Bureau of Mines Report of Investigations/l97'7 

Directionally Controlled Drilling 

THillISld 
Report of Investigations 8231 

Directionally Controlled Drilling 

To Horizontally Intercept Selected 

Strata, Upper Freeport Coalbed, 

Greene County, Pa. 

By William P. Diamond, David C. Oyler, and Herbert H. Fields 

CONTENTS 

Paee 

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

Introduction ..... ..................,..................................... 1 

Acknowledgments .......................................................... 2 

Drilling program ....................................................... 2 

General drilling plan .............................................. 2 

Equipment and site layout ........................................... 2 

Geologic factors controlling direction of drilling ....................... 4 

Description of Dyna-Drill .............................................. 8 

Directional control using the Dyna-Drill ................................. 9 

Sperry-Sun single-shot surveying techniques .............................. 9 

Calculation of single-shot surveys, dogleg severity, and well projections 10 

Single-shot survey calculation .................................... 10 

Dogleg severity calculation ..................................... 11 

Method of choosing a slant hole projection .......................... 12 

Problems encountered ................................................. 13 

Coal thickness ...................................................... 13 

Mechanical problems .................................................. 16 

Environmental protection ........................................ 16 

Cost analysis .............................,.............................. 17 

Conclusions and recornendations . ........................................ 20 

References ........................................................... 21 

ILLUSTRATIONS 

Plan view of equipment layout at drill site .......................... 3 

Plan view of drill site and underground workings in the Pittsburgh 

coalbed ............................................................ 5 

Section view of proposed slant hole well path with geologic column ... 6 

Section view of actual well path drilled ............................. 7 

Dyna-Drill tool assembly ............................................. 8 

Geometry of single-shot survey and dogleg angle cal.culations ......... 10 

Plan view of drill paths with coal thicknesses of Freeport horizon 

intercepts and nearest corehole .................................. 14 

Plan and section views of drill paths with portion drilled through 

Freeport horizon ................................................... 15 

Plan and section views of sidetracks above the Freeport coalbed ...... 17 

TABLE S 

1 . Definitions of terms used in single-shot survey and dogleg severity 

calculations ....................................................... 11 

2 . Project cost breakdown ........................................ 18 

3 . Breakdown of major item lost-time cost ............................... 19 
DIRECTIONALLY CONTROLLED DRILLING TO HORIZONTALLY 

INTERCEPT SELECTED STRATA, UPPER FREEPORT 

COALBED, GREENE COUNTY, PA, 

by 

William PB Diamond, David C. Oyler, and Herbert Ha Fields3 

ABSTRACT 

A 3-inch pilot hole was directionally drilled to intercept the Freeport 

coalbed horizon horizontally at Mather, Pa., as part of a Bureau of Mines 

degasification project. The original concept was to continue the horizontal 

drilling into the coalbed, after the initial intercept, with a total of three 

horizontal holes eventually being completed. However, the erratic thickness 

(0.0 to 4.3 feet) of the Freeport coalbed at Mather was not sufficient to support the horizontal drilling degasification technique, and the site was abandoned after six attempts to locate adequate continuous coal thicknesses. The 

drilling of coreholes in the immediate vicinity of proposed well paths to 

evaluate coal thickness is essential prior to future slant hole operations. 

Although mechanical failures of the new directional drilling equipment, 

mud pump and rig breakdowns, directional control problems, and exploratory 

horizontal drilling in the Freeport horizon more than doubled the anticipated 

cost of the pilot hole, continuing improvements in directional drilling equipment and techniques should significantly reduce the time and costs of future 

drilling operations. 

INTRODUCTION 

The Bureau of Mines in its continuing research in coalbed degasification 

is currently evaluating directional drilling techniques for methane drainage 

of large areas from a single surface location. Large quantities of methane 

gas are expected to be drained from coalbeds using this technique. The 

Freeport coalbed at a site near Mather, Pa., was selected for this research 

drilling project since desorption of coal cores in sealed canisters indicated 

that over 200 cu ft of methane per ton of coal is present in the Freeport 

coalbed at depths of 1,000 feet. 

l~eologist. 

2~eneral engineer. 

3~ining engineer. 

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

Bureau of Mines, Pittsburgh, Pa. 
The Freeport coalbed has not been mined in the area of the research site, 

but mining operations are planned for the future. The purpose of this 

research was to provide information on the use of directional drilling techniques for degasification in advance of mining for both mine safety and energy 

resource utilization. This report details the equipment specifications, 

drilling technology, and cost of the slant hole to the Freeport coalbed. An 

evaluation of the geologic factors that necessitated the abandonment of the 

initial research site after reaching the Freeport coalbed horizon is included, 

and precautions for future site selection are given. 

