Bruceton, Pa. 

UNITED STATES DEPARTMENT OF THE INTERIOR 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Cecil D. Andrus, Secretary 

BUREAU OF MINES 
This publication has been cataloged as follows: 

Elder, Curtis H 

Geology and gas content of coalbeds in vicinity of Bureau 

of Mines, Bruceton, Pa. / by C. H. Elder and M. C. Irani. 

[Washington] : U.S.. Dept. of the Interior, Bureau of Mines, 

1977. 

22 p. : maps, diagrams ; 27 cm. (Report of investigations - Bureau of Mines ; 8247) 

Bibliography: p. 20. 

1. Coal - Geology - Pennsylvania - Bruceton Region. 2. Mine 

gases. 3. Geology - Pennsylvania - Bruceton Region. I. Irani, 

Meherwan C., joint author. 11. United States. Bureau of Mines. 

111. Title. IV. Series: United States. Bureau of Mines. Report 

of investigations - Bureau of Mines ; 8247. 

TN23.U7 no. 8247 622.06173 

U.S. Dept. of the Int. Library 
CONTENTS 

Page 

Abstract ................................................................ 1 

Introduction ............................................................ 1 

Geology ............................................................... 3 

Structure .. .....................o................e............... 3 

Stratigraphy ....................................................... 5 

Pennsylvanian System .................................................... 5 

Monongahela Group .................................................. 5 

Conemaugh Group ................................................... 5 

Allegheny Group .................................................... 6 

Pottsville Group ................................................... 7 

Mississippian System ..................................................... 8 

Mauch Chunk Formation .............................................. 8 

Formation testing ....................................................... 8 

Mud analysis well log .............................................. 8 

Geophysical log .................................................... 8 

Formation pressures ..................................................... 13 

Gas content of coalbeds ................................................ 16 

Gas and water analyses ...........................................o... . 17 

Hydraulic stimulation .. ................................................ 18 

Sumary ................................................................. 19 

References .............................................................. 20 

Appendix..-Ultimate and proximate coal analyses ......................... 21 

TRATI ONS 

Geologic structure map of Bureau of Mines Bruceton Station area .... Structural axes of a portion of Allegheny County ................... Geologic stratigraphic cross section ................................ Mud log of borehole 1 .............................................. Mud log of borehole 2 .............................................. Gamma ray-density caliper log of borehole 1 ........................ Garmna ray-density caliper log of borehole 2 ........................ Pressure chart, drill stem test 1, Mercer coalbed interval ......... Pressure chart, drill stem test 2, Mercer coalbed interval ......... Pressure chart, drill stem test 3. Clarion coalbed ................. Pressure chart, drill stem test 4, Middle Kittanning coalbed ....... Pressure chart, drill stem test 5. Freeport coalbed ................ Plot of coalbed pressures versus depth ............................. Hydraulic stimulation pressure and flow charts ..................... 

TABLES 

1 . Drill stem shut-in pressure tests. borehole 1 ...................... 2 . Gas content of coalbed ............................................. 3 . Gas sample analyses ................................................ 4 . Water sample analyses ............................................ 
GEOLOGY AND GAS CONTENT OF COALBEDS IN VICINITY 

OF BUREAU OF MINES, BRUCETON, PA. 

C. HI Elder ' and MI C. lrani 

ABSTRACT 

Two degasification test boreholes were drilled to depths of 1,238 and 

1,212 feet on Bureau of Mines property at Bruceton, Pa., as part of the 

~ureau's long-range coal degasification program. The holes provided detailed 

geologic information and geologic sections, which were correlated with 

regional stratigraphic cross sections prepared by the Pennsylvania Geological 

Survey. Gas content determinations and coal analyses were made on the Upper 

Freeport, Middle Kittanning, Clarion, Brookville, and Mercer coalbeds; gas 

content of the coalbeds ranged from 53 to 165 cubic feet per ton. Formation 

pressure and gas flow tests were conducted on selected coalbed intervals in 

borehole 1; formation pressures ranged from 292 to 473 psig. The middle 

Kittanning coalbed was hydraulically stimulated using very heavy gelled water, 

but gas production remained low because gel residue and formation water 

inhibited the flow of gas. Gas contents in the Clarion, Upper Brookville, and 

Mercer coalbeds were anomalously low owing to the proximity of porous sandstones which act as reservoirs for gas migrating from coalbeds. 

INTRODUCTION 

The present study was conducted as a part of the Bureau of Mines comprehensive long-range coal degasification program. The objective was to develop 

specific information on physical properties of coalbeds relative to gas content and to apply and evaluate a stimulation technique for increased gas drainage. For such experimental work the most convenient site was at the Bruceton 

Station of the Bureau of Mines near Pittsburgh, Pa.; the program also provided 

an opportunity to develop detailed geologic information and correlation of the 

coalbeds present in the Bruceton area. 

