft was 150 psia, which is 41.5 psi greater 

than the pressure curve calculated for water at original 

ground temperatures and extending just to the ground 

surface. The pressure at -528.5 ft was 260 psia, or 39.5 

psi greater than the reference curve for original ground 

temperature. 

A major aquifer containing water flowing at ~ 170°C 

and with an overpressure close to 39 psig evidently 

exists near -240 ft, which is about 200 ft below the top 

of the Lava Creek Tuff. Movement of water may be 

mainly horizontal rather than vertical, and this aquifer 

appears to be nearly isolated from shallower levels, 

probably because of hydrothermal self-sealing. 

Curve C of figure 26 confirmed the temperature reversal at depth, but near-surface temperatures seem 

likely to be too high because of inadequate equilibration 

after bleeding off its g~s cap. A series of maximum-
NORRIS BASIN 49 

TABLE 12.-Temperatures, pressures, and other observations from Y-5 (Rabbit Creek) drill hole, Midway-Lower Basin 

Date and time Observation Temp. oc) Thermometer No. 

Static water Wellhead 

1967 depth, fV level, pressure, ft 1 2 psig1 

Comments 

7/26 1350 

7/27 0800 13.0 

7/28 1210 (34.4) 

1337 (49) 

7/30 1923 66.3 

7/31 0755 66.3 

8/1 0742 

8/2 ~8~:~ } 8/3 - 0730 gg} - 0745 8/4 0730 ~~u } 1530 8/5 0745 ~!~:~ } 8/6 0930 g~:~} 817 0720 ~~~:~ } 8/8 0745 ~~~:~ } 8/9 0730 ~~g} 

8/10 07-33 417.8 

0806 417.7 

8/11 0740 !~~:~ } 8/12 0747 497.7 0815 (245.7) 

8/13 1137 537.6 

8/14 0736 537.8 10/19 1013 533.5 

1053 

1105 (249) 

10/22 

6/13/68 510 

231.5 9/20/69 530 5/26170 529 9/28171 529 

172.0 

199.5 

103.3 

173.1 

211.2 

248.2 

277.9 

277.9 

327.8 

377.8 

467.8 

(37) 

38 

(44) 

(84) 

