1 

Bureau of Mines Report of lnvestigations/l982 

Degasification of the Mary Lee Coalbed, 

. 

By John H. Perry. Leonard J. Prosser. Jr., 

and Joseph 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 pub1 ication has been cataloged as follows : 

r 

Perry, John H 

Degasification of the Mary Lee Coalbed, Brookwood, Ala. 

(Report of investigations ; 8669) 

Bibliography: p. 13. 

Supt. of Docs. no.: I 28.23:8669. 

1. Coal mines and mining-Alabama-Safety measures. 2. Mine 

gases. 3. Methane. I. Prosscr, L. J. (Leonard J.). 11. Cervik, 

Joseph. 111. Title. IV. Series: Report of investigations (United 

States. Bureau of Mines) ; 8669. 

TN23.U43 [TN295] 622s [622'.81 81-607163 AACR2 
CONTENTS 

Page 

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

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

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

Long-hole drilling at No . 4 Mine ............................................... 2 

Drill site ................................................................ 2 

Drill operations .......................................................... 5 

Control during drilling ................................................... 5 

Surveying ...................................................................... 7 

Gas flow and pressure measurements for hole 1 .................................. 7 

Reduction of face emissions .................................................... 9 

Grouting ....................................................................... 12 

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

References ................................................................ 13 

ILLUSTRATIONS 

Warrior Basin. Ala ........................................................ 3 

Drill site at No . 4 Mine .................................................. 4 

Standard long-hole drill string ........................................... 5 

Modified drill string with 3-inch bit ..................................... 5 

Plot of hole 1 ............................................................ 6 

Upwardly cocked drill assembly ............................................ 7 

Plain view-- hole 1 ........................................................ 8 

Flow and pressure data for hole 1 ......................................... 9 

Methane recordings. August 1979 .......................................... 10 

Methane recordings. January 1980 .......................................... 10 

Methane history of degasified section ..................................... 11 

Methane recordings. October 1979 .......................................... 11 

Grouted hole ........................................................... 12 

TABLES 

1 . Drilling parameters for standard drill string ............................. 6 

2 . Drilling parameters for modified drill string ............................. 6 

3 . Drill log of hole 2 ....................................................... 7 
DEGASlFlCATlON OF THE MARY LEE COALBED, BROOKWOOD, ALA. 

By John Ha Perry, Leonard Ja Prosser, Jra, and Joseph Cervik 

ABSTRACT 

The Bureau of Mines has developed several techniques for draining 

methane from coalbeds in advance of mining. Drilling long horizontal 

holes from an underground location is one such technique, which was 

successfully demonstrated in the Pittsburgh and Sunnyside Coalbeds. 

The same technique has now been applied in the Mary Lee Coalbed at 

Jim Walter Resources, Inc. 's No. 4 Mine, Brookwood, Ala. , where two 

holes were drilled horizontally--one to a depth of 1,010 feet (308 m) 

and the other to 540 feet (165 m). The 1,010-foot (3083) hole proved 

successful in degasifying a portion of the Mary Lee Coalbed. The hole 

drained methane for 1 year, during which time the initial gas flow of 

200,000 ft3/d (5,663 m3/d) declined to 65,000 ft3/d (1,840 m3/d). Total 

gas production was 40 x lo6 ft3 (1.1 x lo6 m3 ). The gas was of commercial quality, with 98 pct methane and a heat rating of 990 ~tu/ft~ 

(36.89 ~j/m~). The methane emissions from the faces of the mine section 

advancing into the degasified zone were reduced by 60 pct. The 540-foot 

(165-m) hole was terminated prematurely when it became impossible to 

maintain an open hole. Because of caving, very little gas was drained 

through this hole. 

'nining engineer. 

2~eologist. 

3~uperv isory geophysicist. 

