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

Rogers C. B. Morton, Secretary 

Jack W. Carlson, Assistant Secretary-Energy and Minerals 

BUREAU OF MINES 

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

.. 

Fields, Herbert H 

Commercial-quality gas from the multipurpose borehole located in the Pittsburgh coalbed, by Herbert H. Fields, John 

H. Perry, and Maurice Deul. [washington] U.S. Bureau of 

Mines [1975] 

14 p. illus., tables. (U.S. Bureau of Mines. Report of investigations 8025) 

Includes bibliography. 

1. Gas, Natural. 2. Mine gases. I. Perry, John H., jt. auth. 

11. Deul, Maurice, jt. auth. 111. US. Bureau of Mines. IV. Title. 

(Series) 

TN23.U7 no. 8025 622.06173 

U.S. Dept. of the Int. Library 

i 
C ONTE NT S 

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

Introduction ............................................................. 2 

Acknmledgments ......................................................... 2 

The multipurpose borehole ................................................ 2 

Horizontal holes ....................................................... 2 

Degasification and dewatering ............................................ 4 

Compressor installation .................................................. 8 

Results and discussions .................................................. 11 

Conclusions .............................................................. 13 

References ............................................................... 14 

ILLUSTRATIONS 

1 . Location of multipurpose borehole in virgin Pittsburgh coalbed ....... 2 . Location of degasification holes underground with respect to 

closest mine workings. to projected main headings. and to 

face cleat ......................................................... 4 

3 . Perspective view of completed multipurpose borehole .................. 5 

4 . Gas and water flow rates ............................................. 8 

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

6 . Daily total gas fl m ................................................. 9 

7 . Individual hole gas flows ............................................ 10 

8 . View of compressor installation ...................................... 11 

TABLES 

1 . Gas production from each horizontal hole. total gas and water 

flow. and in situ pressure record .................................. 6 

2 . Analyses of four samples from total gas emission ..................... 12 
COMMERCIAL-QUALITY GAS FROM A MULTIPURPOSE BOREHOLE 

LOCATED IN THE PITTSBURGH COALBED 

by 

Herbert H. Fields, '~ohn H. perryf2 and Maurice Deul 

ABSTRACT 

The Bureau of Mines has been promoting health and safety in mining since 

its establishment in 1910. One area of research covers methane control in 

coalbeds; this report describes a multipurpose borehole used for both degasification and the production of commercial-quality gas. 

The multipurpose borehole was drilled into a barrier pillar, and seven 

horizontal degasification holes and one pressure point hole were drilled 

radially out from its perimeter. On January 28, 1974, after 505 days of degasification, a compressor was installed to the exhaust stack of the multipurpose 

borehole (2), and pipeline--quality gas was introduced into a commercial pipeline. As of February 4, 1975, over 171 million cubic feet of gas had been 

purchased by the gas company. 

The in situ pressure at a depth of 200 feet into the coalbed and the 

average gas flow and water flow from the degasification holes as they were 

completed and closed off were 203 psig, 1,200,000 cfd, and 6.8 gpm, respectively. Twenty-four hours after the seven holes were connected through individual pipes to the atmosphere, the total gas and water flows and the in situ 

pressure dropped, respectively, to 971,000 cfd, 1.3 gpm, and 18 psig. Five 

hundred days later,the corresponding values were 620,000 cfd, 0.15 gpm, and 

10.5 psig. Daily flows have been as high as 800,000 cfd, and as low as 

360,000 cfd, during the last 500 days. 

On February 4, 1975, after 882 days of degasification, 576 million cubic 

feet of gas had been removed from the Pittsburgh coalbed; apparently a much 

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

This study indicates that horizontal boreholes drilled into a coalbed from 

the bottom of any shaft will effectively remove gas from the Pittsburgh 

coalbed. 

l~ining engineer. 

Physicist . 3~upervisory research geologist . 
INTRODUCTI ON 

The Bureau of Mines has promoted 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 coal in degasifying a portion of the Pittsburgh coalbed. 

