Bureau of Mines Report of Investigations/l976 

Methane Emissions 

From an Advancing Coal Mine 

Section in the Pittsburgh Coalbed 

UNITED STATES DEPARTMENT OF THE INTERIOR 
gh, Pa. 

RIOR 
This publication has been cataloged as follows: 

Jeran, Paul W 

Methane emissions from an advancing coal mine section in 

the Pittsburgh coalbed, by P. W. Jeran, D. H. Lawhead, and 

M. C. Irani. [washington] U.S. Bureau of Mines [I9761 

10 p. illus. (U.S. Bureau of Mines. Report of investigations 

8132) 

Includes bibliography. 

1. Methane. 2. Mine gases. I. Lawhead, David H., jt. auth. 

11. Irani, Meherwan C., jt. auth. 111. U.S. Bureau of Mines. IV. 

Title. (Series) 

TTN23.U7 no. 8132 622.06173 

U.S. Dept. of the Int. Library 

J 
CONTENTS 

Page 

Abstract ................................................................ Introduction ............................................................ Acknowledgments ......................................................... Geology ................................................................. Data sources ............................................................ Mining history .......................................................... Monitoring history ...................................................... Discussion .............................................................. Smry ................................................................. References .............................................................. 

ILLUSTRATIONS 

Location sketch map of 5 North bleeders ............................ Structure of base of Pittsburgh coalbed ............................ Columnar section Pittsburgh through Redstone coalbeds .............. Location map of core test boreholes ................................ Isopach of Pittsburgh coalbed ...................................... Sketch map of 5 North bleeders ..................................... Sketch map of clay vein location ................................... Sketch map of sensor assembly locations ............................ Graph of average daily methane volume-percent recorded from 

sensor 1 ......................................................... Graph of daily methane emissions from 5 North bleeders ............. Graph of average daily methane emissions during production and idle 

periods .......................................................... Graph of average length of virgin rib exposed ...................... Plot of daily methane emission versus average length of rib exposed 
METHANE EMISSIONS FROM AN ADVANCING COAL MINE SECTION 

IN THE PITTSBURGH COALBED 

by 

Pe We.Jeran, De He Lawhead, and Me Ce lrani 

ABSTRACT 

The methane emissions from an advancing coal mine section were continuously monitored for 120 days. During this time, the section advanced 

2,000 feet into virgin Pittsburgh coalbed producing 54,565 tons of coal with 

a total methane emission of 91 million ft3. Analysis of the data gathered 

showed that daily methane emissions did not correlate with overburden thickness and daily coal production. A good correlation was found between the 

daily methane emission and the average length of rib exposed to virgin coal. 

INTRODUCTION 

Methane gas is a hazard in underground coal mining. It enters the mine 

ventilation system from tbe breakup of coal, from the face and virgin ribs, 

and from the gob. Each of these sources contributes to the total emission 

from the mine, which can be monitored by a continuous-recording methanometer 

(4),4 installed at the exhaust fans of the mine. However, to identify and 

study the factors that determine methane emission, each individual underground 

source must be monitored separately. A system of underground methanometers 

has been developed for this purpose (2). 

Based on a survey of the average daily methane emissions from mines in 

individual major coalbeds (z), a correlation was developed between total mine 

emission measured at exhaust fans and depth and production. To determine if 

methane emissions from a local working place would show the same correlation, 

the methane emitted from an advancing section was monitored continuously while 

the section was mined under a range of overburden thicknesses. The working 

place chosen was remote from prior mining and relatively free from stratigraphic or geologic structural changes, in the Pittsburgh coalbed, at the 

Consolidation Coal Co.'s Loveridge mine near Fairview, W. Va. 

lGeologis t . a~ining engineering technician. 

3~ining engineer. 

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

references at the end of this report. 
,Property outline 

-- 0- -0 -0- 

I 

I 

E 

0 - 2,000 

Scale, ft 

FIGURE I. - Location sketch map of 5 North bleeders. 

