By L. J. Prosser, Jr., G. L. Finfinger, 

and J. Cervik 

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

James G. Watt, Secretary 

BUREAU OF MINES 

Robert C. Horton, Director 
This publication has been cataloged as follows: 

Prosser, L. J. (Leonard J.) 

Methane drainage study using an underground pipeline, Marianna Mine 58. 

(Report of investigations ; 8577) 

Bibliography: p. 29, 

1. Coal mines and mining-Safety measures. 2. Mine ventilation. 3. 

Methane. 1. Finfinger, Gerald L. 11. Cervik, Joseph. 111. Title. IV. Series: Report of investigations (United States. Bureau of Mines) ; 8577. 

TN23.U43 [ TN2951 622s r6221.81 81-1765 AACR2 
CONTENTS 

Abstract ................................................................ Introduction ............................................................ Acknowledgments. ........................................................ Test site ............................................................... Drilling equipment and procedures ....................................... Hole surveying .......................................................... Methane control during drilling ......................................... Pipeline safety controls ................................................ Discussion of flows ...................................................... Gas flows during drilling .......................................... Gas and water flows after drilling ................................. Gas utilization .................................................... Summary ................................................................. Conclusions ............................................................. References .............................................................. ILLUSTRATIONS 

Location of test site .............................................. Location of underground pipeline and vertical borehole ............. Steel pipeline and cribbing blocks ................................. Gas-water separator ................................................ Surface venting facility .......................................... ts 

Hydraulic drill .................................................... Centralizer ........................................................ Drilling assembly with two centralizers separated by 18-foot NQ 

drill collar ..................................................... Drilling assembly with rear centralizer removed .................... Survey system ...................................................... Stuffing box and 4-inch valve ...................................... Pressure gage and vent tubing ...................................... Methane pipeline control system .................................... PVC plastic pipe and pipeline ...................................... Location of pneumatic shutoff valve in methane drainage pipeline 

system ........................................................... Hole 3 gas flow rates during drilling .............................. Hole 4 gas flow rates during drilling.. ............................ Trajectories of holes 1 and 4 ...................................... Hole 2 gas flow rates during drilling .............................. Gas pressure buildup at control hole A ............................. Gas pressure buildup-- holes 1 and 2 ................................ Sandstone channel and clay veins ................................... Initial shut-in gas pressures-- holes 1 and 2 ....................... Daily methane flows-- holes 1. 2. 3. and 4 .......................... Total daily methane and water flow rates ........................... Cumulative methane production ...................................... 
TABLES 

- Page 

Penetration rates with 3-1/2-inch bit, Fairview, W. Va., area....... 

Penetration rates with 3-1/2-inch bit, Marianna Mine 58............. 

Penetration rates with 3-5/S-inch bit and modified drilling assembly 

Time study.......................................................... 

Hole depth versus survey time (hole 2).............................. 

Initial gas flows of holes 1, 2, 3, and 4........................... 

Composition and heating value of coalbed gas and natural gas........ 
METHANE DRAINAGE STUDY USING AN UNDERGROUND 

PIPELINE, MARIANNA MINE 58 

L- J. Prosser, Jr., 1 G. L. Finfinger,2 and J. Cervik 3 

ABSTRACT 

The Bureau of Mines has completed an underground degasification project 

in which an underground piping system was used to transport methane from the 

coalbed to the surface. In a 10-month period four horizontal holes were 

drilled to an average depth of 1,450 feet. All four holes were surveyed vertically and azimuthally. In 991 days of degasification, 255 MMcf of gas was 

drained from the coalbed. The underground piping system proved to be a safe 

and effective means of transporting methane from the coalbed to the surface. 

INTRODUCTION 

Methane in coalbeds constitutes a serious hazard when it is released into 

the mine atmosphere. To provide a safe working environment, the concentration 

of methane in mine air must be maintained at a level well below the lower 

explosive limit. Traditionally, ventilation air has been used to dilute methane to nonexplosive levels. However, increased production, due to modern mining techniques, can produce situations in which methane emission rates exceed 

the capacity of the ventilation system. When this occurs, mining must be 

halted until a safe methane level is reached; such situations increase the 

hazards from ignitions and explosions and adversely affect production (7).4 - 

Drainage of methane in advance of mining is inherently a safe method for 

controlling methane emissions during mining and contributes to efficient use 

of mining equipment. The Bureau of Mines has demonstrated that drainage of 

methane through horizontal holes drilled from a shaft bottom is a successful 

method of removing methane in advance of mining (5). Over a 3-year period, 

approximately 802 MMcf of methane was removed from the Pittsburgh coalbed, and 

mine entries driven into the degasified zone experienced a 70-pct reduction in 

'~eolo~ist, Eastern Field Operations Center, Bureau of Mines, Pittsburgh, Pa. 