ACKNOWLEDGMENTS 

The authors greatly appreciate the cooperation of the Jefferson-Morgan 

Mining Co., a division of Jones & Laughlin Steel Corp., Mather, Pa.; DynaDrill Co., Long Beach, Calif.; Sperry-Sun, Houston, Tex.; Paramount Exploration, Inc., Waynesburg, Pa.; and Bob Croom, Inc., Lafayette, La., for helping 

make this work possible. Many individuals, too numerous to mention, were 

especially helpful, but we acknowledge posthumously the devotion and professional concern exhibited by Ken Austin, the late president of Paramount 

Exploration, Inc., who for the last 5 years of his life was deeply involved in 

the technical aspects of producing gas from coalbeds. 

DRILLING PROGRAM 

General Drilling Plan 

The Freeport coalbed horizon was known to be approximately 930 feet below 

the surface at the drill site. A drill path was calculated which, starting 

with a 5" tilt of the rig and 6" deviation per 100 feet of drilled depth, 

would intercept the coalbed horizontally. A 3-inch pilot hole was to be 

drilled to the Freeport coalbed and 50 feet horizontally into the coalbed with 

a 2-3/8-inch ~~na-~rill.~ Standard BQ drilling rod was used with a 60-foot 

section of stainless steel rod just above the Dyna-Drill tool. The nonmagnetic rods are necessary for directional surveying. 

The initial hole was to be reamed to a 10-inch diameter using a stinger 

extending 2-1/2 feet beyond the d r i l l b i t to keep the hole on course. Seveninch casing was to be cemented in place to just above the coalbed. From the 

bottom of the casing, the pilot hole would be underreamed to a 10-inch diameter for a horizontal distance of 50 feet. From this large hole, at least 

three individual 3-inch holes were to be drilled at various angles to a depth 

of approximately 3,500 feet into the coalbed. 

Eaui~ment and Site Lavout 

A hydraulically operated Reed Exploratory rotary drill was used on this 

hole. The drilling assembly was mounted on an International Harvester 

model F2010A truck with a 208-inch wheelbase. The mast height was 45 feet 

4~eference to specific equipment, trade names, or manufacturers does not imply 

endorsement by the Bureau of Mines 
with the hydraulic cylinders retracted and 79 feet when fully extended. The 

rear-end loader was capable of handling 30-foot lengths of drill pipe. Hoist 

capacity was 70,000 pounds, and pulldown capacity was 26,000 pounds. Power 

was provided by a Cumins NT855-P380 diesel engine developing 380 bhp at 2,100 

rpm. A Grimmer Schmidt 903-82 air compressor rated at 660 cfm at 100 psi and 

575 cfm at 210 psi also was mounted on the rig. 

The hole was drilled with Baroid's Dextrid colloidal, organic, polymer 

mud. The Dextrid additive produces a mud with a very low filtration rate, 

from 6 to 13 ml per 30 min, averaging about 8 ml per 30 min, which aids in 

shale stabilization. A red shale section approximately 300 feet above the 

Freeport coalbed is particularly troublesome, causing frequent drilling 

Townsh~@ rood 
problems due to swelling and sloughing of the shale. Mud weights typically 

ranged between 8.3 and 8.4 lb/gal. The funnel viscosity (1,000 cu cm) ranged 

from 30 to 33 sec. No hole problems were encountered with the mud system used 

during the 4-1/2 months of drilling operations. 

The fenced-in drill site is approximately 165 feet wide and 180 feet deep 

for a total area of about 30,000 sq ft. Figure 1 shows the placement of the 

drill rig, mud pit and pump, supply and office trailers, and other equipment 

necessary for the drilling operation. The drilling area was surrounded by a 

6-foot-high, chain-link fence as a safety precaution since the site is near a 

residential area. Adequate lighting was provided for night drilling operations. The drill rig and mud pump were enclosed with plywood buildings to 

reduce noise levels during drilling. 

GEOLOGIC FACTORS CONTROLLING DIRECTION OF DRILLING 

The direction of drilling for the slant hole and subsequent horizontal 

holes was dependent upon geologic factors. The Freeport coalbed does not 

maintain a constant thickness in the area of the drill site, varying from no 

coal to nearly 8 feet. It is desirable to drill the horizontal holes in the 

thickest and least variable parts of the coalbed. This will aid in keeping 

the advancing horizontal holes in the coalbed and out of the surrounding 

strata. Also, the greatest amount of coal will be subject to degasification 

in the thicker parts of the coalbed. 

Before the start of the drilling project, corehole data in the immediate 

vicinity of the drill site indicated that the freeport coalbed thins in the 

northwest, northeast, and southeast quadrants, and is thickest in the southwest quadrant. The area of the thickest coal (greater than 5 feet) was presumed to be located between S 4" W and S 85" W, with the surface location as 

the origin. 

A critical factor for maximum gas flow from coalbeds is the cleat system. 