During 1973, this mine was known to have produced an average of 

10,000 tons d-l, with an average methane emission of 12.1 million ft3d-I 

(2). The mine has two sets of mains driven into the virgin coal. A set 

of entries driven off either of these mains, remote from parallel workings, 

would meet the needs of the proposed investigation. 

The 5 North bleeders off West mains was chosen for the experiment 

(fig. 1) The geological reconnaissance and the study of the core logs 

indicated that the coalbed and adjacent strata should be uniform throughout 

the projected development. 

ACKNOWLEDGMENTS 

The authors acknowledge the cooperation of the Mountaineer Division of 

Consolidation Coal Co. .in the successful completion of the project. The 

authors especially thank K. Kincell, M. Hudak, and H. Gandy for their 

assistance. 

GEOLOGY 

The topography over the mine has a well-developed dendritic drainage 

pattern, which has left narrow ridges between typically V-shaped stream 

valleys. The relief between ridge and valley elevations averaged 450 feet. 

The structure of the Pittsburgh coalbed shown in figure 2 was compiled 

from company supplied data. The coalbed gently dips northwest toward the 

axis of the Waynesburg syncline located beyond the western boundary of the 

mine property. 
Coal 

section Pittsburgh 

edstone coal beds. 

0 I 2 

Smle, miles 

Pittsburgh coalbed. 
Figure 3 shows the major lithologies immediately above the Pittsburgh 

coalbed within the mine property. Using the driller's logs from the core 

test holes located in figure 4, a series of maps were drawn to examine 

lithology variations over the mine property. These maps showed no abrupt 

changes in the lithologies over the Pittsburgh coalbed within the mine area. 

The isopach of Pittsburgh coalbed (fig. 5) shows it to be continuous and 

fairly uniform in thickness within the mine property. 

A geologic reconnaissance and structural survey of the available mine 

workings showed well-developed coal cleat (8) that rotates clockwise slightly 

from N 74" W in the south to N 70" W in thenorth. Two small normal faults 

of limited lateral extend were judged to be local and attributed to sedimentary slumping. No clay veins were observed in the active workings. 

DATA SOURCES 

The methane analyzer system (2) developed at the Bureau of Mines was used 

for continuous recording of the volume-percent of methane in the ventilation 

air at selected locations. Basically, the system is composed of sensor 

assemblies installed at desired locations in the mine, power supplies for the 

sensor assemblies located in fresh air underground, and a central receiving 

station, generally located at the surface, .that records the output from each 

sensor. The resulting data are accurate to k0.04 vol-pct methane in air on a 

scale from 0 to 2 pct. , 

The mine operators provided copies of mine maps and daily coal production 

figures. The air readings used in all calculations were provided by mine 

personnel. 

MINING HISTORY 

The 5 North bleeders are a set of five entries driven on 60-foot centers 

north off West mains (fig. 6). The section was advanced 2,700 feet into 

virgin coal. This section mined under overburden that declined from an 

average 1,350 feet over room 7 (the point where monitoring began) to an 

average 950 feet over room 27. The nearest parallel workings were almost 

4,000 feet away. 

Throughout the mining of the section, the coal and adjacent strata 

remained as shown in figure 3. The only discontinuity was a clay vein first 

encountered inby room 11 in the right return airway and subsequently mined 

through by all the entries (fig. 7). This clay vein did not exceed 12 inches 

in thickness and extended from roof to floor. Its extent to the left and 

right of the section is undetermined. 

Mining up to the clay vein was rapid with production of coal averaging 

over 1,000 tons d-l and gas emissions of less than 400,000 ft3d'l. When mining 

encountered the clay vein, gas emission increased and coal production declined. 

Mining around the well block between rooms 15 and 17 was slowed by gas emission and ventilation problems due to the irregular entries. Methane emissions 

continued to retard mining after the face had advanced past the well block. 
Scale, ft 

LEGEND 

Sensor location 

FIGURE 6. - Sketch map of FIGURE 7. - Sketch map of clay vein location. 

