By A. A. Campoli, J. Cervik, and S. J. Schatzel 

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

William P. Clark, Secretary 

BUREAU OF MINES 

Robert C. Horton, Director 
Library of Congress Cataloging in Publication Data: 

Campoli, A. A. (Alan A*) 

Control of longwall gob gas with cross-measure boreholes (Upper 

Kittanning Coalbed). 

(Report of investigations / United States Department of Interior, Bureau of Mines ; 8841) 

Bibliography: p. 17. 

Supt. of Docs. no.: I 28.23:8841. 

1. Fire-damp. 2. Coal mines and mining-Safety measures. 3. 

Mine ventilation. 4. Boring. I. Cervik, Joseph. 11. Schatzel, Steven J. 111. Title. IV. Series: Report of investigations (United States. 

Bureau of Mines) ; 8841. 

TN23.U43 [TN305] 622s [622',8] 83-600321 

< e 

1 
CONTENTS 

Page -I 

kbstract ........................................................................ iIntroduction ................................................................... kcknowledgments ................................................................ Study area ..................................................................... ~ross-measure borehole system design ........................................... I Drilling equipment and procedures .............................................. iPiping system and flow measurement procedures .................................. Surface venting facility ....................................................... Production data ................................................................ Gob gas production ........................................................... Water production ............................................................. Partial vacuum applied to cross-measure boreholes .............................. Effects of the cross-measure system ............................................ Summary and conclusions ........................................................ References ..................................................................... ILLUSTRATIONS 

Generalized stratigraphic column of Pennsylvanian system ................... Stratigraphic column above Upper Kittanning Coalbed ........................ Bethlehem Mines Corp.'s Cambria 33 Mine (Upper Kittanning Coalbed) ......... Longwall test panel ........................................................ Schematic of cross-measure borehole design parameters ...................... Electrohydraulic drilling unit ............................................. Hydraulic drill control unit ............................................... Expandable mechanical packer ............................................... Stuffing box ............................................................... Synthetic diamond wafer bits ............................................... ETA drill rod being added to drill string .................................. Plastic standpipe with sockets ............................................. Cross-measure borehole equipment ........................................... Surface venting facility ................................................... Methane flow rates ......................................................... Gob gas flow rates ......................................................... Hole life versus inclination angle ......................................... Hole life versus penetration into gob ...................................... Cross-measure. longwall return. and total methane flow rates ............... Effect of the cross-measure system on the mine ventilation system .......... TABLE 

1 . Production his tory of cross-measure boreholes .............................. 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

centimeter kW kilowatt 

degree L liter 

foot ~/min liter per minute 

cubic foot per minute m meter 

gallon mm millimeter 

gallon per minute m3/s cubic meter per second 

hour Pet percent 

horsepower rad radian 

inch VAC volt alternating current 

kilopascal 
CONTROL OF LONGWALL GOB GAS WITH CROSS-MEASURE BOREHOLES 

(UPPER KITTANNING COALBED) 

By A. A. Carnpoli, ' J. Cervik, and S. J. Schatzel 

ABSTRACT 

The cross-measure borehole technique is being studied by the Bureau of 

Mines as an alternative to the use of surface gob boreholes as a means 

of controlling methane in gobs during longwall mining. Small-diameter 

holes are drilled from underground locations into strata overlying the 

mined coalbed. When the roof strata are fractured by the mining operation, a partial vacuum applied to the boreholes draws the methane out of 

the fractured strata and prevents it from entering the mine ventilation 

system. 

Tests in the Upper Kittanning Coalbed showed that 50 pct of the methane produced by the longwall mining operation was captured by the crossmeasure boreholes. Borehole inclination and penetration into the gob 

are two important borehole parameters that affect the performance of the 

cross-measure borehole system. 

' Mining engineer. 

'supervisory - geophysicist. 

Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
- Lower Freeport Coal bed (Dl Q, Lower Freeport Limestone 

F 

LI 

Free port Sandstone 

Upper Kittanning Coalbed (c') 

Johnstown Limestone c 

cn Upper Worthington Sandstone 

'-0 2 E 

a 'F 

E 

L 

9 

cn Middle Kittanning coal group (C) C .- 

C 

C 

0 

+ 

. - Lower Worthington Sandstone 

Y Lower Kittanning "rider" 

coalbed (B) 

Lower Kittanning Coalbed ( 6) 

FIGURE 1. - Generalized stratigraphic column 

of Pennsylvanian system. Letters in parentheses 

are local seam designations. 

Lower 

- Freeport 

Coalbed t 

v- 

* 

W 

0 

Z 

2 

- cn 

n 

Upper , Kit tanning 

Coalbed 

Upper 

,Freeport 

Coal bed 

Bone coal Shale 

Coal I: Sandstone 

Clay F;i7-1 Limestone 

FIGURE 2. - Stratigraphic column above Upper 

Kittanning Coalbed. 
The underground pipeline is located in 

the center entry of the three-entry re- 

/" turn air gateroad. All cross-measure 

boreholes were drilled from the center 

entry, which was supported by a line of 

cribs and remained open and passable 

after the panels on both sides were 

removed. 

i' 

Eroluor8on 

0Ol"t 

Surfoce borehole 

C. J 

FIGURE 3. - Bethlehem Mines Corp.'~ Cambria FIGURE 4. - Longwall test panel. 

33 Mine (Upper Kittanning Coalbed). 
CROSS-MEASURE BOREHOLE SYSTEM DESIGN 

The design of the cross-measure borehol-es was based on European information 

and knowledge gained in a prior Bureau of 

Mines study (7, pp. 2, 4, 13). Figure 5 

shows the fTnal borehole parameters, 

which were determined through in-hole 

surveys. 

The endpoints of the cross-measure 

boreholes were spaced 250 ft (76 m) 

apart. All boreholes were drilled over a 

support pillar to protect the borehole 

when the longwall face passed the collar. Borehole length, inclination, and 

horizontal direction were chosen to 

accomplish the following: 

1. Maintain the height of the borehole 

over the far end of the support pillar at 

least eight times the coalbed thickness 

(fig. 5, E). Estimates of the height of 

the rubblized zone in the gob range from 

4 to 8 times coalbed thickness. 

* Cross-measure borehole number 

A - Inclination, degrees 

B - Horizontal angle, degrees 

C. - Hole length, feet 

D - Ter~ni nal height of hole, feet 

i - Height of hole dt end of supported length, feet 

F - Penetration over 1 ongwall panel, feet 

G - Distance froin endpoint to origin of hole, feet 

H - Distance from start of panel to endpoint of hole, feet 

Plan view 

Elevation view 

FIGURE 5. - Schematic of cross-measure borehole design parameters. 
FIGURE 6. - Ele~troh~draulic drilling unit. 
FIGURE 7. - Hydraulic drill control unit. 

hydraulic fluid is a fire-resistant 60/40 

water emulsion fluid. 

The first 26 ft (7.9 m) of each borehole was drilled with a 4-in (102-mm) 

diamond core bit, and the cores were removed in 30-in (76.2-cm) sections. The 

remainder of the hole was drilled with a 

1.9-in (48-mm) bit. Because abnormal 

methane flows could be encountered during 

drilling of the 1.9-in (48-mm) hole, all 

drilling was conducted through a stuffing 

box attached to a 4-in (1021nm) expandable mechanical packer (fig. 8). Return 

water and drill cuttings were transported 

to a well-ventilated area 30 ft (9.1 m) 

downstream from the drill site through a 

hose connected to the mechanical packer 

(fig. 9). The packer, stuffing box, and 

valve at the end of the drainage hose 
FIGURE 9. - Stuffing box. 

provided the means to shut-in the bore- A synthetic diamond wafer bit [1.9 in 

hole if abnormal methane flows were (48 mm)] was used to drill the crossencountered during drilling. However, no measure boreholes (fig. 10). Penetration 

abnormal flows occurred during the drill- rate through the sandstones and shales 

ing of any of the holes on the test averaged 70 ft (21.3 m) per shift, and 

panel. bit life was exceptional. Only one bit 
FIGURE 10. - Synthetic diamond wafer bits. A, New; B, worn. 

was used to drill all cross-measure boreholes on the test panel. Figure 10 compares a new bit (A) to one that had 

drilled over 3,100 ft (945 m) of rock 

(B). The diamond wafers are chipped and 

worn to the point where the matrix had 

been rubbing on the rock surface during 

drilling. The worn bit (B) can be salvaged by removing the diamoxd wafers and 

rotating them about 180" (3.1 rad). The 

cost to salvage the bit is about half the 

cost of a new bit. 

