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

Thomas S. Kleppe, Secretary 

BUREAU OF MINES 

Thomas V. Falkie, Director 
This publication has been cataloged as follows: 

Fields, Herbert H 

Degasification and production of natural gas from an air 

shaft in the Pittsburgh coalbed, by H. H. Fields, Joseph 

Cervik, and T. W. Goodman. [Washington] U.S. Bureau of 

Mines El9761 

23 p, illus., tables, (U.S. Bureau of Mines, Report of investigations 8173) 

1, Mine gases, 2. Gas, Natural, I, Cervik, Joseph, jt, auth. 

11. Goodman, Tobias We, jt. auth. 111, U.S. Bureau of Mines, 

IV. Title, (Series) 

TN23.U7 no. 8173 622.06173 

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

Page 

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

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

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

The 18-foot-diam shaft site .............................................. 2 

Horizontal holes ......................................................... 3 

Degasification and dewatering ............................................ 8 

Discussion of flow data .................................................. 13 

Gas analysis ........................................................ 13 

Interference effect ................................................. 14 

Shut-in effect ...................................................... 16 

Pittsburgh coalbed: flows from individual holes .................... 18 

Shaft drilling patterns ............................................. 21 

Observations on gas flow from horizontal holes in other coalbeds .... 22 

Conclusions and recommendations .......................................... 22 

ILLUSTRATIONS 

Location of shaft site invirginPittsburghcoalbed ................. 3 

Location of degasification holes underground with respect to 

closest mine workings. to projected main headings. and to 

face cleats ....................................................... 4 

Degasification hookup. during and after drilling .................... 5 

View of drill ....................................................... 6 

View of drill controls .............................................. 6 

View of drill powerpack unit (electrohydraulic) ..................... 7 

Arrangement for grouting 4-inch-diam steel pipe into coalbed ........ 7 

Typical degasification setup for each of the four headings in 

the 18-foot return air shaft ...................................... 8 

Total gas and water flow rates ................................... 9 

In situ pressure .................................................... 9 

Individual hole gas flows; hole 1 ................................... 10 

Individual hole gas flows; hole 2 ................................... 10 

Individual hole gas flows; hole 3 ................................... 11 

Individual hole gas flows; hole 4 ................................... 11 

Individual hole gas flows; hole 5 ................................... 12 

Gas flows; holes 1 and 2 ............................................ 12 

Gas flows; holes 3, 4, and 5 ........................................ 13 

Shut-in gas pressure buildup; holes 1, 2, 4, and 5 .................. 17 

Shut-in gas pressure buildup; holes 1, 2, 3, 4, and 5 ............... 17 

Shut-in gas pressure buildup; hole 3 ................................ 18 

Calculated trend curve of initial gas emission rates from 

degasification holes .............................................. 19 

Recommended direction of holes with respect to butt and face 

cleat systems ..................................................... 21 
TABLE S 

Page 

1. Comparative gas analysis ............................................ 14 

2. Initial gas flow data for degasification holes of the 18-foot 

shaft and multipurpose borehole .................................... 15 
DEGASIFICATION AND PRODUCTION OF NATURAL GAS 

FROM AN AIR SHAFT IN THE PITTSBURGH COALBED 

by 

H. HI Fields, 1 Joseph Cervi k,2 and T. W. Goodman 

ABSTRACT 

\ 

The Bureau of Mines conducted research to determine the effectiveness of 

long holes drilled in solid virgin coal in degasifying an area of the Pittsburgh coalbed showing that horizontal holes drilled into a virgin coalbed from 

the bottom of any shaft will effectively remove methane gas in commercial 

quantities from the Pittsburgh coalbed. 