5 North bleeders. 

At room 23, the decision was made to shorten crosscut center lines to 80 feet 

to improve ventilation. A zone of heavy roof encountered between rooms 19 and 

21 required additional roof bolts. Some of the bolt holes were reported to 

have audible gas emissions. Mining ceased on January 4, 1974, at room 27. 

MONITORING HISTORY 

Monitoring began on September 7, 1973. Additional sensors were installed 

as mining progressed (fig. 8). At the time of installation, each sensor was 

generally 100 feet back from the active face. All sensors were located in the 

return airways except sensor 1, which was used to monitor the intake air. 

This sensor was first installed at location 1A. Later it was moved to 
ir 

0 

LEGEND Z 

Sensor location 

0 600 

Scale, ft 

location 1g when mining had reached the 

well block to determine if any gas was 

entering the intake air from the clay 

vein, and then to location 1C to determine if any gas was entering-the intake 

air from the well block (fig. 9). 

Neither the clay vein nor the well 

block contributed methane to the intake 

air after the face had been advanced 

past them. 

During the experiment, the sensor 

nearest the face only once recorded a 

higher methane volume-percent than 

those located outby. This was when the 

clay vein was mined through. At all 

other times the peak volume-percent 

occurred from 1,000 to 1,500 feet outby 

the face indicating a large gas emission from the ribs. 

DISCUSSION 

In the 120 days of monitoring, 

this section emitted a total of 

91 million ft3 of methane, of which 

49 million ft3 came from the left side 

and 42 million ft3 came from the right. 

The slightly lower emissions from the . . right are attributed to some depletion FIGURE 8; - Sketch map of sensor assembly of gas in the virgin coal to this side 

locations. due to the development 3 years earlier 

of the 3 North mains some 4,000 feet distant. 

Figure 10 shows the continual rise of emissions throughout the experiment 

from almost 300,000 ft3d-1 initially to over 1.2 million ft3d-1 at the end, 

whereas both overburden thickness and daily coal production declined. Emissions generally declined during idle periods. 

TIME, days 

FIGURE 9. - Graph of average daily methane volume-percent recorded from sensor 1. 
0 20 40 60 80 100 120 

TIME, days TIME, days 

1,200 

- 

-0 I 

R - 1,000 rr) 

0 

w" 

Z 2 800- 

t; 

I 

2 600- 

E 

FIGURE 10. - Graph of daily methane emis- FIGURE 11. - Graph of average daily methsions from 5 North bleeders, ane emissions during ~roduction and idle periods. 

1 I I I I I Ill 11. 

KEY 

- -- Production days -- - . - - Idle days . - - - - 

-- - - - - - - 

- 

- - - - 

- 

To evaluate the emission due to coal production, the average methane 

emissions during production periods and idle periods were calculated and 

plotted (fig. 11). The average emissions were found to increase with time, 

and average daily emissions on weekends generally exceeded average daily 

emissions during the preceeding production period. 

The data from the methane sensors closest to the face and the average 

daily air volumes recorded at the face were used to calculate the volumes 

of methane entering the mine inby these sensors. This amounted to 41 million 

ft3, or less than half of the total gas from the section. Thus, most of the 

methane came from the ribs. The 41 million ft3 includes the emissions from 

between 100 and 500 feet of virgin rib between the sensor location and the 

active face. The (average) length of virgin rib exposed versus time was 

plotted. The resultant curve (fig. 12) is similar to that of average gas 

emissions during production and idle periods. Based on this similarity, a 

plot was made of daily methane emissions versus average length of virgin 

rib (fig. 13). A linear regression of these data yielded (I)-- - 

DME = 499L - 103,921 , 

where DME = daily methane emissions (ft3d-l) 

and L = average length of virgin rib (ft) 

with a correlation coefficient of 0.98. A correlation coefficient of 1.0 

indicates a perfect fit of the line to the data. In this site, the methane 

emissions correlate directly with the length of the virgin rib with 95 pct of 

the variation in the emissions explained by the length of virgin rib. 
TIME, days 

4 8 12 16 20 24 28 

AVERAGE LINEAR FEET OF RIB, lo2 ft 

FIGURE 12. - Graph of average length of FIGURE 13. - Plot of daily methane emisvirgin rib exposed. sion versus average length 

of rib exposed. 