Early geologic studies and maps of the area do not give detailed stratigraphic information for coalbeds below the Pittsburgh coalbed in the immediate 

3 vicinity of Bruceton (7). Studies at the outcrop areas of several of the 

coalbeds show they are-discontinuous in Allegheny County (5, - 7) . Coalbed 

1Geologist. 

a~upervisory mining engineer. 

Both authors are with the Pittsburgh Mining and Safety Research Center, 

Bureau of Mines, Pittsburgh, Pa. 

3~nderlined numbers in parentheses refer to items in the list of references 

preceding the appendix. 
formation pressures had never been measured, and the presence of gas in the 

coalbeds had never been recorded. There have been no earlier attempts to produce gas from coalbeds in the vicinity of Bruceton, Pa. 

Two boreholes were drilled to depths of 1,238 and 1,212 feet on Bureau of 

Mines property at Bruceton, Pa. Sedimentary rock strata encountered in the 

boreholes are described later in the report and correlated to the stratigraphic sequence established in unpublished regional cross sections constructed by W. R. Wagner, of 

the Pennsylvania Geological 

Survey (1) . Correlations 

are shown on a cross section 

constructed from selected 

geophysical logs of wells 

6 to 17-112 miles distant 

from the two test boreholes. 

Drill stem tests were conducted to evaluate formation 

pressures and gas flows from 

the coalbeds. Each coalbed 

was analyzed for gas content. 

The Kittanning coalbed was 

hydraulically stimulated 

using very heavy gelled 

water in an attempt to 

increase gas flow for 

degasification. 

The two test holes will 

provide sites for future 

research in stimulation techniques using different 

fluids to achieve formation 

fracture, such as nitrogengenerated foam or new water 

gelling agents, which will 

provide better water recovery potential. The cored 

holes can be used to test 

new logging techniques or 

other types of remote -sensing 

0 2,000 feet LEGEND - equipment for formation 

Heavy- duty road evaluation. 

0 600 meters ---- ---- Scale Light-duty road 

, Structure contour on Lithologic data col- 

.go0 Pittsburgh coalbed lected during drilling, cor- _--,/ No coal ing, and testing provide a 

,900~ Contour interval, 20 ft geologic s e c t i o n f o r regional 

stratigraphic correlation 

FIGURE 1, - Geologic structure map of Bureau of Mines and assist in making more 

Bruceton Stat ion area, accurate interpretations of 
the regional geology and assessment of mineral resources in the Allegheny 

County area. 

GEOLOGY 

Structure 

The area at Bruceton where the two boreholes were drilled (figs. 1-2) is 

folded into gentle anticlines and synclines with a general northeast-southwest 

0 4 

I , ,I ,I , 

I miles Scale Kilometers 

0 6 12 

FIGURE 2. - Structural axes of a portion of Allegheny County. 
Carnegie 054 Camegie 040 

Wash~ngton County Allegheny County 

Br uceton No. I Bruceton No.2 

Allemeny County Allemeny County 

Pittsburgh HZ5 Pittsburgh FZ

Allegheny County Allegheny County 

+ 

FIGURE 3. - Geologic stratigraphic cross section. 
trend. The major structures in the vicinity of the boreholes are the 

McMurray syncline, Amity anticline, and Duquesne syncline (1). The McMurray 

syncline is a broad gentle fold which appears in the Glassport 7-1/2-minute 

quadrangle northwest of Bruceton and trends N 10" E to Pittsburgh, Pa., where 

it swings to the northeast. The Amity anticline trends N 30" E, its axis passing just east of Bruceton through Homestead, Pa. The test boreholes were 

drilled on the west limb of this anticline. The Duquesne syncline is a broad 

structure lying southeast of, and parallel to, the Amity anticline and west of 

the Monongahela River. It is complicated by several minor folds. 

Stratigraphy 

The stratigraphic section penetrated by the test boreholes consists, in 

descending order, of the Monongahela, Conemaugh, Allegheny, and Pottsville 

Groups of the PennsylvanianSystem, and the Mauch Chunk Formation of the 

Mississippian System (fig. 3) (5, L) . 

PENNSYLV~NIAN SYSTEM 

Monongahela Group 

The Pittsburgh Formation, the basal member of the Monongahela Group, 

crops out of the rolling hills in the vicinity of the test boreholes. The 

interval of the Pittsburgh Formation penetrated by the boreholes consists of 

interbedded sandy shales and sandstones. The Pittsburgh coalbed, the basal 

member of the formation, has been mined out in the area of the drill sites. 