2~upervisory geologist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, Pa. 

3~upervisory geophysicist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, Pa. 

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

the end of this report. 
methane emissions during mining. Emissions began to decline when mine entries 

were 3,500 feet from the shaft. 

Degasification from mine workings requires underground pipelines to 

transport methane to the surface where it can be sold or utilized at the mine 

site. Piping methane from underground locations to the surface was first 

attempted in Great Britain about 200 years ago (1). Large-scale operations 

were initiated in the 1940's at many collieries in the Ruhr, the Saar, Belgium, France, and Great Britain. However, in the United States no large-scale 

operations were undertaken until recently. The first methane drainage and 

underground pipeline integrated in the production cycle is located in MidContinent Coal and Coke Coats Dutch Creek No. 1 Mine (10). This installation 

is similar to European advancing longwall drainage systems where holes are 

drilled into overlying strata and vacuum pumps draw methane from the fracture 

zone above the mine coalbed (3). 

The present paper describes a degasification project conducted by the 

Bureau of Mines at Marianna Mine 58, Marianna, Pa. The project utilized an 

underground pipeline for transporting methane from the mine to the surface. 

Gas emissions were reduced, and a methane-monitoring system provided a continuous check on the integrity of the pipeline system. 

ACKNOWLEDGMENTS 

The cooperation of Bethlehem Mines Corp. during this study is greatly 

appreciated. The authors wish to thank D. Sparks, manager; C. McGlothin, mine 

superintendent; D. Patterson, chief engineer; L. Sprague, assistant chief 

engineer; and George Concilio, engineer, for assistance in planning and conducting the work described in this report. 

TEST SITE 

The degasification program at Bethlehem Mines Corpmfs Marianna Mine 58, 

Marianna, Pa., was conducted in a section which was advanced about 5,000 feet 

into virgin coal (Pittsburgh coalbed) (fig. 1). Four horizontal holes were 

drilled ranging in length from 982 to 2,505 feet. Two holes were drilled on 

the left side and two holes on the right side of the section (fig. 1). A 

fifth hole in the middle of the section is 200 feet long and is used to monitor gas pressure in the coalbed. 

A 6-inch-diameter steel pipeline (schedule 40) transports methane from 

underground locations to the surface (fig. 2). Total length of the pipeline 

is 1,150 feet, and pipe sections are joined with compression couplings. Cribbing blocks on 5-foot centers are used to protect the pipeline from roof falls 

as well as supporting the pipeline (fig. 3). 

Gas flowing through the underground pipeline contains water vapor which 

condenses as it travels to the surface through the vertical borehole. Consequently, the underground pipeline is connected to the vertical borehole 

through a gas-water separator which drains water from the system (fig. 4). 

Gas produced during and after drilling is vented at the surface. The pipeline 

is grounded, and the surface venting facility is equipped with an approved 

flame arrester (fig. 5). 
Scale, f t Hole 1, 1,068 ft 

FIGURE 1. - Location of test site. 

I 

LEGEND 

Permanent stopping 

Stopping with door 

-R Regulator - 

- Intake air 

8-i

b

O, 

Sca

-Return air 

FIGURE 2. - Location of underground pipeline 

borehole. 
FIGURE 3. - Steel pipeline and cribbing blocks. 
FIGURE 4. - Gas-water separator. 
FIGURE 5. - Surface venting facility. 
DRILLING EQUIPMENT AND PROCEDURES 

All holes were drilled with a hydraulically operated drill (fig. 6). The 

power unit for the drill was kept in a fresh air entry and was equipped with a 

40-hp, 440-v-ac motor and hydraulic pump. Feed length of the drill unit was 

30 inches. The drill string included a 3-5/8- or3-1/2-inch drag bit and two 

centralizers (3-7/16-inch OD) (fig. 7) separated by an 18-foot NQ drill 

collar which was 2-3/4 inches in OD and 1-7/8 inches in ID and weighed about 

200 pounds. The heavy drill collar stiffened the drilling assembly and added 

weight to the bottom side of the drag bit. 