The in situ pressure at a depth of 214 feet into the coalbed and the 

average gas and water flows from the five degasif ication holes were 3 lb/in2 

gage and 860,000 ft3/d and 1.7 gal/min, respectively. On June 19, 1975, after 

593 days of degasification, a compressor was installed and pipeline quality 

gas was introduced into a commercial pipeline. As of June 1, 1976, after 

1,022 days of degasification, over 753 million cubic feet of gas had been 

drained and 117 million cubic feet of gas had been purchased by the gas company for use in the local community of Wadestown, W. Va. The gas drained to 

date is six times the gas estimated to be in the area subtended by the holes. 

Methane emissions at the working face of 1 West mains, Federal No. 2 mine has 

been reduced by 50 pct, proving the value of methane drainage by horizontal 

degasification holes drilled from shaft bottoms ahead of mining. 

INTRODUCTION 

The Bureau of Mines has been responsible for the promotion of health and 

safety in mining since its establishment in 1910. Presently, in addition to 

other areas of research, it is engaged in methane control involving removal of 

methane from virgin coalbeds, from major panels being pillared, and from old 

gobs. Specifically, this study was designed to determine the effectiveness of 

long holes drilled in solid virgin coal in degasifying an area of the Pittsburgh coalbed. 

Methane exists under pressure in micropores, joints, and fractures of 

gassy coalbeds, and also may be present in adjacent strata. A static in situ 

gas pressure of 275 ~b/in~~ (gage) has been measured in the Pittsburgh coalbed 

l~inin~ engineer. 

supervisory geophysicist. 
and the permeability of this bed has been found to be high compared with that 

of other coal bed^.^ Dynamic gas pressure is a function of the piping sys tem 

and ranges from 3 to 197 inches water gage and is regulated by hole size, 

collector piping system, and volume of gas available. Further, in a number of 

mines where gas wells are located in the Pittsburgh coalbed, significant bleed 

off of methane from thewells is evident." 

After 921 days of degasification, 596 million cubic feet of methane has 

been removed from the multipurpose borehole in a virgin area of the Pittsburgh 

~oalbed.~ As of March 15, 1975, it is still flowing at a daily rate of 

500,000 ft3/d into a commercial pipeline.6 This indicates that a much larger 

area of virgin coal is being degasified than is defined by the holes. This 

study shows that horizontal holes drilled into a virgin coalbed from the bottom of any shaft will effectively remove methane gas in commercial quantities 

from the Pittsburgh coalbed. 

ACKNOWLEDGMENTS 

The cooperation of the managements of Eastern Associated Coal Corp., 

Federal No. 2 mine, Pittsburgh, Pa., and Consolidated Natural Gas Supply Corp., 

Clarksburg, W. Va., is greatly appreciated. 

THE 18 -FOOT-DIAM SHAFT SITE 

The shaft utilized in this study is an 18-foot-diam, concrete-lined 

return air shaft located in a return airway of a projected set of 10 headings 

in 1 West mains of Eastern Associated Coal Corp., Federal No. 2 mine, approximately 4,000 feet from the nearest mine workings (fig. 1). The 18-foot-diam 

shaft is constructed with a set of four headings--one each in the north, 

south, east, and west directions. The Pittsburgh coalbed is 7 feet high at 

the shaft site. 

3~ervik, Joseph. An Investigation of the Behavior and Control of Methane Gas. 

Min. Cong. J., v. 53, No. 7, July 1967, pp. 32-37. 

"~abetakis, M. G. , T. D. Moore, Jr. , A. E. Nagel, and J. E. Carpetta. Methane 

Emission in Coal Mines--Effects of Oil and Gas Wells. BuMines RI 7658, 

1972, 9 pp. 

5Fields, H. H. , J. H. Perry, and M. Deul. Commercial Quality Gas From the 

Multipurpose Borehole Located in the Pittsburgh Coalbed. BuMines RI 8025, 

1975, 14 pp. 

'~eul, Maurice, and A. G. Kim. Coal Beds: A Source of Natural Gas. Oil and 

Gas J., v. 73, No. 34, June 16, 1975, pp. 47-49. 
a Honey Run 

%intake shaft 

- 

Scale, ft 

FIGURE 1. - Location of shaft site in virgin Pittsburgh coalbed. 