The Pittsburgh Formation is 75 and 47 feet thick in boreholes 1 and 2, 

respectively. 

Conemaugh Groue 

The Conemaugh Group is divided into the Casselman and Glenshaw Formations 

in descending order. The Conemaugh Group consists of a series of interbedded 

shales, red and green shales and claystones, thin limestones, thick sandstone 

members, and local very thin coalbeds. The Conemaugh Group is 653 and 657 

feet thick in boreholes 1 and 2, respectively. 

The upper portion of the Casselman Formation crops out in the valley 

bottoms at Bruceton. The Pittsburgh Limestone Member in the upper portion of 

the Casselman Formation consists of several thin limestones interbedded with 

calcareous shales and calcareous sandstones. Five limestones 4 to 6 feet in 

thickness occur in the 125-foot interval immediately below the Pittsburgh 

coalbed. 

The Clarksburg Limestone Member occurs at a depth of 280 feet in borehole 1. The limestone is 4 feet thick and is underlain by gray, calcareous 

shale and clay in borehole I. It is absent in borehole 2. 

The Duquesne Limestone Member, a freshwater limestone encountered at a 

depth of 340 feet in borehole I, is 8 feet thick at this location. In borehole 2, the limestone is 4 feet thick and very shaley. 
The Ames Limestone Member marks the top of the Glenshaw Formation. This 

6-to 8-foot-thick fossiliferous marine limestone, penetrated at a depth of 

420 feet in borehole 1, is absent in borehole 2. The interval between the 

Pittsburgh coalbed and the Ames Limestone commonly ranges from 265 to 350 feet 

thick; in borehole 1 the interval is 346 feet. 

The Saltsburg Sandstone Member underlies the Ames Limestone as two separate units in borehole l. The top unit, 38 feet thick, is shaley at the top 

and coarsens downward from a fine-grained sand to a coarse-grained sand. The 

two units are separated by a dark-gray-to-black shale approximately 4 feet 

thick. The bottom unit is 34 feet thick and consists of fine-grained sand 

with some thin shale stringers at the top. 

The Pittsburgh red beds, commonly present below the Ames Limestone, are 

not present in the drill site area. The lower part of the Glenshaw Formation 

consists of interbedded shales, thin limestones, and sandstones. 

The Mahoning coalbed is the first coal encountered below the Pittsburgh 

coalbed and is generally not minable in this area. At depths of 702 and 

680 feet in boreholes 1 and 2, respectively, the Mahoning coalbed is 9 inches 

thick. 

Allegheny Group 

The Allegheny Group is subdivided into three formations: Freeport, 

Kittanning, and Clarion, in descending order. Although the lithologies in 

the Allegheny Group vary considerably, sandstone is the dominant lithotype 

in boreholes 1 and 2. 

The Upper Freeport coalbed marks the top of the Freeport Formation. It 

was encountered at depths of 728 and 704 feet in boreholes 1 and 2, respectively. The Upper Freeport consists of an upper bench of 2 feet of coal 

separated from a lower 4-foot bench by 3 feet of gray-to-black shale. Analysis of the Upper Freeport coal cores showed a high ash content, indicating a 

high inert-mineral-matter content. The Pennsylvania Geological Survey reports 

the Upper Freeport coalbed in Allegheny County commonly ranges from 24 to 72 

inches in thickness and locally may be dirty, thin, irregular, or entirely 

absent (2). The coalbed is underlain by 10 feet of dark-gray shale. The 

remaining portion of the Freeport Formation is white, medium-to-coarse 

sandstone. 

The Kittanning-Clarion Formation boundary could not be determined in the 

section penetrated by the test boreholes owing to the absence of the Lower 

Kittanning coalbed. The top of the Kittanning-Clarion Formation is marked by 

the Johnstown Limestone Member, encountered at 800 and 764 feet in boreholes 1 

and 2, respectively. The remaining section of the Kittanning-Clarion Formation consists of interbedded sandstones and shales. The Middle Kittanning 

coalbed occurs at drill depths of 834 and 808 feet in boreholes 1 and 2, 

respectively. It is 3 to 4-112 feet thick. A section of interbedded sandstones and shales, equivalent to the Lower Worthington and Lower Kittanning 

Sandstone Members, underlies the Middle Kittanning coalbed. The Lower 
Kittanning coalbed, when present, separates these sandstone members and marks 

the top of the Clarion Formation. The Clarion coalbed was penetrated at drill 

depths of 980 feet in borehole 1 and 966 feet in borehole 2, and was 1 and 

3 feet thick, respectively. The Clarion coalbed and associated shale overlie 

the Clarion Sandstone Member of the Clarion Formation. The sandstone is 

38 feet thick, white to gray, fine grained, and argillaceous. The base of the 

sands tone is conglomeratic in borehole 2. 