The drill unit was limited to a length 

of about 54 in (137 cm) (fig. 6) because 

coalbed height is about 45 in (114 cm) 

and holes were inclined upward 23" to 33" 

(0.40 to 0.58 rad). Drill rods are 1.6 

in (41 mm) in diameter and 15 in (381 mm) 

long (fig. ll), which required frequent 

interruptions in drilling to insert drill 

rods. The rods were screwed into one 

another with a special coarse taper 

thread (ETA) for rapid connection and 

dismantling. No centralizers were used 

during drilling because of the small difference in diameter between the drill 

rods and bit. Downhole surveys showed 

little variation in borehole trajectory. 

Plastic standpipes were cemented into 

each cross-measure borehole after the 

completion of the drilling phase. The 

cementing phase is important because if 

not completed properly, mine air could 

short-circuit into the cross-measure 

borehole, reducing its ability to draw 

methane from the gob. 
FIGURE 11. - ETA drill rod being added to drill string. 
Two grouting procedures were tested to 

determine the best method of grouting the 

standpipes. In holes 1 through 7, 9, and 

10, 5-ft (1.59) lengths of 2.25-in (57- 

mm) diameter plastic pipe were joined 

with sockets. Total length of standpipe 

was about 20 ft (6.1 m) (fig. 12). Short 

15-in (38-cm) plugs of cement were emplaced every 30 in (76 cm) along the 

plastic pipe. If roof movements during 

mining cause a misalignment of the hole, 

the plastic pipe bends at the socket 

joints and because the cement is emplaced 

in short plugs, cracking would be minimal. In holes , , and 12, 1.25-in 

(32-mm), 2.5-in (64-mm), and 2-in (51-mm) 

diameter plastic pipes, respectively, 

were grouted 18 ft (5.5 m) into the 

holes. Drilling the hole and grouting 

the plastic standpipe required about five 

8-h shifts by a three-person crew. 

PIPING SYSTEM AND FLOW MEASUREMENT PROCEDURES 

Access to the surface was provided by a 

688-f t (2109) long, 12-in (30.5-cm) 

diameter surface borehole (fig. 4). The 

borehole was cased with 8-in (20.3-cm) 

steel pipe and cemented the entire 

length. A 6-in (15.2-cm) crushproof 

plastic pipeline [4,750 ft (1,448 m)] 

connected the surface borehole to the 

cross-measure boreholes. 

Movement of a gas through a plastic 

pipeline can cause a static charge buildup on the pipeline. A static charge can 

ignite explosive methane-air mixtures. 

To dissipate the static charge, the entire pipeline was wrapped with bare copper wire, which was attached to copper 

grounding rods. These rods were placed 

in 10-f t (3-m) holes drilled into the 

bottom and packed with charcoal. The 

grounding rods were spaced 500 ft (152 m) 

along the pipeline. 

The pipeline entry adjacent to the test 

panel (fig. 4) sloped about 1 pct downward from hole 12 to 1; at the rightangle bend, the slope increased to 3 

pct downward toward the vertical borehole. Water flow from the cross-measure 

boreholes was discharged directly into 

the main pipeline; at the right-angle 

bend, the water was collected in a 2-in 

(51-mrn) metal pipeline installed directly below the main pipeline. Water 

was drained from the metal pipeline 

periodically. 

Gas flow (methane plus air) from each 

cross-measure borehole was calculated 

from gas pressure drop measurements with 

P' 

FIGURE 12. - Plastic standpipe with sockets. 
h / / venturi meter, 2inl 

L~lastic pipe, 

.Ball valve, 

2 in 

-Plastic pipe, 

2.25-in OD 

FIGURE 13. - Cross-measure borehole equipment. 

a mercury manometer across a venturi, and 

the concentration of methane in the gas 

flow was measured with a 0- to 100-pct 

methanometer (fig. 13). The partial 

vacuum at each hole was measured with a 

mercury manometer at a pressure tap. 