Degasification experiments conducted underground in coal mines (5) have shown 

that horizontal holes drilled perpendicular to--and therefore intersecting the 

largest number of--face cleats will yield 2.5 to 10 times more gas than holes 

drilled perpendicular to the butt cleat. The underground mine nearest to the 

drill site is the Gateway mine, operating in the Pittsburgh coalbed, approximately 600 feet above the Freeport. The face cleat measured in this mine 

strikes at N 68" W (7). Recent investigations by the Bureau of Mines (8) indicate that cleat systems maintain similar orientation throughout a vertical 

section at one location. Therefore, it was assumed that the face cleat in the 

Freeport coalbed would be near N 68" W. Taking into account the thickest coal 

in the southwest, and the desirability of penetrating the coalbed as nearly 

perpendicular to the face cleat as possible, the initial hole was drilled 

S 13" W. 

Sunderlined numbers in parentheses refer to items in the list of references at 

the end of this report. 
Two important factors in selecting a surface location for the hole were 

the presence of abandoned mine workings in the Pittsburgh coalbed beneath the 

site and environmental considerations. Figure 2 is a map of the drilling 

location with the underground passageways and coal pillars superimposed. It 

was essential to drill through a solid block of coal and not through a minedout area. Encountering a mined-out area would have resulted in a loss of 

expensive drilling fluids and would have necessitated cementing to fill the 

void, reaming a larger hole, and setting a string of casing through the coalbed, or else redrilling the hole from a different surface location. Either 

alternative would entail lost time and added expense. 

The southern portion of the location is heavily wooded and bounded by an 

80-foot cliff into Tenmile Creek. To minimize the effect of drilling operations on the environment, the surface location was placed on the unforested, 

northern portion of the site. The horizontal displacement of the proposed 

well path at the anticipated depth of the Pittsburgh coalbed was calculated to 
NOTES 

Fcwmm~on data ore from0 core hole approxlmotely 1.000ft from the 

drilling stte 

Well plot assumes Sosurface dev~otlon of dr~ll r~g 

6- per DO-11 devmlmn Plot based upon 1004t statlons w~th 

stra~ght-l~ne segments between statlons 

I I 

400 500 600 700 800 900 1,000 1.100 

DISTANCE, 11 

lant hole well path with geologic column. 
be approximately 90 feet (fig. 3). The center of the large block of coal, 

approximately 140 feet south of the northwest corner of the location, was 

chosen as the target in the Pittsburgh horizon. The prime surface location 

then was determined to be along N 13' E to S 13' W from the center of the 

block of coal and at a horizontal distance of 90 feet (fig. 2). The pilot 

hole was drilled with slightly less deviation than expected in the top section, 

but the block of coal was encountered at a vertical depth of 333 feet (597 

feet above sea level) and 70 feet from the surface location (fig. 4). 

5" 

! 

TL~ilt ondrill rig 

0 I I I I I I 1 I I I I 

I \Surface elevotion 930.33 ft 

I I 

NOTE: MD'measured depth from surface,ft - 

- 

- 

~Pittsburgh coalbed 

with enlries 
DESCRIPTION OF DYNA -DRILL 

To drill a hole from a near vertical position at the surface and intercept a coalbed horizontally nearly 1,000 feet below requires the use of 

special drilling techniques. To achieve directional control, a Dyna-Drill was 

selected. The Dyna-Drill tool (fig. 

Bent housing and 

connecting rod assembly 

- 

- 

- 

I l- Bearing and drive 

shaft assembly 

Nonmagnetic 

drill rod 

- Muleshoe subassembly 

b-,Rotating bit subassembly 

a- Diamond plug bit 

5) is essentially a positive displacement 

mud motor encased in a housing and 

attached to a drill bit. The drill bit 

is driven by the downhole motor without 

drill pipe rotation. Because the drill 

pipe does not turn, it is possible to 

orient the drill pipe and the attached 

Dyna-Drill tool to control the direction 

of penetration. 

A 2-318-inch Dyna-Drill with a 

3-inch Christensen NX diamond plug bit, 

style D-41, was used during routine 

drilling of the pilot hole. A specially 

designed diamond sidetracking bit was 

used when sidetracking was necessary. A 

mud pump pressure of 400 to 600 psi was 

normally required to start the mud pump 

motor in the Dyna-Drill tool when on the 

bottom. Occasionally, pressures as high 

as 1,000 psi were required for new 

assemblies. A 300-psi mud pressure differential over the off-bottom operating 

pressure at 25-gpm flow rate is ideal 

for maximum control and penetration. 

Larger Dyna-Drill tools are available which would eliminate reaming the 

pilot hole. A larger Dyna-Drill was not 

used because of the greater difficulty 

in controlling angle of deviation, which 

is very critical in the drill path 

needed to intercept the coalbed horizontally. The rental cost of the larger 

Dyna-Drill also is much higher, making 

it prohibitively expensive for projects 

of long duration. 

Several subassemblies on the DynaDrill tool must periodically be changed 

because of wear which could cause malfunctions. The bearing and U- joint 

packages must be changed after about 100 

hours of use. Improvement of these 

assemblies may extend their inhole operating time. The motor assembly normally 

FIGURE 5. - Dyna-Drill tool assembly, 
can run 500 to 600 hours or more, depending on how free of extraneous matter 

the drilling fluid is. There was no indication of wear on the motors used on 

this project. This probably was due to the low solids content and general 

high quality of the drilling mud used. 