HORIZONTAL HOLES 

Five 3-112-inch-diam horizontal degasification and one in situ pressure 

hole were drilled: Two degasification and one pressure hole in the North 

heading and one degasification hole in each of the other three headings. The 

degasification holes were drilled ranging in depth from 670 to 2,126 feet and 

the pressure hole was drilled to a depth of 214 feet. The direction of holes 

with respect to face and butt cleats, relationships of shaft to a projected 

set of entries being driven toward the shaft, location of gas wells, and 

length of holes are shown in figure 2. 
Cleat system 

Intake ------------ - -- --- - 

Gas we1 Is - 

- - 

t 

500 

m't 

O- z 00- 

a 

Scale, f t - 

4,000 f t 

Nearest mine workings 

FIGURE 2. - Location of degasification holes underground with respect to closest mine workings, to projected main headings, and to face cleats. 

A 30-hp, electrohydraulic horizontal drill was used to drill the 3-1/2- 

inch-diam degasification holes. Gas flow during drilling was controlled at 

the face by drilling through a Bureau-designed stuffing box which separated 

the gas from water and drill cuttings (figs. 3-6). Both during and after 

drilling, gas was piped to an 18-inch-diam, 7-foot-high receiver tank and then 

to the surface through an 8-inch-diam pipe. The stuffing box was attached to 

a 4-inch-diam pipe fitted with a 4-inch valve so the hole could be shut in, if 

necessary. The 4-inch-diam, 21-foot-long steel pipe was grouted into a 25- 

foot-deep, 6-inch-diam hole drilled into the coalbed (fig. 7).' 

Wervik, J. , H. H. Fields, and G. N. Aul. Rotary Drilling of Holes in Coalbeds for Degasification. BuMines RI 8097, 1975, 21 pp. 
-Coal 

4in 

v

Wate

FIGURE 3. - Degasifi
FIGURE 5. - View of drill controls. 
r1/2-in valve 

Y~Wtin valve 

.~. 

..., . :, . .:... 

. . 

', ,.: 

. .. . . . 

. .. . .. 

.. . ... . 

. . . 

7 

Grout pump 

I 

FIGURE 7. - Arrangement for grouting 4-inch-diam steel pipe into coalbed. 
FIGURE 8, - Typical degasification setup for each of the four headings in the 18-foot 

return air shaft. 
1,200 I I I I I I ?6 I I I 1 )r 

0 - u 

\ 

C 4 holes + 1,000- 5 

0" 

W 

4 E 

a 

CT 

V) 

600- w I 3 d i? 

/ -2 

Water flow /' I I 

L- J - I 

I I I I I 1 I 0 

0 100 200 300 400 500 600 700 

TIME, days 

FIGURE 9. - Total gas and water flow rates. 

TIME, days 

FIGURE 10. - In situ pressure. 
TIME. days 

280 

240,- 

FIGURE 11. - Individual hole gas flows; hole 1. 

I'I'18111gI

-- Is1 day 

8/15/73 

Hole I completed tiole I 
700 I'I I'l 

Hole 3 

147th doy- 600-- 12/28/73 

Hole 3 cwnpleted 

I I, I It1 I 0 I 100 200 300 400 500 600 70

TIME, days 

FIGURE 13. - Individual hole gas flows; hole 3. 
I,I I,I 

0 I00 200 300 400 500 

600 

TIME. dcys 

350 

300- 

FIGURE 15. - Individual hole gas flows; hole 5. 

Ill I'I 

Hole 5 

I I 
I I 

250 - 

Hole 5 completed A 

0 

-0 

m1200- .e 

0 

0 

0- - 

150- 

In" 

W 

-J 

I00 - Hole 4 completed 

(1: 

2 

3 

0 i;i 50- 

cn 

a 

(3 

0. 