Return air from the longwall mining operation was channeled through a 

single entry before it entered the 

main returns (fig. 4--evaluation point). 

Periodically, the volume of air was measured with an anemometer at the evaluation point. Gas bottle samples were also 

taken simultaneously and analyzed with a 

gas chromatograph to determine methane 

concentration in the return air. Thus 

the total methane flow from the longwall 

mining operation is the sum of the flows 

from the cross-measure boreholes and 

in the return air from the longwall 

(fig. 4--evaluation point). 

SURFACE VENTING FACILITY 

The surface venting facility (fig. 14) producing flows up to 200 ft3jmin (0.09 

was protected by a flame arrestor, light- m3/s) and a partial vacuum up to 3.5 in 

ning arrestor, and check damper to of mercury (11.8 kPa), removed the gob 

prevent backflow into the pipeline. gas. The exhauster was driven by a 5-hp 

An ignition-proof exhauster, capable of (3.7-kW) 440-VAC motor. 
FIGURE 14. - Surface venting facility. 
The total flow of gob gas (methane plus gas analyzer. The instrument was set to 

air) at the surface was calculated from sound an alarm in the mine office when 

individual cross-measure borehole gas methane concentration dropped below 25 

flows. The methane concentration in the pct. The partial vacuum at the intake 

gas flow at the surface was measured and to the exhauster was also measured 

recorded continuously with an infrared periodically. 

PRODUCTION DATA 

GOB GAS PRODUCTION 

Gob gas was extracted from 11 of the 12 

cross-measure boreholes. Hole 1, the 

only borehole that failed to produce gob 

gas, was drilled with its endpoint only 

27 ft (8.2 m) from the starting point of 

the panel (fig. 5, - H). Apparently the 

strata in this area did not fracture; 

thus no flow paths were created to permit 

gob gas movement toward the hole. 

No free flow of methane occurred from 

any cross-measure borehole. Even with an 

applied partial vacuum, flow did not 

occur until the face passed 75 to 100 ft 

(23 to 30 m) beyond the end of the hole; 

it did occur before the face passed the 

collar of the hole, however. 

Figures 15 and 16 show methane and gob 

gas (methane plus air) flow rates, respectively, for each cross-measure borehole. Generally, the flow rate curves 

for each cross-measure borehole follow 

the same pattern except for holes 4 and 

8. For these two holes, the methane flow 

rates declined to zero but the air flow 

from each hole increased, which indicated 

direct communication with the mine ventilation air. For holes 2, 3, 5, 6, 7, and 

9, when gob gas flow declined, the methane flow also declined. Eventually the 

holes were shut-in because the methane 

concentration in the gob gas flow dropped 

below 25 pct. Subsequently, the gob gas 

flow declined to a negligible quantity, 

indicating gob compaction and fracture 

system closure. A complete production 

KEY 

x- x Total 

Hole 

No. 

++ 2 

3 

Oc t. Nov. Dec. Jan. Fe b. Mar. AP~ 

TIME, months 

FIGURE 15. - Methane flow rates. 
149 days (table 1). Borehole inclination 

(fig. 5, F) and penetration into the gob 

(fig. 5, F) were two important parameters 

that appear to affect gas production life 

of boreholes. Figure 17 shows borehole 

Grouting of the standpipe 18 ft (5.5 m) 

or more into a hole is recommended over 

the use of socket joints and plugs of 

cement because the cost is less and the 

procedures are simpler. 

TABLE 1. - Production history of cross-measure boreholes 

Reason gas production was terminated 

Hole never produced gob gas. 

Gob compacted and flow declined to zero. 

Do. 

Methane concentration fell below 25 pct 

with dramatic increase in gas flow rate. 

Gob compacted and flow declined to zero. 

Do. 

Do. 

Methane concentration fell below 25 pct 

with dramatic increase in gas flow rate. 

Gob compacted and flow declined to zero. 

Complete production history not obtained. 