The Brookville coalbed marks the base of the Clarion Formation and the 

Allegheny Group. The Brookville coalbed is divided into two benches at both 

drill sites; both benches are 1 foot thick. The two benches are separated 

in borehole 1 by 6 feet of gray coarse-grained sandstone, which changes 

laterally to dark-gray-to-black carbonaceous shale in borehole 2. The bottom 

bench of the Brookville coal has a high inert-mineral content. Cross sections 

by the Pennsylvania Geological Survey also indicate that this coalbed is 

probably discontinuous in the greater Pittsburgh area (z). 

Pottsville Group 

The Pottsville Group consists predominately of interbedded sandstones, 

shales, and some discontinuous coalbeds. The Homewood Sandstone, at the top 

of the Pottsville Group, is poorly developed in this area. It consists of 

interbedded sandstones and sandy shales. Farther to the south and southeast 

in southwestern Pennsylvania and northern West Virginia, the Homewood is a 

thick, cross -bedded sandstone. 

Only one of several Mercer coalbeds is present at the drill sites. A 

1-foot coalbed was penetrated at the 1,135- and 1,103-foot drill depths in 

boreholes 1 and 2, respectively. A 14-foot sandstone overlying the Mercer 

coal contained gas, which flowed during a drill stem test. 

The Connoquenessing Sandstone in the lower Pottsville Group is very 

poorly developed or absent over the crest of the Amity anticline at this 

location. Thick Connoquenessing Sandstone is present in the synclines east 

and west of the drill site and Amity anticline axis. 
MISSISSIPPIAN SYSTEM 

Mauch Chunk Formation 

The Mauch Chunk Formation of the Mississippian System is unconformably 

overlain by the Pottsville Group of the Pennsylvanian System. The Mauch Chunk 

Formation ranges from 0 to 300 feet thick regionally. It was encountered at 

1,150 feet inboreholel and at 1,136 feet in borehole 2. Eighty-eight and 

76 feet of Mauch Chunk Formation was penetrated in boreholes 1 and 2, respectively. The formation is characterized by varicolored red, green, and gray 

shales interbedded with some thin argillaceous sandstones and limestones. The 

test holes terminated after penetrating 14 feet into the Wymps Gap Limestone 

Member of the Much Chunk Formation (3). - The Wymps Gap Member is a tan-tobrown fine crystalline limestone. 

FORMATION TESTING 

Mud Analvsis Well Loa 

The mud analysis well log is a formation evaluation tool using gas detection equipment during drilling to locate and evaluate gas-bearing strata. 

Formation gases are circulated to the surface by the drilling medium. They 

are collected in a trap placed in the flow line and analyzed by a hot-wire 

detecting device. 

Drill cuttings are collected during drilling, and a complete lithological 

description is made with the aid of a binocular microscope. The formation 

sample description is made with the aid of a binocular microscope. The formation sample descriptions and drill penetration rates for selected intervals 

are correlated to drill depth. These data are continuously plotted on a log 

(figs. 4-5). Additional engineering and test data such as cored intervals, 

drill stem pressure test intervals, and drill bit records also are recorded. 

Geophysical Log 

Gamma ray logs (figs. 6-7) were used to correlate the strata with other 

holes which had been drilled nearby for exploration and production of gas and 

oil. The gamma ray logging tool measures natural gamma radiation emanation 

from the various rock types encountered in the borehole. A caliper logging 

tool was used to measure the variation in diameter from the bottom to the top 

of the drilled holes. 
DRILLING RATE, GAS 

mm/ft READING 

450- 500 - 

550 - 

600 - 

- 

g650- 

W 0 

700 - 

5-19-74 

BOO 

850 0 3 6 9 

DRILLING RATE, 

mln/ft 

G

REA

FIGURE 4. - Mu

API GAMMA RAY UHTS 

0 80 160 240 320 

6 8 10 Q I4 16 18 20221 

CALIPER SCALE, HOLE 

DIAMETER, in BULK DENSITY CALIPER SCALE, HOLE 

DIAMETER, In 

BULK DENSITY 

API GAMMA RAY UNITS 

CALIPER SCALE, HOLE BULK DE

DIAMETER, in 

FIGURE 6. - Gamma ray-density caliper log of borehole 1. 
API GAMMA RAY UNITS API GAMMA RAY UNITS 

CALIPER SCALE, HOLE 

DIAMETER, in 

BUL

FIGURE 7. - Gamma ray-density caliper log of borehole 2. 
FOEWATION PRESSURES 

Formation pressures were measured by a drill stem test (DST) in which a 

set of formation packers, special valves, and pressure-recording gages are 

introduced into the borehole on the end of a string of drill pipe (4). The 

formation packers are set to isolate a selected portion of the boreEole and 

thereby allow fluids in the isolated zone to enter the drill pipe during flow 

periods. Formation pressures are measured in the isolated zone during shut-in 

periods. The valves allow for timed shut-in and flow periods. Five drill stem 

tests were conducted to determine pressures in four coalbeds encountered in 

borehole 1 (figs. 8-12). Formation pressures and gas and water recovery data 

are shown in table I. 