116.6 

116.8 

147.3 } 147.3 161.1 } 161.1 

164.4 } 164.6 

169.3 } 169.6 

~~~:~ } 

~~~ :~ } 

~~~:~ } 

(167.6) 

(167.8) 

165.6 

(167.7) 

165.6 

(166.8) 

165.6 

165.7 

(168.6) 

164.2 

165.4 

(170.2) 

170.1(?) 

(170.4) 

165.8 

147.3 

161.1 

164.5 

169.5 

168.7 

169.3 

168.2 

167.8 (max.) 

169.0 

169.0 

4 

4 

4 

8 

4 

8 

4 

8 

4 

8 

4 

8 

4 

8 

4 

8 

4 

8 

4 

8 

4 

4 

8 

8 

8 

8 

11 

11 

11 

13 & 14 

13 & 14 

-5.3 

(-3.1) 

(-8.4) 

-8.1 

+3.9 

+4.2 

(+ 17) 

(+28) 

(+86) 

(+93) 

(+93) 

(+91) 

(+91) 

(+92) 

(+90 ) 

(+89) 

(+88) 

(+9ll 

7 to 7% 

8 

14 to 18 19 Yz to 20 13toll\', 

13 to 14Y2 

36 

39 

39'4 to 39Yz 39 to 39Y2 40 

39Yz to 40 401

/4 

38 to 88Y2 38'4 to 38Yz 38 to 38\4 

38\4 to 881

/2 39 

38% to 381'> 38'>4 to 88Y2 37% to 48 

38 to 38% 371

4 to 38'>4 38'4 

36% to 39 37% to 38Yz 72 to 45 45Yz 

46 to 46 Yz 

83 to 48 

84 to 46 

90 to 52 

84 to 43 42 

After drilling to - 19 ft at 1350; caving. Montmorillonite then added, 

drilled to -20 Y2 ft at 1645. Water level not reliable; caved to -13 ft. Then drilled to - 32 ft at 1640; 

set 4-in. casing to -32 ft and cemented. After drilling to -35ft. Then drilled to - 49ft at 1300. Y2 hr after circulation; best shallow water level; then drilled to -67 ft at 

1450. - 50 hr after circulation; gas-rich water; slight wellhead water pressure first evident. - 64 hr after circulation. Then drilled to-103ft at 1230; set and cemented 3-in. 

casing to - 103 ft; good cement job, top and bottom. 

Drilled out cement to - 103 ft. All wellhead water pressure - 7 psig. 

Then drilled to -173 ft at 1510. Water, some gas. Then drilled to -:Hl'/2 ft at 1535. Wellhead water pressure - 11 Y2 psi? 

Then drilled to - 2481/2 ft at 1445. % hr after circulation; all water pressure. Then drilled to - 278ft at 1620; increasing problems with high wellhead 

pressures. 

Wellhead water pressure close to 39 psig. 

39 hr after circulation. Then drilled to -328 ft at 1605. Temperature reversal? Thermometers not insulated. 

Then drilled to - 378 ft at 1605. Thermometer not insulated. Thermometer not insulated. Insulated; reversal confirmed. Then drilled to -418 ft at 1615. 

Not insulated. Insulated. Then drilled to -468 ft at 1640. Not insulated. Insulated; then drilled to - 498 ft at 1550. 

Insulated. 

Uninsulated to test previous maximum temperature (169.5°C). Then 

drilled to -538 ft at 1515, total depth. 

Insulated. 

Insulated. -40 hr after circulation. 

Not insulated so not reliable. Insulated, but not adequate? 

To previous maximum. Pressure at -267 ft, 148±1 psig, or 41.5 psi above reference pressure 

curve. Thermistor series; figure 26, curve C. 

Bottom pressure 248 psig. Bottom pressure 251 psig. Bottom pressure 248 psig. 

Checking temperatures through maximum. 

'Data in boldface considered most reliable ; data in parentheses, least reliable. 2Relative to ground surface; positive levels in parentheses, calculated from wellhead pressures considered to be least aflected by vapor. 

thermometer temperatures were obtained on September 27, 1971 (shown as +'s on fig. 26), ~2 hr after 

bleeding off the gas cap, and minimizing leakage during 

the measurements. These suggest that predrilling and 

postdrilling temperatures differ only slightly near the 

surface and at depths below about 240 ft, but that major 

changes resulted from flow of hot water from -240ft up 

to aquifers of lower initial pressures and temperatures 

near the bottom of the casing, perhaps along a porous 

zone noted in the core near -110ft. 

NORRIS BASIN 

Y-9 (NORRIS I) DRILL HOLE 

SITE SELECTION 

Norris Basin is perhaps Yellowstone's most fascinating thermal area because of its highly varied activity 

(Allen and Day, 1935), its great contrasts in chemical 

composition of fluids, and its major-rank geyser 

(Steamboat, by far the most spectacular geyser in the 

Park from 1961 through 1970, when major eruptions, 

at least temporarily, ceased). In addition, the highest 

temperature previously measured in the Park was in 

Carnegie II at Norris-205°C at-246ft (Fenner, 1936). 

The chemical geothermometers, silica content, 

sodium/potassium ratio, and N a-K-Ca relationships 

(Fournier and Truesdell, 1970, 1973; White, 1970), suggest temperatures at depth of at least 250°C. 

High temperatures and pressures, potentially as 

much as 575 psia at a saturation temperature of250°C, 

were a recognized hazard, especially in view of Fenner's 

(1936) graphic description of the drilling problems he 

encountered in 1930. We wanted to obtain data on this 

high-temperature environ1nent, but we also needed 

sufficient altitude at the wellhead for the hydrostatic 

pressure of expected liquid water to counterbalance 

most of the vapor pressure of steam at high temperatures. The cooler borders of the Norris system were 

therefore favored on the assumption that the borders 

expand downward and that very hot internal parts 

could be pentrated at relatively greater depth by a vertical drill hole. The new Norris Basin bypass road, constructed in 1966-67, provided access to a pine-covered 

ridge just east of the Norris Museum that seemed to 
50 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

CASING RECORD TEMPERATURE, IN DEGREES CELSIUS 

0 40 60 80 100 120 140 160 180 200 

CONDENSED 

LOG 

220 0.---~~~~--,---,----.-,rr~~---.---,--~----.---,----,---,---,----,---,---,---,~-,-- --r-~ 

of 4-in. 

casing 

::::::-x-- _ Curve D. 32 ft 

X - -e..... ' ./ . Reference boilingX · ' ' ( temperature curve for 

+ " \ 40 pounds per square inch 

100 103ft 

of 3-in. 

casing 

Curve B. 

Bottom-hole temperatures 

as drilling progressed 

.+ ~ ~. 1 (gage) wellhead water pressure 

· V Lava Creek 

1-

w 

w 

u_ 

~ 

I -

1-

Cl. 

w 

D 

200 

300 

400 

500 

TD 

538 

EXPLANATION 

0 Bottom-hole temperature -16 hr 

after circulation ceased 

408 Bottom-hole temperature, indicating hours 

(or other specified time) after 

circulation ceased 

-- Thermistor temperatures June 13, 1968, 

1 0 months after hole completed 

X Themistor temperatures coming out of 

hole after "down" series of June 13, 1968 

1 Equival~nt depth, corrected for differences 

in static water level for comparison 

with curve A 

+ Maximum-thermometer temperatures, 

Sept. 27, 1971 

Curve A. 

Reference boiling-temperature 

curve for pure water, assuming 

water table at ground surface, and 

at altitude of - 7,500 ft 

\.. Tuff; partly 

~+ welded vapor-

~' phase zone 

• ~ alternating 

\ with more I+ densely welded 

devitrified tuff 

below 141 ft 

Thermistor aeries, 

June 13, 1 i68 

FIGURE 26.--Temperatures and other data, Y-5 (Rabbit Creek) drill hole, Midway-Lower Basin. 

have the desired characteristics. Fenner's drill hole, 

here called Carnegie II, and the varied thermal activity 

near Congress Pool were only 300 to 400 ft to the north, 

and other intense thermal activity that included 

Steamboat Geyser was 600 to 1,200 ft to the southwest. 

By late September of 1967 nearly all tourists had left 

the Park, and drilling could be conducted on the north 

edge of the new Norris parking area with little danger 

to the public. 

of the Lava Creek Tuff (dashed segment of curve B). 

The basal 3 ft of the upper member B from -125 to 

-128 ft consists of crystal-rich air-fall tuff. At or near 

PHYSICAL MEASUREMENTS AS DRILLING PROGRESSED 

·this depth the static water level rose about 10ft in the 

hole, indicating a higher fluid pressure. A slightly lower 

temperature gradient occurs below -125 ft, probably 

extending down to about -216ft (another dashed segment of curve B), where a slight reversal in temperature 

occurred along with another increase in fluid pressure. 

At the next deeper data point, -232ft, water rose in the 

hole to ground level. The reversal probably terminated 

Physical data are shown in table 13 and figure 27. near -280 ft, with temperatures thereafter increasing 

Near-surface temperatures increased with depth on a at a nearly constant rate of ~ 1 °C/16. 7 ft (nearly 10 

nearly constant gradient to about -160ft (curve B); a times the worldwide ttnormal" conductive gradient). 

reliable water level (water table?) was first identified at Wellhead pressures increased irregularly below 

-28.8 ft when the drilled depth was 61 ft. The first -300ft and became troublesome at depths below -550 

changes in fluid circulation and static water level prob- ft. An apparent wellhead water pressure of 42 psig was 

ably occurred with penetration of a relatively perme- noted when the drilled depth was 502ft, but at greater 

able contact at about -125ft between members B and A 1 depths water pressures could not be distinguished with 
NORRIS BASIN 51 

TABLE 13.-Temperatures, pressures, and other observations f'rom Y -9 (Norris I) drill hole, Norris Basin 

Date and time Observation Temp. Thermometer Static water Wellhead 

1967 depth, ft.' OCJ No. level, pressure, Comments ft. I 2 psig' 

9/27 1545 (11 ) (-3.8) Set up and drilled to - 11 ft. at 1535: lost circulation at about -10 ft. 9/28 0818 8.8 21.0 (-6.3 ?J Temperature at fill, -8.8 ft. Perched water table? 9.2 21.5 Tem~erature 0.4 ft. into mud and sand. 1055 (16) 1-10.2) Dril ed to-16ft.; 15 min after circulation. 1205 (17.7) (16.5) (-9.4) 5 min after drilling to -21 ft at 1145. 1310 (19.7) (20) (-11 .0) 1 hr after circulation; set and cemented 21 ft of 4-in. casing. 9129 1000 10.0 24.5 On cement; then drilled to - 50 ft at 1325. 1325 50.1 (25 .0) (-3.1) 3 min after circulation. 1337 50.1 (30.0) (-4.7) 15 min after circulation. 1357 50.1 (37.0) (-8.5) 35 min after circulation; then drilled to -61 ft. at 1435. 1450 60.8 (39) (- 12.8) 15 min after circulation. 1535 60.8 (50 ) ( -22.4) 1 hr after circulation. 9/30 0805 60.8 69.0 -28.8 Then drilled to -100 ft. at 1100. 1215 100 -24.8 1 hr after circulation; water level steady. Then set 100 ft of 3-in. casing, cemented. 10/1 0945 88.7 94.5 On cement. 1012 0820 88.7 96.4 } 96.1 ? On cement. Then drilled to - 152 ft at 1325. 0833 88.7 95.9 8 ]0/3 0810 152.0 137.2 } 137.4 4 -18.5 Then drilled to -202ft at 1200. 137.6 8 10/4 0800 202 158.8 } 158.9 4 -15.2 Then drilled to - 232ft at 1550. 159.0 8 10/5 0810 232.4 164.4 } 164.3 8 +0.4 First water level above ground. Then drilled to - 282 ft. at 1410. 164.3 8 1016 0806 282.1 163.9 4 No insulated. 163.7 8 Not insulated. 163.3 8 + 1.8 Insulated (down 20 min). Then drilled to - 343 ft. at 1545. 1017 0845 343 166.6 } 167.0 8 0 Insulated; water level not measured. 0900 342.3 } 342.8 167.3 4 Not insulated; then drilled to - 403 ft. at 1440. 10/8 1100 402.6 171.7 } 171.5 4 8 to 0 Pressure decreased as gas bled off. 1125 171.4 -8.1 - to+ Water level below ground but then surged up to discharge-gas effect. 10/9 0820 !g~ :~ } 402.3 171.7 } 172.0 4 ( + 17 ?) 7 to 9 Water, some gas; then drilled to -452 ft at 1500, slight positive pressure 0833 172.2 8 between runs. 1500 +3.1 Immediately after circulation ceased. 10/10 0820 !~~ ~ } 452.1 173.3 } 173.6 4 18\12 All water? 0833 173.8 8 (+38 ?J 16 to 191

/2 Water pressure - 16 psi? Then drilled to -502 ft at 1445. 10/11 0845 ~8~ ~ } 502.3 175.6 } 176.1 4 (+100 '?) 42 to 49 All water at 42 psig? 176.6 8 Gas increased with increasing pressure; then drilled to - 552 ft. at 1610; intermittently erupting between runs. 10/12 0855 ·- 552 180.0 } 180.0 4 95 to 60 Pumping of cold water fails to decrease pressure; 63 psig with rods full of 0910 180.1 8 75 to 56 water. Then drilled to - 593ft at 1620; water level intermittently below ground between runs. 10113 0855 ~~~ Z } 592.9 181.2 } 181.5 4 (+172 ?) 110 to 72 Water pressure 72 psi? Superheated steam at 150°C, 68 psig from side 181.8 valve; after closure pressure rose to 102 psig. Then drilled to -642ft. at 1630. - 1800 (+ 216 ?) 90 Leakage all water. 10/14 0856 - 642 185.3 } 185.5 4 (+ 187 ?) 105 to 78 Water pressure 78 psi? Then drilled to -663 ft at 1245. Now normally 0914 185.7 8 erupting water from rods with core barrel down and latched, prior to 

10/15 0955 663.2 core retrieval or pulling rods. 185.9 8 ( +134 ?J 78 to 56 Water pressure 56 psi? 10/16 0953 ~~~ i } 663.2 186.2 } 186.5 4 85 to 88 Pressure nearly constant. 1006 l86.9 8 10/17 0852 663.0 87 to 99 Broke thermometers 4 and 8; then drilled to -692 ft at 1650. 10/18 0831 ~~~ ! } 692.4 188.3 } 188.1 11 101 to 71 Becoming increasingly difficult to reenter hole after changing bits; 0851 187.9 9 drilled to -723 ft at 1550. 10/19 0834 ~~~:g } 723.0 189.6 } 189.6 11 (+ 154 ?) 104 to 64 Then drilled to - 773 ft. at 1620; each eruption from rods prior to core 0852 189.7 9 retrieval is similar to geyser eruption with duration - 61

/2 min with 

10/20 0850 772.9 193.0 11 (+ 175 ?) 92 to 73 initial "bursting" phase and ending in steam phase. 

} 192.9 Then drilled to -813 ft at 1715. 0904 192.9 9 

10/21 0902 ~i~:g } 812.8 195.4 } 195.7 9 (+ 177 ?) 85 to 74 Decided to terminate drilling; pulled rods and changed valves. 0936 195.9 9 to 94 

10/23 0854 813.0 195.4 } 195.7 11 129 to 140 0910 813 .0 195.9 9 

10/29 725 136 In-hole pressure 281 ± 3 psig at -725 ft. 6/10/68 807.8 195.2 138 Thermistor series, figure 27; pressure constant; indicated water level in 

132 hole - 210ft. 9/13/69 796 In-hole pressure series, pressure constant (132 psig all vapor) to 202-ft depth; 357 psi at bottom, calculated water overpressure 49 psi; curve C, 

9124/69 figure 28. 25 sacks cement pumped in hole, pressured to 200 psi. 

'Data in boldface considered most reliable ; data in parenthese, least reliable. 2Relative to ground surface; positive levels in parentheses calculated from wellhead pressures considered to be least affected by vapor- but all may be so affected. 

confidence from total wellhead fluid pressure, which 

was clearly affected by gas. 

SUMMARY OF DRILLING PROBLEMS 

No serious problems were encountered in the hole. 