The path of a bit in the vertical plane is controlled by a combination of 

bit sizes, bit thrust and rotational speed (rpm), and by location of centralizers on the drill collar (fig. 8). A drilling assembly with a 3-5/8-inch bit 

tends to wear the bottom side of the hole and arc downward more readily than 

an assembly with a 3-1/2-inch bit. Therefore, thrust levels must be higher to 

compensate for the tendency of the 3-5/8-inch bit to arc downward (4). - 

Previous Bureau experience in drilling the Pittsburgh coalbed in the 

Fairview, W. Va.,area had revealed marked differences in drilling characteristics of the upper and lower portions of the coalbed (4). The upper 3 to 

3.5 feet, which contains numerous streaks and bands oT pyrite, appears harder 

during drilling than the lower part of the coalbed, which is predominately 

free of impurities and consequently softer. This characteristic of the Pittsburgh coalbed is also in evidence at Marianna Mine 58. Based on this characteristic and other horizontal drilling studies, a 3-112-inch bit was initially 

chosen for drilling at the Marianna Mine 58 site. 

Marianna Mine 58 is located about 30 miles north of the Fairview, W. Va., 

area, where overburden thickness is about 800 feet compared with 500 feet at 

the Marianna Mine. Comparison of tables 1 and 2 shows that bit penetration 

rates are greater at the Marianna Mine drill site, with a lower rotational 

speed (rpm) of the bit at comparable levels of thrust. The lower bit penetration rates in Fairview, W. Va., area may be due to greater overburden pressure 

on the coalbed. 

TABLE 1. - Penetration rates with 3-1/2-inch bit, 

Fairview. W. Va.. area 

TABLE 2. - Penetration rates with 3-1/2-inch bit, 

Marianna Mine 58 

Thrust, lb 

800.................. 

1,20...... 

1,500 or greater....... 

Bit rotation, 

rPm 

700-900 

400-600 

200-300 

Thrust, lb 

850mmmmmmmm.~mmmmmm.. 

1,225 .................. 1,70. 

Penetration 

rate, ipm 

4-7 

10 

15 or greater 

Bit rotation, 

rPm 

150 

300 

150 

Penetration 

rate, ipm 

8-10 

12-14 

16-24 
FIGURE 6. - Hydraulic drill. 

FIGURE 7. - Centralizer. 
Not to scale 10-in centralizer, 

7 3%-in OD, 

10-in centralizer, 

Drill casing \ 18-ft drill collar' 5' 3~in bit 

FIGURE 8. - Drilling assembly with two centralizers separated by 18-foot NQ drill collar. 

The penetration rate of a drilling assembly (fig. 8) with a 3-518-inch 

bit is greater than that of an assembly with a 3-112-inch bit (4). Because of 

the soft nature of the lower portion of the coalbed at Marianna-Mine 58, the 

drilling assembly with a 3-5/8-inch bit arced into the floor repeatedly and 

could not be controlled with combinations of bit thrust and rotational speed. 

Therefore, the rear centralizer was removed, cocking the 18-foot drill collar, 

front centralizer, and bit about 0.1" upward in the hole (fig, 9). No problems were encountered in controlling this modified drilling assembly at the 

Marianna Mine 58 site. All holes except hole 1 were drilled with the modified 

drilling assembly. Table 3 summarizes the effect of bit thrust and rotational 

speed on bit trajectory and penetration rates. Comparison of tables 1, 2, and 

3 shows that penetration rates of the modified drilling assembly are greater 

by a factor of about two. 

TABLE 3, - Penetration rates with 3-518-inch bit and 

modified drilling assembly 

Table 4 is an analysis of the time spent completing holes 1, 2, and 4. 

Between 53 and 74 pct of each shift was lost time, which included portal to 

portal, water supply and electrical problems, equipment failures, etc. Of the 

Thrust, 

lb 

850 

1,275 

1,700 

2,500 

Not to scale In- in ~antmIi7nr 7 ,,, wwll,,~,,,,,, 3gin OD, 

Bit rotation, 

rPm 

300 

300 

150 

250 

18-ft drill collar 

Drill casing, 

5 /33 -in bit 

Effect on 

bit trajectory 

Downward......,.... 