DIRECTIONAL CONTROL USING THE DYNA-DRILL 

The amount of deviation achieved by thelDyna-Drill can be varied by using 

either interchangeable bent subs or housings of various angles. Bent housings 

of 30 and 45 minutes were used on this hole. The higher the sub or housing 

angle, the greater the amount of deviation. A standoff ring also can be 

incorporated as part of the tool above the bent assemblies to hold the tool 

slightly off the bottom on the low side and thereby increase the penetration 

angle. The deviation was primarily controlled by varying the bit pressure: 

The higher the bit pressure, the greater the amount of deviation. The changes 

in bit weight were read at the surface as changes in mud pressure. Using bit 

weights to control angle also affected penetration rates. In formations such 

as shale, where a tendency to build angle at too great a rate was experienced, 

lowering the bit pressures produced a decrease in penetration rate. Penetration rates in sandstone and limestone were not affected as severely by changes 

in bit pressure. 

Azimuth control of the pilot hole was not as critical as the angle of 

inclination, but for side tracking and drilling multiple horizontal holes in a 

coalbed from the bottom of a single slant hole, it did become important. Control of azimuth was obtained by turning the bend in the bent housing to the 

left or right. This technique of azimuth control was also tried as a method 

to slow the rate of increase of inclination, but was found to be of little 

value. 

SPERRY -SUN SINGLE -SHOT SURVEYING TECHNIQUES 

To determine the exact position of the advancing slant hole, Sperry-Sun 

single-shot surveys were made every 10 feet of measured depth. These surveys 

provided data to calculate the direction of penetration, the true vertical 

depth, and the coordinates of the survey point. These data, in conjunction 

with the proposed drill path plot (fig. 3), were used to determine what DynaDrill subassemblies, mud pressures, and tool orientation were used to maintain 

the proper well path. 

The single-shot survey system consisted of a wire line instrument package 

and a drill pipe subassembly (mule-shoe sub) attached just above the DynaDrill tool. The instrument package was lowered to the bottom of the hole 

through the drilling rod. Inside the instrument package were a directional 

compass and a lens and lamp system, whichmadea permanent photographic record 

of the true magnetic directions and the inclination of the hole. The actual 

survey point was above the bottom of the hole since the Dyna-Drill tool was 

about 9 feet long and the survey tool fit into the mule-shoe sub directly 

above the Dyna-Drill. To remove the extraneous magnetic effect of regular 

drill rods, it is necessary to use stainless steel or aluminum pipe. Sixty 

feet of stainless steel BQ rod was used above the mule-shoe sub. 
The lens system which produced the photographic record was set off by a 

hand-wound, mechanical clock. The clock can be set with a delay of up to 

1 hour. Clocks with 30-minute and 2-hour delays also are available. Normally 

a 10-minute delay is sufficient to lower the survey instrument to the bottom. 

As the angle of the hole reached about 55" to 65O, it became necessary to pump 

the survey tool to the bottom of the hole due to the friction against the 

inside of the drill rod. A pump-down stuffing box was attached to the top of 

the drill rod for this procedure. This assembly has a connection for the mud 

line and a small hole in the top through which the wire line of the survey 

tool passes. 

CALCULATION OF SINGLE -SHOT SURVEYS, DOGLEG SEVERITY, 

AND WELL PROJECTIONS 

Single -Shot Survev Calculation 

The single-shot surveying tool gives a reading of the well position in 

terms of an inclination angle 8, , a bearing angle QB , and a drilled length AL 

(fig. 6). These values are trigonometrically broken up into two sets of components: ALat and ADEP; ATVD and AVS. The sum of these values from all previous surveys of the hole gives the new hole position. The latitude and 

departure then give the bottom-hole position in a plan view, and the vertical 

section and true vertical depth give posltion in a cross section along the projected path of the well. The equations for calculating components are given 

with their definitions in table 1. 

The tangential method was used on this project for calculation of the 

single-shot surveys. More complex methods may be used to calculate hole 

SINGLE-SHOT SURVEY 

1 

DOGLEG ANGLE 

FIGURE 6. - Geometry of single-shot survey and dogleg angle calculations. 
position. For instance, the drilled distance may be more accurately approximated as the arc of a circle. At short surveying intervals as used here, the 

inaccuracy caused by using the sum of a large number of triangles becomes 

negligible . 

TABLE 1. - Definitions of terms used in single-shot survey 

and dogleg severity calculations 

Term Definition 

Projected well azimuth planned for the well. Given in 

degrees E or W of N or S. 

Azimuth actually drilled along. Obtained from the singleshot reading. Given in degrees E or W of N or S. 

Inclination of the hole with the vertical. Obtained from 

the single-shot survey. Given in degrees. 

AL Length drilled between surveys. Given in feet. 