All authors are with the Pittsburgh Research Center, Bureau of Mines, Pittsburgh, 

Pa. 
INTRODUCTION 

The Bureau of Mines has demonstrated 

that large quantities of methane can be 

removed from underground coalbeds by 

means of long horizontal holes drilled 

into the coalbed. To date, most of this 

research has been concentrated in the 

Eastern United States, with some research 

- in the State of Vtah (1, 3, 1, - 7) .4 

Three primary factors determine the 

amount of gas that can be drained from a 

coalbed. The volume of methane in the 

coal, the in situ pressure, and the permeability of the bed. Coalbeds that have 

relatively high permeability and in situ 

pressure can be successfully drained of 

their methane. The Pittsburgh Coalbed, 

which has an in situ pressure of 275 psig 

(1,896 k~a), is a prime example. Three 

demonstration projects in this coalbed 

have removed more than 1.8 x lo9 ft3 

(51 x 106m3) of methane; about 

700 x lo6 ft3 (19.8 x lo6 m3) of this gas 

has been sold (3, 5). A single project 

in Utah removed-35x lo6 ft3 (991,000 m3) 

of methane from the Sunnyside Coalbed 

(l) 

There is a correlation between the 

volume of gas per ton of coal and the 

depth of the coalbed. The greater the 

depth, the more methane there will be in 

a ton of coal (2). The deepest coal 

mines in the United States are mining the 

Mary Lee Coalbed at a depth of 2,000 feet 

(610 m) . The Mary Lee Coalbed is part 

of the Warrior Coal Basin, which encompasses more than 800 mi2 (2,072 km2) 

of Jefferson, Walker, and Tuscaloosa 

Counties, Ala. (fig. 1). 

The overburden of the Warrior Basin 

varies from zero to 2,500 feet (762 m). 

In one area of the basin, the overburden 

changes 1,500 feet (457 m) within 

0.5 mile (0.8 km) (2). The overburden at 

Jim Walter ~esource~' No. 4 Mine is about 

2,000 feet (610 m) (4). - 

The face cleat of the Warrior Basin 

coalbeds is generally oriented between 

N 53" E and N 68" Em In the NO. 4 Mine, 

the face cleat is about N 60" E, and the 

coalbed is divided into two benches, 

separated by an 18- to 24-inch (46- to 

61-cm) binder. 

The methane content of the Mary Lee 

Group is estimated to be almost 

1 x 1012 ft3 (28 x lo9 m3). Of this 

total, 700 x lo6 ft3 (20 x lo6 m3 ) is 

held in the Mary Lee Coalbed. Almost 

90 pct of this gas is held in the coal 

where the overburden exceeds 1,000 feet 

(305 m). In situ gas pressures as high 

as 800psig (5,516 kPa) have been 

measured. 

ACKNOWLEDGMENTS 

The cooperation of the personnel and Incots NO. 4 Mine is greatly appreciated. 

management of Jim Walter Resources, 

LONG-HOLE DRILLING AT NO. 4 MINE 

Drill Site Mary Lee Coalbed is divided into two 

benches. The upper bench is about 

This project was designed to degas- 20 inches (51 cm) thick and the lower 

ify a portion of the Mary Lee Coalbed bench is about 5 feet (1.5 m) thick. The 

from the northeast corner of the NO. 4 binder separating the two is about 2 feet 

Mine (fig. 2). At this location, the (0.6 m) thick. 

Figure 2 shows the location of the 

enderlined numbers in parentheses two degasification holes drilled into the 

refer to items in the list of references lower bench. The first hole was drilled 

at the end of this report. to a depth of 1,010 feet (308 m) in a 
3 

WALKER COUNTY 

LEGEND 

0 Warrior Basin 

- 

Scale, mi 

FIGURE 1. - Warrior Basin, Ala. 
i Hole I, 

1,010 ft 

I Degasif ication holes 

Jim Walter ~esources' 

No. 4 Mine 

h 

Z .. r. 

I 

• 0 Production . shaft .! 

? 

*. L( 

., 

I, 

Scale, ft 

FIGURE 2. - Drill site at No. 4 Mine. 
N 15O W direction and crosses the face jammed. Hole collapse occurs predomicleat. The second hole was drilled to a 

depth of 540 feet (165 m) parallel to the 

face cleat direction. 

