Bureau of Mines Report of Investigations/ 1972 

Methane Emission in Coal Mines: 

Effects of Oil and Gas Wells 

- - 

UNITED STATES DEPARTMENT OF THE INTERIOR 
Report of Investigations 7658 

Methane Emission in Coal Mines: 

Effects of Oil and Gas Wells 

By M. G. Zabetakis, T. D. Moore, Jr., A. E. Nagel, and J. E. Carpetta 

Pittsburgh Mining and Safety Research Center, Pittsburgh, Pa. 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Rogers C. B. Morton, Secretary 

BUREAU OF MINES 

Elburt F. Osborn, Director 
CONTENTS 

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

Introduction ............................................................ 1 

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

Test site ............................................................... 2 

Instrumentation ......................................................... 2 

Results and discussion .................................................. 4 

Conclusions ............................................................. 9 

ILLUSTRATIONS 

1 . Federal No . 2 mine map .............................................. 3 

2 . Simplified ventilation scheme. Federal No . 2 mine ................... 4 

3 . Enlarged view of northeast quadrant ................................. 5 

4 . Methane flow rate. left air course. northeast quadrant .............. 6 

5 . Methane flow rate. right air course. northeast quadrant ............. 7 
METHANE EMISSION IN COAL MINES: EFFECTS OF OIL AND GAS WELLS 

by 

M. G. Zabetakis,' T. D. Moore, Jr.,2 A. E. N0~e1,~ and J. E. Carpetta4 

ABSTRACT 

The method of moving averages was found useful in assessing the nature of 

methane emission in coal mines. Emission rates were influenced markedly by 

the presence of abandoned oil and gas wells in the vicinity of the mine. Such 

wells appeared to increase the flow rate of methane into the mine by a factor 

of 2 to 30 in an active mine in the Pittsburgh coal seam. 

A recent detailed study by the Bureau of Mines of the effects of water 

infusion on methane flow in a coal mine revealed that while the rate of emission appeared to decrease with distance from the face, actual measured con6 centrations of methane fluctuated markedly about the average. Because such 

measurements are required when assessing the effectiveness of a particular 

methane control procedure, a complete methane survey was made during a recent 

idle period in the Federal No. 2 mine. Measurements were made of the methane 

concentration, air flow rate, and pressure at a number of points within the 

mine. An attempt then was made to correlate high emission rates with the 

characteristics of the coalbed and the location of oil and gas wells in the 

vicinity of the mine. 

The Bureau has been concerned, since its inception, with the hazards 

associated with oil and gas wells that pass through coalbeds. A study was 

made some years ago of the explosion hazards and the waste of coal associated 

6 with such wells. Subsequently, a summary was prepared of the precautions to 

XResearch supervisor, Methane Control and Ventilation. 

'~ining engineer. 

'~echanical engineer. 4 Mining engineering technician. 

6~etinbas, Abdurrahman, R. P. Vinson, Joseph Cervik, and M. G. Zabetakis. 

Methane and Dust Control by Water Infusion. Pittsburgh Coalbed (Fairview, 

W. Va.). BuMines Rept. of Inv. 7640, 1972, 17 pp. 

 i ice, George S., 0. P. Hood, and others. Oil and Gas Wells Through Workable 

Coalbeds: Papers and Discussions. BuMines Bu11.65, 1913, 101 pp. 
7 be taken when drilling oil or gas wells through workable beds. More recently, 

a study was made of the hazards of storing natural gas underground in coalmining areas. 8 

The cooperation of the Eastern Associated Coal Corp., Pittsburgh, Pa., 

during this study is greatly appreciated. The authors particularly want to 

thank William Laird, vice president--engineering, William Hylton, superintendent, and James Hayhurst, mine foreman, Federal No. 2 mine, for assistance in 

planning the work described in this report. Joseph Pasini 111, research 

supervisor, Petroleum and Natural Gas Research, Morgantown Energy Research 

Center, Bureau of Mines, Morgantown, W. Va., assisted in evaluating the conditions of the oil and gas wells considered in the report. 

TEST SITE 

The Eastern Associated Coal Corp. Federal No. 2 mine (fig. 1) operates in 

the Pittsburgh coalbed near Fairview, W. Va. The coalbed is 9 feet thick; 

7 feet is mined at present, with the remainder left to control roof and bottom 

stresses. The overburden thickness ranges from about 734 to 842 feet. 

In this area, the Pittsburgh coalbed has a well-developed cleat system; 

the face (main) cleat trends N 70' W and the butt cleat N 20" E. The permeability of the coalbed is primarily due to the cleat system. 

