Bureau of Mines Report of Investigations/l979 

Directional Drilling 

For Coalbed Degasification 

Program Goals and Progress in 1978 

By David C. Oyler, William P. Diamond, 

and Paul W. Jeran 

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

Cecil D. Andrus, Secretary 

BUREAU OF MINES 

Lindsay D. Norman, Acting Director 
Oyler, I). (' 

Directional drilling for c~3albed degasification : program 

goals and progress in 1978 ,' by D. C. Oyler, W. P. Diamond, 

and P. W. Jeran. [Washing~on] : U.S. Dept. of the Interior, 

Bureau of Mines, 1979. 

15 p. : ill., diagrs. : 2; cm. (lieport of investigations - I3urcau 

of h1i11c.s ; 8380) 

13ibliograplly: 11. 13. 

I. Llinc ,gase\. 2. Mine \.cntil;ition. 3. Llethane. 1. I)iamolld, 

W'illiam I>., joint autllor. 11. ,lrrnn, I'nul W., joint author, 111. 

[!nitc*(i St;~tcs. 13urc;1ii of blinc.s. 1V. 'l'itlc, V. Series: (;nited 

States. I3urc;lu of \lines. Ilrport of i~lvrs~ig;~tions . I%ureau of 

$lil>c\ : 8380 

TN23.U7 no.8380 622.06173 

1'.S. 1)ept. of the Irit., Office of I.ibrnry and Information Scrvices 
CONTENTS 

Page 

Abstractu . ................,........o............o...........o........... 1 

Background and introduction ........ .................o................... 1 

~cknowledgment .......................................................... 2 

Program objectives ...................................................... 2 

Selection of sites for directional coalbed degasification systems ....... 3 

~rilling program ............... .............~~.~~...o**.~*~.~....~*.. .*a 3 

Directional hole .. ................................................. 3 

Results of drilling core and dewatering holes at anticipated 

coalbed intercept . .............................................. . 7 

Vertical monitoring holes .............................O............ 10 

References ..........................................................O.O. 13 

Appendix...Jollytown and Mather slant hole histories ...... .............. 14 

ILLUSTRATIONS 

1 . Section view of proposed slant-hole well path with geologic column .. 4 

2 . Plan view of drill sites and proposed slant- and horizontal-hole 

well paths ................OO...........O.........................O 5 

3. Dyna-Drill tool assembly .. ...o............................oo...... 6 

4. Schematic diagram of completed dewatering hole and proposed 

monitoring holes ..... ..................................o...... .*a. 8 

5 . Section and plan views of actual dewatering hole drill path ......... 9 

6 . Schematic diagram of proposed surface facility at dewatering hole.,. 10 

7 . Schematic diagram of water-level-sensing device to be installed on 

monitoring holes ........o......................................... 11 
DIRECTIONAL DRILLING FOR COALBED DEGASlFlCATlON 

Program Goals anti Progress in 1978 

by 

David C. Oyler, 1 William P. Diam~nd,~ and Paul W. Jeran3 

The Bureau of Mines is cooperating with the U.S. Department of Energy in 

a directional degasification project at the Emerald mine near Waynesburg, Pa. 

This project is designed to combine the highly successful underground horizontal degasification technology with surface drilling methods. The objective of 

this program is to demonstrate that directional drilling can be used as a 

technique for degasifying coalbeds ahead of mining to reduce the hazards of 

methane-air explosions in coal mines. 

The directional hole at the Emerald mine is designed to start vertically 

and enter the Pittsburgh coalbed horizontally. A 3-inch-pilot hole entered 

the Pittsburgh coalbecl at a vertical depth of 999 feet, The hole will be 

reamed to 8-3/4 inches in diameter, and 5-1/2-inch casing will be cemented in 

place. Three individual 3-inch-diameter, 3,000-foot horizontal gas collection 

holes will be drilled into the coalbed in a "bird footff pattern. 

A corehole and vertical dewatering hole have been completed at the anticipated coalbed intercept. The dewatering hole was drilled to130 feet below the 

Pittsburgh coalbed, a depth of 900 feet, and 880 feet of 7-inch-OD casing was 

cemented in place. Seven vertical holes for monitoring the extent and progress 

of degasification have been drilled within the horizontal drilling area. 