Drill Operations 

A horizontal drill unit, powered by 

an electrically driven hydraulic pump, 

was used for drilling. The power head 

was equipped with a 3-foot (915-m) feed 

length. Initially, the standard longhole drill string was used (fig. 3). It 

consisted of a 3-112-inch (88.9-mm) drag 

bit, two 3-7116-inch (87.3-mm) OD centralizers separated by an 18-foot (5.5-m) 

NQ drill collar, and a BQ drill rod 

2-3/16 inches (55.6 mm) OD. The NQ drill 

collar was 2-314 inches (69.9 mm) OD and 

1-718 inches (47.6 mm) ID, and weighed 

about 200 pounds (90.6 kg). 

This standard drill string caused 

problems. After drilling 120 feet 

(37 m), the drill tools became wedged 

in the hole because of the collapsing 

and/or squeezing of the hole. Hole collapse is evident when drilling produces 

excess coal cuttings and large fragments 

of coal. These coal fragments from the 

resulting oversized hole wedge the bit, 

nantly in softer coalbeds, such as the 

Mary Lee. Hole squeezing is attributable 

to overburden pressure. In this case, 

the hole flattens because of stresses, 

and the drill string becomes jammed in 

the undersized hole. It is possible for 

squeezing and collapse to occur in 

the same hole. The Mary Lee is both 

soft (friable) and deeply deposited 

(2,000 feet (610 m)). 

Because of this situation, alternative drill strings were employed in the 

Mary Lee Coalbed. A string consisting of 

only a 3-inch (76.2-mm) drag bit and RQ 

rod was used (fig. 4). The smaller diameter bit produces fewer cuttings. 

Removal of the drill collar and centralizer allows more area around the drill 

rod for the cuttings to be flushed. 

Also, as the hole increases in depth, it 

is further outby the mine opening, which 

decreases the risk of hole squeezing. 

Control During Drilling 

With the standard drill string 

(fig. 3), the path of the bit in the vertical plane is controlled in three ways: 

By the thrust applied to the bit, by the 

drill collar, and centralizers in place. rotational speed of the bit (revolutions 

Normally, water is used to flush the coal per minute), and by centralizers on the 

cuttings from the hole, but when collapse heavy NQ drill collar. The drill collar 

occurs, the large coal fragments and cut- stiffens the drilling assembly and 

tings wedged around the drill string pre- adds weight to the bottom side of the 

vent flushing, and the tools become drag bit. A drilling assembly with a 

10- in centralizer, 

3q6-in OD 

10- in centralizer, 

7/16-in OD 

{BQ drill casing \18-ft NQ drill collar / / 

&-in bit 

FIGURE 3. - Standard long-hole drill string. 

BQ rod 

FIGURE 4. - Modified drill string with 3-inch bit. 
3-518-inch (92.1-m) bit tends to wear TABLE 1. - Drilling parameters 

the bottom side of the hole and arc down- for standard drill 

ward more readily than one with a 

3-112-inch (88.9-m) bit, and thrust 

s tring 

levels must be higher to compensate for 

this tendency. Because the drilling of 

the Mary Lee required removing the drill 

collar and centralizers and using a 

3-inch (76.2-m) bit, the normal control 

techniques were not applicable. 

TABLE 2. - Drilling parameters 

Thrust 

400-600 Holding. 

Hole 1 was drilled in the return to 

a depth of 1,010 feet (308 m) (fig. 2). 

The final 890 feet (271 m) were drilled 

using only a 3-inch (76.2-m) bit and BQ 

rod. Controlling the bit in a vertical 

plane was attempted by adjusting bit 

thrust and rotational speed, but without 

the drill collar and stabilizers, control 

was not obtained. However, because of 

the softness of the coal and the hardness 

of the floor rock, the hole trajectory 

naturally followed the bottom of the 

coalbed for its entire length (fig. 5). 

Table 1 shows control parameters for 

a standard drill string. These can be 

compared with the drilling parameters in 

table 2 for the modified drill string 

consisting of a 3-inch (76.2-m) bit and 

BQ rod. Increasing thrust and lowering 

rotational speed normally tends to bring 

the standard drill string upward 

(table 1); no response was experienced 

with the modified drill string (table 2), 

regardless of thrust and rotational 

speeds. 

for modified drill 

string 

Because the modified drill string 

with the 3-inch (76.2-m) bit could not 

be controlled, the bit diameter was reduced to 2-518 inches (66.7 mm) in an 

attempt to prevent the bit from undercutting the hole and arcing downward. 