TABLE I. - Drill stem shut-in pressure tests, borehole 1 

Coalbed 

interval, 

feet 

No. 

Test 

interval, 

feet 

DST 1 

DST 2 

DST 3 

DST 4 

lWater recovery was measured in feet of water in the 

Coalbed 

DST 5 1 726 - 747 

1,048-1,238 

1,128-1,238 

970- 992 

819- 847 

Freeport. . I . 1 { 728- 730 (upper) 

733- 737 (lower) 

Formation 

pres - sure, 

I I 

$rill string when test 

psig 

Mercer... ... 361 

. . .do.. . . . Clarion.. . . . Middle 

Kittanning. 

tools were removed from borehole. 

2 Gas flows were measured at the surface with an orifice meter during the first 

flow period of test. 

3 No gas to surface. 

Water 

in 

drill - 

pipe, 1 

1,135-1,136 

1,135-1,136 

980- 983 

834- 838.5 

NOTES. --Gas flows in tests 1 and 2 are attributed to a 14-foot -thick sandstone 

overlying the 1-foot-thick Mercer coalbed. Pressure in Mercer coalbed 

is assumed to be equivalent to pressure recorded because of close 

proximity of sandstone to the coalbed. Pressure curves and reduced 

flow in test 2 indicate a depleting reservoir of limited volume. 

a Gas, 

f t3/day 

feet 

315 

Gas flow in test 4: 10 feet of water frothed with gas. 

5,890 

Gas flow in test 5: 40 feet of water frothed with gas. 
TIME, min TIME, min 

FIGURE 8. - Pressure chart, drill stem test 1, Mercer FIGURE 9, - Pressure chart, drill 

coalbed interval, stem test 2, Mercer coalbed 

interval, Italicized numbers 

are explained in figure 8, 

400 - - 

N 

C .- 6 

\ 

e 300- - 

C 

W 

OC 

3 

g 200- - 

W 

e 

a i100 - (3 ' '5 - / 

0, 1 Ill I 

0 60 108 790 

78 

TIME, min 

FIGURE 10, - Pressure chart, drill stem test 3, 

Clarion coalbed, Italicized numbers are explained in figure 8, 

0 84 188 

24 118 

TIME, min 

FIGURE 11, - Pressure chart, drill 

stem test 4, Middle Kittanning 

coalbed, ltal icized numbers 

are explained in figure 8, 
N 

.s 300- - 

\ 

D FIGURE 12. - Pressure chart, drill stem test 

W 

u 200- - 5, Freeport coalbed, Itali- V) 

W I J-5 cized numbers are explained g loo- 3: - in figure 8. 

0, i 11 11 1 d 

0 79 170 20 111 TIME, min 

The Brookville coalbed was not tested. Formation pressures for all the 

coalbeds were plotted versus depth and compared with hydrostatic pressures 

(fig. 13). All formation pressures were less than hydrostatic, indicating 

that there are no abnormally high pressures in the coalbed. The formation 

pressures in the coalbeds appear to be controlled by the local piezometric 

water level in each coalbed (5, p. 819). 

600 I I I 1 I I I I I I I I I 

500 - 

400 - Hydrostatic pressure 

N 

E 

. - 

\ 

n 

C 

$300- 

3 

v, 

v, 

W 

[r 

n 

200 - 

- 

0 200 400 600 800 1,000 1,200 1,400 

DEPTH, ft 

FIGURE 13. - Plot of coalbed pressures versus dept he 
GAS CONTENT OF COALBEDS 

During drilling of boreholes 1 and 2, coalbed cores were taken when possible, for analysis by the Bureau of Mines direct method of determining mining 

coalbed gas content (5). When core drilling was done using air as a drilling 

medium, desorption of gas was plotted versus square root of time to graphicallydetermine gas loss between coring and insertion into sample container. 

The coal samples were allowed to desorb to completion at atmospheric pressure. 

Results are summarized in table 2. Proximate analyses were made of the core 

samples of coals to determine the approximate amount of inert mineral matter 

present, which can be roughly equated to ash percentage. The inert mineral 

matter does not adsorb gases (appendix). Gas concentrations for the coals on 

an ash-free basis were calculated for comparative purposes to show relation of 

gas concentration to depth and determine geological factors which could cause 

anomalous low gas concentrations in some coalbeds. 