Vertical section Horizontal distance drilled parallel to the projected 

well path. Bearing of this line is 0,. 

Latitude Total distance drilled N or S of the surface location. 

Departure Total distance drilled E or W of the surface location. 

True vertical depth Total vertical distance drilled from the surface. 

Projection on the horizontal of the drilled distance. 

HP = ALbSINB, 

ATVD Vertical distance drilled in QL feet. ATVD = AL*COSQl 

ADEP 

AVS 

Distance drilled E or W of NS line in AL feet. 

~DEP = [~L.SIN~, ] [SINQ, 3 

Distance drilled N or S of an EW line in AL feet. 

ALat = [AL~SINQ,] -[COSQ, ] 

Vertical section distance drilled in AL feet. 

AVS = [AL*sIN~,] [COS(Q,-o,)] 

8 D Dog leg angle . 

Dogleg Severity Calculation 

The rate of change in angle is important because if this rate of change 

is too large, it may not be possible to run casing in the hole. The dogleg 
angle 8, (fig. 6) is measured from both the change of inclination and the 

change of bearing between two points. 

The following equation is used to calculate dogleg severity between two 

points : 

This formula gives the dogleg angle over a distance equal to AL(AL=ALl=AL2) 

because it represents the change in angle from point A_ to point B (fig. 6) 

The accuracy of the single-shot survey computations must be quite high. 

If only two-place accuracy were used, the cosine value might be greater than 

one. This is obviously incorrect since the cosine function varies from -1 to 

+l. This is one reason why it is convenient to use a small computer or calculator for these computations. It gives accurate values of 8, with much 

greater ease and speed than can be obtained from either hand computation or 

tables. Tables of dogleg values are available, although the table known to 

the authors reads only to deviations of 65". 

It is important that the dogleg be kept within the maximum deflection 

angle of the casing to be run. Over a short interval of severe dogleg, it is 

possible to ream the hole to run casing despite a dogleg greater than the maximum allowable deflection. However, the necessary diameter of the reamed hole 

increases rapidly even with small angle differences. 

Method of Choosing a Slant Hole Projection 

Before the start of drilling, it is necessary to construct a projected 

well path from the surface to the target horizon (fig. 3). This "ideal" path 

is then used as a guide for the actual drilling. The most desirable well path 

is a circular arc from the surface to the coalbed. A well path of this geometry will minimize dogleg angles. It also allows drilling to shallower target 

depths than any other well path. 

For a circle, the angle subtended by a particular arc is-- 

where A~/AL = central angle subtended by an arc of AL feet, 

AL = arc length (a drilled distance AL), 

TD = radius of a circle (the vertical distance from the coalbed to 

the surface), 

and 

180 

-- - conversion factor--radians to degrees. 
The expected vertical depth to the Freeport coalbed (TD) at Mather, Pa., 

was 928 feet, and the arc length (AL) was set for convenience at 100 feet. 

The equation then gave the change of inclination per 100 feet (~/AL) as 6.17". 

Because of possible problems in running casing in holes with large dogleg 

angles, Ao/AL was set at 6" per 100 feet to minimize the problem. This meant 

that the initial hole could not be started vertically at the surface and still 

allow the well path to reach the target. The drill rig was designed to work 

at angles up to lo0. Surface angles from 0" to 10" were mathematically tested 

to determine the proper angle of the initial hole. An angle of 5" at the surface was found to be sufficient. 

The well path projections were made using the same calculations as were 

used for the single-shot surveys, except that AL was set at 100 feet, A0 was 

set at 6", and 8, was set at 0". The horizontal projection points were then 

plotted, and straight lines were drawn between them to complete the proposed 

well path. 

PROBLEMS ENCOUNTERED 

Coal Thickness 

The major problem encountered, which eventually led to the abandonment of 

the slant hole drilling project at Mather, Pa., was the extremely erratic 

thickness of the Freeport coalbed. Corehole data available before the start 

of drilling indicated that the thickness of the Freeport coalbed was erratic 

in the northwest, northeast, and southeast quadrants surrounding the drill 

site. The coalbed in these quadrants ranged in thickness from no coal to 

nearly 8 feet. Seven coreholes within the prime drilling confines of S 4" W 

to S 85" W, and at distances of 1,300 to 22,000 feet from the surface location 

of the slant hole, indicated 5.9 to 8.5 feet of Freeport coalbed. The first 

slant hole penetration of the Freeport horizon was only about 750 feet away 

from a corehole (fig. 7), which indicated a thickness of 6.75 feet of coal. 

However, less than 0.5 foot of coal (No. 1, figs. 7-8) was encountered on the 

first slant hole penetration. 

The first penetration of the Freeport horizon was plugged back, and a 

second attempt to drill into the coalbed was made with a shift of the drill 

path to the west to intercept the coalbed closer to the corehole containing 

6.75 feet of coal. This second hole intercepted less than 0.4 foot of 

Freeport coal (No. 2, figs. 7-8), at a distance of 690 feet from the corehole. 