The crew was experienced, and equipment and techniques were then available for controlling high temperatures and wellhead pressures. Bottom-hole temperatures were generally much below the reference boilingtemperature curve. As we had hoped, no high wellhead 

pressures were encountered until the hole was about 

400ft deep. Below-500ft, however, observed wellhead 

fluid pressures increased notably and ranged from 

about 60 to 140 psig at all depths below -550 ft. The 

hole nearly always erupted when fittings were disconnected and drill rods or core barrel were withdrawn (fig. 

4C), but the crew became skilled in controlling these 

eruptions; also, each was limited by low permeability of 

the rocks and the small amount of available water in the 

hole. We had hoped (and also feared) to penetrate the 

base of the thick lower unit of the Lava Creek Tuff, 

where high permeability and extreme fluid pressures 

were likely to occur. We drilled through 685 ft of 

homogeneous tuff of the lower unit to a total depth of 
52 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

813ft, with no evidence that more than half of the unit 

had been penetrated. 

POSTDRILLING MEASUREMENTS AND INTERPRETATION 

A temperature profile made June 10, 1968, nearly 8 

months after completion, is shown in figure 27. At 

depths below 400ft the temperatures agree remarkably 

well with bottom-hole temperatures measured as drilling progressed (curve B); this indicates that predrilling 

ground temperatures can recover from disturbances 

from drilling and that this gradient of ~ 1 °C/16. 7 ft 

produces no obvious convection in the hole. Temperatures of curve Care slightly above curve B from-400ft 

up to about -240 ft, and the contrast then increases 

spectacularly upward, where 180.3oC was measured at 

-210ft; the same temperature prevailed nearly to the 

top of the hole. The wellhead pressure of 138 psig (149 

psia) is close to the vapor pressure of water at 180.3°C 

(146.5 psia), and the difference may be explained by 

partial pressures of other gases. 

CASING RECORD TEMPERATURE, IN DEGREES CELSIUS 

. CONDENSED 

LOG 

0 20 40 60 80 100 120 140 160 180 200 220 0.-~~~y---,---,---~--~--~--~--~-=~--~--~--~----~--~--,---,---~--~--~~~--~--~ 

100 

200 

300 

1- 400 w 

w 

lL 

~ 

I 

1-

a_ 

w 

0 500 

600 

700 

800 

of 4-in. 

casing 

100ft 

of 3-in. 

casing 

TD 

813 

Curve B. 

Curve C.-------t 

Thermistor series : 

June 10, 1968 I 

+ I 

I 

I 

I 

I 

I 

? ?'_j 

Bottom-hole temperatures 

as drilling progressed 

EXPLANATION 

0 Bottom-hole temperature about 16 hr 

after circulation ceased 

40 8 Bottom-hole temperature, indicating 

hours after circulation ceased 

• Thermistor temperature profile June 10, 1968, 

- 8 months after completion 

1 Equivalent depth, corrected for differences 

in static water level for comparison 

with curve A 

Curve A 

Reference boiling-temperature 

curve for pure water, assuming 

water table at ground surface and 

at altitude of - 7,500 ft 

FIGURE 27.-Temperatures and other data, Y-9 (Norris I) drill hole, Norris Basin. 
NORRIS BASIN 53 

In-hole pressures measured 15 months later (fig. 28, 

curve C) were constant at 132 psig from the surface to 

-202 ft. As we had suspected, vapor evidently filled the 

top of the hole. The observed gage pressure of 132 psig 

(143 psia) is that of saturated steam at 179.3°C. During 

the 15-month interval between the thermistor and the 

pressure measurements, the wellhead pressure had declined about 6 psi and the indicated level of water in the 

hole rose about 8 ft. Of much greater significance, however, were the major changes that must have occurred 

during or soon after drilling. The change was probably localized by a prominent, nearly vertical, kaolinite-filled fracture identified in the drill core from -212 

to -216 ft. A little hot water probably flowed in this 

aquifer prior to drilling, thus accounting for the break 

in temperature at this depth in curve B of figure 27 

(shown by dashed-line extensions of nearby gradients). The initial aquifer temperature prior to drilling 

PRESSURE, IN POUNDS PER SQUARE INCH (ABSOLUTE) 

~ 

w 

w 

u.. 

~ 

I 

~ 

0... 

w 

0 

0 100 wo 300 400 o~~~---,----.---.----,---,----~~---.---.----.---,----,----.---.----.---,----,---,----,--~ 

Curve A. 

Reference boilingpressure curve 

Curve B. 

Curve C. 

Calculated hydrostatic 

pressure for 

original ground 

temperatures 

Measured pressure 

curve, Sept. 13, 1969 

Curve D. 

Calculated 

hydrostatic 

pressure for 

water at 4° Celsius 

FIGURE 28.-In.-hole pressures of Y-9 drill hole compared with other reference curves. 
54 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

the hole could not have been much above 164°C since 

high wellhead fluid pressures were absent. A major 

change in local regime evidently was induced by the 

drill hole, resulting in a decrease in resistance to flow in 

this aquifer. The exact nature of the change is not 

known, but presumably the short circuit provided by 

the drill hole permitted flow to increase as the clay plug 

was eroded. The increased rate of flow then permitted 

access of water of much higher temperature than had 

formerly existed at this depth. Temperatures increased 

over previous ground temperatures by about l5°C at 

-212ft and by about 160°C at-10ft (because of highpressure steam). 

This change clearly did not occur immediately upon 

penetrating the -212-ft level, but developed gradually 

over the following week. Puzzling variations in gage 

pressure (see column 5 of table 13, which converts the 

most reliable pressure data to equivalent static water 

levels) and increasing proportions of gas in the discharged fluids became especially evident during drilling below -450ft. The changes near-212ft probably 

were delayed by the circulation of cold drill water. The 

rate of hot inflow probably also increased as the kaolinite filling of the fracture was flushed out. The close 

agreement between the deep parts of curves B and C of 

figure 27 provides strong, even conclusive evidence that 

the zone below-300ft could not have been involved in 

the change. The data suggest instead that hot fluids, 

initially near 165°C but increasing to 180°C, flow into 

the hole near-212ft. Vapor evidently separates from 

water at this level, with some steam flowing upward 

and condensing in the casing. Water, perhaps with some 

vapor, may flow out of the hole into the extension of the 

same permeable fracture at about the depth of separation, -212ft. However, some water flowed up the hole to 

about-202ft during the measurements of September 

13, 1969, accounting for the observed pressures and 

calculated temperature of that date. The nature of some 

of the changes that occurred in Y-9 is still not clearly 

understood, especially why the same narrow depth zone 

(same fracture?) seems to control both entry and exit of 

the thermal fluids. We speculate here that discharge 

and eruption from Y-9 cleared the entry channel, and 

that the resulting increase in pressure and the intermittent eruptions from the hole also cleared the exit 

channel to establish communication with other permeable fractures. 

The water column from -212 to about-280ft (curve 

C, fig. 27) is gravitationally stable, with no significant 

motion either upward or downward but heated a little 

by conduction from the overlying water. 

Other aspects of our data from Y -9 are considered in a 

later section that considers all Norris drill holes. 

Y-12 (NORRIS II) DRILL HOLE 

SITE SELECTION 

Y-12 was sited on the edge ofPorcelain Terrace in the 

northeastern part of Norris Basin. Access was by an 

abandoned road that extended through the basin from 

its northern junction with the new Norris bypass road. 

The surface of the old road had been torn up and partly 

restored to natural conditions, but the Park Service 

granted us temporary access. The drill hole was collared 

in the old roadbed about 200ft east of Opal Spring on the 

crest of Porcelain Terrace; the collar is about 9 ft above 

the terrace and 42 ft below the collar of Y~9 (table 3). 

The precise location ofY-12 was a compromise between 

a border position of relative safety and a position near 

Porcelain Terrace, where geochemical data provided 

evidence for subsurface temperatures at least as high as 

250°C (Fournier and Truesdell, 1970). The selected site 

is near mature trees and is 7 5 ft on the cool side of the 

present limit of the area where temperatures and heat 

flow are too high for trees to grow. Ground to the north is 

still cooler, as judged by the presence of trees and the 

absence ofhydrothermal activity, but a small ~~hot spot" 

called the Annex area lies about 300 ft east-southeast of 

the site. The drill hole is actually within a zone of 

stunted trees that connects the hotter areas. Measurement by snowfall calorimetry (White, 1969) have since 

indicated for these areas of stun ted trees in Norris Basin 

a total heat flow of about 500 heat-flow units, or ~350 

times the world ((normal" conductive heat flow. These 

facts, along with proximity to Porcelain Terrace on the 

west, provided nearly a certain guarantee of very high 

subsurface temperatures. 

PHYSICAL MEASUREMENTS AS DRILLING PROGRESSED 

Physical data are shown in table 14 and figure 29. The 

water table was first identified at about -18 feet and 

about 7 ft below t •e water levels in Porcelain Terrace. 

Static water levels at drilled depths of 180 to 460ft, in 

contrast, were very close to or slightly above the top of 

Porcelain Terrace, where springs had discharged prior 

to the 1959 Hebgen Lake earthquake. Static water 

levels above ground surface and moderately high wellhead pressures characterized all drilled depths below 

about 500 ft. 

Near-surface temperatures increased rapidly to 

about-74ft, perhaps along a straight-line conductive 

gradient. Bottom-hole temperatures at greater depth 

generally are remarkably close to the reference boiling-temperature curve A of figure 29. This drill hole 

provides another example of our conclusion that, if a 

reference boiling-temperature curve had not been 

available prior to our Yellowstone drilling, we should 
NORRIS BASIN 55 

TABLE 14.-Temperatures,pressures, and other observations from Y-12 (Norris II) drill hole, Porcelain Terrace, Norris Basin 

Date and time Observation Temp. Thermometer Static Wellhead 

1968 depth, ftl ocl No. water level, pressure, Comments ft' 2 psig1 

5/27 1300 Started drilling; to -21 ft at - 1600 where 20 ft of 4-in. casing was set and cemented. 5/28 0830 g:~ } 17.2 54.0 } 54.2 On cement; then drilled to -62 ft at 1305. 0835 54.5 5/29 0805 ~~:g} 62.0 90.0 } 90.8 - 17.9 Then drilled to -111 ft at 1510. 0815 91.6 1700 111.0 135.3 11 1\12 hr after circulation. 5/30 0800 110.3 137.9 0 Water level below ground; before it could be measured, water surged up 

0800 and erupted; 3-in. casing to -110 ft; cemented top and bottom. 5/31 74.3 125.7 11 (?) On cement. Near original ground temperature, or modified? Then drilled to -180 ft at 1445. 1535 - 180 (122.3?) 6 - 12.6 1

/2 hr after circulation; thermometer snagged. 6/1 0750 i~8 ~ } 180.0 (150.6?) 6 -10.0 Mercury dropped in thermometer? 0800 155.7 11 Then drilled to -250 ft at 1345. 1500 ~~g:~ } 250.3 156.7 } 157.8 5 - 11.4 1 hr after circulation. 1515 158.9 9 - 11.3 1\14 hr after circulation. 6/2 1140 250.3 167.6 } 167.6 11 (--10) Measuring tape greasy. 167.7 9 6/3 0830 250.3 i~~:6 } 167.5 11 -8.6 0840 9 Then driiled to -320 ft at 1420. 1615 - 320 i~~:i } 162.7 5 -10.1 2 hr after circulation. 11 

6/4 0730 320.2 ~ 176.9 ~ 5 0742 320.1 320.1 177.2 177.0 11 -7.9 0755 320.1 176.8 1 H.T. All H.T. thermometers range from 93° to 260oC and require pressure 

390.4 corrections that have been applied. Drilled on to -390 ft at 1305. 1520 176.1 5 2 hr after circulation. 6/5 0800 390.3 i~!:~ } 184.6 9 -7.3 11 Then drilled to-460ft at 1210. 1645 460.4 185.8 5 -7.4 4\lz hr after circulation. 6/6 0740 !~~:~ } 460.3 i~~ ~ } 189.0 11 -7.3 Then drilled to -532 ft at -1230; slight positive pressure below -507ft. 0755 1 H.T. 617 0806 531.3' ~ 192.9 .f Then set 530 ft BX casing, cementing top and bottom. 0815 531.5 531.5 194.2 193.4 9 2+1.2 . 0840 531.7 . 193.1 11 6/8 Drilled out cement, then on to -569 ft at 1620. 6/9 1150 569.2 194.7 5 (+ 38?) 32 to 16 16 psig wellhead water pressure? Low permeability below casing. 6110 0745 567.4 195.3 11 (+41?) 17 to 8 All water at 17 psig, bled down to 8 psig; then drilled to -637 ft at 1300. 6/11 0750 637.4 } 637.2 i~~ g } 198.6 9 32 to 7\lz All water at - 20 psig. 0810 637.0 11 (+36?) 15 to 7 Permeability still very low. Drilled to -707\lz ft at 1335. 1345 (+36) 15 - 10 min after circulation-all water. 1645 (+70) 29 3 hr after circulation--all water pressure. 6/12 0743 707.2 ~g~:~ } 203.8 1 H.T. (+86?) 36 to 21 All water out of36 psig bleeding down to 21 psig because oflow permeabil- 0805 11 ity? Drilled to -757 ft at 1510. 6/13 0753 756.4 } 756.5 ~g~:6 } 207.4 1 H.T. - 14 to - o to 9\12 0808 756.7 11 8\12 0815 - 10to21\lz Pressure increased to 21 Yz psig in 10 min, then constant; drilled to -792 

ft at 1530. 6/14 0750 789.9 209.2 1 H.T. (+58?) 24 to 16 All water pressure, bleeding down; drilled to - 867 ft at 1540. 6/15 0753 866.9 217.5 1 H.T. ? 7 to 18, Drilled to -937 ft at 1510. 

to 8\12 6/16 0915 936.0 } 937.4 ~~~:~ } 225.3 1 H.T. (+67?) 28 to 15 All water discharged; 28 psig pressure bleeding down; permeability still 0935 936.7 2 H.T. 15 to 16 low. 6/17 0754 936.5 ~~~:i } 225.2 1 H.T. (+95?) 39'h to 25 All water discharged at first, then bled down, water and gas. 2 H.T. 23 Drilled to -994 ft at 1540 but 10-ft core on bottom. 6/18 0752 983.2 ~~g:~ } 230.3 1 H.T. (+86?) 36 to 9 All water, 36 psig, bleeding down to 9 psig, water and gas. 

2 H.T. 6/19 0755 983.4 ~~g:~ } 230.3 1 H.T. (+72?) 30 to 4 All water at 30 psig, then bleeding down; drilled to -1,035\lz ft at 1530. 