I 

0 100 200 300 4 00 500 600 700 

TIME, days 

FIGURE 17. - Gas flows; holes 3, 4, and 5. 

DISCUSSION OF FLOW DATA 

When all the holes were completed, the initial total gas flow, the 

in situ pressure, and total waterflow after the first 24 hours of operation 

from the five 3-112-inch-diam holes were 994,000 ft3/d, 18 lb/inag, and 2.95 

gal/min, respectively. Waterf low averaged 0.6 gal/min/hole. Initial measurements were influenced by the long drilling period. 

Gas Analvsis 

The methane gas is of pipeline quality and is not expected to require 

remedial treatment for acceptance into the gas company's supply line (table 1). 
TABLE 1. - Comparative gas analysis, pct 

Interference Effect 

Table 2 summarizes the comparative data on the degasification holes at 

the 18-foot shaft and the multipurpose borehole. Table 1 shows a comparison 

of gas composition from the multipurpose borehole and the 18-foot shaft. At 

both locations the gas emitted contains about 9 pct carbon dioxide. Gas compositions are comparable at these sites, about 2.6 miles apart. 

18-ft -dim 

shaft 

0.05 

10.7 

.12 

0.0 

88.6 

Ethane (C,%).. ...... Carbon dioxide (CO, ) . Oxygen (0,). ......... Nitrogen (N, ) ........ Methane (CH,). ....... 

Average gas flow per 100 feet of hole (table 2) is higher at the 18-foot 

shaft than the multipurpose borehole. This is to be expected. Seven holes 

were drilled from the bottom of the multipurpose borehole, and because of the 

length of the holes (average length 618 feet), gas flow from any one hole is 

soon affected by the adjacent holes. This effect is called "interference." 

One hole robs gas that would flow into the adjacent holes which are interconnected by the fracture system of the coalbed. The interference effect is 

more pronounced on adjacent holes drilled at an angle of 25" or more to the 

face cleat. 

Multipurpose 

borehole 

0.16 

9.06 

.34 

1.24 

89.10 
TABLE 2. - Initial gas flow data for degasification holes 

of the 18-foot shaft (set 1) and 

multipurpose borehole (set 2) 
SHUT -IN EFFECT 

The use of underground pipelines in coal mines to transport methane to 

the surface is being considered because air required to dilute large quantities of methane produced during and after drilling is not available generally. 

In addition, diluting methane with air to permissible levels underground is a 

waste of a natural resource. 

Piping methane from underground locations to the surface is not a new 

concept and the earliest attempts at work of this nature were made in Great 

Britain about 200 years ago. Large-scale operations, which did not occur 

until after 1943, were applied at many collieries in the Ruhr, the Saar, 

Belgium, France, and Great Britain. However, in the United States, no largescale operations were undertaken during this period until recently. 

Many problems relating to the operation of underground pipelines must be 

solved before the system will be operational. One of these problems is leakage caused by improper installation or alinement of the pipeline. Leakage can 

be prevented or minimized by pressure testing (hydraulic or pneumatic) before 

the line is placed in service. A method for determining a reasonable test 

pressure which will vary from one coalbed to another or within the same coalbed is outlined in the paragraphs that follow. 

Most coalbeds have an associated gas reservoir pressure. In the Pocahontas No. 3 coalbed, the reservoir pressure is 650 ~b/in~~;~ and in the 

Pittsburgh coalbed, the reservoir pressure is 275 lb/in2 .lo Gas pressure 

gradients are known to exist around mine openings.ll These gradients are 

steeper near active face areas in sections advancing into virgin coal compared 

to rib areas in the returns that have been exposed for months. In the Pittsburgh coalbed, measurements at an active face show that the gas pressure at a 

depth of 175 feet is 34 ~b/in~~. At the collar of the hole, the gas pressure 

in the coalbed is near atmospheric. Therefore, the gas pressure gradient is 

0.19 ~b/in~~/ft. A horizontal hole must be drilled at least 1,450 feet to 

reach a point in the coalbed where gas pressure is approaching the reservoir 

gas pressure (275 1b/inag) of the coalbed. The gas pressure versus depth 

curve approaches reservoir pressure asymptotically. Therefore, in order to 

reach reservoir pressure drilling must exceed a depth of 1,450 feet. 