Held angle.. ....... Upward............. 

Sharply upward..,.. 

FIGURE 9. - Drilling assembly with rear centralizer removed. 

Penetration rate, 

ipm 

12-15 

24 

30-36 

42-48 
average time available to each shift for drilling and surveying, drilling occupied 67 to 80 pct and surveying 20 to 33 pct. 

TABLE 4. - Time study 

water problems, electrical problems, 

drill malfunctions, sensor 

malfunctions)..... .................. min.. 

Number of work shifts..................... 

Work shift...........................min.. 

Time lost per shift (portal to portal, 

Average time for drilling and surveying 

per shift...........................nin.. 

Average drilling time per shiEt......min.. 

Average surveying time per shift.....min.. 

Total depth............. .............. ft. 

Initial bearing of collar................. 

Hole 1 

60 

480 

Hole 2 Hole 3 YqTif- Hole 4 

Vertical inclination of coalbed (above or I I I I 

below horizontal). ................. .deg.. 1 +0.5 1 -0.5 1 +0.5 1 +0.5 

'NO time study data available owing to testing of experimental survey 

instrument. 

HOLE SURVEYING 

Vertical inclination of the hole during drilling was obtained with a 

Sperry-Sun,5 single-shot survey instrument (fig. 10). The essential elements 

(fig* 10C) of the single-shot surveying instrument are the inclination unit, 

which is-in the form of an inverted plumb bob, batteries to furnish electrical 

power, and a timer which controls the electrical circuits and illuminates the 

angle unit at a preset time to record the inclination of the bit on a film 

disk. 

Special loading and developing tanks permit handling of the exposed film 

disk in daylight or without turning off cap lamps underground. When the 

inclination of the hole is to be determined, the surveying instrument is 

placed in its protective casing which is then inserted into the drill rod and 

pumped using water to the end of the hole. At the preset time, the film disk 

is exposed, after which the instrument is retrieved by a wire line attached to 

the protective casing. The film disk is removed, developed, and read (4). - 

The Bureau's experience in horizontal drilling indicates that a hole 

should be surveyed for vertical inclination at least every 20 feet to insure 

that projected hole trajectory is maintained. If the hole begins to deviate, 

then appropriate drilling parameters, such as bit thrust and rotational speed, 

must be varied to correct hole deviation in the vertical plane. Experience 

shows that although surveying is time consuming (table 5), maintaining the 

vertical angle of inclination of the hole within lo of the projected trajectory 

5~eference to specific equipment does not imply endorsement by the Bureau of 

Mines. 
FIGURE 10. - Survey system. A, Survey instrument; K, protective case; C, survey instrument components. 

will prevent costly time delays due to loss of control of hole trajectory and 

subsequent drilling in roof or floor strata. Table 5 shows that the average 

time per survey is about 16 minutes at hole depths of 1,000 feet. When hole 

depth is about 2,000 feet, the average time per survey doubles and surveying 

occupies over 50 pct of the time available for drilling and surveying per 

shift. 
TABLE 5. - Hole depth versus survey 

time (hole 2) 

Hole depth, ft Average time 

survey, min 

The trajectory of a horizontal hole in the azimuth plane cannot be determined by projecting a line based on the bearing of the hole at or near the 

collar. The hole must be surveyed to determine its location in the azimuth 

plane. Experience shows that a hole may turn either to the right or to the 

left, contrary to the popular belief that a hole will turn to the right 

because of the clockwise rotation of the bit during drilling. In some cases, 

a hole may turn to the left and then deflect to the right. 