BACKGROUND AND INTRODUCTION 

Since 1964 the Bureau of Mines has corlducted an expanded program of 

research in coalbed degasification. This program has evolved to include 

degasification through the use of horizontal holes drilled underground ei-ther 

in mines or from shaft bottoms (2-&)L and surface vertical boreholes using 

modified oilfield technology (7-8, - - 10). Horizontal holes were found to have 

~eneral engineer. 

2 Supervisory geologist. 

~eolo~is t . All authors are with the Pittsburgh Mining and Safety Researcl~ Center, Bureau 

of Mines, Pittsburgh, Pa. 

'underlined numbers in parentheses refer to items in the list of references 

preceding the appendix. 
the ad 

the co 

Howeve 

vanta 

albed 

r, th 

ges of relatively low drilling costs and the ability to intersect 

cleat or fracture system, thus increasing permeability to gas flow. 

is drilling required underground access and facilities, which often 

interfered with the mining cycle. The requirement of access to the coal often 

limited the value of the degasification holes due to the limited time and/or 

distance they could be drilled ahead of mining. Hydraulically stimulated 

vertical holes eliminated the latter problems, but had the disadvantages of 

requiring large numbers of surface sites, higher costs, and production and 

maintenance problems. 

The concept of directionally drilled degasification holes was originally 

considered by the Bureau of Mines as a means of combining the best elements of 

the surface vertical borehole and underground horizontal drilling techniques, 

The Bureau of Mines drilled a 3-inch-diameter directional hole in 1973 on the 

property of Consolidation Coal Co.'s Blacksville No. 2 mine near Jollytown, 

Pa., as a modification to a vertical hole drilling program. The project 

showed that a circular arc directional hole could be drilled to reach a coalbed and that a hole could be successfully drilled horizontally in coal up to 

450 feet. Mechanical difficulties and later a lack of site access when a dam 

was built near the hole made further investigation of the gas drainage capacity of the hole impossible until mid-1976. 

A second project was begun in 1974 with the goals of drilling long holes 

in the coalbed, draining large quantities of gas, and determining the economic 

feasibility of the technique on a production basis. Using the Jollytown 

project as a model, a drilling plan was drawn up, and drilling equipment purchased, This equipment included a specially designed drill rig, BQ wireline 

drill rod, drill pipe, and a mud pump. A pilot hole was drilled near Mather, 

Pa., in late 1975 (1). The project failed to achieve its goals because of an 

insufficient coal tf;ickness to maintain the horizontal drilling technique, but 

a great deal of useful experience was gained. A review of the Bureau of Mines 

past directional drilling experience is summarized in the appendix. 

A third directional drilling project is now in progress on the property 

of the Emerald Mines Corp. near Waynesburg, Pa, This project is funded by the 

U.S. Department of Energy with the Bureau of Mines providing research planning 

and technical management. The purpose of this paper is to outline the drilling program and report on the preliminary accomplishments. 

ACKNOWLEDGMENT 

The cooperation of the management and personnel of the Emerald Mines 

Corp., Waynesburg, Pa., is greatly appreciated. 

PROGRAM OBJECTIVES 

The major objective of this program is to demonstrate that directional 

drilling can be used as a technique for degasifying coalbeds ahead of mining 

to reduce the hazards of methane-air explosions in coal mines. Specific 

objectives of the project are to improve the techniques (and hence, lower the 

cost) of directional drilling for coalbed degasification, and to determine the 
actual limit of horizontal drilling using the system described here. Coalbed 

reservoir data will be collected from seven vertical monitoring holes within 

the project area for reservoir modeling. The monitoring data will provide 

information on the progress and extent of degasification with time, and will 

allow the analysis of the effectiveness of various experimental procedures 

to be performed on the degasification system. 

SELECTION OF SITES FOR DIRECTIONAL COALBED DEGASIFICATION SYSTEMS 

A number of factors must be considered in selecting sites for directional 

drilling for coalbed degasification in advance of mining. The coalbed should 

contain sufficient quantities of gas to require degasification and be deep 

enough to allow a well path to reach the horizontal with a reasonable angle 

build rate (in the range of 3" to 6" per 100 feet drilled or a minimum 800 to 

900 feetof cover). In general, a particular coalbed contains more gas at 

greater depths; therefore, depth of the coalbed is a criterion common to both 

prerequisites. It is also essential to have enough lead time to permit effective degasification before starting mining operations. 