2H.T. 15 to 5 1554 4 24 min after circulation stopped. 1658 24 l 1

/2 hr after circulation stopped. 2120 (+75) 31 Yz All water pressure. 6/20 0730 1,035.5 ~~!:g } 234.4 1 H.T. (+83) 34'h to 131

/z All water pressure, bleeding down; drilled to - 1,088 ft at 1458. 2 H.T. 1520 (+70) 29 20 min after circulation; pressure gradually increasing. 1550 (+91?) 38 50 min after circulation. 1705 (+79) 33 2 hr after circulation; reason for pressure decrease not clear. 6/21 0745 1,087.8 ~~~:~ } 237.5 1 H.T. (+77) 32 to 14 All water pressure, 32 psig, bleeding down. Hole erupted; decided to 2 H.T. terminate drilling at - 1,088 ft; changed valves with packer. 9/13/69 1,079 (+120?) 50 to 33 Wellhead water pressure 50 psig? Bottom-hole pressure 425 psia, cal- culated water overpressure. 6/2171 1,078.5 33 to 72 The initial bottom-hole pressure was 433.3 psig with a steady wellhead pressure of33. Water was then vented from the top at 4 gpm for 37 min. At the end of that time the wellhead pressure had increased to 72 

9/21172 1,081.0 43 1

/2 to 46 Yz psig and the bottom pressure had declined to 341.4 psig. Bottom-hole pressure 446.4 psig. 

1Data in boldface considered most reliable; data in parentheses, least reliable. 2Relative to ground surface; positive levels in parentheses calculated from wellhead pressures considered to be least affected by vapor. 

have invented one! Corrections for existing static water 

levels and wellhead water pressures (fig. 29) indicate 

that equivalent depths plot nearly on this reference 

curve at all depths from -160 to -400 ft. Equivalent 

depths plot below curve A at greater depths down to 

-900ft but are again nearly on curve A from-983ft to 

the bottom of the hole. 

Temperatures as originally measured and associated 

pressures at first seemed anonmlous at and below -983 

ft; pressure-corrected depths Cequivalent" depths) consistently plotted above our reference curve A, which 

seemed to have · no logical explanation in a system of 

coexisting water and vapor. The anomaly was resolved 

when calibration of the high-temperature thermometers (200°-500°F, equivalent to 93.3° to 260.0°C) used at 

depths below 700ft showed them to have much larger 
56 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

pressure corrections than our other thermometers, for 

which pressure corrections were within the errors of 

measurement. 

SUMMARY OF DRILLING PROBLEMS 

Temperatures, as we had hoped, attained by far the 

CASING RECORD TEMPERATURE, IN DEGREES CELSIUS CONDENSED 

LOG 

0. 140 160 180 200 220 240 0~~~~------~----~----~~~~~--.---.--.---.--.---r--.---r--~--r--.~-r--.-~ 

100 

200 

300 

530ft 

BX casing 

Bottom-hole temperatures 1 

!l5. • 

as drilling progressed Y2 

EXPLANATION 

0 Bottom-hole temperature -16 hr 

after circulation ceased 

4

& Bottom-hole temperature, indicating hours 

after circulation ceased 

1 Equivalent depth adjusted to water 

overpressure and water level at 

ground surface 

Reference boiling-temperature 

curve for pure water, assuming 

water table at ground surface 

and at altitude of-7,500 ft 

FIGURE 29.-Temperatures and other data, Y-12 (Norris II) drill hole, Norris Basin. 

Member B of 

Lava Creek 

Tuff 

Member A of 

Lava Creek 

Tuff 
NORRIS BASIN 57 

highest levels yet measured in Yellowstone Park 

(237%°C) but pressures were never very troublesome, in 

part because permeabilities of the rocks were very low. 

In addition to our usual two shallow strings of casing, a 

BX string was set at -530 ft to insure control of the hole 

if extreme pressures were encountered at greater 

depths, but such pressures were not found. 

Excessive wear of the thin BX wire-line drill rods 

caused considerable delay and became a serious hazard 

near and below -900 ft; an increasing number of rods 

were being rejected because of excessive wear. At 

-1,088 ft our supply of additional usable BX drill rods 

was exhausted, and all those in use were so worn that a 

new set was necessary to continue drilling. By then, 964 

ft of the lower unit of the Lava Creek Tuff had been 

penetrated with no evidence of nearing the basal contact. We had hoped to reach this contact, but if highly 

permeable ground had been suddenly penetrated, 

perhaps along with extreme water pressures and total 

fluid pressure of 575 psia or more, our light equipment 

was likely to be inadequate. So, regretfully, we decided 

to quit while we were still ahead! 

POSTDRILLING MEASUREMENT 

We obtained no reliable postdrilling temperature 

profiles in Y-12. Our thermistor cable was only 1,000 ft 

long and its lack of consistent reliability at temperatures near 200°C discouraged its use in Y-12. A 

maximum-thermometer profile was not considered 

worth the effort because the hole was too impermeable 

to sustain in-hole pressures, as discussed below. 

In order to clarify interpretation of the wellhead pressure data determined as drilling progressed, the in-hole 

pressure data of curve C of figure 30 were obtained on 

September 21, 1971, with water filling the hole and with 

leakage almost completely eliminated. As expected, 

curve C is remarkably similar to reference pressure 

curve A, but with an indicated wellhead water pressure 

of ~48 psi above the reference curve A and a bottomhole water pressure of 40 psi above the same curve. 

CurveD was measured on July 2, 1972, after venting 

the hole for 20 minutes at an estimated rate of 4 gpm. 

This curve is on and below the reference pressure curve 

at all depths below -175ft, and the bottom-hole pressure is more than 110 psi below curve C. Only near the 

surface were pressures relatively high because the high 

temperatures of the previously discharged fluid had 

heated the near-surface rocks; after the hole was shut 

in, steam pressures corresponding to these temperatures at saturation were maintained until the rocks 

could cool. 

We conclude that permeabilities are so low in the 

open hole below the BX casing that any leakage is only 

slowly replaced by inflow. When leakage is greater than 

inflow, pressures decrease, boiling occurs throughout 

the hole, and heat flows by conduction from surrounding 

rocks to vaporize part of the available water, thereby 

decreasing temperatures. 

CARNEGIE II (NORRIS) DRILL HOLE 

SITE SELECTION 

Allen, Day, and Fenner desired a ((typical acid area" 

for the second Carnegie hole drilled in 1929 and 1930 

and here called Carnegie II. According to Allen and Day 

(1935, p. 473-475), the selected site was on the border of 

Norris Basin in a small muddy flat Hdotted with many 

small shallow hot springs of acid or mixed (acidchloride-sulfate) type, and one large spring, Congress 

Pool, of mixed water * * * A rather thorough study of 

thermal activity at Norris Basin had led to the conviction that underground conditions more intense than 

those at Old Faithful would be encountered here. 

Superheated steam was confidently predicted." Allen 

and Day had concluded from their Yellowstone work 

and earlier studies at Mt. Lassen (Day and Allen, 1925) 

and The Geysers (1927) that superheated magmatic 

steam is a fundamental cause ofhydrothermal activity, 

mixing near the surface with ground water. The alkaline geyser areas were thought to be characterized by 

relatively deep penetration of ground water, while the 

areas of acid or ((mixed'' waters were thought to be 

related to shallow penetration of ground water. They 

viewed as highly significant the relatively rare 

superheated fumaroles where surface temperatures exceeded that of boiling water at existing atmospheric 

pressure (Allen and Day, 1935, p. 32, 35--39). At that 

time four superheated-steam vents occurred in Norris 

Basin within 300 yards of the Carnegie II drill site, with 

temperatures ranging from 112° to 139°C. Allen and 

Day (1935, p. 39) also stated emphatically that Hsteam 

superheated at the surface must have remained 

superheated throughout its passage from the magma." 

The evidence seems clear from the above quotations 

that the major objective of Carnegie II was to drill 

through a near-surface water-saturated zone into a zone 

of superheated magmatic steam, and that such a zone 

was assumed to underlie Norris Basin at a depth of only 

a few hundred feet. 

We prefer alternate explanations for all ofthese concepts. For example, superheated steam is commonly 

derived from liquid water in environments where the 

supply of liquid is limited and the stored heat of solid 

phases is vaporizing all available water (White and 

others, 1971; this report, table 13, 10/13/67). Even the 

Carnegie II drill hole vented dry steam (transparent 

and almost certainly slightly superheated) from a 
58 

1-

w 

w 

lL 

200 

400 

z 600 IIa.. 

w 

0 

800 

1000 

PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

TEMPERATURE, IN DEGREES CELSIUS 

100 150 

\ 

CurvoD~' . Measured pressure \\ 

July 2, 1972 after \ 

venting 20 min , 

at ~4 gallons \ ' 

per minute ~ 

EXPLANATION 

Measured temperature 

& July 20, 1968 

\:7 Sept. 13, 1969 

0 Sept. 21, 1971 

Measured pressure 

' 

Curve B. 

Reference boilingtemperature curve 

Curve C. 

Measured pressures 

Sept. 21, 1971 with no 

flow from top of well 

\~ 

\ \ 

~ 

\ 

\ 

\~ ~ \ 

0 Sept. 21 , 1971, no flow 

c:J July 2, 1972, after venting 

' ' ' 

~ \ 

' \ 

\ 

\ 

\ 

\ 

~ 

\~ 

\ 

\ 

\ 

\ 

200 

\ Curve E. 

~/ Calculated boiling-

' temperature curve 

\ for 49 pounds per 

\ square inch overpressure 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

~\ \ 

\ 

\ 

\ 

\ 

\ 

\ 

I 

I 

\ 

I 

I 

I 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

.. I 

\ 

\. 

I 

\ 

I 

I 

I \ I 

I 

I 

I 

I 

I 

250 

1200 L_ ________ l_ ________ ~--------~--------~--------_L ________ _L ________ _L ________ ~--------~--------~ 

0 100 200 300 400 500 

PRESSURE, IN POUNDS PER SQUARE INCH (ABSOLUTE) 

FIGURE 30.-In-hole temperatures and pressures of Y-12 drill hole after completion, compared with other data. 
NORRIS BASIN 59 

water-saturated environment (Fenner, 1930, figs. 11 

and 12; table 16, 9/9/30), although Fenner, Allen, and 

Day were evidently not aware of this fact; Allen and 

Day state (1935, p. 4 75) that ((steam issuing from this 

test hole was not itself superheated." Because of the 

thermodynamic characteristics of~O, saturated steam 

separated from liquid water at temperatures up to 

236°C {and pressures up to 452 psig) and permitted 

to decompress at constant enthalpy will become 

superheated-that is, the steam is too hot to coexist 

with liquid water (White and others, 1971, fig. 2). In 

light of our present experience, we consider Fenner's 

figures 11 and 12 as clear evidence for superheated 

steam because the steam is transparent (and therefore 

lacks dispersed water droplets) for about 6 in. beyond 

the end of the discharge pipe. This difference in appearance consistently distinguishes vapor-dominated (dry 

steam) and hot-water geothermal fluids. 

guarantees the existence of convective upflow of fluids, 

with total heat flow in excess of 1,000 heat-flow units, 

over 700 times the world average conductive heat flow. 

We can now predict most of the problems that Fenner 

actually encountered, and such dangerous sites were 

consciously avoided. 

PHYSICAL MEASUREMENTS 

The physical data recorded by Fenner are shown in 

table 15 and figure 31. Most of these data are included in 

his published account, but the record is supplemented 

from his unpublished notes. 

Because of drilling problems, caving ground, and frequent eruptions, relatively few temperature measurements were made in Carnegie II. These temperatures 

increased irregularly but consistently plotted below our 

reference curve A, except near the bottom of the hole. 

Startling temperature and pressure changes occurred 

between September 10, 1930 (159°C at 243.6 ft, with 

wellhead pressure of 97 to 88 psig) and September 16 

when the drilled depth was only 3 feet greater (246.5 ft); 

the temperature had then increased to 205°C and observed pressures ranged from 225 to 297% psig. 

We now have the benefit of much drilling and other 

experience in geothermal areas that was not available 

to the Carnegie scientists in their pioneering efforts. 

The abundance of thermal emissions, intense acid alteration, and absence of pine trees at the Carnegie II site 

Date 

10/15/29 10/18/29 10/19/29 1930 

8/12 

8/15 

8/17 

8/18 

8/19 

8/21 

8/23 

8/24 

8/25 

8/26 

8/27 

8/30 

9/1 

9/3 

9/4 

9/5 

9/6 

917 

9/8 

9/9 

9/10 

9/11 

9/12 

9/1 6 

9/17 

9/18 

9/20 

9/22 

9/23 

9/24 

10/2 10/5 1017 

Observation depth, ft' 

12 

12 (- 20) 

(-20) 

56 

72 

202.8 200 

213 

(107) 

243.6 

246.5 

TABLE 15.-Temperatures, pressures, and other data from Carnegie II drill hole, Norris Basin 

[From Fenner (1936) and unpublished notes] 

Temperature oct 

95 

115 

121 

141 

135 

(144) 

159 

205 

Wellhead 

pressure, psig 

15 

46 

35 

55 

48 to 112 130 

132 

181 to 170 97 to 88 89 

225 

250 

297Vz to 265 

? 250 

250 to 277 1

/z 

250 

250 to 265 265 

252'h 

145 to 113 

Comments 

Setting up drill rig on "hot ground," south side of Nuphar Lake; "no steam vents in immediate vicinity." "A little steam coming out"; no data on water levels. Terminated drilling for season. Unpublished notes indicate depth may be -26 ft(?J. 

Drilled to -20 ft, fall 1929; boiling at bottom (below water table). Started drilling again. First hard rock 28 ft below ground; disintegrates to "sand" at shallower depths; hole filled(?) with cement. Drilled out cement to 31 ft; new hole to -34 ft. Drilled out to - 65 ft. After "blowing," perhaps a consequence of static water level above ground surface; drilled depth - 71 ft but thermometer only to - 56 ft. Drilled to - 107 ft; leaking outside casing (3-in. casing to about - 40ft(?). Drilled to - 129 ft but caved; measurements 1 hr after "blowing." Drilled to - 134 ft, caving. Drilled to -159 ft, caving. Drilled to -175 ft, caving. Drilled to - 186Vz ft; rods stuck. Recovered drill rods; 2Vz-in. casing installed, depths not stated, inside 3-in. casing, but notes imply to - 80 ft; evidently hung in hole, not cemented. 