During this study (November 3-5, 1971), the mine was idle so that methane 

concentrations and ventilation rates could be readily measured throughout the 

mine. The mine's ventilation system was found to exhaust about 675,000 cfm of 

mine air containing 0.70 volume-percent methane during this period. These 

values, as well as those obtained at various other points in the mine, are 

summarized in figure 2. The intake air courses are labeled with air flow 

rates, and the returns with air and methane flow rates and methane 

concentrations. 

INSTRUMENTATION 

A complete set of measurements (velocity, pressure, temperature, crosssectional area, and methane concentration) was obtained at selected locations 

throughout the mine. Calibrated, portable instruments were used in each case; 

Taylor and ~avis' anemometers were used for the velocity measurements, Wallace 

and Tiernan altimeters for pressure, mercury in glass wet and dry bulb thermometers for temperature and humidity, cloth tape measures for length, and 

7Herbert, C. A. Notes on Precautions To Be Taken When Drilling Oil or Gas 

Wells Through Workable Coalbeds or Through Mine Workings. BuMines Inf. 

Circ. 6195, 1929, 8 pp. 

'wheeler, Henry P., Jr., and William E. Eckard. Underground Storage of 

Natural Gas in Coal-Mining Areas. BuMines Inf. Circ. 7654, 1952, 11 pp. 

'Reference to specific makes or models of equipment is made to facilitate 

understanding and does not imply endorsement by the Bureau of Mines. 

2 WJTH MAWS 

6n.mo Air. cfm 

lora) Methorn, pct 

4.121 hWh. Cfm 

FIGURE 2. -Simplified Ventilation Scheme, Federal No. 2 Mine. Methane concentrations in 

volume-percent appear in followed by the methone flow rates in 

cubic feet per minute. 

RESULTS AND DISCUSSION 

The measurements obtained by the underground crews were adjusted, where 

necessary, against laboratory calibration curves and subsequently displayed on 

a large mine map. These measurements were used to obtain air and methane 
Main cleat 

Butt 

@ Oil well, abandoned 

0 Qi well. active 

FIGURE 3. - Enlarged View of Northeast Quadrant. 

quantity balances. Methane flow rates were computed from the measured methane 

concentrations and interpolated air flow rates. A summary of these data is 

given in a simplified schematic presented in figure 2. For example, in the 

northeast quadrant, 72,100 cfm of (intake) air is split at a face area with 

44,280 cfm passing to the left, 26,600 passing to the right, and the balance 

returning along the 1 East Mains. The left split picks up 0.26 percent and 

the right split 0.58 percent methane at the face to yield methane flow rates 

of 115and155 cfm, respectively. Additional methane is picked up as the air 

passes along each return. As noted in earlier studies in the Pittsburgh 

coalbed, the methane emission rate is generally higher in entries adjacent to 

virgin coal than in those near old workings; similarly, rates usually are 
higher when a return intersects the main or face cleat rather than the butt 

cleat at right angles. 

In addition, as mixing is not instantaneous (entry widths are approximately 15 feet), and emission rates are not uniform along any passageway, 

methane concentrations fluctuate markedly along any active entry.10 An 

attempt was made to analyze these fluctuations by using the method of moving 

averages. This statistical technique, ordinarily used in time series analysis 

to determine trends in business cycles, appears to work well here. In brief, 

all methane flow rates were recorded in sequence at 100-foot intervals along 

each entry. Averages then were computed for rates 1 through 5, 2 through 6, 

3 through 7, and so forth. These then were assigned to the third, fourth, 

fifth, and succeeding points. For example, if we again consider the area in 

the northeast quadrant (fig. 3), we find the methane flow rate (Q) rises 

slowly in passing from point 0 toward point 1 and then more quickly as point 1 

is passed; the flow rate levels off as point 2 is passed, and then rises again 

as we approach point 3. The smoothed (measured) data are presented in the 

lower half of figure 4. The first recorded value i8 the "raw" point obtained 

at 0, the next is the average value obtalned from the first five points, and 

so forth. (Similar data are 

Q3 presented by Cetinbas and 

coworkers .I1) The slope of 

this (measured) curve is 

given'in the upper half of 

=: 

\ -2 this same figure. This 

E "- represents the methane flow u rate per foot of entry or 

face area (dQ/dX). 

I Interestingly, it exhibits % two very pronounced peaks. 

Comparison of these peaks 

with the data presented in 

figure 3 indicates the first 

oil well 81 and perhaps oil 

200 well 80; the second peak 

corresponds very closely to 

the position of abandoned 

oil well 91. A similar 

E 300 is probably due to gas 

I trend was found in proceeding from 0 to A, B, . . . ""L a E-------- (fig. 5). The first peak corres~onds to abandoned 

Y0 I I I I bleeding along the main 

I 2 cleat from the abandoned gasL 0 1,000 2.000 3.000 4.000 5.000 ;o well 257, and7the third 

DISTANCE Oo, ft to well 272. Again, the 

r 

Y I I I I 1 

FIGURE 4. - Methane Flow Rote, Left Air Course, "Work cited in footnote 5. 