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

gassy coalbeds, and also may be present in adjacent strata. An in situ gas 

pressure of 275 psi has been measured in the Pittsburgh coalbed, and the 

permeability of this bed has been found to be high, compared with that of 

other coalbeds (L) .4 Further, in a number of mines where gas wells are 

located in this coalbed, significant bleed off of methane through the well 

barrier has been found (3). Because of the high in situ gas pressure and 

permeability of the Pittsburgh coalbgd, considerable degasification can be 

effected over a significant area, if accomplished ahead of mining. This 

report continues previous work (2) and provides additional information on 

degasification by drilling long holes in the coalbed from the enlarged bottom 

of a borehole and conducting the gas through a piping system to the surface 

for venting and later for utilization. The previous report (2) describes 

the engineering design. 

The cooperation of the management of Eastern Associated Coal Corp. , Pittsburgh, Pa. , the management of the Federal No. 2 Mine, and the management 

of Cons olidated Gas Supply Corp. , C larksburg, W. Va . , is greatly appreciated. 

THE MULTIPURPOSE BOREHOLE 

The borehole utilized in this study is located in the barrier pillar 

130 feet east of the outside heading of a projected set of ten, 3 South mains 

headings. Figure 1 shms the location to be approximately 1 mile from the 

existing faces of 3 South mains. The borehole was called multipurpose because 

after completion of degasification, or when the 3 South mains headings have 

been developed to the borehole, it may be used as an intake airway and later 

as a return airway. Still later, when the pillar line has been established, 

the borehole can be used to degasify the gob area nearby. While serving 

as an intake airway, the borehole may be used as an emergency escapeway, with 

power cables and cmunication lines instalLed in the two degasification 

pipes located outside the 48-inch-OD casing. 

HORIZ ONTAL HOLES 

Seven horizontal degasification and one pressure point hole were drilled 

radially out from the perimeter of the multipurpose borehole. The 

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

at the end of this report. 
FIGURE 1. - Location of multipurpose borehole in virgin Pittsburgh coalbed. 
\ No 2 hole. €350 ft deep 

FIGURE 2. - Location of degasification holes underground with respect to closest mine 

workings, to projected main headings, and to face cleat. 
FIGURE 3. - Perspective view of completed multipurpose borehole. 
In situ gas pressure and gas and water volume measurements are made at approximate 10-day intervals, and are listed in table 1 and figures 4-7. 