Drilled depth - 215 ft; casing problems. Drilled depth - 220Vz ft; temperature soon after circulation, but not erupted; pressure after "blowing." Lost circulation into permeable zone near 220-ft depth. Drilled to - 230ft; high temperature from upflow; pressure without blowing. Drilled to - 242 ft. Drilled to - 243 ft 7 in.; pressure with valve partly open. Large block of cement around casing at surface. Thermometer wedged. Depth still - 243 ft 7 in. Thermometer recovered but jarred (146°C), 2d measurement. Depth -244.8 ft. Depth -246.5 ft; pressure suddenly increased. Same depth, after closing valve "for a moment"; Fenner's photographs (1936, p. 286, 287) indicate flow of superheated steam, no liquid water. Leakage starting around concrete. More concrete at surface reinforced with iron bars (297 1

/z psig or - 309 psia requires subsurface temperature of at least 215°C). Thermometer lowered on drill tools, valve at side wide open; hole diameter reduced. Valve open all night, closed before measurement. Valve open; pressure increased after closing valve. Depth -248.9 ft. After drilling to -254.8 ft, with valves closed 1 hr. Depth -263.3 ft. Depth -264.8 ft; lost rod with thermometer. Casing ruptured at -36 ft; blowouts appearing in ground to south and west, then north. Abandoned attempts to continue. Pumped in 100 sacks cement (100 lb each); new blowout - 75 ft northwest of drill hole. New steam vent -50 ft west of drill hole; other vents to south and west diminishing. 

'Data in parentheses considered less reliable . 
60 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

These data are not directly comparable to ours for 

reasons specified in our discussion of Carnegie I in 

Upper Basin. As compared to our temperatures, most of 

Fenner's probably were much below predrilling ground 

temperatures, but his wellhead pressures were probably somewhat higher because liquid water was generally not permitted to accumulate in the hole to offset in 

part the vapor pressures related to temperature. 

Wellhead water pressures were not identified by 

Fenner as such; the data suggest that static water levels 

above ground surface may have been first encountered 

from -65 to -71 ft (table 15). At all greater depths, 

observed wellhead pressures are probably combinations 

of high water pres'sure and gas accumulation in unknown proportions. 

The water table also was not specifically identified by 

Fenner but was probably slightly less than -12 ft 

(ground level at the drill site is ~ 12 ft above the surface 

of N uphar Lake, which is assumed to establish the base 

level for the local water table). 

Fenner's skeleton collection of drill cores from Carnegie II was made available to us for restudy (White, 

1955). R. L. Christiansen's intimate knowledge of the 

detailed stratigraphy of ash-flow tuffs of the Yellowstone Group permitted him to recognize the contact between the two members of the Lava Creek Tuff at a 

depth of about -78ft in Carnegie II. 

SUMMARY OF DRILLING PROBLEMS 

Temperatures and pressures encountered in Carnegie II drill hole were extremely high, as indicated by 

Fenner's (1936) account, the cited quotations from 

Allen and Day (1935), and the data of table 15. Their 

driller, Vance Butler, was the most highly qualified 

man of his time, having drilled the early exploratory 

holes at The Geysers (Allen and Day, 1927). 

Shortly after drilling began, a strong flow ofsteam 

developed (Allen and Day, 1935, p. 475); temperatures 

and pressures increased rapidly until, at a depth of 

-246ft, 205°C and 297% psig were measured. These are 

records for such a shallow depth, not yet (1974) surpassed in geothermal drilling. Considerable difficulty was 

experienced in controlling the steam, which from time 

to time burst through the surrounding ground in new 

CASING RECORD 

0 20 

TEMPERATURE, IN DEGREES CELSIUS 

CONDENSED 

LOG 

1-

w 

w 

LL 

~ 

::C 

1-

0.. 

w 

0 

40 60 80 100 120 140 160 180 200 220 0~--~--~----==============~--~~~-==---~--~--.---.---.---.---.----.---,---,---.--~ 

100 

200 

300 

400 

500 

Depth of 

casing? 

TO 

265 

Curve B. 

Bottom-hole temperatures 

measured as drilling 

progressed (Fenner, 1936) 

Curve D. 

General shape of curve likely 

to represent predrilling 

ground temperatures 

FIGURE 31.-Temperatures and other data, Carnegie II drill hole, Norris Basin (from Fenner, 1936). 

Member A 

\ 

of Lava 

Creek Tuff 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 
NORRIS BASIN 61 

jets. These signs of danger increased so rapidly that at a 

depth of 265 ft the work was stopped. According to 

Fenner's unpublished notes, ((Butler* * * seems somewhat apprehensive that the situation may get out of 

hand if there are further large increases in pressure; a 

crater might be formed by forcing out the not-too-strong 

roof rock*** Butler says that such a great volume of 

steam combined with such high pressure is outside his 

experience." Five tons of cement were then pumped into 

the hole. 

Fenner's maximum temperature of 205°C (with corresponding vapor pressure of about 250 psia or ~239 

psig) is not consistent with his maximum recorded wellhead pressure of 297 ¥2 psig, which requires a subsurface temperature of at least 215°C (neglecting water in 

the hole, and partial pressures of other gases). We have 

no convincing explanation for this anomaly; two possibilities are that removal of the thermometer from the 

violently discharging hole resulted in loss of mercury 

from above the maximum-recording restriction, or his 

gage was indicating pressures that were too high. 

Additional problems not specifically described or 

defined were caused by porous acid-leached rhyolite tuff 

in the upper 25 ft or more in the drill hole and the lack of 

securely anchored casing in hard rocks at depths below 

80ft. Casing depths and cementing procedures were not 

described, either in Fenner's published account or in his 

unpublished notes. 

INTERPRETATION OF DATA 

We are convinced that most of Fenner's measured 

temperatures were significantly below original ground 

temperatures; a notable exception was the spectacular 

increase in temperature of 46°C over a period of 6 days 

when the drilled depth increased only from 243.6 ft to 

246.5 ft. This change was almost certainly induced by 

the drill hole, and the temperatures surely do not represent original ground temperatures. Our reasons are 

based in part on integrated evidence from all three 

Norris drill holes, as discussed in the following section. 

SUMMARY OF SUBSURFACE RELATIONS, NORRIS BASIN, 

AND CHANGES INDUCED BY THE DRILL HOLES 

Generalized subsurface geologic and temperature 

data from all three Norris Basin drillholes are shown in 

figure 32. The near-surface rocks consist of the upper 

member of the Lava Creek Tuff. Diagnostic rocks near 

the contact between the two units of this formation 

(Christiansen .and Blank, 1972, p. B8--B9) were positively identified near -128 and -124 ft in Y-9 and 

Y-12~ respectively. The same contact zone is partly displayed in the drill core from Carnegie II near -78 ft 

(R. L. Christiansen, written commun., 1968). The contact (plotted in fig. 32) dips 2° . northeast, with no evidence for warping or faulting along the line of the holes. 

Temperature contours are also shown in figure 32. 

Temperatures measured in Y-9 (fig. 27, curve B) and 

Y-12 (fig. 29, curve B) as drilling progressed are probably within 2° or 3°C ofpredrilling ground temperatures. 

Fenner's data cannot be treated in the same way because, as we have seen, most of his measured temperatures were probably considerably below original ground 

temperatures. This of course cannot be known with 

certainty but note, for example, that all of his temperatures (except for 205°C) plot well below the reference 

boiling temperature curve. This is in spite of the fact 

that the hole was sited in an area of considerable upflow 

of thermal fluids and much heat. Predrilling relations 

in this area (Allen and Day, 1935, p .. 473, 474) and 

photographs of trees near the drill site (Fenner, 1936, 

fig. 9) suggest that total heat flow at the drill site was 

then considerably more than 1,000 heat-flow units 

(White and others, 1971, p. 84-88; White, 1969), or over 

700 times the worldwide average for conductive heat 

flow. Such large heat flows and the existing hot springs 

demand much convective upflow of water and heat and a 

corresponding change in temperature contours. But 

Fenner's measured temperatures, as shown in figure 32, 

permit no rise of temperature contours near Carnegie II 

and, in fact, temperatures are lower than for similar 

altitudes in Y-9 and Y-12 where immediate upflow is 

absent. For these reasons the inferred temperature contours near Carnegie II in figure 32 are based on curve D 

of figure 31, which we offer here as our best estimate of 

the ground temperatures likely to have existed before 

the hole was drilled. For simplicity, the fractures likely 

to have controlled the upflowing fluids near Carnegie II 

are omitted from figure 32. 

A more serious problem is to explain the marked 

increases in temperature with time in Y-9 near-212ft 

and in Carnegie II near -246 ft. Figure 32, with its 

inferred temperature contours, provides a plausible 

model for reaching higher temperatures by rapid upflow 

from greater depths as a result of the drilling of the 

holes. Figure 32 assumes the existence of very hot fluids 

at depth within the plane of this section. We do know 

that temperatures as high as 237¥2°C exist in Y-12 and 

that geochemical data, cited previously, indicate temperatures at least as high as 250°C in the Norris system. 

Upflow with a horizontal component from north and 

west of Carnegie II and Y-9, rather than upflow in the 

plane of this section, is an alternate possibility. 

The temperatures near Y-12 (fig. 29) are generally 

close to the reference boiling-temperature curve and do 

not require high wellhead water pressures. According 

to our deduced temperature contours for Carnegie II, 

however, wellhead water pressures were high at all 

depths below about-70ft. In view of our findings that 

high water pressures characterize all other drilled 

geyser basins of Yellowstone, the assumption of high 
62 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

pressures in the centers of major upflow at Norris is very 

reasonable. For example, if water at 210oc exists under 

Carnegie II at an altitude of7 ,050 ft (as in fig. 32), a high 

wellhead water pressure is a necessary consequence, 

probably on the order of 70 psig. 

According to interpretations shown in figure 32, the 

180oC eventually measured in Y-9 near-210ft and the 

205°C measured in Carnegie II at -246% ft did not 

occur in the original natural system nearer than about 

200 ft below the points of measurement. Self-sealing of 

natural channels by silica and other minerals presumably has greatly inhibited discharge from this system 

and has also caused high water pressures. High pressures, in turn, permitted temperatures to be much 

above boiling in an unconfined hydrostatic environment. The drilling of a hole upsets the natural regime 

and short-circuits aquifers of differing static fluid pressures. The kaolinite-filled fracture described from Y-9 

at -212 to-216ft evidently was cleared of its kaolinite 

sw 

Y -9 (Norris I) 

drill hole 

filling, short-circuiting other channels of the whole sys-: 

tern. With slow natural flow, the tongue of moderately 

hot liquid ( ~ 165°C) was losing .most of its excess heat by 

conduction to cooler walls. With more upflow of water at 

190°C or hotter, the excess heat first heated the channel 

walls and then, more and more, boiled the water to 

steam. The fluid pressure at -210ft increased from an 

estimated predrilling level of 95 psia to _,..__ 145 psia (fig. 

28). This increase of 50 psi could have been important 

in increasing the flow of fluid from the drill hole through 

the fracture on the outflow side. 

A similar response best explains the great increase in 

temperature in Carnegie II at about-245ft. Fenner's 

graphic descriptions of increasing steam flow from 

newly activated nearby vents indicates that the drill 

hole was short-circuiting natural channels between the 

deep high-temperature environment and the surface. 

The sudden increase in p.ressure noted at 246% ft ~table 

15) presumably signifies the penetration-of an aquifer 

0 1 00 200 FEET 

0 25 50 METRES 

: MemberB 

of Lava 

__ Creek Tuff 

-.~1~ 

Member A 

of Lava 

Creek Tuff 

~E 

6200'~--------~----------------------------------------------------------------------------~ 

FIGURE 32.-Vertical section through Norris Basin drill holes Y-9, Carnegie II, and Y-12, showing bedrock, measured bottom-hole~ep}.­

peratures, and inferred temperature contours. Note contrast between measured and.inferred temperatures in Carnegie II drill hole. 

The inferred fracture near Y-9 presumably connects with others (not shown) that account for the activity near Carnegie II and 

Congress Pool. : · 
MAMMOTH HOT SPRINGS 63 

TABLE 16.-Temperatures, pressures, and other observations from Y-10 (Mammoth Terrace) drill hole 

Date and time Observation Temp. 1967 depth, ft 1 OCI 

10/25 10/26 0915 20.5 57 

1055 (36) 

10/27 0835 !~:~ } 0845 47.7 ~i:f} 71.3 

10/28 0905 

0915 i~~:~ } 153.3 ~~:~ } 73.1 

10/29 1116 242.4 l 73.0 } 1121 242.3 . 242.3 72.0 72.4 1205 242.3 72.2 10/30 0840 242.1 72.4 

-1630 333 10/31 0839 331.3 ~~ :~ } 73.0 

11/1 -1000 199 6/22/68 192 