Geologic factors also must be considered. The coal should be continuous 

over the drilling area and be free of faults, rolls, and wants so that horizontal holes may be more easily kept in the coalbed. It would also be desirable 

for the horizontal holes to be drilled perpendicular to the face cleat to 

maximize gas production (2). However, since multiple horizontal holes are to 

be drilled at the bottom of a single directional hole, it would be impractical 

or impossible to drill all holes perpendicular to the face cleat. 

Dewatering of a coalbed is essential for efficient and effective degasification. A vertical dewatering hole is presently considered the best method 

to accomplish this task in a directionally drilled degasification system. The 

recommended location for a dewatering hole is just beyond the coal intercept 

point of the directional hole. For a circular arc directional hole, this 

point is about the same distance from the surface location of the directional 

hole as the vertical distance to the coalbed. For example, if the vertical 

distance to the coal is 1,000 feet, the coal intercept and the dewatering hole 

should be approximately 1,000 feet away, Selection of sites for the two holes 

must be planned as a unit since the selection of one site will greatly constrain selection of the other. 

DRILLING PROGRAM 

Directional Hole 

The general drilling plan was to drill a 3-inch-diameter pilot hole on a 

circular arc starting vertical at the surface and intercepting the Pittsburgh 

coalbed horizontally at a vertical depth of 999 feet (EM-19, fig. 1). The 

hole will be reamed to a diameter of 8-314 inches after the coalbed has been 

intercepted on an acceptable drill path, Before starting the horizontal 

portion of the drilling, 5-112-inch-OD casing will be cemented in the directional hole. Three horizontal holes (fig, 2) for gas drainage will then be 

drilled in the coalbed, each to a planned horizontal extent of 3,000 feet. 
HORIZONTAL DISTANCE, ft 

200 L 

FIGURE 1. - Section view of proposed slant-hole well path with geologic column. 
0 120 240 360 meters 

Scale 

Key Mop 

FIGURE 2. - Plan view of drill sites and proposed slant- and horizontal-hole well paths. 

The pilot hole was drilled using a 2-3/8-inch-diameter ~~na- rill" 

(fig. 3) and a 3-inch-diameter Christensen d r i l l b i t constructed of whole 

stone drill bortz (diamonds) and General Electric Strata Paxs. The drill 

pipe was BQ wireline drill rod. The hole was started vertically for 

approximately 50 feet before beginning an angle build up of approximately 

6.0" per 100 feet of drilled depth. 

Control of the pilot hole was accomplished by the use of 45- and 

30-minute bent housings (with or without standoff rings) on the Dyna-Drill 

(fig. 3). Azimuth was controlled by rotation of the tool face. Drilling 

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

endorsement by the Bureau of Mines. 
- Nonmagnetic 

drill rod 

parameters, including pump pressure, mud 

volume pumped, penetration rates, and 

pulldown pressure, are recorded using a 

geolograph. These data will be used to 

determine the optimum drilling parameters for maximum penetration rate with 

acceptable directional control. 

- Directional surveying of the pilot Muleshoe subassembly hole and Dyna-Drill orienting was performed using magnetic singleshot equipment and a muleshoe orienting sub. A 

nonmagnetic stainless s tee1 Dyna-Drill 

and 80 feet of stainless steel drill rod 

were used to minimize the effects of the 

drill string on azimuth readings. Surveying was done at either 10- or 20-foot 

7 Motor assembly 

Bent-housing and 

connecting-rod assembly I tintervals (each joint or every other 

joint), and calculations were made using 

angle averaging and radius-of-curvature 

methods. Frequent well projections were 

made to determine whether the hole was 

too far off course. Once the hole was 

near the coalbed, an effort was made fo 

guide its path toward the vertical 

dewatering hole. 

The mud system used was a low 

solids, polymer mud. Two types of 

polymer were used, one to prevent fluid 

loss and the other to provide gel 

strength and aid in removal of drill cuttings. This system, used throughout all 

drilling on the Mather hole, kept the 

hole open without problems for 4 months, 

n The directional hole will be reamed 

-- to 8-3/4 inches by running the BQ drill 

Bearing and drive rod in the completed pilot hole and 

shaft assembly drilling over it with a reaming bit. 

This procedure will insure that the reamRotating-bit subassembly ing bit does not leave the pilot hole 

drill path. 