Hole 2 was drilled with the 2-518-inch 

(66.7-m) bit, but the hole trajectory 

still could not be controlled. The bit 

arced toward the floor and followed the 

bottom of the coalbed. Drilling was 

stopped at 330 feet (101 m), and a 

2-112-inch (63.5-m) diameter centralizer 

was added directly behind the bit 

LEGEND 

x - Survey points 

FIGURE 5. - Plot of hole 1. 

Thrust Bit rotation, 

r Pm 

50 

75 

75 

75-100 

100 

17 5 

lb 

1,275 

2,125 

2,550 

2,975 

3,400 

7,250 

Bit angle 

trajectory 

No change. 

Do. 

Do. 

Do. 

Do. 

Do. 

N 

5,671 

9,452 

11,342 

13,233 

15,123 

32,248 
z5/8-in bit, 

FIGURE 6. - Upwardly cocked drill assembly. 

(fig. 6). The centralizer cocked the TABLE 3. - Drill log of --- hole 2 

drilling assembly (bit, centralizer, and 

BQ rod) about 0'54' upward. Table 3 

shows the results of bit thrust and rotational speed on hole trajectory during 

drilling from 330 to 480 feet (101 to 

146 m). Some control over bit trajectory 

was exercised. However, the data are 

inconclusive because the test terminated 

when the hole collapsed or squeezed at 

540 feet (165 m). 

SURVEYING 

A Sperry sun5 single-shot survey instrument was used to survey during drilling. In most drilling operations, the 

inclination of the bit and length of the 

hole are used to compute the location of 

the hole within the coalbed. From this 

information, the drilling parameters are 

determined to better keep the hole within 

the coalbed. However, since the horizontal hole trajectory naturally followed 

the Mary Lee Coalbed, the survey information was used in this case to determine 

the contour of the coalbed. 

Bit 

rotat ion, 

rpm 

62 

75 

7 5 

100 

100 

The Sperry Sun has a magnetic compass to determine the azimuth of the 

hole. This is used to plot the location 

of the hole with respect to the mine 

projections. It is important to know 

the location of the hole, so that it 

will not be inadvertently mined through. 

Depth 

The uncontrolled gas flow from such a 

situation could present a hazard to 

mining. 

Vertical 

inclination, deg. 

89.8 

91.5 

NAP 

NAP 

89.5 

ft 

380 

430 

440 

450 

480 

Usually, a 1,000-foot (305-m) hole 

can be plotted with an accuracy of 

25 feet (1.5 m). However, this was not 

the case here. Mine section 3 was about 

20 feet closer to hole 1 than anticim 

116 

131 

134 

137 

146 

pated, and the hole was mined into just 

as grouting had started. There are two 

plausible explanations for this. Either 

the magnetic correction was not 3' at the 

underground drill site, or the survey instrument was off by 3". However, there 

is no evidence to support these assumpThrust 

tions. The error was not recognized 

until every point of the section intercepted by the hole was surveyed. Figure 7 shows the hole as projected by the 

Sperry Sun and its actual location. 

lb 

2,975 

3,400 

3,400 

2,550 

2,550 

GAS FLOW AND PRESSURE MEASUREMENTS FOR HOLE 1 

N 

13,233 

15,124 

15,124 

11,343 

11,343 

Hole 1 was shut in so that an in drilled 100 feet (30.5 m) to the west. 

situ pressure monitoring hole could be This hole was drilled to a horizontal 

were allowed to reach equilibrium pres5~eference to specific equipment does depth of 100 feet (30.5 m) and grouted, 

not imply endorsement by the Bureau of so that the in situ pressure at that 

Mines. depth could be monitored. Both holes 
SECT I0 

LEGEND 

667 Mine spad number 

4 Entry number 

x Locations of hole 

intercept 

Projected hole 

OLD WORK1 NGS 

0 100 

Scale, ft 

FIGURE 7. - Plain view-hole 1. 
were allowed to reach equilibrium pressure. The long hole reached a steady 

pressure of about 70 psig (483 kPa) and 

the in situ pressure hole leveled off at 

22.5 psig (155 kPa). 