Study was terminated when mining of 

panel was completed. 

Do. 

Do. 

Hole 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

Gas production 

life, days 

0 

7 3 

32 

149 

16 

7 1 

5 6 

14 

3 7 

45 

2 0 

8 
HOLE LIFE, days 

FIGURE 17. - Hole life versus inclination angle, 1 I 

- 

WATER PRODUCTION loo I2 I I 

9 0 

0 20 40 60 80 100 120 140 160 

Only cross-measure boreholes 3 and 8 HOLE LIFE, days 

produced water when initially drilled. 

Water production was 1.5 and 10 gal/min FIGURE 18. - Hole l ife versus penetration into gob. 

(5.7 and 37.9 L/min), respectively. When 

undermined, water flow from hole 3 in- (3.8 to 30.3 L/min). Holes 1, 5, 9, 10, 

creased to 6 gal/min (22.7 L/min) and and 12 did not produce water at any time. 

flow from hole 8 decreased to 1 gal/min No correlation appears to exist between 

(3.8 L/min). Holes 2, 4, 6, 7, and 11 water production and terminal height of 

started to produce water after undermin- the boreholes (figs. 4 and 5, - D). 

ing; flow ranged from 1 to 8 gal/min 

PARTIAL VACUUM APPLIED TO CROSS-MEASURE BOREHOLES 

The exhauster located on the surface 

borehole operated at maximum partial 

vacuum [3.5 in mercury (11.8 k~a)] 

throughout the study. Because of frictional losses in the pipeline, the partial vacuum at the cross-measure boreholes was always less and will vary among 

the holes. For example, the maximum partial vacuum measured at a cross-measure 

borehole was 3.0 in Hg (10.1 kPa) and gob 

gas flow was 27 ft3/min (0.013 m3/s). At 

another hole, the partial vacuum was 0.9 

in Hg (3.0 kPa) and gas flow was 107 

ft3/min (0.050 m3/s). Gob permeability 

is the dominant factor affecting flow 

and partial vacuum at a cross-measure 

Pressure measurements with a U-tube 

water manometer indicated the partial 

vacuum in the gob at each cross-measure 

borehole dissipated in less than a minute 

after the surface exhauster was turned 

off . Subsequently, all cross-measure 

boreholes were put on production except 

one which remained shut-in. Gas pressure 

in the gob was measured in the shut-in 

hole over a 24-h period. The partial 

vacuum in the gob remained zero. These 

data indicate that no communication 

exists between adjacent holes and that 

areas exist in the gob that are not being 

drained by the cross-measure boreholes. 

Either the cross-measure boreholes should 

borehole. Flow is high and partial be spaced closer to one another, or a 

vacuum is low in a loose gob; in a tight surface exhauster capable of a larger 

gob flow is low and partial vacuum is flow at a greater partial vacuum should 

high. be used. 
EFFECTS OF THE CROSS-MEASURE SYSTEM 

Methane enters mine workings during 

longwall mining from fractured roof and 

floor strata and from the mined coalbed. 

Ventilation and methane surveys conducted 

at the tailgate of the longwall showed 

that the flow of methane from the mined 

coalbed during mining was about 20 ft3/ 

min (0.01 m3/s). During nonmining periods, the flow was negligible. The contribution of floor strata to methane 

in the gob is unknown. Coalbeds in the 

roof strata are known methane source 

beds. 

Figure 19 shows that the cross-measure 

borehole system captured about 50 pct of 

the methane produced by the mining 

operation. The other half was removed by 

the mine ventilation system. Methane 

flows in both systems declined during the 

life of the panel. 

The effect of the cross-measure borehole system on methane in the mine ventilation system was dramatic. Figure 20 

shows that the methane flow in the return 

air from the longwall increased by a 

factor of over 2 when the cross-measure 

borehole system was not in operation. 

These data clearly demonstrate the effectiveness of the boreholes in controlling 

methane in the gob. 

SUMMARY AND CONCLUSIONS 

The cross-measure borehole technique is 

a viable method of controlling methane in 

gobs of retreating longwalls in the Upper 

Kittanning Coalbed. About 50 pct of the 

methane produced by the mining operation 

was captured by the cross-measure borehole system. Use of an exhauster with a 

higher flow capacity and partial vacuum 

would increase the quantity of methane 

captured by the cross-measure borehole 

system. 