TABLE 1. - Gas production from each horizontal hole, total gas and 

water flow, and in situ pressure record 

In situ 

gas 

pressure, 

psi 

20.3 

20.3 

- 

- 

- 

- 

- 

20.0 

- 

- 

- 

- 

- 

15.0 

- 

- 

- 

- 

- 

- 

- 

12.7 

12.5 

12.5 

12.5 

12.5 

12.1 

12.1 

11.8 

11.8 

11.8 

11.8 

11.8 

11.5 

11.5 

11.3 

11.3 

11.3 

11.3 

11.3 

11.3 

11.3 

11.3 

Day 

1 

5 

10 

22 

25 

29 

44 

53 

72 

80 

93 

99 

108 

117 

124 

136 

144 

155 

164 

175 

185 

194 

205 

215 

225 

253 

265 

275 

285 

295 

305 

315 

325 

335 

345 

355 

365 

375 

385 

395 

405 

415 

Date 

9-11-72 

9-15-72 

9-20-72107 

10-02-72 

10-05-72 

10-09-72 

10-24-72 

11-02-72 

6411-13-7274 

11-21-72 

11-29-72 

12-12-7249 

12-18-72 

12-27-72 

1-05-73 

1-12-73 

1-24-73 

2-01-73 

2-12-73 

2-21-73 

3-03-73 

3-13-73 

3-23-73 

4-02-73 

4-12-73 

4-22-73 

5-22-73 

6-01-73 

6-11-73 

6-21-73 

7-01-73 

7-11-73 

7-21-73 

7-31-73 

8-10-73 

8-20-73 

8-30-73 

9-09-73 

9-19-73 

9-29-73 

10-09-73 

10-19-73 

10-29-73 

Average 

waterf low 

discharge 

l,OOOcfdperhole, 

gpm 

6.8 

6.0 

5.5 

5.0 

4.5 

4.0 

3.5 

3.0 

2.0 

1.7 

1.5 

1.4 

1.2 

1.0 

.9 

.8 

.75 

.69 

.6 

.5 

.49 

.40 

.36 

.34 

.34 

.34 

.34 

.33 

.32 

.31 

.31 

.30 

.30 

.31 

.30 

.29 

.29 

.28 

.27 

.26 

.26 

.26 

.25 

Total gas 

emission, 

1,121 

971 

7 13 

586 

524 

545 

445 

462 

491 

465 

409 

410 

457 

459 

481 

500 

5 15 

507 

461 

5 08 

528 

538 

522 

493 

6 18 

592 

620 

680 

679 

652 

722 

586 

591 

738 

687 

689 

667 

724 

633 

660 

8 03 

7 14 

638 

Hole 

1 

201 

146 

88 

78 

82 

67 

69 

56 

49 

55 

55 

58 

60 

72 

71 

74 

71 

74 

75 

73 

69 

93 

89 

74 

82 

81 

78 

86 

70 

70 

88 

82 

74 

73 

80 

70 

73 

88 

78 

70 

Total 

Hole 

2 

257 

233 

171 

141 

126 

131 

107 

111 

118 

93 

82 

82 

91 

92 

96 

100 

98 

96 

92 

97 

100 

102 

99 

94 

124 

118 

104 

116 

114 

110 

122 

99 

99 

124 

116 

120 

120 

130 

114 

125 

153 

136 

121 

gas 

Hole 

4 

159 

155 

114 

94 

84 

87 

71 

74 

78 

65 

57 

58 

64 

64 

67 

70 

67 

66 

60 

61 

63 

65 

63 

59 

99 

95 

86 

95 

94 

90 

100 

81 

82 

102 

95 

87 

87 

94 

82 

86 

104 

93 

83 

Hole 

8 

150 

68 

50 

41 

37 

38 

31 

32 

34 

56 

49 

49 

55 

55 

58 

60 

72 

71 

55 

66 

69 

70 

68 

64 

74 

71 

86 

95 

94 

90 

100 

81 

82 

102 

95 

100 

100 

109 

95 

99 

121 

107 

96 

emission, 

Hole 

5 

171 

136 

100 

82 

73 

76 

62 

65 

69 

60 

53 

53 

59 

60 

62 

65 

62 

61 

51 

66 

69 

70 

68 

64 

74 

71 

86 

95 

94 

90 

100 

81 

82 

102 

95 

94 

93 

101 

89 

92 

112 

100 

89 

1,000 

Hole 

6 

104 

126 

93 

76 

68 

71 

58 

60 

64 

56 

49 

49 

55 

55 

58 

60 

72 

71 

60 

71 

74 

75 

73 

69 

80 

77 

92 

95 

101 

97 

107 

87 

88 

110 

102 

87 

87 

94 

82 

79 

96 

86 

77 

cfd 

Hole 

7 

79 

107 

78 

64 

58 

60 

49 

51 

54 

79 

70 

70 

78 

78 

82 

85 

72 

71 

69 

76 

79 

81 

78 

74 

74 

71 

92 

102 

101 

97 

107 

87 

88 

110 

102 

107 

107 

116 

101 

106 

129 

114 

102 
TABLE 1. - Gas production from each horizontal hole, total gas and 