TABLE 2. - Gas content of coalbeds 

Brookville. ...... { 1 1 2.5 

Freeport: 

Upper bench .... Lower bench .... Middle Kittanning 

Clarion .......... 

Coalbed 

thickness, 

feet 

3,195 

3,143 

2,336 

1,855 

Mercer.. ........ .I 1,888 1 3,110 1 1.6 

I Gas I 

concen - tration 

53 

(ashfree 

basis), 

cm3 / g 

(STP) 

1,516 

5,940 

12,071 

5,505 

l~ercent ash from proximate analysis of coalbed (append 

a~he Pennsylvania Geological Survey reports the Upper Freeport coalbed is variable in composition and may locally be "dirty" (8). - 

Based on thickness, the Freeport, Middle Kittanning, and Clarion are the 

more important coalbeds for gas production in the study area. Differences in 

the gas content of the coalbeds may be due to the depth, physical differences 

in the coals, and sedimentary environmental histories of the individual beds 

(1) 

0.4 

1.8 

5.1 

2.9 

In the Freeport, Middle Kittanning, and lower bench of the Brookville 

beds, where shale roof and floor inhibit gas migration from the coal, the gas 

content increases with depth (table 2). The Clarion, upper bench of the 

Brookville, and Mercer coals have anomalously low gas contents. These coals 

have porous gas-laden sandstone roof rock, or gas-laden sandstone in close 

proximity. Gas from these coals may have migrated into the sandstone, depleting gas concentration in the coalbeds. 

15 

61 

165 

95 
The mineral content of coalbeds reduces their adsorptive capacity. The 

greater the mineral matter content, the lower the gas content per unit weight 

of coal at standard temperature and pressure (STP). 

GAS AND WATER ANALYSES 

Samples of gas and water were taken from the two boreholes and analyzed 

(tables 3 and 4). The gases from the coals in borehole 1 and from the Middle 

Kittanning coalbed in borehole 2 are similar in composition to gases from 

other Pennsylvanian coalbeds. Typically, coalbed gas is high in methane and 

has only trace amounts of higher hydrocarbon gases. One gas sample obtained 

from the Middle Kittanning coalbed soon after stimulation treatment had an 

anomalously high hydrogen and CO, content, which may be due to chemical reactions in the acid in the gelled water used during the stimulation treatment. 

TABLE 3. - Gas sample analyses, percent 

TABLE 4. - Water sample analyses 

Coalbed 

Kittanning, borehole 2l... 

Composite, borehole l2 .... itt tannin^^. .............. 

Water samples from the coalbeds showed a high concentration of dissolved 

solids and salts. 

ND--Not detected. 

l~i~h hydrogen and carbon dioxide percentages in this sample are attributed to 

chemical reactions of the acidic hydraulic stimulation fluid in the borehole. The sample was taken soon after stimulation treatment (sample date, 

March 14, 1975). 

alThis is a composite gas sample from all coalbeds in borehole 1 because all 

coal intervals were perforated to allow for gas flow. 

3~here was some air contamination during sampling (sample date, July 7, 1976). 

C2% 

0.25 

1.8 

.1 

PH. ........................ Alkalinity ............pp m.. 

Dissolved solids ......pp m.. 

Sulfate as SO 4........ppm.. 

Calcium as CaC0 3......ppm.. 

Magnesium as CaCO 3....ppm.. 

Iron ..................pp m.. 

Potassium ............ .ppm.. 

Sodium ................pp m.. 

Chloride.. ............pp m.. 

Hz 

2.3 

.35 

ND 

CsHe 

0.07 

.32 

.04 

CH* 

84.4 

95.8 

80.1 

Composite 

from 

borehole 1 

10 

93 

43,140 

119 

6,318 

692 

0 

8.3 

12,800 

25,200 

Kittanning coalbed, 

borehole 2 

6 

415 

62,700 

115 

2,300 

9,200 

30 

0 

20,000 

36,000 

C4q0 

0.018 

,044 

.006 

02 

1.4 

.2 

3.7 

Cs%2 

0.0035 

.0035 

.0012 

N2 

6.2 

1.5 

14.9 

C02 

5.3 

.004 

1.2 

Co 

ND 

ND 

ND 
HYDRAULIC STIMULATION 

Hydraulic stimulation is a process used to increase fluid flow from a 

formation. Stimulation is achieved by inducing or extending a vertical parting in a selected section of a formation or coalbed by applying hydraulic 

pressure with controlled injection of gelled water or other fluids (2). - 

The Kittanning coalbed in borehole 2 was hydraulically stimulated on 

January 21, 1975, using 30,000 gallons of water premixed with 1,800 pounds of 

M~-T-G~~* and 20,000 pounds of 10- to 20-mesh sand as a propping agent. The 

initial fracture was induced in the coalbed with 4,000 gallons of water containing 60 pounds of WG-6 gel. Following this, the sand-laden My-T-Gel fracturing fluid was injected to extend and prop the fracture. The treatment was 

completed by flushing the sand-laden fluid from the casing. 