6/24/68 

9/20/69 184 

Static water level, f"t'2 

- 11.8 

- 15.1 

(+14) 

(+ 29) 

(+30) 

(+ 98) 

(+96) 

Wellhead 

pressure, 

psig1 

6 

12% 

12'h to 13 

41 

40 to 40% 

34 

37 to 37'/z 

78 to 41 

Comments 

Drilled to -22 ft at 1340; set 21 ft of 4-in. casing and cemented. Most of cement evidently washed; temperature and water level probably 

good. 

Water level when drilled depth 36 ft; drilled l)n to -86 ft at 1400, with first eruption; first gas (H2S and C02 ?) at-70ft. Set and cemented 86ft of 3-in casing. On cement; then drilled to -153 ft at 1640 with pressure increasing. 

Wellhead water pressure (evidently not gas accumulation because con- stant). Then drilled to -243 ft at - 1615. 

Water pressure, steady. Different thermometer, not insulated. Same as above, insulated. Water pressure; drilled to -333ft at 1600; 2-ft cavities near -262ft and -322 ft. Pressure increased near -333 ft. Insulated thermometer. Different thermometer, not insulated, no significant difference. Drilled to - 370 ft at 1215. Terminated drilling, changed valve. Top of caving ground in hole; collected fluid samples. Total pressure at -192 ft, 125 psia; calculated water overpressure - 39 psi; much above pressure measured 10/29 and 10/30 so probably in- fluenced by upflow. 

Replaced leaking 3-in. valve and adaptor. Total pressure at - 184 ft, 121 psia; calculated overpressure - 38 psi. 

'Data in boldface considered most reliable; data in parentheses least reliable. 2

Relative to ground surface; positive levels in parentheses, calculated from wellhead pressures considered least affected by vapor; assumed factor of2.4 is somewhat high. 

(vertical fracture?) not shown in figure 32, but assumed 

to be permeable and communicating with much higher 

temperatures at depth. Tongues of rapidly moving hot 

fluids cooled, first by loss of heat to channel walls, then 

by increased boiling. The high-pressure fluids flowed up 

the hole and out into fractured and hydrothermally 

altered wall rocks, thus accounting for the spectacular 

increase in flow of steam at the surface that Fenner 

noted. The 210°C and deeper contours of figure 32 consequently were distorted upward. 

MAMMOTH HOT SPRINGS 

Y-10 (MAMMOTH TERRACE) DRILL HOLE 

SITE SELECTION 

Y-10 was drilled to obtain data on the thickness, 

history, and subsurface conditions of Mammoth Terrace, which is the largest hot-spring deposit in Yellowstone National Park and one of the most impressive 

travertine (CaC03 ) deposits in the world. 

The selected site is about 60ft east-northeast of Bath 

Lake near the southwest limit of present surface activity, and is adjacent to Upper Terrace Drive. Surface 

altitude is 6,742 ft, which is 4ft above the level of warm, 

nondischarging Bath Lake. For comparison, the altitude of Hot River 2 miles to the northeast, which 

probably represents the subsurface discharge of most of 

the Mammoth system, is about 5,650 ft. The highest 

recognized postglacial travertine of the Mammoth system is near 7,150 ft in altitude thus indicating that 

wellhead pressures that might be obtained in a deep 

drill hole at the site could be as much as 150 psig, 

equivalent to 400 ft of water. 

PHYSICAL MEASUREMENTS 

Data are shown in table 16 and figure 33. The water 

table was first identified at -11.8 ft, about 8ft below the 

surface of Bath Lake. Such a relationship is not surprising in Mammoth Terrace, where former vents and 

cracks are frequently dry down to levels considerably 

below nearby discharging springs. 

Near-surface temperatures increased rapidly to 

about -40 ft and then leveled off, with little or no 

significant change below -50 ft. A maximum temperature of 73.1 oc, measured at-153ft, persisted, perhaps 

with a very slight reversal, to the bottom of the hole 

(table 16). A high wellhead pressure was first suspected 

at -70 ft and was clearly evident at -153 ft; a major 

increase in wellhead water pressure (to ~40 psig) occurred near -330 ft. Later in-hole pressure measurements (table 16) indicate wellhead water pressures of34 

to 41 psig, but these occurred after some caving in the 

hole and probably reflect the water pressures of deeper 

levels. When the hole was permitted to stand for nearly 

10 months, wellhead fluid pressures as high as 78 psig 

were observed. Such pressures were obviously related to 

accumulation of gas, which forced the water level 

downward. 

High subsurface temperatures had not been expected 

in Y-10, for travertine-depositing waters nearly always 

have lower subsurface temperatures than sinter-depositing waters (White, 1970). Temperatures slightly 

above 70°C have commonly been observed in surface 

springs of Mammoth; the highest ever recorded (Allen 

and Day, 1935, p. 371, 372) was 74.5°C. Fournier and 

Truesdell (1970) predicted a subsurface temperature of 

72°C for the Mammoth system, based on a silica content 

of 55 ppm in typical spring water and assuming subsurface equilibration with chalcedony (rather than quartz). 

A few analyses report somewhat higher silica contents 

(72 ppm, Allen and Day, 1935, p. 373; 60 ppm, White 
64 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YElLOWSTONE NATIONAL PARK 

TEMPERATURE. IN DEGREE$ CB.SIUS 

CONlENSED LOG 

140 160 180 200 22Q 

eB. 

Botlom-hOie ternpenlllna 

• driling pOQi a ss all 

T...,.._wilh 

. loclll dllltics 

(172-1M ft-and 

221-231 II) 

Curve A:. 

Reference~ 

curve for pure watar. 8SSUfNng 

water 1able al !JOUnCI Slriloe 

lW1d at altitude ~-7 ,500 ft 

-E X P LA N AT I 0 N 

Sllllle.mudllone. 

......... 

-ldslol-~ ~?)age 

1 Equivalent daplh. correciBd for clftelencas 

in static water IIWellor corr.,.ison 

wilh curve A 

FictJRE 33.-Temperatures and o~ data, Y-10 (Mammoth Terrace) drill hole. 

apd others, 1963, p. F54). A content of72 ppm indicates 

subsurface temperatures as high as 1190C if in equilibrium with quartz, but only 880C if chalcedony is the 

controlling phase. 

SUMMARY OF DRILLING PROBLEMS 

Y-10 was a relatively easy hole to drill because of its 

low temperatures (table 16). The principal problems, 

routine by this time, involved the moderately high 

wellhead water pressures and unusually high content of 

dissolved gases. Because of this gas content, the hole 

actually had eruption tendencies that were similar to 

those drilled in the geyser basins, where water vaporized rapidly when discharged to atmospheric pressure. Even though the temperature of the fluids discharged from Y-10 was relatively low and not very 

hazardous to the drill crew, condensing water vapor 

greatly decreased visibility and hampered operations 

during eruptions in the cold fall atmosphere. 

Caving ground was encountered at depths below the 

3-inch casing at -86 ft and was especially troublesome 

below -190 ft. Cavernous ground (or soft uncemeBted 

sediments) was noted in Jurassic(?) rocks near -262 

and -322 ft. We could have cased off these zones and 

drilled to greater depths but our major objectives had 

been attained so drilling was terminated at -370 ft. 

INTERPRETATION OF DATA 

The Mammoth travertine terraces are the nearsurface expression of a huge convection system that is 

everywhere at relatively low temperature. The drill 

hole shows remarkably constant temperatures that 

were close to 73°C at all depths below 50 ft and almost 

identical with the maximum observed in surface 

springs. Evidently all of the water of the system is 

heated to this temperature or only a little higher, and it 

rises as liquid water and dissolved gases with no 

significant change until total vapor pressure has decreased to a few atmospheres. The partial pressure of 

dissolved gases is then high enough for a carbondioxide-rich phase to form; no true boiling of water 

occurs. 
MUD VOLCANO AREA 65 

The minimum partial pressures of dissolved gases 

may be calculated from the data of table 16. A wellhead 

pressure of78 psig (89.5 psia) was measured September 

20, 1969, a year after leakage of gas through the main 

valve was eliminated. This high pressure resulted from 

exsolution of gas, depressing the water level in the hole 

to the bottom of the casing at -86 ft. The ground temperature at that depth is close to 73°C and the corresponding vapor pressure of water is 5.1 psia. Therefore 

the partial pressure of gases, other than water vapor, at 

the gas-water interface was at least 84.4 psia (5.8 atmospheres, more than 16 times the vapor pressure of 

water!); this is the highest pressure of gases other than 

water vapor yet observed for Yellowstone fluids. 

Allen and Day (1935, p. 86) found that carbon dioxide 

ranges from 97.1 to 99.5 volume percent of total gases at 

Mammoth; our best samples from Y-10 contained 96 to 

97 percent c~. Thus the partial pressure of carbon 

dioxide must be at least 5.5. atmospheres. This is a 

minimum partial pressure because gas is presumably 

escaping from the hole into the country rock below the 

casing; with a deeper casing, presumably the water 

level would be depressed even more and the measured 

wellhead pressure would exceed 891h psia. 

These data suggest that water and dissolved gases 

rise until hydrostatic pressure has decreased to a value 

somewhere above 90 psia, where the gases start to exsolve. Because of high wellhead water pressures, the 

depth of first exsolution may be as low as 170 ft. 

Subsurface pH's are below 6.5 and are controlled by 

the partial pressure of carbon dioxide. Because the solubility of calcite is directly proportional to carbon dioxide concentration, calcite precipitates as carbon dioxide 

exsolves from the rising water. 

Travertine deposited near the surface is porous and, 

in places, may even be cavernous. Our drill cores show 

that, with burial, old travertine becomes more dense 

because of subsurface deposition of calcite in pore 

spaces. At depths below 170 ft or so, where all carbon 

dioxide is in solution, the rising water may be unsaturated with respect to calcite and dissolution could be 

occurring. The principal cavities noted in drilling, however, were in Cretaceous rocks below the oldest travertine. 

MUD VOLCANO AREA 

Y-11 (SULPHUR CAULDRON) DRILL HOLE 

SITE SELECriON 

The Mud Volcano area was selected for drilling to test 

geochemical evidence that pointed to this area as a 

vapor-dominated system (White and others, 1971). The 

thermal springs of the area are characterized by acidsulfate and nearly neutral bicarbonate-sulfate waters 

that contain very little chloride, and rates of discharge 

are consistently low. Similar springs occur even near 

the Yellowstone River, which cuts across the spring 

group and is the local base level for the water table. 

Vigorous streams of gas bubbles are discharged from 

the river bottom with little or no associated temperature anomaly, indicating the absence of associated hot 

water. In contrast, the major geyser basins are characterized by water relatively rich in chloride and by rates 

of individual spring discharge that can be exceedingly 

high. 

The significance of chloride in distinguishing between vapor-dominated and water-dominated geothermal systems seems to have been first emphasized by 

White (1957) in explaining why some systems produce 

only dry steam with minor associated gases (C~, ~S, 

H:.B<la) from deep wells, and other geothermal systems 

(including all drilled areas with true geysers) yield hot 

chloride water accompanied by some steam. The common chlorides of sodium, potassium, calcium, and magnesium are all highly soluble in water and are selectively leached from rocks in contact with hot water. In 

contrast, these chlorides have low volatilities at temperatures below about 4000C. These facts explain why 

springs in water-producing areas are moderate to high 

in chloride content, but springs in areas producing dry 

steam are low in chloride. For example, the Geysers 

geothermal area discharges superheated steam from 

producing wells, and the natural springs of the area 

have less than about 15 ppm chloride (White, 1957; 

White and others, 1971). 

We looked for low chloride levels to tentatively identify and then to confirm by drilling a vapor-dominated 

system in Yellowstone Park. The whole Mud Volcano 

group has the desired characteristics; a specific site near 

Sulphur Cauldron was selected because of its access by 

road to a picnic ground (since abandoned) and its proximity to Yellowstone River for a supply of drill water. 

The selected drill site is just inside the border of an 

oval-shaped treeless area of high total heat How. The 

heat-How contours shown in figure 4 of White, Muffier, 

and Truesdell (1971, p. 85) were mapped by snowfall 

calorimetry(White, 1969)while Y-11 wasbeingdrilled. 

The location of the drill hole relative to the 900 

heat-How unit contour and the tree line indicates that 

total heat How at the site is about 800 heat-How units 

(more than 500 times the average worldwide conductive 

heatftow). 

PHYSICAL MEASUREMENTS AS DRILLING PROGRESSED 

The data are shown in table 17 and figure 34. These 

data have been described previously (White and others, 

1971) but are included here to provide a complete record 

of our research drilling in Yellowstone Park. The measured bottom-hole temperatures in Y-11 are generally 
66 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSTONE NATIONAL PARK 

TABLE 17.-Temperatures,pressures, and other observations from Y -11 (SulphurCauldron)drill hole, Mud Volcano Group 

Date and time 1968 

5/14 

5/15 0835 

1210 

1525 5/16 0815 

0823 

1325 

5/17 0800 

1645 5/18 0750 

0808 

1300 

5/19 1040 

1100 5/20 0754 

0805 

0812 

0822 

1400 

5/21 0745 

0757 

1220 

1545 

5/22 0800 

0812 

5/23 0815 

0830 

- 1100 

5/27 not 

noted 6/10 1000 

7/10 - 1300 7/28 

9/21169 

9/24 

Observation 

depth, ft1 

6.7 

(27.1) 

59.4 

~~:g } 56.9 

91 

44.9 

(137.0) 