Several tests were conducted in the Honey Run shaft to determine gas 

pressure increase at the collar of the hole when the hole is shut-in or when 

the main underground pipeline is blocked. When either occurs, gas flows 

8~romilow, J. G., and J. H. Jones. Drainage and Utilization of Firedamp. 

Colliery Eng., v. 32, No. 6, June 1955, pp. 222-232. 

 ent ti bas, Abdurrahman, R. P. Vinson, J. Cervik, and M. G. Zabetakis. Methane and Dust Controls for Longwalls: Pocahontas No. 3 Coalbed, Grundy, 

Va. BuMines RI 7849, 1974, 16 pp. 

1°~ields, 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. 

''work cited in footnote 4. 
within the coalbed are redistributed. Because gas pressures at the back part 

of the hole are higher than those near the collar, gas will begin to flow from 

the hole into the coalbed near the collar and eventually into the mine opening. 

Referring to figure 2, during the first test, hole 3 was shut-in and gas 

pressure buildup was monitored while holes 1, 2, 4, and 5 remained open to 

flow. Over a period of 42 

175 I I I I I I hours, gas pressure in 

nected through the more permeab le face cleat. Therefore, 

one would expect gas to 

2 75- v, 

I I I I I I I I 

0 5 10 15 20 25 30 35 40 45 

TIME, hours 

hole 3 increased from near 

atmospheric to 29.5 lb/in2g. 

However, gas flow rate from 

the adjacent hole 5 

increased from 114,000 to 

170,000 ft3/d. Flow at 

hole 1 increased also from 

85,000 to 107,000 ft3 /d. 

No increase in flows was 

Hole 5 

150 - - 

- 

n (r 

FIGURE 18. - Shut-in gas pressure buildup; holes 1, 2, 4, 

and 5. 

7' 

- ,* loo- L - 

o J 

cross over to hole 5 easily. 

However, the increase in gas 

flow from hole 1 is more 

difficult because gas from 

the vicinity of hole 3 or 5 

must flow through the less 

permeable butt cleat to 

reach hole 1. 

A 

- Hole I 

() 

P 0 

In a second test, all 

holes were shut-in and gas 

pressure was monitored at 

each hole. Figure 19 shows 

the buildup pressure at each 

hole for a period of about 

21 hours. During this 

shut -in period, gas flow 

through the faces and ribs 

of the shaft increased and 

when the methane concentration reached 2 pct, the test 

was terminated. The shut -in 

u 

50 

111 I!/ I pressures ranged from a low 4 6 8 I I I 

10 112 lh I 1 I I I 8 20 22 j4 of 21.3 lb/in2g at hole 4 to 

TIME, hours 

a high of 32.6 1b/inag at 

observed at holes 2 and 4. 

Hole 2 These results are shown 

- plotted in figures 18 and Hole 4 

FIGURE 19. - Shut-in gas pressure buildup; holes 1, 2, 3, hole 3 (fig. 20) . 4, and 5. 

19. Holes 3 and 5 are con- 
I I 

5 10 15 20 25 30 35 40 45 

TIME, hours 

FIGURE 20. - Shut-in gas pressure buildup; hole 3. 

The tests show that gas pressure in a blocked pipeline will not build up 

to the reservoir pressure of the coalbed. Leakage of gas into the mine opening through coal surrounding the hole and the redistribution of gas within the 

coalbed from higher gas pressure to lower pressure zones prevents the buildup. 

The shut-in gas pressure will be highest immediately after the hole is drilled. 