Drilling on this hole continued with the well path (fig. 8, top) dipping 

almost 8 feet below the initial contact with the coalbed, and no additional 

coal was encountered. The well path was controlled back up through the elevation of the original intercept and 11 feet above, with no coal encountered 

(No. 3, figs. 7-8). The final bottom-hole location of this hole was 386 feet 

out from the initial intercept and only about 520 feet from the nearest corehole (fig. 7), which had 6.75 feet of coal. 

The third hole into the Freeport horizon encountered 3.4 feet of coal 

(No. 4, figs. 7-8). However, control problems with the Dyna-Drill resulted 

in intercepting the coalbed at too steep an angle to permit reaching a 
I 

-Pittsburgh coalbed 

Total vertical distance= 334 fl 

- 

- 

- 

KEY I I 

1 

= point of intersection with Upper Freeport horizon -750 ft I I I 

<0.5ft,etc= t hickness of Upper Freeport coal, ft I I I I 

MD=measured depth from surface,ft 

No. I ' chronological order of penetration 

of Upper Freeport coal 

1,1001 I I I I I 1 I I I I 1 I I I 1 

0 100 200 300 400 5CO 600 700 800 900 1,000 1,100 1,200 1,300 1,400 

LATITUDE, ft 

FIGURE 7. - Plan view of drill paths with coal thicknesses of Freeport horizon intercepts 

and nearest corehole. 

horizontal drill path at the coalbed horizon within any reasonable horizontal 

distance. This hole was abandoned and another sidetrack begun with the intent 

of reentering the Freeport as close to the previous penetration as possible, 

but with a horizontal drill path that could be continued in the coalbed. 

Control problems were again encountered with the Dyna-Drill on the next 

attempt to enter the coalbed horizontally. This was partly due to an attempt 

to use a new 2' bent sub in place of the bent housing. This sub could not 

build angle and was replaced with the 45-minute bent housing. It would have 

been desirable to shift this drill path still farther west than the previous 

holes; however, the problems with attempting to reach a horizontal attitude 

precluded controlling the azimuth of the hole. The well path entered the 

coalbed at a shallower angle than the previous attempt, but still not close 

enough to horizontal to remain within the 4.3 feet of coal (No. 5, figs. 7-8) 

encountered. The well path dipped 13 feet below the top of the coal before it 

could be brought to horizontal and controlled back to the depth of the initial 
560ioo 710 7810 810 8bo 9bo 9j0 9A0 I,O:O I,O~O I,I~O 1,1410 IJ~O 1,210 pbo 13bo 

A 

1,340 1.380 

LATITUDE, ft 

I I 

4 

240 - - 

280 - - 

320 - 4 

W 

[L 

360 - 4 

Q -, No6 

a . . W 

n '9 1,853MD 400 - KEY - 

No I= chronolog~col order of penetrotlon of Upper Freeport horlzon 

-----= section dr~lled through Upper Free port hor~zon 

440 - MD=neosured depth from surface location,ft 

480 - 

- 1,916MD - 

- 

- - 

Sect~on view 

520 

980 I 1 1 I 1 I I I I I I I I I I 1 

700 740 780 820 860 900 940 980 1,320 1,060 1,100 1,140 1,180 1,220 1,260 1,300 1,340 1,380 

Vert~cal exaggerat~on X2 HORIZONTAL DISTANCE, ft 

', No 3 

- 

Plan vlew '\ 1,916MD 

FIGURE 8, - Plan and section views of drill paths with portion drilled through Freeport 

horizon, 

penetration. The hole was continued to a point 390 feet beyond and 1 foot 

above the initial penetration of the coalbed; again no coal (No. 6, figs. 7-8) 

was encountered. At this point, it was decided that the Freeport coalbed at 

the Mather, Pa., location was too erratic in thickness to support the slant 

hole drilling technique for degasification in advance of mining. The hole was 

subsequently plugged and abandoned. 
Mechanical Problems 

Several mechanical problems adversely affected the timely and economical 

completion of the pilot hole. Completion time of the pilot hole was 126 

24-hour days, of which 38 days were downtime. An additional 9 days were lost 

for holidays, primarily at Christmas and New Year. Twenty days of the mechanically related downtime was encountered with failures of the new Dyna-Drill 

tool size designed for this type of drilling. Sufficient field testing of the 

new tool was not possible before the start of the project. The Dyna-Drill 

problems were mainly failures of shafts and U-joints. Spare parts for the new 

tools were in short supply until late in the project. 

The d r i l l r i g was also newly modified for slant hole drilling and was 

essentially untested before being used on the project. Downtime directly due 

to the mechanical problems with the rig was 5 days. 

Mud pump problems resulted in the loss of 3 days of drilling time. The 

first pump used was a small, belt-driven Bean triplex pump which was thought 

to be contributing to the Dyna-Drill failures by not maintaining the proper 

mud flow. Larger chain-driven mud pumps were then used, but they experienced 

many mechanical breakdowns, probably partly due to their age. (A new mud 

pump was ordered 11 months before the beginning of the project, but the backlog of orders precluded delivery when needed.) 