water flow, and in situ pressure record--Continued 

Day 

Total gas 

emission, 

1,000 cfd 

429 

435 

445 

457 

465 

475 

486 

495 

505~ 

517 

528 

535 

545 

555 

575 

585 

597 

605 

615 

628 

635 

646 

650 

660 

670 

680 

690 

700 

710 

720 

730 

740 

750 

760 

766 

7932 

804 

828 

854 

868 

882 

Hole 

Average ( In situ 

Date 

11-12-73 63 109 75 

11-18-73 89 154 106 

11-28-73 70 122 83 

12-10-73 65 106 82 

12-18-73 72 125 85 

12-28-73 67 115 79 

1-08-74 64 111 76 

1-17-74 79 136 93 

1-27-74 73 127 87 

2-08-74 64 111 76 

2-19-74 67 115 79 

2-26-74 68 118 81 

3-08-74 57 98 67 

3-18-74 65 112 77 

4-07-74 49 103 59 

4-17-74 51 101 66 

4-29-74 53 106 69 

5-07-74 53 106 69 

5-17-74 57 109 57 

5-30-74 76 106 75 

6-06-74 78 108 78 

6-17-74 81 139 81 

6-21-74 76 114 82 

7-01-74 77 119 82 

7-11-74 77 118 76 

7-22-74 53 111 74 

7-31-74 70 120 84 

8-10-74 52 107 69 

8-20-74 52 107 70 

8-30-74 77 115 81 

9-09-74 52 100 67 

9-19-74 77 119 82 

9-29-74 57 109 57 

10-09-74 64 111 76 

10-15-74 65 112 77 

11-11-74 75 200 100 

11-22-74 74 198 115 

12-12-74 78 186 105 

1-07-75 81 187 107 

1-21-75 77 182 150 

2-04-75 77 187 89 

lcompressor installed. 

flooded. 

Total gas emission, 1,000 cfd waterf low I gas 

Hole I Hole I Hole ( Hole I ole I Hole I Hole discharge pressure, 

per hole ,, psi 
TIME, days 

1,000 

800 

FIGURE 4. - Gas and water flow rates. 

COMPRESSOR INSTALLATION 

0 

)r 

- I 0 

-Q CT 

600 - t 

Yrc, 

- k! 

0 - Gas flow is regulated 3 

r' Gas flow at compressor LL 

9 400. 

LL W 

cn 

a 

(3 766 days----- 3 

-2Y 

a 

LT 

W 

/Wafer flow - > 

a 

I I I , .o 

0 100 200 300 400 500 600 700 800 

On January 28, 1974, the gas being exhausted into the atmosphere was 

connected to a commercial pipeline (fig. 8). The methane gas is of pipeline 

quality and has not, as yet, required remedial treatment for acceptance into 

the gas company's supply line. However, should daily flow exceed 600,000 cfd, 

it is possible the CO, will need to be removed. 

10 

.- t 

E 

\ - 

o 

-8. 

W 

-J 

\ 1 - 

A rotary compressor was installed; the discharge pressure varies from 25 

to 35 psig, and the negative pressure on the intake side fluctuates between 20 

and 30 inches water gage. Daily gas flow into the commercial gas line has 

averaged 522,000 cfd. Because of mechanical problems with the compressor, it 

was operated intermittently for the first 2 months. Numerous adjustments were 

needed to regulate temperature, flow, water condensation, and intake and 

discharge pressure. These problems were routinely corrected. 

- 

After installing the compressor, and after inducing a negative pressure 

of 25 inches water gage, the in situ pressure dropped from 11.3 to 9.0 psig 

due to a defective inflatable packer; the packer was replaced and the in situ 

pressure has increased to 11.0 psig. Vacuum is regulated at the discharge 

end of the compressor by returning part of the gas to the intake side. The 

amount of gas discharged is governed by the limits of the compressor and the 

allowable pressure in the commercial pipeline. When the flow from the borehole system exceeds the capacity of the compressor, the gas returned to the 

- 

Compressor instal led, 

and gas piped to 

gas company pipelkine 
TIME, days 

FIGURE 6. - Daily total gas flow. 

TIME, days 

FIGURE 5. - In situ pressure. 