METHANE CONTROL DURING DRILLING 

Gas flow during drilling was controlled with a Bureau-designed stuffing 

box which separated gas from water and drill cuttings. The stuffing box was 

attached to a 4-inch-diameter pipe fitted with a 4-inch valve so the hole 

could be shut-in if necessary (fig. 11). The 4-inch-diameter pipe was 21 feet 

long and grouted in place. Gas was ducted from the stuffing box to the 6-inchdiameter pipeline and then to the surface through the 8-inch-diameter vertical 

borehole. The vertical flow through the 8-inch-diameter borehole created a 

natural draft which maintained a negative pressure in the vent tubing and 

prevented methane leakage from the stuffing box into the mine entry. The negative pressure (-0.5 inch water gage) in the vent tubing was monitored with 

a pressure gage (fig. 12). Because of the negative pressure in the vent tubing, some air is drawn into the stuffing box through small openings where the 

drill rod enters the stuffing box. The methane concentration in the vent tubing was monitored continuously and varied between 80 and 100 pct during the 

drilling phase. 
FIGURE 11. - Stuffin
FIGURE 12. - Pressu
PIPELINE SAFETY CONTROLS 

Methane sensors are installed every 500 feet in the entries containing 

the pipeline. The power supply for the sensor system operates on 110 v ac and 

is located in a fresh air entry (fig. 13). The sensors are intrinsically safe 

and approved for use in coal mines. 

A 314-inch polyvinyl chloride (PVC) plastic pipe is strapped to the top 

of the pipeline along its entire length (fig. 14). This plastic pipe is connected to the pneumatic valves which are installed on each hole after drilling 

has been completed (fig. 15). The valves are spring-loaded and held open by 

air pressure (55 psig) supplied by a small nonpermissible air compressor rated 

at 1.05 cfm, 80 psig. This unit is located in a fresh air entry near the control panel and is wired to the methane sensor control panel. 

The methane sensors control the pneumatic valves on each horizontal hole 

and will close them automatically if a sensor ceases to function, if the electrical line to a sensor is broken, or if the methane concentration in the 

pipeline entry exceeds 1 pct. If any of these conditions exist, a relay in 

the control panel powers a solenoid which vents the compressed air in the PVC 

line. Power to the compressor is automatically cut off when air pressure in 

the plastic line drops below 50 psig. The PVC pipe is brittle and shatters on 

impact. A roof fall that severs the main pipeline will also shatter the PVC 

pipe. When this occurs the pneumatic valves will close as air pressure in the 

line decreases. 

DISCUSSION OF FLOWS 

Gas Flows During Drilling 

Gas flows were monitored during drilling of each hole. These flows were 

determined from velocity measurements taken with an anemometer inside the ducting which connected the gas-water and drill cutting separator to the underground pipeline. The measured velocity was corrected for ducting diameter, 

and methane flows were monitored throughout the drilling phase. The correction for ducting diameter was determined in the laboratory. 

The Pittsburgh coalbed in the area of Marianna Mine 58 contains a sandstone channel and clay veins (8) which can form cells that limit the drainage 

area of a horizontal hole. clgY veins are generally associated with fractured 

roof strata and produce abnormal methane flows when penetrated by mining or a 

horizontal hole. 

The drill site at Marianna Mine 58 is in a section where mining was abandoned because of severe gas problems. When the study began, the section had 

been idle for about 2-1/2 years. Consequently, gas flows from holes could be 

expected to be much lower than flows from holes drilled in an active section. 

Hole 3 was drilled to 1,238 feet at a fairly constant rate, and gas flows 

during drilling increased linearly at a rate of 89 cfdlft of hole drilled 

(fig. 16). Gas flows from hole 4 increased at a rate of 86 cfd/ft to 420 feet 
FIGURE 13. - Methan
FIGURE 14. - PVC plastic pipe and pipe!ine. 

Methane 

detector 8-in pipe,v to surface 

FIGURE 15. - Location of pneumatic shutoff valve in methane drainage pipeline system. 

600 700 8 00 900 1,000 1,100 1,200 1,300 

DEPTH, ft 

FIGURE 18. - Trajectories of holes 1 and 4. Dotted pattern indicates rock. 
the far side of the sandstone, gas flow from the hole increased by 50,000 cfd. 

Based on this drilling and information from core hole logs, the discontinuity 

was assumed to be a sandstone channel. 

Hole 1 was not drilled at a constant rate; consequently, the flow data 

are difficult to interpret. The gas flow rates during drilling of hole 2 were 

168 cfdlft to 440 feet and 41 cfd/ft between 440 and 2,150 feet (fig. 19). At 

2,220 feet, gas flow increased to 214,000 cfd from 144,000 cfd at 2,150 feet, 

indicating that a clay vein had been intercepted. Drilling terminated in the 

floor at 2,505 feet. The lower gas flow rate between 440 and 2,150 feet was 

again probably due to a clay vein that shielded the hole and prevented free 

migration of gas to the hole. 