Kissell, McCulloch, and Elder (z) have reported the methane content of 

the virgin ~ittsburgh coalbed in the Loveridge mine area to be 5.8 cm3g'1 or 

about 186 ft3 ton-l. If all of this gas is assumed to have been present 

prior to mining and all of it released during mining, the 54,565 tons mined 

would only have contributed 10 million ft3. Adding the gas from the outlined 

pillars only accounts for 29 million ft3 of methane, leaving 68 pct of the 

total methane emissions to come from the surrounding virgin coalbed. 

Kissell and Deul (6) have reported that the breakage of coal at the face 

contributes little to methane emissions. We know that the coal at the face 

does not contain methane under pressure and therefore its methane content is 

significantly below the 5.8 cm3g-1 reported by Kissell, McCulloch, and Elder. 

The methane emissions must therefore come from the virgin ribs, and the data 

gathered in this experiment verify this. 

With the instruments used in this experiment, it is now possible to 

monitor continuously and simultaneously methane emissions from several sections of a mine for long periods of time. The resultant data would isolate the 

variations in methane emissions from individual sections of the mine and 

allow more detailed study of the parameters controlling methane emissions in 

local areas. 
In the advancing section used for this study, the rock strata above and 

below the coal were not significantly disturbed. In retreat mining, these 

adjacent rock strata would be disturbed and any gas that they contained would 

enter mine workings. 

S UMMARY 

A 5-entry section was monitored for 120 days for methane emissions. 

During this time, the section advanced about 2,000 feet into virgin Pittsburgh 

coalbed. Although overburden and daily coal production declined, daily gas 

emissions increased. 

The data accumulated indicate that a large part of the methane entering 

the section came not from the immediate face but from the ribs adjacent to 

virgin coal. This is clearly illustrated by a graph of daily methane emissions versus the length of virgin rib exposed (fig. 13). Furthermore, linear 

regression of the graphed data shows that 95 pct of the variation in methane 

emission is attributable to the length of virgin rib. 

At the study site, the primary source of methane is the surrounding 

virgin coalbed, and this section acted like a long borehole drilled into a 

gas reservoir--the daily volume of methane produced increased with borehole 

length. 
REFERENCES 

1. Fruend, J. Mathematical Statistics. Prentice-Hall, Inc., Englewood 

Cliffs, N. J., 1962, 390 pp. 

2. Irani, M. C., P. W. Jeran, and M. Deul. Methane Emission From U.S. Coal 

Mines in 1973, A Survey. A Supplement to IC 8558. BuMines IC 8659, 

1974, 47 pp. 

3. Irani, M. C., P. W. Jeran, and D. H. Lawhead. Methane Analyzer System 

To Record Continuously the Methane Content of Coal Mine Ventilation Air. 

BuMines RI 8009, 1975, 14 pp. 

4. Irani, M. C., A. Tall, B. M. Bench, and P. W. Jeran. A ContinuousRecording Methanometer for Exhaust Fan Monitoring. BuMines RI 7951, 

1974, 18 pp. b 

5. 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. 

6. Kissell, F. N., and M. Deul. The Effect of Coal Breakage on Methane 

Emission. Trans. Soc. Min. Eng., AIME, v. 256, June 1974, pp. 182-184. 

7. Kissell, F. N., C. M. McCulloch, and C. H. Elder. The Direct Method of 

Determining Methane Content of Coalbeds for Ventilation Design. 

BuMines RI 7767, 1973, 17 pp. 

8. MCCU~~OC~, C. M., M. Deul, and P. W. Jeran. Cleat in Bituminous Coalbeds. 

BuMines RI 7910, 1974, 25 pp. 

*U.S. GOVERNMENT PRINTING OFFICE: 1976-603-755/96 

INT.-BU.OF MINES,PGH.,P A. 2 116 1