The coalbed fractured at 2,400 psig (fig. 14). The average treating 

pressure throughout the job was 1,500 psig at an average injection rate of 

13.2 bbl/min. During the treatment 20,000 pounds of 10- to 20-mesh sand 

proppant was used. A chemical breaker was mixed with the gel to break the 

high viscosity of the fluid for recovery and cleanup of the borehole. The 

instant close-in pressure after treatment was 800 psig; the pressure declined 

to 700 psig in 10 minutes. 

Since treatment, gas and water emissions from borehole 2 have been very 

low (350 to 1,350 ft3/day and 2 to 3 bbl/day water). This is attributed to 

formation blockage by formation water in very small pores, coal fines, and gel 

residue. The breakdown of the gel depends partially upon heat and pressure. 

5,000 I I 1 1 1 I I 

Break formation 

- 

Sand, Ib/gal 

W 

IZ 

a 1,000 .- 

or I 

I I I 1 I I I A 

5 10 15 20 2 5 30 35 40 45 

TIME, rnin 

FIGURE 14. - Hydraulic stimulation pressure and flow charts. 

4Reference to specific products does not constitute endorsement by the Bureau 

of Mines. 
The fact that treatment was done in January during very cold weather with 

cold water in a low-pressure formation suggests that the gel that was squeezed 

into very small pores did not break down easily, and that the pressure was too 

low to move the gel or gel residue from the low-permeable paths. 

SUMMARY 

There are five coalbeds below the Pittsburgh coalbed in the Bruceton 

Station area. Two of these coals, the Upper Freeport and Middle Kittanning, 

are more than 3 feet thick and are at minable depths. During the Bureau's 

studies the coalbed formation gas pressures were less than hydrostatic for the 

depth of the coalbeds. 

The gas content of the coalbeds ranged from 15 to 165 ft3/ton--the 

Kittanning coalbed having the highest. The gas content of the coalbeds is 

affected by its mineral content, which reduces its adsorption capacity. 

Migration of gas to porous sandstones in close proximity to some of the coalbeds (Clarion, Brookville, and Mercer) may also be a cause of the lower gas 

content obsewed in these coals. 

Hydraulic stimulation with very heavy gelled fluid was not effective in 

increasing gas flow for degasification. Production rates of water were very 

low, indicating blockage by gel residue and fine coal particles, and water 

production averaged only 2 to 3 bbl/day. Gas production fluctuated from 

350 to 1,350 ft3/day during extended production intervals ; such fluctuations 

usually result from changes in water production due to pump stoppage. 
REFERENCES 

Bertard, C., B. Bruyet, and J. Gunther. Determination of Desorbable Gas 

Concentration of Coal (Direct Method). Internat. J. Rock Mech. and Min. 

Sci., v. 7, July 1970, pp. 43-65. 

Elder, C. H., and M. Deul. Hydraulic Stimulation Increases Degasification 

Rate of Coalbeds. BuMines RI 8047, 1975, 17 pp. 

Flint, N. K. Geology and Mineral Resources of Southern Somerset County, 

~ennsylvania. Pa. Geol. Survey Bull. C56a, 4th series, 1965, pp. 39-96. 

Johnston Testers. Practical Drill Stem Testing Manual. 73 pp. 

Kissell, F. N., C. M. McCulloch, and C. H. Elder. The Direct Method of 

Determining Methane Content of Coalbeds for Ventilation Design. BuMines 

RI 7767, 1973, 17 pp. 

Thrush, P. W. (ed. and comp.). A Dictionary of Mining, Mineral, and 

Related Terms. Bureau of Mines, 1968, 1269 pp. 

Wagner, W. R., and W. S. Lythe. Stratigraphic Framework of the Greater 

Pittsburgh Area, Parts 1 and 2. Pa. Geol. Survey, unpublished open 

file report; available for consultation at Pittsburgh office of the 

Pennsylvania Geologic Survey. 

Wagner, W. R., L. Hegman, R. E. Gray, D. J. Belz, R. Lund, A. S. Cote, and 

C. D. ~dgerton. Geology of the Pittsburgh Area. Pa. Geol. Survey 

General Geology Rept. G59, 1970, 145 pp. 
APPENDIX.--ULTIMATE AND PROXIMATE COAL ANALYSES 

I As received I Moisture free I Moisture and 

I I ash free 

CLARION BED 

Proximate analysis, percent: 

Moisture ................................ Volatile matter......................... 