Diamond plug bit 

Immediately after the reaming is 

FIGURE 3. - Dyna-Drill tool assembly. completed, a string of 5-112-inch-OD 

K-55 casing, 4.95- to 4.8-inch ID, will 

be run and cemented in the hole from bottom to surface. It is planned that 

the bottom of the casing will extend approximately 50 feet horizontally into 

the coalbed. 
The entire mud system, including all mud in the hole, will be changed 

after cementing, and clear water will be used on the horizontal holes. This 

will be done to prevent loss of coalbed permeability, which might take place 

if additives were used that could plug or block fracture openings. 

The 2-3/8-inch Dyna-Drill and BQ drill rod will be used to drill the 

3-inch-diameter horizontal holes in the coalbed. After the first hole (H-1) 

is drilled to the maximum length considered either economically or physically 

feasible, holes H-2 and H-3 will be sidetracked in the directions shown on 

figure 2. 

The surface facility of the completed hole will include a wellhead for 

servicing the well, gas flow measuring equipment, water separator, flare stack, 

flame arrestor, and gasline shutoff valves. All of the equipment will be 

installed in a protective wellhouse. 

Results of Drilling Core and Dewatering Holes at Anticipated Coalbed Intercept 

Before drilling began on the directional hole, a corehole (EM-78-1, 

fig. 2) was drilled near the anticipated coalbed intercept. The corehole was 

used to confirm the presence, thickness, and elevation of the coalbed, and to 

provide stratigraphic information for correlation to the directional hole, 

Samples of the Washington, Waynesburg, Sewickley, and Pittsburgh coalbeds were 

obtained for gas content evaluation by the direct method (6, - 9). A stratigraphic column of this corehole is shown on figure 1. 

Experience at the Jollytown site indicated that conventional sucker-rod 

water-pumping equipment will not function properly in a horizontal position. 

The efficient production of gas from coalbeds is dependent upon the dewatering 

of the coal. A vertical dewater hole (EM-20, fig. 2) was drilled near the 

anticipated intercept of the coalbed and adjacent to the corehole (EM-78-1). 

A schematic of this hole is shown in figure 4. The dewatering hole was 

drilled as a "straight" hole, but a multishot directional survey of the hole 

showed that the well path deviated considerably (fig. 5). The deviation 

probably occurred because the drill pipe was not adequately stabilized, but 

the deviation is not expected to cause any problems. 

The dewatering hole was drilled 17-1/2 inches in diameter to a depth of 

16 feet and 16-inch-diameter conductor pipe was set, A 14-3/4-Filch-diameter 

hole was then rotary drilled using foam, to a depth of 215 feet rr'riere 203 feet 

of 10-3/4-inch-OD casing was cemented in place, This intermediate casing was 

set to seal off lost circulation zones encountered in the corehole at the same 

site. The casing was cemented using thixiotropic cement to prevent losing a 

large volume of cement to the lost circulation zones, A 25-percent overrun 

was specified on the cement volume to insure sealing off the lost circulation 

zones and to provide an adequate bond on the casing. There was only minimal 

circulation of cement to the surface, indicating that the lost circulation 

zones had taken cement. The cement job proved to be successful in that the 

lost circulation problems were eliminated. Full returns of cement were 

obtained when the 7-inch primary casing was later set, further indicating a 

successful cementing procedure on the intermediate casing. 
Slots jetted through 

3%- in - diam hole 

cored to maximum 100 ft 

below Pittsburgh Coalbed with sand screen . 

( Pittsburgh cored 1 

Float shoe and plug 

FIGURE 4. - Schematic diagram of completed dewatering hole and proposed monitor- - 

ing holes. 

The hole was then rotary drilled to approximately 135 feet below the 

Pittsburgh coalbed using one 9-518-inch-diameter bit and one 9-112-inchdiameter bit. Before setting the final string of casing, a suite of geophysical logs (including density, neutron, and garmna ray) were run to determine 

the exact measured depth of the coalbed. This was necessary for the proper 

positioning of the casing collars and centralizers above and below the coalbed. 

A caliper log was run to calculate the volume of cement needed to set the 

casing and to determine the well bore diameter adjacent to the coalbed. If 

the hole had been excessively washed out in the coalbed, the cementing 
Nor 

FIGURE 5. - Section and plon views of actual dewatering 

hole drill path. 

DEWATERING HOLE 

EM-20 

Surfoce elevation 1,122.03 feet 

Section view Section view 

technique for the casing 

would have required special 

equipment to keep the cement 

out of the coalbed interval. 