As degasification proceeds over a number of years, the shut-in pressure 

declines. If methane gas is piped underground in coal mines, a 90 1b/inag 

test pressure for underground pipelines appears reasonable in the Pittsburgh 

coalbed (Fairview, W. Va. , area) based upon a safety factor of two. 

Pittsburgh Coalbed: Flows From Individual Holes 

Attempts were made to drill each hole to a depth of about 1,000 feet, and 

holes are numbered in order of drilling. Hole 1 was terminated at a depth of 

670 feet because the rotating drill pipe wore the casing thin. A liner casing 

has been installed for safety. 

Gas and water flows from hole 1 are shown in figure 11. Upon completion 

of hole 1, drilling of hole 2 was started. The effect of drilling hole 2 on 

gas flows from hole 1 is clearly shown by comparison in figures 11 and 12. 

Approximately 35 days after hole 1 was completed and hole 2 was being drilled 

at a depth of 500 feet, gas flow from hole 1 was dropping rapidly. At their 

collars, holes 1 and 2 are about 15 feet apart. At a depth of 500 feet along 

hole 2, these holes are about 600 feet apart and they are interconnected 

through the more permeable face cleat of the coalbed. Further evidence of an 

interference effect between these holes at a time of 270 days is shown in 

figure 16. Gas flow from hole 1 drops rapidly. Waterflow from hole 1 at this 

time is declining steadily but at hole 2, a small but steady increase in 

waterflow is observed. Gas and water flows from hole 1 subsequently declined 

to zero, which was caused by a blockage near the collar of the hole. When 
cleaned, initial gas flow was 190,000 ft3 /d which declined to 76,000 ft3/d in 

10 days. Water flowed at a steady rate of 0.5 gal/min. 

Gas flow from hole 2 shows a sharp dropoff at a time of about 400 days 

(fig. 12). There is no apparent reason for this dropoff, except possible 

blockage of water from hole 1. This blockage causes an accumulation of water 

in the coalbed which affects gas flow from hole 2. 

The in situ gas pressure monitoring hole is located between holes 1 and 2 

(fig. 2), and the gas pressure history is shown in figure 10. The rise in gas 

pressure between 400 and 550 days is due to blockage of gas flow from hole 1. 

When hole 1 was cleaned of debris, gas pressure in the coalbed dropped from 27 

to 15 ~b/in~~ in 2 hours and to 10 ~b/in~~ 10 days later. 

Hole 3 was drilled at an angle of 90" to the face cleat and flows are 

plotted in figure 13. Initial gas flow was highest for this hole and subs tantiates previous observations12 that higher flows in the Pittsburgh coalbed 

are obtained from holes which intercept the face cleats at a right angle. 

Flow decreases as the angle increases with respect to the butt cleat (fig. 21). 

The sharp decline in flow from hole 3 at about 250 days coincides with drilling of hole 4 and subsequent gas flow does not appear to affect gas flow from 

hole 2. These holes are interconnected through butt cleats. Undoubtedly, 

0 90 180 270 360 

DISPLACEMENT, degrees 

Hole paral lel to : 

B - Butt cleat 

F - Face cleat 

Least squares fit curve 

to the data 

Equation GFR= 306 t 226 cos 2 8 

GFR= gas f low/day/foot of hole 

in ft3/day/ft 

8= angle of hole measured clockwise with 

respect to an arbitrary O0 line 

parallel to the butt cleat 

FIGURE 21. - Calculated trend curve of initial gas emission rates from degasification holes. 

12Work cited in footnote 10. 
interference effects will occur but are more gradual and, therefore, difficult 

to discern. 

Drilling of hole 5 caused a slight but rapid dropoff in gas flow from 

hole 3 (fig. 13; 480 days). Hole 1 also shows a sharp drop at this time which 

is coincidental. This dropoff in gas flow was caused by complete blockage by 

debris. Partial blockage started on the 260th day (fig. 11). Flow from this 

hole was restored when cleaned of debris (fig. 11; 575 days). 