Fixed carbon............. ............... Ash.. ................................... Ultimate analysis, percent: 

Hydrogen ................................ Carbon............................. ..... Nitrogen ................................ Sulfur. ................................. Oxygen (indirect) ....................... Ash..... ................................ Heating value .................. ...~tu/lb .. 

MIDDLE KITTANNING BED 

Proximate analysis, percent: 

Moisture. ............................... Volatile matter......................... 

Fixed carbon ............................ Ash... .................................. Ultimate analysis, percent: 

Hydrogen ................................ Carbon .................................. Nitrogen ................................ Sulfur .................................. Oxygen (indirect) ....................... Ash.. ................................... Heating value ..................... ~tu/lb.. 

1.3 

29.8 

44.4 

24.5 

4.3 

61.5 

1.0 

2.5 

6.2 

24.5 - 

FREEPORT BED - -UPPER BENCH 

1.1 

36.5 

50.0 

12.4 

4.9 

70.7 

1.1 

7.3 

3.6 

12.4 - 

NAP 

30.2 

44.9 

24.9 

4.2 

62.3 

1.0 

2.5 

5.1 

24.9 - 

Proximate analysis, percent: 

Moisture ................................ Volatile matter......................... 

Fixed carbon... ......................... Ash.... ................................. Ultimate analysis, percent: 

Hydrogen ................................ Carbon.......... ........................ Nitrogen ................................ Sulfur.. ................................ Oxygen (indirect) ....................... Ash.. ................................... Heating value ..................... ~tullb.. 

NAP 

40.2 

59.8 

NAP 

5.6 

82.9 

1.4 

3.3 

6.8 

NAP 

14,838 

NAP 

36.9 

50.6 

12.5 

4.8 

71.5 

1.1 

7.4 

2.6 

12.5 - 

1.7 

17.6 

16.9 

63.8 

2.5 

25.2 

.5 

1.9 

6.2 

63.8 - 

NAP 

42.2 

57.8 

NAP 

5.5 

81.7 

1.3 

8.5 

3.0 

NAP 

15,092 

FREEPORT BED - -LOWER BENCH 

NAP 

17.9 

17.2 

64.9 

2.3 

25.6 

.5 

2.0 

4.8 

64.9 - 

NAP 

51.1 

48.9 

NAP 

6.6 

72.9 

1.4 

5.6 

13.6 

NAP 

12,620 

Proximate analysis, percent: 

Moisture........................... ..... Volatile matter......................... 

Fixed carbon....... ..................... Ash... .................................. NAp --Not applicable. 

NAP 

21.1 

24.8 

54.1 

1.6 

20.7 

24.5 

53.2 

NAP 

46.0 

54.0 

NAP 
Moisture and 

ash free 

As received Moisture free 

Nitrogen ............................... Sulfur .................................. Oxygen (indirect) ....................... Ash ..................................... 

I I I ... -.. 

FREEPORT BED-- LOWER BENCH.. Continued 

Heating value .................... : ~tullb .. I . 1 . 13, 632 

BROOKVILLE BED -.-UPPER BENCH 

Proximate analysis. percent: 

Moisture ................................ Volatile matter ......................... Fixed carbon ............................ Ash ..................................... Ultimate analysis. percent: 

Hydrogen ................................ Carbon .................................. Nitrogen ................................ Sulfur ................................... Oxygen (indirect) ....................... Ash ..................................... 

5.9 

77.4 

Ultimate analysis, percent: 

Hydrogen ................................ Carbon .................................. 

Moisture ................................ Volatile matter ......................... Fixed carbon ............................ Ash ..................................... Ultimate analysis. percent: 

Hydrogen ................................. Carbon .................................. 

2.9 

34.9 

Heating value ..................... ~tu/lb .. I . . I 15, 391 

BROOKVILLE BED . -LOWER BENCH 

Nitrogen ................................ Sulfur .................................. Oxygen (indirect) ....................... 

2.9 

35.5 

Proximate analysis. percent: 

Ash ..................................... 

I 

Heating value ..................... ~tu/lb .. I . . I 13, 140 

MERCER BED 

Proximate analysis. percent: I I I 

Moisture ................................ Volatile matter ......................... Fixed carbon ............................ Ash ..................................... Ultimate analysis. percent: 

Hydrogen ................................ Carbon .................................. Nitrogen ................................ Sulfur .................................. Oxygen (indirect) ....................... Ash ..................................... Heating value ..................... Btu/lb .. I . I . 14. 831 

NAp . -Not applicable .