The bearings of the clay vein intercepted by holes 2 and 4 were determined by observing interference effects between holes. All holes were shut-in 

for about 24 hours. Gas pressure at the pressure-monitoring hole (hole A) 

increased from 8.4 to 11.2 psig (fig. 20). Then hole 1 was opened and gas 

pressure at hole A immediately began to decline, indicating an interference 

effect. If a clay vein, which obstructs flow, had been located between holes 

1 and A, no gas pressure change would have been observed at hole A. Subsequently, hole 4 was opened and a further decrease in gas pressure was 

immediately observed at hole A (fig. 20). This test indicated that there 

probably were no clay veins to obstruct flow laterally between holes 1 and 4. 

The gas pressure buildups for holes 1 and 2 are shown in figure 21. 

After about 23 hours, shut-in gas pressure at holes 1 and 2 were 6.4 and 

7.7 psig, respectively. When hole 1 was opened, no change in gas pressure 

was observed at hole 2. The holes are 12 feet apart at the collars. This 

indicates the clay vein intercepted by hole 2 at 2,220 feet is probably 

located between holes 1 and 2 (fig. 22). Similarly, the gas pressure buildups for holes 3 and 4 were 4.7 and 4.4 psig, respectively. When hole 4 was 

opened, no pressure change occurred at hole 3. The holes are 37 feet apart 

at the collars. This indicates that the clay vein intercepted by hole 4 at 

740 feet is probably located between holes 3 and 4 (fig. 22). 

Two clay veins were mapped in the section near the drill site (fig. 22). 

A thick clay vein (2-112 to 3 feet) crosses the section about 1,000 feet outby 

the face area, and a thin vein ( 1 t o 2 inches) crosses the right side and terminates near the middle of the section about 500 feet outby the face (fig. 22). 

Shut-in gas pressures of horizontal holes generally decrease because of 

the large quantities of methane drained from the coalbed. Initial shut-in 

gas pressure of holes 1 and 2 measured after the completion of drilling were 

11 and 13.1 psig, respectively (fig. 23). After 660 days of degasification 

the shut-in gas pressure declined to 6.4 and 7.7 psig, respectively (fig. 21), 

or about 40 pct for both holes. 

oooadonao 

ounaaoooo 

OUDOCJDOOO 

0 u 400 800 1200 

Scale, ft 

FIGURE 22. - Sandstone channel and clay veins. 
FIGURE 23. - Initial shut-in gas pressures-holes 1 and 2. 

Gas and Water Flows After Drilling 

After drilling is completed, the hole is connected to the 6-inch-diameter 

underground pipeline. The following equipment is installed between the collar 

of the hole and pipeline (fig. 15): 4-inch-diameter manual valve, pneumatic 

valve, gas-water separator, venturi meter, 2-inch diameter steel pipe, and 

2-inch-diameter manual valve. 

The pneumatic valve, which is controlled by the methane sensor system, 

was discussed previously. Generally, holes drilled into coalbeds produce 

water and methane, which are separated at the gas-water separator. Water 

level in the separator is controlled by a float valve on the outside of the 

tank. The venturi is used to monitor methane flows by measuring a gas pressure differential across the venturi. Finally, the hole is connected to the 

main pipeline with 2-inch-diameter steel pipe. Manual valves are located at 

the collar and main pipeline for safety. These valves isolate the equipment 

between the collar and main pipeline for cleaning, repair, or replacement. 

Initial gas flow from horizontal holes in other areas of the Pittsburgh 

coalbed is about 250 cfd/ft of hole length (2). The initial gas flows from 

holes 1 through 4 at Marianna Mine 58 were much less (table 6) and ranged 

from 81 to 126 cfd/ft of hole. The lower flows are due to clay veins and a 
sandstone channel which isolate large blocks of coal (8). Degasification is 

confined to those large blocks of coal outlined by theclay veins and sandstone channel and subsequently penetrated by a drainage hole. In addition, 

the section was abandoned for about 2-1/2 years, allowing gas to bleed from 

the coalbed fracture system to the mine opening before the drilling program 

started. 