1.000 

900 

2. 

0 0

m' 

= BOO - m - 

9 

i 2 700 - VI 

w 766 days -- 

2 600 - 

u J 

!5 

+ 500- 

400 

0 00 200 300 400 500 600 70 0 

I I I I I I I 

- 

I 1 

- 

I I 

0 100 200 300 400 500 600 700 800 
I I I 1 I1 - 

- 

No. 4 - 

- . . .. . .? .. . 3 

I I 

I r-TI I - 

No. 2 A 

- 

120' I I I I 1 I 1 I I 

- 

No. I - 

. 766 days- - 

-. . - 

- 

- . .. . . . 40 I. I I 1 I I I I I 1 I I 

- 

0 100 200 300 400 500 600 700 800 

TIME, days 

FIGURE 7. - Individual hole gas flows. 
intake side causes a backup of gas in the entire system; this explains the 

drop in the rate of emission from the borehole that started when the compressor was first connected, as shown in figure 6. The discharge pressure varies 

between 14 and 27 psig. Maximum allowable discharge temperature is 180" F. 

RESULTS AND DISCUSSIONS 

The total gas flow from the borehole after 180 days was 91 million cubic 

feet, a daily average of nearly 500,000 cfd. The water discharge per hole and 

the in situ pressure were 0.34 gpm and 12.7 psig. Based on the average depth 

of hole (618 feet), about 9,600,000 cubic feet, or 384,000 tons of coal is 

within the roughly circular area defined by the radial holes. The gas content 

per ton of coal is estimated to be 120 cubic feet. This calculates to be 46 

million cubic feet of gas in the defined area, indicating that a much larger 

volume of coal has been degasified than is subtended by the drainage holes. 

After another 200 days (400 total days), the total amount of gas removed 

from the coalbed was 231 million cubic feet; the overall average increased to 

577,000 cfd. The gas volume emitted is12 times the gas estimated to be in the 

area subtended by the seven horizontal holes, indicating that an everincreasing volume of coal is being degasified. The in situ pressure and 

water flow were 11.3 psig and 0.25 gpm. The methane content of the gas is 

more than 87 percent (table 2). 
TABLE 2. - Analyses of four samples from total gas emission 

The daily flow rate fell for the first 150 days, from 971,000 cfd to 

504,000 cfd. An equation for the daily flow rate (DFR) for the first 150 

days would be-- 

DFR = exp (-0.032004d + 13.09461) cfd + 500,000 cfd 

1 < d < 150 where d is the number of days. - - 

Sample 3, 

6-21-74 

0.05 pct 

9.24 

.07 

.35 

90.28 

Sample 2, 

9-15-72 

321 ppm 

9.0 

1.2 

2.4 

87.4 

Ethane (C,%) ........................ Carbon dioxide (CO,). .......... .pct.. 

Oxygen (0,). .................... pct.. 

Nitrogen (N,) ...................p ct.. 

Methane (CH,) ...................p ct.. 

From the 160th day, the daily flow rate increased by 900 cubic feet of 

gas per day. The daily flow rate equation for this period is approximated 

by-- 

Sample 4, 

7-21-74 

0.27 pct 

8.51 

.01 

.20 

90.88 

Sample 1, 

7-10-72 

300 ppm 

9.5 

.6 

2.0 

87.9 

DFR = 505,000 + 733 (d - 160) 160 5 d 5 400 

or exp (0.014838d + 6.143162) + 500,000 cfd 

where d is again the number of days. These equations give values within 

8 percent of the actual recorded values. 

Fluctuations in barometric pressure affect the free flow of gas from 

the multipurpose borehole, as would be expected, but the data are subject to 

such large irregularities due to waterflow and temperature variations that 

we have not subjected them to statistical analysis. 

As of February 4, 1975, 171 million cubic feet of gas had been piped to 

the gas company's line. Figures 4-6 reflect the changes in gas and water, flow 

and in situ pressure before and after the compressor was placed in operation. 