Depth of penetration into the gob and 

inclination of a cross-measure borehole are two important parameters that 

affect the quality and quantity of gob 

gas produced by a borehole. Borehole 

inclination should be at least 31° (0.54 

rad), and larger angles should be tested 

to determine if performance can be improved further. Borehole penetration 

into the gob (fig. 5, F) should be limited to about 100 ft (35 m). 

1 

III(I I I[I11 111 I/ 

Key 

- M~ne ventrlation system 

- n-Cross-measure system 9 ,", ?- 

t' I 1 - 1 

/ 1 I - / I I 

// I I 

/ I I 

- I / I - 

/ I I 

/ 

/ 

/ - - I -tl \ ' \ I 

- Y - 

Illllllllllll lllllI_ 

OPERATING TIME, days OPERATING TIME, days 

FIGURE 19. - Cross-measure, longwal l return, and FIGURE 20. - Effect of the cross-measure system on 

total methane flow rates. the mine venti lation system. 

- - 

ota from longwall panel - 

- 1. - 

'% 

- 1- - 

-- '. longw wall return 1- ----- - - \ 

1- - - -- 

Cross- measure system - - 

I I I I I 

I I I I 
Seven of the 12 crosslneasure boreholes 

produce water ranging from 1 to 10 gal/- 

min (3.8 to 37.9 L/min). Gas-water separation devices will be required on each 

borehole if the main pipeline is not 

sloped to drain water. No correlation 

appears to exist between water production and terminal height of boreholes 

(fig. 5, 2). 

The cross-measure boreholes were spaced 

250 ft (76 m) along the test panel. 

Communication tests between boreholes 

indicated the spacing should be reduced 

or a larger capacity exhauster should be 

employed to improve the performance of 

the cross-measure borehole sys tem. The 

first crosslneasure borehole should be 

drilled so that the end of the borehole 

is about 100 ft (30 m) from the starting 

end of the panel. The end of hole 1 was 

about 27 ft (8 m) from the starting end 

of the test panel and it produced neither 

air nor methane. Apparently no fracturing occurred around hole 1. 

REFERENCES 

1. Cervik, J. Methane Control on 

Longwalls--European and U.S. Practices. 

Ch. in Longwall-Shortwall Mining, Stateof -the-Art. Society of Mining Engineers, 

New York, 1981, pp. 75-80. 

2. Fennelly, S. D. Face-Ends, A Challenge for the 1980's. Coll. Guard., 

v. 288, No. 11, 1980, 498 pp. 

3. Heising, C., and H. Becker. Dust 

Control in Longwall Workings. Paper in 

Proceedings 2nd International Mine Ventilation Congress (Reno, NV, Nov. 4-8, 

1979). Society of Mining Engineers, New 

York, 1980, pp. 604-607. 

Coalbed, Somerset County, Pa. BuMines RI 

8575, 1981, 41 pp. 

5. Matuszewski, J., and L. Lunarzewski. Control of Dangerous Methane Accumulations. Paper in Proceedings 2nd 

International Mine Ventilation Congress 

(Reno, NV, -Nova 4-8, 1979). Society of 

Mining Engineers, New York, 1980, 

pp. 384-393. 

6. Puglio, D. G., and A. T. Iannacchione. Geology, Mining and Methane Content 

of the Freeport and Kittanning Coalbeds 

in Indiana and Surrounding Counties, Pa. 

BuMines RI 8406, 1979, 35 pp. 

4. Iannacchione, A., J. P. Ulery, 7. Schatzel, S. J. Underground Gob 

D. M. Hyman, and F. E. Chase. Geologic Gas Drainage During Longwall Mining. BuFactors in Predicting Coal Mine Roof -Rock Mines RI 8644, 1982, 14 pp. 

Stability in the Upper Kittanning 

hU.S. GOVERNMENT PRINTING OFFICE: 1983-705-020l100 INT.-BU.0 F MIN ES,PGH.,PA. 27277