TABLE 6. - Initial gas flows of holes 1, 2, 3, and 4 

'~e~th at which hole initially hit rock. 

When a hole is shut-in, methane leaks around the 21-foot steel pipe and 

enters the mine opening through the coalbed. Tests conducted to determined 

methane leakage rates into the mine opening when all holes were shut-in showed 

the leakage rates were significant. Holes 1 and 2 are located in the left 

return and holes 3 and 4 in the right return. Before the holes were shut-in, 

combined flow of holes 1 and 2 was 169,000 cfd (117.2 cfrn), compared with 

80,000 cfd (56 cfm) for holes 3 and 4. The flow of methane from face and ribs 

was 17,700 cfd (12.3 cfm) in the left return immediately outby holes 1 and 2 

and 18,100 cfd (12.6 cfm) in the right return immediately outby holes 3 and 4. 

Initial gas 

flow, - cfd/ft 

126 

112 

81 

95 

Hole 

1 

2 

3 

4 

Twenty-four hours after all holes were shut-in, methane flows from face 

and ribs in the left and right returns increased to 145,200 cfd (100.9 cfm) 

and 91,300 cfd (63.3 cfrn), respectively. The combined leakage rate is 

127,500 cfd (89.3 cfm) for holes 1 and 2 and 73,200 cfd (51.2 cfm) for holes 

3 and 4. Consequently, 80 pct of the total flow from all holes leaks into 

the mine opening when holes are shut-in. 

Daily methane flows for each hole are shown in figure 24. In each case 

when the hole was reopened after being shut-in, methane flows had declined 

considerably, which substantiates the leakage rate measurements discussed in 

the previous paragraph. Flows after about 660 days of degasification are 

about one-half initial flow rates. 

Hole length, 

f t ' 950 

2,505 

1,238 

- '840 

- 

Initial gas 

flow, cfd 

120,000 

280,000 

100,000 

80,000 
TIME, days 

FIGURE 24. - Dai ly methane f lows-holes 1, 2, 3, and 4. Dashed portions of curves represent 

interval when hole was shut-in; dark symbols indicate water flow. 

300 

200 

I 

u rC 

0 

z , 

5 

Holes 3 and 4 did not produce water. Daily flow rates for holes 1 and 2 

are shown in figure 24. Waterflow from hole 1 declined to zero flow after 

about 400 days of degasification. Total daily methane and water flow rates 

are shown in figure 25. Cumulative production after 991 days of operation is 

255 MMcf of methane (fig. 26). 

I I I I 

'3 Hole 2 \ 

\ 

\ 

- \ ' 1 0. \ 

I 

I \ \ 

1 

- I \ \ \\\----4 \.--- --- 

I 

-, 

I 

r 

I I 

I I I I 

Hole I 

- - 

0 - 0. 

100- \\.\ "- - 

o-~-**----~ I I 

-2 0 E 

3- 

-I 2 

a 

W 

t 

03 

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

I I I I 

Hole 4 

- - 

- - O0-. . 

I 

3 300 

LL 

cn 

a 

a 

200 

100- 

0 

.% 

I I 1 1 

Hole 3 

- - 

-\ - ' \ ^ 

I I I I 
TIME, days 

FIGURE 25. - Total dai ly methane and water flow rates. Dashed portions of curves represent 

interval when hole was shut-in; dark symbols indicate water flow. 

TIME, days 

FIGURE 26. - Cumulative methane production. Dashed portion of curve represents interval 

when hole was shut-in. 
Gas Utilization 

The composition and heating value of gas in coal are very similar to 

those of natural gas (6), as shown in table 7. The analysis shows the gas 

drained from this portion of the Pittsburgh coalbed is interchangeable with 

natural gas or is suitable for utilization. 

TABLE 7. - Composition and heating value of coalbed gas and natural gas, pct 

Pittsburgh (Marianna)........ 

Pocahontas No. 3............. 

Kittanning................... 

Lower Hartshorne............. 

Mary Lee..................... 

Natural gas (e).............. 

ND Not detected. 

lot her hydrocarbons. 

2~2, C02, and He. 

Effective horizontal drainage technology requires an underground pipeline 

and a vertical borehole to the surface to remove the methane from the mine. 