Northeast Quadrant. I1work cited in footnote 5. 

gas-oii well 264, the next 
methane appears to pass more 

readily along the main cleat 

even though a shorter path 

would be available if it 

were to pass through the 

butt cleat. 

The effects of these 

wells can be determined by 

subtracting the peak contributions from the total 

emission rate of methane. 

This has been done in each 

case by use of the broken 

curve in figures 4 and 5 to 

compute the "expected" flow 

rates (the average emission 

rate pet foot of entry is 

about 0.008 cfm/ft for paths 

0, 1, 2, 3, 4, and 5, and 

0.05 cfmlft for paths 0, A, 

B, C, D, E, and P). Thus, 

while the measured methane 

flow rate along the left 

return is 225 cfm at 

4,500 feet from point 0, the 

expected flow rate is 70 cfm. 

On this basis, the contribution from the wells is 

155 cfm. The corresponding 

figures at approximately 

5,000 feet from 0 along the 

right return are 600 to 

275 cfm; the contribution 

from the wells in this case 

is 325 cfm, or 58 percent of 

the total. These methane 

OISTANCEW. ft flow rates (155 and 325 cfm) 

require approximately 

68,500 cfm of air to attain 

FIGURE 5. - Methane Flow Rate, Right Air Course, the exhaust level found here 

Northeast Quadrant. (0.7 volume-percent methane). 

Accordingly, the power 

required to supply this amount of air across the 4.8-inch water gage pressure 

drop encountered in this mine isla 

Air hp = Hq 4.8 x 68,500 - 51.8 - - 

6,350 6,350 

IzKingery, D. S. Introduction to Mine Ventilation Principles and Practices. 

BuMines Bull. 589, 1960, p. 27. 
where H = pressure loss in inches of water 

and q = air flow rate in cfm 

This represents an expenditure of approximately $380 per month ($4,560 per 

year) at a modest $0.01 per kilowatt-hour rate. Further, the loss in coal 

(approximately 10,000 tons per well), as well as the disruption of a uniform 

mining plan and the increase in resistance of the air course that results when 

a barrier is left in place around a well, raises a question regarding the 

advisability of continuing present practices. Work at the Bureau's Morgantown 

Energy Research Center has shown that a well can be safely sealed below the 

coal and mined through in certain instances. Several wells (for example, 91, 

257, and 264) are presently being investigated to determine what effect 

cleaning out and sealing to the base of the coal will have on the methane concentration in the section of the mine. 

The "expected1' curves (figs. 4 and 5) were constructed by adding to the 

methane flow rate at the origin (point O), the steady-state flow rate along 

the entry. This is quite evident in figure 4, where the llexpected" curve is 

parallel to the l'measured" curve near the origin, between 1,100 and 1,700 feet, 

and at distances beyond about 3,000 feet. Surprisingly, except for the 

effects of the wells, the steady-state flow rate along each rib appears to be 

fairly constant. If we assume that the ribs were formed at a uniform rate, 

then the data presented in the upper graphs of figures 4 and 5 can be converted to plots of methane flow rate per foot of entry against time. 

stewart13 has shown that the expected solution in this case takes the form 

where C, is the initial gas concentration in the coal, D is the diffusivity, 

t is the time, and q is the methane flow per unit area of rib. Thus 4 would 

be expected to decrease with time for constant C, and D. By analogy, dQ/dX 

would also decrease with distance under these conditions. Actually, dQ/dX 

appears to be constant if we subtract the effects of the oil and gas wells so 

that D (and therefore the permeability) must increase with time. stewart14 

ascribes this increase to a change in stress and the concomitant "relaxation 

of cleat and bedding joints." However, if we consider the moisture removed by 

the ventilation air (on occasion, in excess of 50,000 gallons per day in this 

mine), we can only conclude that such an increase also must be related to a 

decrease in the water content of the coal. 

lastewart, Ian McC. Diffusional Analysis of Seam Gas Emission in Coal Mines. 

Canadian Min. and Met. Bull., April 1971, pp. 62-70. 

14work cited in footnote 13. 
CONCLUSIONS 

The method of moving averages appears to be a useful technique in 

assessing the nature and origin of methane emission into a coal mine. Using 

this technique, an analysis of the flow of methane into the Federal No. 2 mine 

indicates that considerable quantities of this combustible can be ascribed to 

the presence of abandoned gas and oil wells in the vicinity of the mine. The 

cost of removing this gas as well as that associated with the loss of coal in 

mining around a well suggests the use of a recently developed Bureau of Mines 

technique to seal and mine through such wells. 

* U.S. om: 1S7a-7106lyZl