Figure 18 shows the calculated trend curve of initial gas emission rates 

from the degasification holes against an angle measured clockwise from the 

butt cleat direction. 

Assume the following equation: 

GFR = 306 + 216 (COS 28), 

where GFR = gas flow per day per foot of hole in cubic feet per day per foot, 

and a = angle of hole measured clockwise with respect to an arbitrary 0" 

line parallel to butt cleat. 

Note that maximum flows are obtained from holes drilled parallel to the butt 

cleat (B), and the flows are greater by about a factor of 4 compared to holes 

drilled parallel to the face cleats (F). One might conclude that to obtain 

the greatest flow rates and quantity of gas from a shaft drilling site, all 

holes should be drilled in directions that areparallel or nearly parallel to 

butt cleats (0" and 180"; fig. 21). However, the previous discussion on 

interference effect shows that the flow from two adjacent holes in this direction will not be doubled. Holes 1 and 2 provide a good example of the interference effect. Both make an angle of about 30" with the butt cleat. Drilling 

another hole between holes 1 and 2 would increase flows only slightly. Note 

that flow into these holes would be primarily along the face cleat (fig. 21). 

Hole 1 intercepts gas flow from the left; hole 2 intercepts gas flow from the 

right. The hole between these two is shielded and the flow rate would 

decline rapidly. 

Initial waterflow from all holes after completion is lower (2.95 gal/min) 

at the 18-foot-diam shaft than at the multipurpose borehole (43.1 gal/min). 

The small waterflow from the holes in the 18-foot-diam shaft is being influenced by a second 18-foot-diam shaft located 425 feet away. This shaft has 

been kept dewatered to the bottom of the coalbed both during and after drilling operations, and acts as a natural drainage sump for the coalbed in this 

area. Consequently, lower water flow rates from the degasification holes are 

observed when compared to the multipurpose borehole. As water is removed from 

the coalbed or if there is no water, gas flow increases until the in situ 

pressure and gas migration flow rates stabilize. In both the multipurpose 

borehole and the 18-foot-diam shaft, the in situ pressure fluctuates within 

the same range (7 to 18 ~b/in~~). 
Shaft Drilling Patterns 

Over a period of 500 days, total gas flow from the shaft site averaged 

884,000 ft3/d (fig. 9). Total waterflow averaged 1.8 gal/min. Drilling of 

additional holes in north and south directions is not expected to increase 

substantially the gas flow from the shaft because of interference effects 

noted previously between holes in these directions. The slight increase in 

gas flow that might result from additional holes is not warranted. However, 

additional holes in the east and west directions may be warranted. No apparend interference effects were noted between holes 1 and 5 or 4 and 2. Interference occurs through the butt cleat, which is not as permeable as the face 

cleat; therefore, the effect is gradual and tends to be masked by normal 

decline in gas flow with time. Therefore, to degasify the coalbed in the east 

and west directions as rapidly as the north and south directions, additional 

holes are warranted in the east and west directions. A recommended pattern 

for the Pittsburgh coalbed is shown in figure 22. 

The influence of gas wells upon gas emission from the horizontal degasification holes was noted only in hole 4 where a significant increase in gas 

flow was observed as the hole was drilled past the well. At a depth of 785 

feet, gas flow from hole 4 was 122,000 ft3/d; at a depth of 856 feet, only 71 

feet further, the flow had increased 98,000 ft3/d to 220,000 ft3/d. The hole 

is approximately 70 feet from the well. 

1 Because the holes were 

All holes approximately 

1,000 ft long 

Face cleat ' 

direction partially or complete closed Butt 'Ieat in during drilling, the flow I direction 

data recorded during drilling are not include in the 

flow charts. The readings, 

when plotted, are not meaningful when compared to the 

constant dynamic gas flow 

curves after all holes were 

connected to the collector 

system. When flow data from 

holes 1 and 2 are compared 

(fig. 16), it is evident 

that the holes are interconnected through the face 

cleats. It also was noted 

that if hole 1 was closed in, 

flow from hole 2 would 

increase correspondingly. 