When the long hole was reopened, its 

flow-rate and the in situ pressure began 

declining rapidly. In 18 days, the gas 

flow dropped from an initial value of 

200,000 to 155,000 ft3/d (5,663 to 

4,389 m3/d), and the in situ pressure 

dropped from 22.5 to 9 psig (155 to 

66 kPa). Both the pressure and flow continued to decline slowly for the next 

6 months. The in situ pressure declined 

to 1.7 psig (12 kPa). The gas flow was 

62,000 ft3/d (1,752 m3/d) when section 3 

was 500 feet (152 m) from the hole. The 

flow reading taken the day before the 

hole was mined through and then grouted 

was 68,000 ft3/d (1,926 m3/d). Figure 8 

shows the flow and pressure data for 

hole 1. Total gas flow from the hole for 

a year was 40 x lo6 ft3 (1.1 x lo6 m3). 

The percentage of methane in the gas was 

between 98 and 99 pct. The gas was analyzed to have a heat rating of 

990 ~tu/ft~ (3,689 ~j/rn~) . 

REDUCTION OF FACE EMISSIONS 

Ventilation surveys were made of 

section 3 after it turned east and 

started to mine toward the 1,010-foot 

(308-m) degasification hole, to determine 

the benefit of degasification to mining. 

All methane and air readings were made 

approximately 150 feet (46 m) back of 

each return from the last open crosscut. 

Wherever possible, continuous-recording 

methanometers were set at each location. 

Methane surveys were taken each month 

from June 1979 to January 1980, with the 

exception of December 1979. Each monthly 

survey lasted about 4 days. 

The recording methanometers were 

used to measure the methane peak concentrations that occurred briefly as the 

mining machine sumped into the coal face. 

There was a marked increase in these 

peaks after the section had advanced 

through the degasification zone. Figure 9 shows typical methane concentration 

recordings taken during the August 1979 

1979 

FIGURE 8. - Flow and pressure data for hole 1. 

200 

-150 Q 

m> 

LC 

m 

2 

100 

5 

S LL * 

50 4 

0 

/R shut -in pressure 

Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. 

7 

- 

e =7 

kt-iole I opened 

- 

- Drillrng 

- 

- 

7 

, 

I 

\ - 

I In s~tu pressure, monitor~ng hole 

I 1.3 

t1 "*51k'11'~1k11 I 1i51k1tt;51 t;51kL1 l2'5I~~~ 25l k' '';51k1 1'i51~' 1;51k1t1A 
I 1 I I 1 I I I - - Left return - Aug. 22, 1979 - 

- - 

- - 

I I I I I I I I 

0 

9p.m. I0p.m. 1lp.m. Midnight Ia,m. 2a.m. 3a.m. 4a.m. 5a.m. 6a.m. 

TI ME 

r I I I I 1 I 1 I 

- - 

Right return - - 

- - C - 

1 I I I 1 1 I 1 

FIGURE 9. - Methane recordings, August 1979, in the degasified zone. 

0 

6pm. 7p.m. 8p.m. 9p.m. 10p.m. 1Ip.m. Midnight laem. 2a.m. 3a.m. 

TI ME 

I I I I I 1 I I - - - Right return - - - 

- 

I I 1 1 I I 1 

FIGURE 10. - Methane recordings, January 1980, beyond the degasified zone. 

survey. Section 3 had advanced to within 

500 feet (152 m) of the degasification hole and was in the degasified zone. 

The baseline readings for the left and 

right returns were 0.38 and 0.22 pct, 

respectively. The methane peaks (A%) 

were only 0.07 and 0.16 pct above the 

baselines. This compares favorably with 

the recordings taken during the January 

1980 survey when the section had advanced 

700feet (213m) beyond the hole 

(fig. 10). The methane peaks recorded in 

the left return increased 0.32 pct, from 

a baseline of 0.58 to 0.9 pct. To determine the overall methane reduction due to 

degasification, handheld methanometer, 

air, and baseline methane recordings were 

calculated and averaged for each monthly 

survey and compared. Bottle samples were 

also taken to check the methanometer. 