Knowing the thickness of 

cement between the casing 

and the coalbed is important 

because the "slotting" tool 

to be used to provide communications between the casing and the formation can 

only penetrate approximately 

12 inches of casing and 

cement. The caliper log 

indicated that the coalbed 

was not "washed out ," and 

a conventional cementing 

technique was used. Thixiotropic cement was used to 

keep infiltration of cement 

into the coalbed and the 

accompanying loss of permeability to a minimum. Eight 

hundred and eighty feet of 

7-inch-OD, K-55, short 

thread and coupling, 

20-lb/ft casing was used 

with a "cement shoe" on the 

bottom. Cased hole geophysical logs, including an 

uncalibrated gamma ray and 

collar log, were run to confirm the position of the 

casing collars and torecheck 

the measured depth of the 

Pittsburgh coalbed. 

t h South West 

100 

- 200 

Water level and pressuremonitoring equipment will be 

installed on the hole and 

data collected until the 

directional hole has entered 

the coalbed and casing has 

been installed. Before starting the horizontal drilling, 

East 

100 

200 

the coalbed in the vertical hole will be hydraulically stimulated through previously cut slots. The stimulation procedure is designed to insure the efficiency of the dewatering process and enhance the degasification of the coalbed 

by increasing the formation permeability (7-8, - - 10). 

- 300 

Scale 

15 30 meters --t---J, 

0 50 100 feet 

- 400 

r t 

i 

a + 

W 

a 

- 500 

- 300 

- 400 

). C 

I + 

n 

W 

a 

- 500 

Plan view 

N 

600 

- 700 

- 800 

W E 

- 870 

- 700 

,Pittsburgh S coal bed 

- 800 
A down-hole plunger pump capable of producing up to 120 bbl/day will 

initially be installed on the dewatering hole. The pump will be run by a 

7.5-hp motor using three-phase,440-~0lt power. The motor and pumping unit 

are capable of pumping over 250 bbl/day with larger down-hole pumps if greater 

water volumes are encountered than anticipated. 

Dewatering is not scheduled to begin until the horizontal drilling portion of the project is completed. If the coalbed is dewatered before horizontal drilling, the drilling fluid and cuttings could reduce the permeability 

of the coalbed. 

Since the dewatering hole should behave as a conventional vertical degasification well and produce gas as dewatering proceeds, it has been engineered 

to produce and monitor both gas and water. The surface facility (fig. 6) will 

also include a flare stack with a flame arrestor to safely vent gas and a 

protective enclosure for the wellhead equipment. A 40- by 15- by 4-foot-deep 

holding pond will be located near the hole for disposal and treatment of the 

produced water, 

Vertical oni it or inn Holes 

Seven vertical boreholes have been drilled to the Pittsburgh coalbed in 

the area to be degasified by the directional hole. These holes (EM-21 through 

EM-27, fig. 2) will be used primarily to monitor the coalbed formation pressures by observing changes in water level in each hole. A lowering of the 

To 

t disposa I 

KEY 

A Pumping unit G Water separator tank 

B Valves H Filter and water meter 

C Tubing head I Gas meter 

D Stuffing box J Meter house 

E Waterline K Flame arrestor and flare stack 

F Gasline 

FIGURE 6. - Schematic diagram of proposed surface facility at dewatering hole. 

pit 
water column height in a hole will indicate the loss of formation pressure 

caused by removal of water and gas from the dewatering and directional holes. 

If the directional hole is surrounded by holes equipped with continuous recording water level devices, both the degree and areal extent of degasification 

can be monitored. The holes will also be completed for the production and 

measurement of gas and water. This will allow short periods of production so 

that formation evaluation tests can be conducted. The holes can also be used 

for general coalbed dewatering should the prime dewatering hole prove inadequate. However, these holes should not be used for production since any 

long-term production from these holes would make it difficult to determine the 

effectiveness of the directional hole, and fluid levels cannot be used to 

determine formation pressures in producing holes. 

The monitoring holes were drilled using cable tool and rotary drill rigs, 

A 6-114-inch hole was drilled to just above the Pittsburgh coalbed, and a 

string of 4-112-inch casing cemented in place (fig. 4). A coring r i g w i l l 

drill out the cement plug, and cores of the Pittsburgh coalbed will be taken 

in each hole so that the 

KEY 

A Casing 

B Recorder 

gas content of the coal may 

be determined. Approximately 100 feet of hole will 

be drilled below the coalbed 

to be used as a sump as in 

the main dewatering hole. 