Significant delays were encountered in the pilot hole drilling owing to 

the difficulty in maintaining the proper well path. These directional delays 

were in addition to those experienced at the coalbed horizon. On three occasions, between vertical depths of 860 and 880 feet, the actual well path deviatedfromthe proposed well path to the extent that corrective measures would 

not bring the hole back on target in time to intersect the coalbed horizontally. 

These situations required the setting of a cement plug through the incorrectly 

drilled zone so that the hole could be sidetracked at a point that would continue the well path at the proper angle. The three sidetracks are shown in 

cross section and plan view in figure 9. 

A total of 23 days was lost during the sidetracking operations. Extra 

time was lost due to problems with the cement failing to harden properly. The 

first plug was made with a cement grout which was allowed to set 24 hours 

before attempting to sidetrack. When this plug failed to harden, several combinations of cements and additives were tried before a solid plug was obtained. 

The final mix used was 1 part Hi-Early cement with 2 parts sand, 3 pct CaC1, 

and 1 pct Gel-flake to achieve a 28-second flow grout. This mixture was 

allowed 36 hours to harden before sidetracking. 

Environmental Protection 

A problem that did not result in lost time but did result in extra 

expenditures was the excessive noise during night drilling, which disturbed 

the nearby residents. Sound-baffling enclosures were constructed around the 

d r i l l r i g and the mud pump, and a water baffle chamber was attached to the 

drill rig exhaust system. These measures significantly reduced the noise 
100 - 1 I I I I 

1,003MD 

f 

4 

y. t

140 - - 

CL 

3 

ILI1 

160 - 

W 

n 

180 - 

Plan view 

200k00 5120 ;40 5k0 5b0 6b0 6L0 6k0 6$0 6k0 7A0 *0 7A0 7$0 

LATITUDE, ft 

800- 

t 

820 - NOTE.-MD= measured depth from surface,ft - I 

!i 

W 

840 - - 

a 

- 0 

I860 - - > 

W 

3 

880 - 

Section view 

gooojoo 220 $0 5ko 5ko 6b0 $20 6h0 do 6k0 7b0 7i0 760Y60 

HORIZONTAL DISTANC E, f t 

FIGURE 9. - Plan and section views of sidetracks above the Freeport coalbed. 

level. Sound levels (measured 100 feet from the drill rig) during drilling 

operations were 70-72 decibels before baffling was installed and 63 decibels 

afterwards. The peaked roof of the rig enclosure was hinged so that it could 

be opened to lower the mast, if necessary. The enclosures were constructed 

and bolted together in sections to make the structures movable and reusable. 

COST ANALYSIS 

The project cost breakdown for the 4-112-month operation of the slant 

hole operations is given in table 2. The total cost of the project, not 

including the Government-owned drill rig,6 was $385,481. 

6The cost of the Reed exploratory drill, purchased in 1975, was $151,000. 
TABLE 2 . . Project cost breakdown 

Item Cost 

Rebillables : 

Physical plant: 

Site preparation ................................................ $6. 439 

Electrical systems and power ..................................... 5. 759 

Fence ............................................................ 2. 699 

Office and supply trailers ....................................... 1, 660 

Water ...... ..................................................... 893 

Telephone ........................................................ 533 

Sanitation . ...................................................... 589 

Total .......................................................... 18. 572 

Directional drilling services ..................................... 55. 792 

Dyna-Drill rental .................................................. 32, 401 

Bits. subs. and casing ............................................. 13. 309 

Drill. rig parts .................................................... 1, 446 

Mud pump rental .................................................... 30, 857 

Drilling mud ....................................................... 6. 218 

Fuel. oil. and storage tanks ....................................... 5, 637 

Geolograph ......................................................... 912 

Welding .......................................................... 1. 885 

Plugback and fishing equipment ..................................... 1. 459 

Noise pollution control ............................................ 2, 799 

Miscellaneous and small tools ...................................... 4. 716 

Travel. transportation. and shipping ............................... 18. 072 

Total . ......................................................... 194. 075 

General and administrative at 19.8 pct ............................. 38. 427 

Grand total .................................................... Labor : 

Supervisors ........................................................ 27. 474 

Drillers ........................................................... 22. 733 

Helpers ............................................................. 35. 894 

Field engineer ...................................................... 2. 704 

Other labor . ........................................................ 7. 206 

Total ......................................................... 96. 011 

Labor overhead at 33 pct .......................................... 31. 684 

Total ........ ................................................. 127. 695 

General and administrative at 19.8 pct ............................. 25 284 

Grand total .................................................... T$m 

Grand total for project .............. ...... .................. 385,481 

The mechanical and geological problems encountered on this research 

drilling project added substantially to the overall costs . For evaluation of 

the total project expenditures. most of the lost time can be placed into three 

categories: Mechanical problems. plugging and sidetracking prior to initial 

coal intercept. and plugging and sidetracking after initial coal intercept . The monetary effect of each of these lost-time categories on the major expense 

items (labor. and equipment and service rentals) is given in table 3 . Approximately $111. 000 was spent for extra labor and equipment rentals while 
drilling the 3-inch pilot hole to the first intercept of the Freeport coalbed. 