At least 2 years will be required before the 3 South mains are developed 

to the multipurpose borehole location. Methane emission will be monitored 

periodically during development of the mains to determine the actual area of 

effectiveness of this degasification technique. It is expected that upon 

maximum practical degasification of the area involved, coal can be mined with 

few hazards from ignitions and explosions, provided the minimum required 

ventilation is utilized. It is further expected that this situation will 

prevail some distances from the borehole. 

Regarding the cost effectiveness of the degasif ication technique used in 

conjunction with the experimental multipurpose borehole, at a contract cost of 

$848,000, the following logic is used: Assume a minimum of 40 minutes lost 

production time per shift in development withinvirgincoal (this loss has been 
measured in Federal No. 2 mine because of methane emission rates at the face); 

at an average production rate of 4 tons per minute, 160 tons of coal would be 

lost per shift. Assume further that 480 tons of raw coal are produced per 

shift in the degasified area, as compared with 320 tons where not degasified. 

On a clean coal basis, the tonnages would become 410 and 275, respectively. 

The face labor costs per shift in both cases would be $450 (all fringe 

benefits included) for a continuous miner operator, a loading machine operator, 

a ventilation man, two shuttle car operators, a mechanic, a general serviceman, 

a boom operator, and a foreman. The face labor costs per ton of clean coal 

would be $1.10 for the degasified area and $1.62 for the nondegasified area, 

a difference of $0.52 per ton. For each 1 million tons of clean coal, the 

savings due to degasification would be $520,000. 

The value of the methane removed from the coalbed in this project as of 

February 4, 1975, is $259,000, assuming a sale price of 45 cents per thousand 

cubic feet of 576 million cubic feet. 

C ONC LUS I ONS 

Based on the results obtained in 882 days, it can be concluded that the 

multipurpose borehole is a useful degasification technique. The final degasification will greatly exceed the estimated amount of gas calculated to be in 

the virgin area subtended by the drainage holes. A special multipurpose 

borehole is quite expensive; there was a need for such a hole 4 years ago when 

there was no access to virgin coal, but if a coalbed needs to be degasified 

in a great hurry, so that mining can proceed, other methods of degasification 

should be tried. 

Instead of drilling a special hole, mine shafts that will ultimately be 

required for ventilation, skip, or man and material shafts, should be sunk to 

the coalbed long be£ ore normally required so that degas if ication through 

horizontal boreholes can be conducted from the shaft bottom. Work is now 

underway at Eastern Associated Coal Corp.'s Federal No. 2 mine using the 

Honey Run return air shaft sunk approximately 2 years ahead of mining. Horizontal drainage holes have been drilled routinely at relatively low cost. 

As of February 4, 1975, five holes have been drilled to depths of 670, 1,067, 

1,167, 2,126, and 960 feet. Gas flows from these holes have been averaging 

more than 900,000 cfd, and as of February 4, 1975, 549 days after work 

started, more than 481 million cubic feet of methane had been exhausted. 

Plans have been completed to conduct this gas into a commercial pipeline. 

Pipeline-quality gas can be safely removed from virgin areas of the 

Pittsburgh coalbed, and in commercial quantities. This will no doubt be an 

incentive for coal and gas companies to develop similar degasification 

programs. Tools and technology are now available, to accomplish degasification of the very gassy Pittsburgh coalbed without special equipment. Work 

is underway to degasify other gassy coalbeds using this technique. 
1. Cervik, J. An Investi.gation of the Behavior and Control of Methane Gas. 

Min. Cong. J., v. 53, No. 7, July 1967, pp. 52-57. 

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

KI 7800, 1973, 27 pp. 

3. Zabe t-,akis , M. G. , T . D. Moore, Jr . , A, E , Nagel, and J. E . Carpe tta . Methane Emission in Coal Mines: Effect of Oil and Gas Wel.1~. 

Bdliries RI 7658, 1972, 9 pp.