Each hole will be 

"'jetted" using the same 

equipment that is to be used 

to "slot" the casing in the 

dewatering hole. This technique performed in the open 

hole will remove the coal 

exposed to drilling fluids 

helping to minimize loss of 

permeability and pressure 

drops (skin damage) caused 

by plugging of the fracture 

system (cleat) near the well 

bore. Each monitor hole 

will be completed with surface equipment similar to 

that in the dewatering hole 

(fig. 6); in addition, a 

water-level-sensing device 

C Keck water- level-sensing device with a continuous data 

recorder (fig. 7) will be 

D Batteries to power Keck device installed on each hole. The 

holes will probably not be E Platform and insulated housing stimulated hydraulically 

FIGURE 7. - Schematic diagram of water- level-sensing unless they are eventually 

device to be instal led on monitoring holes. used for sustained gas 

and/or water production. 
SUMMARY 

Work was begun in September 1978 on a project to drill a directional 

coalbed degasification hole at Emerald Mine near Waynesburg, Pa, A 3-inchdiameter circular arc pilot hole was drilled to intercept the Pittsburgh 

coalbed horizontally at a vertical depth of 999 feet. The hole will be reamed 

to 8-314 inches in diameter so that 5-112-inch-OD casing can be cemented in 

place. A vertical dewatering hole and a corehole have been completed at the 

coalbed intercept point of the directional hole. Seven vertical monitor holes 

have been drilled and cased in the horizontal drilling area, and the holes 

will be equipped to measure coalbed pressures, 
REFERENCES 

Diamond, W, P., D. C. Oyler, and H. H. Fields. Directionally Controlled 

Drilling To Horizontally Intercept Selected Strata, Upper Freeport 

Coalbed, Greene County, Pa. BuMines RI 8231, 1977, 21 pp. 

Fields, H. H., J. Cervik, and To W. Goodman. Degasification and Production of Natural Gas From an Air Shaft in the Pittsburgh Coalbed, 

BuMines RI 8173, 1976, 23 pp, 

Fields, H. H., S. Krickovic, A, Sainato, and M. G. Zabetakis. Degasification of Virgin Pittsburgh Coalbed Through a Large Borehole. BuMines 

RI 7800, 1973, 27 pp. 

Fields, H. H,, J, H, Perry, and M. ~eul, Commercial-Quality Gas From a 

Multipurpose Borehole Located in the Pittsburgh Coalbed, BuMines 

RI 8025, 1975, 14 pp. 

Kissell, F. N. The Methane Migration and Storage Characteristics of the 

Pittsburgh, Pocahontas No. 3, and Oklahoma Hartshorne Coalbeds. 

BuMines RI 7667, 1972, 22 pp, 

Kissell, Fo 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. 

Effective Placement of Coalbed Gas Drainage Wells. U,S, Dept. 

of Energy RI-PMOC-2(78), 1978, 16 pp. 

Lambert, S. W., and M. A. Trevits. Methane Drainage: Experience With 

Hydraulic Stimulation Through Slotted Casing. BuMines RI 8295, 1978, 

16 PP* 

McCulloch, C. M., J. R. Levine, F. N. Kissell, and M. Deul. Measuring 

the Methane Content of Bituminous Coalbeds. BuMines RI 8043, 1975, 

22 PP* 

Steidl , P. F. Foam Stimulation To Erlilance Production From Degas if ication 

Wells in the Pittsburgh Coalbed. BuMines RI 8286, 1978, 10 pp. 
APPENDIX.--JOLLYTOWN AND MATHER SLANT HOLE HISTORIES 

The Bureau of Mines drilled the first directional hole into a coalbed in 

1973 on the property of Consolidation Coal Co.'s Blackville No, 2 mine near 

Jollytown, Pa. The 3-inch hole was started at a 20' angle at the surface and 

intercepted the Pittsburgh coalbed at a vertical depth of 776 feet. The 

actual drilled distance along the circular arc to the coalbed intercept was 

approximately 1,310 feet. 