~~~:~ } 135.8 

187 

~~~:~ } 186.8 

~~~:8 } 187.0 

237 

~~~:~ } 236.9 

~g~:~ } 306.6 

~g~:6 } 306.6 

346.8 

- 346 

- 345 

315.9 

128 

91.9 

Temp. OCl 

43.0 

(36.0) 

87.0 

104.4 } 106.4 105.4 

123.3 

73.0 

116.1 

137.0 } 137.1 137.2 

(120.3) 

~~~:! } 151.9 1514} 153.4 151 9 150.9 . 

151.9 

154.5 

151.1 } 151.6 152.0 

174.3 

174.7 

175.7 } 175.9 176.1 

191.6 } 191.4 191.1 

~~u} 161.3 

158.6 

131.7 

Thermometer No. 

9 

11 

9 

9 

9 

9 

11 

9 

9 

11 

9 

1 

11 

9 

11 

11 

11 

9 

11 

11 

9 

11 

9 

Static 

water 

level, ft1 

- 7.6 

- 7.5 

-17.0 

- 16.1 

- 15.5 

- 15.2 

V2 to - 3 

'Data in boldface considered most reliable; data in parentheses, least reliable . 

less reliable than in other Yellowstone drill holes because all drill water was lost into permeable ground 

from -122 ft to -187 ft; at greater depths only about 

half of the drill water returned to the surface. In spite of 

excessive loss of drill water, most bottom-hole measurements made 16 hr or more after circulation ceased 

are probably within a few degrees of original ground 

temperatures. As with other holes, the setting of two 

strings of casing (at -20 and -90 ft) interfered with 

collection of satisfactory near-surface data. The temperature of 123.3°C at -91 ft was obtained only 114 hr 

after circulation ceased and before the second string of 

casing was set. A flow of steam and water into the 

bottom of the hole no doubt assisted in rapid approach to 

the original temperature; a considerably higher temperature at this depth seems unlikely, judging from 

relations to other nearby measurements (curve B, fig. 

34). The temperature of 151.9oC measured at -187 ft 

seems especially reliable in view of identical averages 

23 and 44 hr after circulation. The decrease in temperature from 154.5° to 151.6°C that occurred overnight at 

-237ft (table 16, 5/20 to 5/21) is significant, especially 

in view of the accompanying increase in wellhead presWellhead 

pressure, psig 

- 1 

511< to 0 

18 

11\4 

Oto1 

39 to 40V2 40 

72 to 47 100 to 73 

132 to 99 

170to148 

60 

64 

66 

64V2 to 67 

60 

54 

34 to 39 

Comments 

Drilled to - 20 ft at 1425; set 4-in. casing, and cemented. On cement at -6.7 ft; temperature probably minimum. 80 min after circulation ceased; good water level. Then drilled to -60 ft at 1430; pressure all gas. 

Gas escaping; 91 oc at water level. Then drilled to -91 ft at 1215. 

70 min since circulation; could have erupted; much H2S; set 90 ft of 3-in. casing and cemented; excellent cement job. On cement; temperature probably minimum? Then drilled to-137ft at - 1600; lost circulation from -122 to - 137 ft. Gas pressure outside rods, water level inside rods; temperature 73°C. at water level. 1\12 hr alter drilling to - 187 ft at 1135; lost circulation from - 137 to -187 

ft. -23 hr after circulation. 

-45 hr after circulation. 

Water level fluctuating, gassy; then di:-illed to - 237 ft at 1100. 3 hr after circulation, pressure fluctuating; water discharging outside of rods. Temperature more valid than on 5/21. Gas at top; no fuS noted; note temperature decrease since 5/20. Then drilled to - 307 ft at 1200; erupted after pulling core; nearly all steam after initial water. Temperature 40 min after eruption; some water with steam at 4 7 psig. Leaking steam a~ 100 psig, decreasing to 73 psig, some water. Side valve pressure outside drill rods, 52 psig. 

Leaking vapor only. Then drilled on, increasingly difficult below -330 ft. Violent eruption at - 347ft, 1530, initially much water (drill water?), then mostly steam. Leaking vapor only. Drill rods in hole a few feet off bottom; exact depth not noted. Decided to terminate drilling. Rods pulled, pumping cold water down outside rods throughout; pressure with open hole below -90ft. Hang up at about - 110ft erupted to clear hole; powerful steam eruption with little water. Note major permanent changes in temperature and pressure after rods out of hole. Thermistor temperature series plotted on fig 34. Temperatures gen- erally steady and reproducible down to -276 ft, fluctuating somewhat at greater depths, up to ±4°C at bottom. Attempted to sample water but hole filled with vapor to existing bottom. Blocked; no access to greater depths; no water below -128 ft. Attempted thermistor series; initial temperature at top 75°C, increasing to 107°C with leakage of gas. Hole full of gas to cave at -92 ft, just below casing; thermistor wedged and lost. Erupted gas, mud, and water, and collected water sample. Pumped in 5 sacks of cement. 

sure. These data are best explained by steam and water 

flowing into the hole at a temperature of about 152°C 

(probably from about -190 ft), with the water fraction 

flowing down the hole and out into adjacent rocks near 

the bottom with consequent cooling effect, while the 

steam phase controlled the pressure in the hole. The 

temperature of 191.4°C measured near -347 ft the 

morning after completion of drilling is nearly 10°C 

above reference curve A of figure 34. 

On several occasions during the drilling of Y-11 the 

hole could not be prevented from erupting for short 

intervals. These eruptions differed notably from those 

of drill holes in the hot-water systems of the geyser 

basins. Where permeability and water supply are adequate, liquid water at 160°C, for example, will erupt at 

constant enthalpy to atmospheric pressure, and 11 percent of the original liquid will be vaporized to steam. 

The remaining 89 percent remains liquid, producing 

effects that are similar to many major geyser eruptions. 

In contrast, during an eruption ofY-11 the local supply 

of liquid water was soon nearly exhausted and steam 

became completely dominant, probably with less than 

10 mass percent of liquid. Although at no time did the 
MUD VOLCANO AREA 67 

CONDENSED 

CASING RECORD TEMPERATURE, IN DEGREES CELSIUS LOG 

0 20 40 60 80 100 120 140 160 180 200 220 

0 

20ft 

of 4-in. 