When the section was 840 feet 

(256 m) from the hole, there was a 

172-f t3 /min (4.9-m3 /min) flow from the 

faces (fig. 11). At a distance of 

40 feet (12 m), the flow was 67 ft3/min 

(1.9 m3/min), a reduction of 60 pct. 

When the section passed 700 feet (213 m) 

beyond the hole, the methane coming from 

the faces was 230 ft3 /min (6.5 m3 /min). 
DISTANCE OF FACES FROM DEGASlFlCATlON HOLE, ft 

Scale, ft 

FIGURE 11. - Methane history of degasified section. 

1.2 1 I 1 1 I I I I 

FIGURE 12. - Methane recordings, October 1979. 

.8 

2 1.2- I I I I I I I 

- Left return 

I - 

- Oct. 26, 1979 - - - 

o 

.8 

-Right return - - intercepted - - I Calibration 7 
FIGURE 13. - Grouted hole. 
thoroughly mixing four stacks of cement, 

water, and fluidifier in a 55-gal 

(2,08 liter) drum. The grout was dipped 

from the drum with a bucket and poured 

into the hopper of the moyno grout pump. 

As the mix in the drum decreased by the 

equivalent of one sack of cement, the 

corresponding amounts of cement, water, 

and fluidifier were added. By continually repeating this procedure, the grout 

pump could be run continuously , which 

reduced the probability of the grout setting. Mixing was continuous during the 

grouting, which took 1.5 hours to complete. Once grouting was completed, only 

a slight amount of methane was perceptible coming from the hole. 

A check of the grouted portions of 

the hole that were later mined through 

showed the annulus between the pipe and 

coal to be completely filled (fig. 13). 

CONCLUSIONS 

The Mary Lee Coalbed can be successfully degasified using long horizontal 

holes. The 1,010-foot (308-m) hole 

removed 40 x lo6 ft3 (1.1 x lo6 m3) of 

methane from the coalbed in 1 year. The 

methane face emissions of the mine section being driven through the degasified 

zone were reduced by 60 pct. 

of the softness of the coal and the hardness of the floor rock, the bit bounces 

off the rock, staying in the hole as it 

is drilled. Only a 3-inch (76.2-mm) 

diameter drag bit and BQ rod should be 

used, because experience has shown that 

when centralizers are used, they become 

wedged in the hole. 

Long horizontal holes can be drilled 

quickly in the Mary Lee Coalbed. Because 

REFERENCES 

1. Cevik, J., H. H. Fields, and G. N. 

Aul. Rotary Drilling Holes in Coalbeds 

for Degasification. BuMines RI 8097, 

1975, 21 pp. 

2. Diamond, W. P., G. W. Murrie, and 

C. M. McCulloch. Methane Gas Content of 

the Mary Lee Group of Coalbeds, Jefferson, Tuscaloosa, and Walker Counties, 

Ala. BuMines RI 8117, 1976, 9 pp. 

3. Fields, H. He, J. Cervik, and T. 

We Goodman. Degasification and Production of Natural Gas From an Air Shaft in 

the Pittsburgh Coalbed. BuMines RI 8173, 

1976, 23 pp. 

4. Fields, H. He, S. Krickovic, A. 

Sainato, and M. G. Zabetakis. 

Degasification of Virgin Pittsburgh Coalbed Through a Large Borehole. BuMines 

RI 7800, 1973, 27 pp. 

5. Fields, H. H., J. H. Perry, and M. 

Deul. Commercial-Quality Gas From a Multipurpose Borehole Located in the Pittsburgh Coalbed. BuMines RI 8025, 1975, 

14 PP* 

6. Irani, M. C., E. D. Thimons, T. G. 

Bobick, M. Deul, and M. G. Zabetakis. 

Methane Emission From U.S. Coal Mines. A 

Survey. BuMines IC 8558, 1972, 58 pp. 

7. Perry, J. H., G. N. Aul, and 

J. Cervik. Methane Drainage Study in 

the Sunnyside Coalbed, Utah. BuMines 

RI 8323, 1978, 11 pp.