Slightly more than $93,000 was spent during the 46 days of exploratory drilling after the first intercept, attempting to locate a sufficient thickness of 

coal to support further development of the slant hole degasification technique. Deducting the approximately $204,000 unanticipated expenses from the 

total project expenditures, an estimate of $182,000 remains as the approximate 

cost of drilling the pilot hole, free from major mechanical breakdowns and 

without plugging and sidetracking, to the top of the Freeport coalbed at 

Mather, Pa. 

TABLE 3. - Breakdown of major item lost-time cost 

A common monetary evaluation of drilling operations is the cost per foot. 

Approximately 3,418 total feet of pilot hole were drilled on the project at a 

cost of $385,400, or $113 per foot. However, most drilling delays due to the 

failure of new equipment and to the unfamiliarity of the drilling crew with 

the new technique occurred during the first 3 months of the project. Most of 

these problems were solved by the time the pilot hole reached the Freeport 

coalbed for the first time, and continuous drilling then approached a reality. 

The total footage drilled up to this first intercept was approximately 1,935 

feet at a cost of $292,253, or $151 per foot of drilling. The total footage 

drilled after the intercept was approximately 1,483 feet at a cost of $93,227, 

or $63 per foot of drilling. This was substantially lower than both the total 

project average of $113 per foot and the $151 per foot average for the project's initial footage. It is hoped that the cost per foot can be further 

reduced with better directional control, with the increased penetration rates 

of new bit designs, and with the greater reliability of the improved DynaDrills used in the later stages of the project. 

The many variables inherent in drilling operations make it virtually 

impossible to obtain problem-free drilling. Thus the problem-free drilling 

costs calculated for this particular drilling operation should not be considered an absolute estimate of cost for future utilization of the directional 

drilling technique. It must also be pointed out that all of these costs are 

for the drilling of the 3-inch pilot hole, and do not include the costs of 

reaming the small hole out to the required larger final size. 

Item 

Labor.. . . . . . . . . . . . . . Directional drilling 

services........ ... Dyna-Drill rental.. . Mud pump rentals... . Total .......... 

Problemfree 

cost 

$47,992 

16,398 

18,698 

8,587 

91,668 , 

Mechanical 

problems 

(29 days) 

$31,412 

14,733 

- 

11,963 

58,108 

Total 

cost 

$152,979 

66,839 

38,817 

36,966 

295,601 

Plugging and 

sidetracking 

prior to coal 

intercept 

(23 days) 

$26,036 

11,807 

5,161 

9,587 

52,591 

Plugging and 

sidetracking 

after initial 

coal intercept 

(46 days) 

$47,539 

23,901 

14,958 

6,829 

93,227 
CONCLUSIONS AND RECOMMENDATIONS 

After review of all data from the project, it is concluded that it is 

feasible to drill a directional hole to a predetermined target. Granted this, 

there is no technical reason why directionally controlled drilling cannot be 

used as a coalbed degasification technique. 

The abandonment of the slant hole at Mather was the result of an insufficient coal thickness to maintain the horizontal drilling technique. It is 

essential in future projects that at least one corehole be drilled to determine 

the coal thickness at a location as close as possible to the projected initial 

coal intercept. In coalbeds where no preliminary geologic data are available, 

or where such data indicate that the coal varies abruptly in thickness, it 

will be necessary to drill additional coreholes along the projected well paths 

to evaluate the feasibility of slant hole degasification. 

The exploratory coreholes will be useful in additional ways. By coring 

the entire section to be drilled, the directional driller will know in advance 

what rock types are likely to be encountered. The drill cuttings can be compared with the lithologic data from the coreholes to keep track of where the 

pilot hole is in the geologic section. 

A major problem expected with the slant hole degasification technique is 

the dewatering of the coalbed. It has been shown in field applications and 

laboratory analysis (1-6) - - that to produce gas from coal most efficiently, the 

inherent water must first be removed from the coalbed. It is recommended that 

the coreholes drilled for geologic data be used for dewatering the coalbed. 

If the dewatering process can be started from the coreholes before or during 

the drilling of the slant hole, higher initial gas flow rates can be expected. 

The cost of drilling the 3-inch pilot hole, problem free, to the top of 

the Freeport coalbed at Mather, Pa., is estimated to be about $182,000. It is 

expected that the total time to drill a pilot hole, problem free, can be 

reduced to approximately 80 days as a result of the increased penetration rate 

of new diamond bit designs and the higher reliability of the modified DynaDrill tool. This reduction in total drilling time will further lower the 

expenditures for labor, directional services, and equipment rental on the 

pilot hole above the coalbed.