The same is true if holes 3, 

4, and 5, respectively, are 

compared (fig. 17). 

FIGURE 22. - Recommended direction of holes with respect to butt and face cleat systems. 
Observations on Gas Flow From Horizontal Holes 

in Other Coalbeds 

The Beckley coalbed near Beckley, W. Vs., is similar to the Pittsburgh 

coalbed. Both are blocky-type coals with well-developed face and butt cleats. 

Drilling studies in the Beckley coalbed indicate that flow rates from holes 

drilled perpendicular to the face cleat are two to three times the flow rates 

from holes drilled parallel to the face cleat. Therefore, the shaft drilling 

pattern for the Pittsburgh coalbed (fig. 22) is applicable to the Beckley 

coalbed. 

The friable-type coalbeds that do not have well-developed face and butt 

cleats tend to have a lower fracture permeability than the blocky type of coalbed. Gas flow from holes tend to be independent of hole direction with 

respect to face and butt cleats. Typical friable-type coalbeds include Upper 

Kittanning and Lower Kittanning, Upper Freeport and Lower Freeport, Pocahontas 

No. 3, and the B seam at the Dutch Creek Mine, Colorado. In general, for 

shaft drilling in friable coalbeds, six holes at 60' between holes appear 

adequate. If the holes are 1,000 feet long, the ends of two adjacent holes 

will be 1,000 feet apart. For holes 2,000 feet long, the ends of two adjacent 

holes will be 2,000 feet apart, and additional holes may be necessary to 

degasify the coalbed rapidly. 

As of June 1, 1976, methane emissions at the active working faces of 

1 West mains heading system at Eastern Associated Coal Corp.,Federal No. 2 

mine,has been reduced by 50 pct. This is significant, and fully demonstrates 

the feasibility of coalbed degasification by long horizontal holes drilled 

from shaft bottoms 2 years or more ahead of mining. Methane emission was 

reduced from 200 to 100 ft3/min at the working faces when development had 

advanced to within 2,700 feet of the shaft bottom. 

CONCLUS IONS AND RECOMMENDAT IONS 

Degasification of the Pittsburgh coalbed has been successfully demonstrated at two sites--the multipurpose borehole and the 18-foot-diam shaft. 

Figure 1 shows location of both shafts in the Federal No. 2 mine. The decline 

of gas flow from the shaft site (fig. 9) shows that flows of methane exceeding 

600,000 ft3/d can be expected for the next 2 or 3 years. Therefore, shafts 

should be located 5 years or more ahead of mining to adequately degasify the 

coalbed surrounding the shaft and to realize maximum benefits from the sale of 

gas. Shaft degasification projects should be planned so that mine entries are 

not closer than 3,000 feet from the shaft area during the planned degasification period. Driving entries toward the shaft will reduce substantially the 

flows from the shaft degasification site. 

As of June 1, 1976, methane emission had decreased from the initial 

stabilized flow of 860,000 to 600,000 ft3 /d. 

It also is significant that the gas from the shaft degasification project was piped for commercial use directly to the community of Wadestown, 

W. Va. No remedial treatment nor blending was required although the CO, 

content was high. 
It is concluded that degasification by long horizontal holes drilled 2 to 

5 years ahead of mining is a most effective way to (1) degasify large virgin 

areas of the very gassy Pittsburgh coalbed; (2) reduce methane emission at 

mine working faces, thereby reducing ignition and explosion hazard ; 

(3) decrease ventilation cost; and (4) increase coal production. 

The average depth of the seven horizontal holes is 618 feet. At the 18- 

foot -diam shaft , gas flows have averaged 884,000 f t3 /d for 1.6 years and the 

average depth of the five degasification holes is 1,166 feet. Therefore, a 

large area of the coalbed will be degasified at the shaft site.