The original hole was drilled using a Joy 22 drill rig, BQ wireline rod, 

and a 1-314-inch Dyna-Drill tool for directional control, Horizontal drilling 

in the coalbed at Jollytown reached 414 feet. At this depth it became impossible to pull the drill string, and a decision was made to establish production 

by "perforating" the 414 feet of pipe in the coalbed, The efficient production of gas from coalbeds is dependent upon several factors including dewatering of the coal. Gas flow rates as high as 25 to 30 Mcfd were reported 

immediately after the hole was swabbed to remove water. A rapid influx of 

formation water killed the gas flow within 15 to 20 minutes, A down-hole 

sucker-rod pump was installed at a depth of 1,310 feet for continuous production of water. The water flow rate began at 14 bbl/day and declined to 

7 bbl/day after several weeks. Gas production during this testing phase 

ranged from 1,200 to 3,800 cfd. 

The BQ rod in the Jollytown hole was overreamed to a depth of approximately 1,000 feet, and the old pipe was removed. A string of 4-112-inch casing was then installed to allow the use of larger down-hole pumps and provide 

a less restricted gas flow. Two additional holes were drilled into the coalbed from the bottom of the casing. The maximum horizontal penetration of the 

coalbed by these holes was approximately 400 feet due to the low pulling 

capacity of the rig. Shortly after this phase of drilling, the coal company 

began construction of a holding pond adjacent to the drill site, necessitating 

a shutdown of research activities for approximately 2 years. 

The Jollytown hole was cleaned out in early 1976, and a down-hole sucker 

rod pump was installed at a depth of 1,410 feet. Water production was 3-112 

bbl/day initially, declining to less than one-half bbllday in approximately 

2 months. The "water" produced was in many instances a black muddy sludge. 

Gas production ranged from less than 1,000 cfd up to 3,100 cfd. Various 

remedies, including moving the pump progressively up the hole to position it 

in less horizontal attitudes, failed to improve the production of water and 

gas. The hole was abandoned in late 1976, 

The Jollytown hole proved that a directional well path could be started 

near vertical at the surface and controlled to intercept a specific small 

target in a comparatively short vertical distance, The experience in attempting to establish production through the slant hole indicated that conventional 

sucker-rod water-pumping equipment would not function properly in a horizontal 

attitude and that other methods of dewatering would be needed, The problem of 

keeping the hole and pump free from particulate matter was thought to result 

from the casing being set too high, leaving approximately 300 feet of open 

hole exposed between the bottom of the casing and the top of the coalbed. 
In the fall of 1975, the Bureau of Mines began a second directional 

drilling project (1). This hole, at Mather, Pa., was to degasify the Upper 

Freeport coalbed in advance of mining. Due to the problem of pulling pipe at 

the Jollytown site, a larger drill rig with greater pulling capacity was used, 

The rig was completely hydraulic to aid in providing a smooth feed of drill 

pipe while using the Dyna-Drill. A newly developed 2-318-inch Dyna-Drill was 

used in place of the 1-314-inch tool used at Jollytown. 

The general drilling plan included a 3-inch-diameter pilot hole drilled 

on a 1,500-foot well path to intersect the coalbed at a vertical depth of 

930 feet, After the intercept of the coalbed, the hole was to be reamed to 

8-314 inches, and 5-112-inch casing was to be installed. Three horizontal gas 

collection holes up to 3,500 feet long were then to be drilled into the 

coalbed. 

The pilot hole was completed to the coalbed intercept point, but not without many difficulties. Most of the problems encountered were mechanical or 

involved directional control. Mechanical problems included rig, Dyna-Drill, 

and mud pump breakdowns, Problems in maintaining the proper well path 

required three plug backs and redrilling prior to the first intercept of the 

coalbed. 

The first penetration of the Upper Freeport horizon at Mather encountered 

only 0.5 foot of coal. Approximately 1,500 feet of exploratory horizontal 

drilling after the initial coalbed intercept and five additional penetrations 

of the coalbed horizon could not locate suffic'ient continuous thickness of 

coal to continue the project. Seven coreholes in the vicinity of the drill 

site indicated 5.9 to 8,5 feet of Upper Freeport coal. The first penetration 

of the coalbed was only 750 feet from a corehole that indicated 6.75 feet of 

coal. 

The Mather project confirmed the feasibility of drilling a directional 

hole to a predetermined target. The 2-3/8-inch Dyna-Drill was developed into 

a usable tool, and considerable experience was gained in directional control 

of the hole, especially in the horizontal phase of the drilling. The project 

also suggested the need for more complete geologic evaluation of drill sites, 

to include the drilling of a corehole at the proposed initial coalbed intercept. The corehole would confirm the thickness and exact elevation of the 

coal for accurate drill path projections. 

2U.S. GOVERNMENT PRINTING OFFICE: 1979-603-002187