Since many horizontal holes can be connected to the underground pipeline and 

vented at a single location on the surface, the methane can be utilized without a complex and expensive gathering system. The Bureau of Mines cooperated 

with Bethlehem Mines Corp. and the Department of Energy on a demonstration 

project at Marianna Mine 58 for generating electricity from the methane gas 

being captured from the four horizontal drainage holes. A turbine generator 

has been installed at a surface location of the Marianna Mine 58 property. 

Methane from the horizontal holes is piped to the turbine generator, which 

converts it to electricity for operation of a mine ventilation fan. A total 

of 20 MMcf of methane has been utilized during the demonstration project, and 

a total of 255 MMcf of methane has been removed from the mine by the four horizontal drainage holes. 

SUMMARY 

Four horizontal drainage holes were drilled ranging from 982 to 2,505 feet. 

Initial methane flow from the holes was 580,000 cfd. The methane is piped to 

the surface through an underground 6-inch steel pipeline 1,159 feet long. 

All holes are equipped with pneumatic valves which are held open with 

compressed air (55 psig). Methane sensors, which are located every 500 feet 

along the pipeline, control the pneumatic valves. If an abnormal methane 

concentration (1 pet) is detected, the sensor sends a signal to the control 

panel, and the compressed-air line to the pneumatic valves is vented, closing 

the holes. 

Clay veins and a sandstone channel were located during the drilling phase. 

The sandstone channel extends over 420 feet along the projected coalbed horizon 
(in hole 1). Methane flows from the horizontal holes were much less than 

flows observed in other areas of the Pittsburgh coalbed. The clay veins and 

sandstone channel isolate large blocks of coal, which limits drainage to the 

isolated blocks of coal penetrated by the horizontal holes. 

Because of the soft nature of the Pittsburgh coalbed at Marianna Mine 58, 

all holes except hole 1 were drilled with a modified drilling assembly which 

consisted of a 3-518-inch bit, centralizer, and 18-foot drill collar. Removal 

of the rear centralizer cocked the assembly 0.1' upward in the hole. 

CONCLUSIONS 

Degasification of the Pittsburgh coalbed has been successfully demonstrated at Marianna Mine 58. Horizontal drainage holes drilled into virgin 

coal in advance of mining have captured a significant amount of methane before 

it could enter the mine's ventilation system. The initial combined gas flow 

of 580,000 cfd of methane decreased to 234,000 cfd after 991 days, with a 

total gas production of 255 MMcf. 

Horizontal holes are an effective method for identifying and locating 

discontinuities in a coalbed in advance of mining. At Marianna Mine 58 clay 

veins and a sandstone channel have been located and penetrated by horizontal 

drilling in virgin areas. Gas flows from horizontal holes are significantly 

reduced in areas of coalbeds in which discontinuities are present. 
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Colliery Eng., v. 32, NO. 6, June 1955, pp. 222-232. 

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pp. 257-264. 

3 . . Methane Control on Longwalls--European and U.S. Practices, 

SME-AIME Annual Meeting, New Orleans, La., Feb. 18-22, 1979, SME Preprint COAL 79-06, 10 pp. 

4. Cervik, J., H. H. Fields, and Go No Aul. Rotary Drilling of Holes in 

Coalbeds for Degasification. BuMines RI 8097, 1975, 21 pp. 

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on Underground Mining, Louisville, Ky., Oct. 18-20, 1977, pp, 25-41. 

7. Kim, A. G. Methane in Pittsburgh Coalbed, Greene County, Pa. BuMines 

RI 8026, 1975, 10 pp. 

8. McCulloch, C. Me, W. P. Diamond, Ro Me Bench, and Ma Deul. Selected Genlogic Factors Affecting Mining of the Pittsburgh Coalbed. BuMines 

RI 8093, 1975, 72 pp. 

9. Moore, B. J., Ro D. Miller, and Re Do Shrewsbury. Analysis of Natural 

Gases of the United States. BuMines IC 8302, 1966, 144 pp. 

10. Reeves, J. A*, Jr. Advancing Longwall Mining at Mid-Continent. Am. Min. 

Cong. J., v. 64, NO. 7, July 1978, pp. 25-29. 

r>U.S GOVERNMENT PRINTING OFFICE. 1981-703-002186