50ft 

65ft Reworked lithic- casing 

vitric tuff 

90ft 

100 of 3 in. 

casing 

Bottom-hole temperatures 

as drilling progressed 

Member B 

119ft of Lava 

200 

1-

w 

w 

lL 

~ 300 

:I 

1-

a.. 

w 

0 

400 

500 

TO 

347 

EXPLANATION 

0 Bottom-hofe temperature - 16 hr 

after circulation ceased 

44 8. Bottom-hole temperature, indicating 

hours (or other specified time) 

after circulation ceased 

..--... Thermistor temperature in completed 

hole, showing fluctuations 

Creek Tuff 

Member A 

of Lava 

Creek Tuff 

Curve C. 

Thermistor series of 

June 1 0, 1968, 17 days 

after completion of 

hole 

Curve A . 

Reference boiling-temperature 

curve for pure water, assuming 

water table at ground surface 

and at altitude of-7,500 ft 

FIGURE 34.-Temperatures and other data, Y-11 (Sulphur Cauldron) drill hole, Mud Volcano area. 

full opened hole discharge dry steam without any liquid, we are confident that a dry discharge would have 

occurred if eruption had continued or if the hole had 

been cased a little deeper to shut off near-surface 

water-bearing channels. In other areas, some erupting 

drill holes in water-saturated rocks of low permeability 

soon exhaust their local water supply and then discharge dry steam, utilizing the stored heat of rocks to 

vaporize the available liquid. Y-11's eruptions cannot 

be explained in this way because the large loss of drill 

water, noted above, proves adequate permeability 

below cased parts of the hole. These facts clearly indicate to us that Y-11 did indeed penetrate into a vapordominated system that differs greatly from the waterdominated systems of the geyser basins. Further 

confirmation of the differences is provided by water 

samples from Y-11 and springs of the Mud Volcano 

group, compared with water from hot-water systems 

(White and others, 1971, table 1). 

times these pressures were close to the calculated vapor 

pressures of water at the measured bottom-hole temperatures. This occurs when little or no water is in the 

hole to offset the pressure of water vapor at existing 

temperatures. For example, the wellhead pressure of 

170 psig ( ~ 181 psia) first observed on May 23 is equivalent to the vapor pressure ofwater at 189.7°C, which 

in only 0. 7oC below the measured temperature. If the 

partial pressures of other gases are neglected, the calculation indicates that less than 4 percent of the drill hole 

was filled with liquid water. This lack of counterbalancing water pressure, combined with high permeabilities 

and high discharge rates of steam, were difficulties that 

forced us to terminate the hole before we had planned. 

POSTDRILLING MEASUREMENTS AND INTERPRETATIONS 

A series of thermistor temperature measurements 

were made in Y-11, 17 days after completion (curve C, 

fig. 34). Temperatures increased rapidly below the surface to about 151 oc at -50ft and rose to 153°C at -268 

SUMMARY OF DRILLING PROBLEMS ft, and then abruptly to 155°C, which was maintained 

Wellhead pressures increased greatly with depth; at approximately to the bottom of the hole. Temperatures 
68 PHYSICAL RESULTS, DRILLING IN THERMAL AREAS, YELLOWSI'ONE NATIONAL PARK 

actually fluctuated slightly at each depth below about 

-260 ft, and fluctuations ranging from about 1 o to 5°C 

were especially notable near the bottom. These 

fluctuations were not instrumental errors and were far 

too large and rapid to be caused by a vapor phase alone. 

The pressure of saturated steam at 1530C (base of the 

nearly constant-zone) is 74.8 psia, which is nearly identical to the measured wellhead pressures during the 

series, ranging from -75% to 78 psia (table 17). Thus 

the coexistence of steam and water is indicated at all 

depths below about -268ft. We concluded from the drill 

records that some water entered the hole near -190 ft 

and flowed down and out into adjacent rocks near the 

bottom while steam flowed up from near the bottom, 

largely filling the hole at all depths above -268 ft and 

thereby controlling pressures above this level. At very 

shallow depths (above -50ft), high conductive thermal 

gradients in rock outside the drill hole permitted condensation of water vapor on the casing, thereby concentrating residual gases and permitting pressure to be 

constant upward as temperature decreased. This interplay of temperature, pressure, and gas content is discussed in more detail by White, Muffler, and Truesdell 

(1971, p. 84-88). 

In-hole measurements on July 10, 1968, showed constant pressure ( -60 psig) to the then-existing bottom of 

CONCLUSIONS 

1. Drilling a hole into a high-temperature hydrothermal system almost always upsets the 

local hydrologic regime by short-circuiting 

aquifers of differing temperatures and pressures. 

Consequently, the usteady-state" temperatures 

measured long after completion of a hole may 

depart greatly from original ground temperatures. 

2. Sequential bottom-hole temperatures taken as 

drilling progresses, with at least 16 hours for 

recovery without drill fluid circulation prior to 

each measurement, provide a temperature-depth 

profile far more representative of original ground 

temperatures than a profile made in a completed 

hole. 

3. Bottom-hole temperatures measured at the same 

depth over several days without fluid circulation 

indicate that almost all recovery of temperature 

occurs within the first 16 hours after circulation 

ceases. Thereafter, the bottom-hole temperature 

may increase as much as a few degrees, or decrease, depending on the hydrologic behavior of 

the drill hole and intersected aquifers. The 16-hr 

bottom-hole temperatures are probably within 1 o 

to 2°C of original ground temperatures except 

where boiling occurs, with resultant loss of heat 

from the wall rocks, or where water flows downward from a cooler zone into an initially hotter 

the hole at-316ft, with no significant difference detected from bottom to top. This indicates the accessible 

hole was completely filled with vapor. Presumably the 

liquid water supply available at high levels on June 10 

had been largely drained by gravity through the shortcircuiting drill hole and was exhausted by July 10. Still 4. 

later attempts to measure in-hole temperatures and 

pressures were largely unsuccessful (table 17); the accessible depth decreased with time, indicating that the 

hole was either collapsing or being filled with clay minerals flowing or being squeezed from adjacent fractures. 

zone. 

Maximum-recording mercury thermometers are 

dependable and rapid for determining bottomhole temperatures in the usual situation where 

temperatures increase downward. A temperature reversal may be suspected wherever recorded values fail to increase With depth, and an 

actual reversal may be detected by insulating the 

maximum thermometer (but the procedure is 

time consuming). Maximum thermometers are 

not subject to the chronic failures of insulation, 

potting compound, and instruments that plague 

the various electrical temperature-measuring 

devices, but are less precise and are much less 

suitable for making temperature profiles in a 

completed hole. 

For other aspects of our model of vapor-dominated 

geothermal systems and the possible relationships of 

Y -11 to the border zone of such a system, the reader is 

referred to White, Muffler, and Truesdell (1971). 

The fact that liquid was only indirectly evident in 

Y-11 on June 10 and seemed to be absent as an 

identifiable phase at all later times is anpther contrast 

with distribution of fluids in all holes drilled in the 

geyser basins. In these holes, vapor commonly accumulated in the upper cased parts, depressing the water 

level down to the base of the cased interval (or to the top 

of the next lower aquifer). A general saturation of 

ground with liquid in the hot-water systems, and a 

dominance of vapor in large pores and fractures of the 

Mud Volcano system, provide the most satisfactory explanation for all observations. 

5. Most Yellowstone drill holes to depths of 100 to 250 

ft show a nearly linear near-surface thermal gradient. This zone is bounded upward by the water 

table or ground surface and downward by the 

first aquifer in which significant fluid flow occurs. 

This linear gradient is best explained by conductive heat flow through water-saturated rocks of 
REFERENCES CITED 69 

nearly constant thermal conductivity; the absence of significant convection is supported by 

the nearly oonstant static water levels measured 

at different drilled depths within the zone. 

6. Although most rocks within the near-surface zone 

of linear gradient were initially porous and 

permeable, temperature and pressure data combined with petrographic observations indicate 

uself-sealing" by deposition of hydrothermal 

minerals. Flow channels are progressively restricted with time, which leads to concentration 

of flow into a few large channels. 

7. Below the zone of nearly constant thermal gradient, many Yellowstone drill holes with static 

water levels near the ground surface are characterized by temperatures close to the reference 

boiling-temperature curve. Where static water 

levels are above ground level because of artesian 

and thern10artesian pressure, temperatures 

may, but do not always, plot above the reference 

boiling-temperature curve by amounts equivalent to the static water level above ground surface. 

8. Yellowstone drill holes located near the centers of 

hot-water upfiow (Y-1 and Y-13) had temperatures that plot well above the reference boilingtemperature curve and also exhibited high wellhead water pressures (high static water levels); 

temperatures were still increasing with depth 

along the liquid-vapor two-phase boundary, with 

no indication within drilled depths of attaining 

the maximum temperature existing in each system (the base-temperature ofBodvarsson, 1964). 

9. Yellowstone drill holes located somewhat away 

from the centers of hot-water upfiow (Y -2, Y -3, 

Y-5, Y-8, Y-11, Y-12, and Y-10) had temperatures nearly on the reference boilingtemperature curve with only slight overpressure, 

and several of these holes {Y-5, Y-8, Y-10) 

showed a leveling off or a slight reversal in temperature with depth. 

10. Temperature-depth curves of three holes (Y -4, Y -6, 

and Y -7) plot below but crudely parallel to the 

reference boiling-temperature curve, with temperatures probably being controlled largely by 

water circulation and thermal conduction outward from nearby hot-water upfiow systems that 

are boiling. 

11. One drill hole, Y-11, penetrated the margins of a 

vapor-dominated geothermal system that had 

been tentatively recognized by geochemical 

criteria prior to drilling. Pores and fractures at 

depth contained both steam and water, with the 

steam, being volumetrically dominant, as the 

hydraulically controlling phase. 

12. Maximum measured temperatures in each area 

(Fournier and Truesdell, 1970, 1973) providet;l 

good to strong corroboration for the silica and 

Na-K-Ca hydrogeothermometers for predicting 

reservoir temperatures from surface hot springs; 

the simple sodium/potassium geothermometer is 

not as reliable in Yellowstone National Park as 

in most high-temperature hot-water systems. 

13. Wellhead fluid pressures may greatly exceed wellhead water pressure, either because gas accumulates in the casing and forces the water level 

downward, or because water rising from a highly 

overpressured aquifer to another of lower overpressure exsolves and entrains vapor bubbles, 

with consequent decrease in density. 

14. Each hole showed an irregular rise in static water 

level with increasing drilled depth. Vertical hydraulic gradients exceeded 0.1 for all holes except 

Y -7. Maximum hydraulic gradients observed 

were 0.30 in Y-4, 0.37 in Y-1 and 0.47 in Y-13. 

15. In-hole pressures showed that the wellhead water 

pressure generally is controlled by the aquifer of 

highest overpressure, except where this aquifer 

has a permeability that is appreciably less than 

that of other aquifers intersected by the drill 

hole. 

16. In-hole pressure measurements indicate that both 

water and vapor can exist in parts of a drill hole 

while water alone is being discharged at the 

wellhead. This situation, as in Y -4 and Y -13, 

results from the How of water and vapor up the 

hole, with both phases being diverted into an 

aquifer. 

17. Pressures much in excess of cold hydrostatic are 

characteristic of the Yellowstone thermal systems and are due to thermoartesian pressure, 

perhaps supplemented by normal artesian pressure. 

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