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

Thomas S. Kleppe, Secretary 

BUREAU OF MINES 

Thomas V. Falkie, Director 
This publication has been cataloged as follows : 

Diamond, William P 

Methane gas content of the Mary Lee group of coalbeds, 

Jefferson, Tuscaloosa, and Walker Counties, Ala., by W. P. 

Diamond, G. W. Murrie, and C. EA. McCulloch. [Wa$hington] 

U.S. Bureau of Mines [1976] 

9 p. illus., tables, (U.S. Bureau of Mines. Report of investigaIncludes bibliography, 

1. Methane. 2. Bituminous coal-Alabama-Analysis. 3. Degassing of coal. I. Murrie, Gary w,, jt. auth. 11, McCulloch, 

Charles M., jt. auth. 111. U.S. Bureau of Mines. IV. Title. 

TN23.U7 no. 8117 622.06173 

U.S. Dept. of the Int. Library 
C ONTE NTS 

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

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

Acknowledgnaents .......................................................... 2 

Geology .................................................................. 2 

Nomnclature ........................................................ 2 

Structure and overburden ............................................ 3 

Coal thickness . .................................................... 3 

Methane gas content ......................... ..... ...................... 6 

Method of calculation ............................................... 6 

Results ............................................................. 6 

Discussion ............................................................... 7 

Conclusion and recammendations ........................................... 7 

References ... ........................................................ 9 

ILLUSTRATIONS 

1 . Study area ......................................................... 2 

2 . Structure map ........... ........................................... 4 

3 . Overburden map ....................................................... 5 

4 . Depth of coalbed versus gas content .................................. 6 

TABLES 

1 . Overburden distribution .............................................. 3 

2 . Methane potentials ................................................... 6 

3 . Methane distribution ................................................. 7 
RETHANE GAS CONTENT OF THE MARY LEE GROUP OF COALBEDS, 

JEFFERSON, TUSCALOOSA, AND WALKER COUNTIES, ALA. 

by 

W. P. Diamond, 1 G. W. Murrie, 1 and Ce Me McCulloch 1 

ABSTRACT 

It is estimated that more than 1 trillion cubic feet of methane is contained within the coals of the Mary Lee group in Jefferson, eastern Tuscaloosa, 

and southern Walker Counties, Ala. Most of this methane will be encountered 

by mining. Coals of the Mary Lee group are presently being mined at depths 

exceeding 1,000 feet and will in the near future be mined at even greater 

depths, where the problem of methane gas affecting the mining operations will 

be acute. It is calculated that approximately 90 pct of the methane is at 

depths greater than 1,000 feet, and over half of the gas is contained within 

only 12 pct of the study area which is under more than 1,500 feet of overburden. Degasification in advance of mining will Tncrease mine safety, reduce 

ventilation expenditures, increase productivity, provide an additional energy 

source, and make it possible to mine parts of deep coalbeds that probably 

could not otherwise be mined. 

INTRODUCTION 

The Mary Lee group contains the greatest coal reserves in the Warrior 

basin, Ala. (L) .2 These coals have been extensively mined in the shallower 

portion of the basin and are now being mined under deeper overburden. Desorption of methane from coal cores taken at various depths within the basin (4) 

indicated that high concentrations of gas were to be expected in coals of the 

Mary Lee group. The high gas emission rates anticipated for mines to be operating in the deeper parts of the Warrior basin prompted this study to estimate 

the methane gas content of the Mary Lee group, delineate areas of high gas 

concentration, and encourage degasification in advance of mining. 

The area seiected for investigation is that part of the Warrior basin 

located in Jefferson, eastern Tuscaloosa , and southern Walker Counties of 

north-central Alabama (fig. 1). This area contains all abandoned and operating mines in the Mary Lee group, as well as those proposed for the near 

future. 

'~eologist. 

2 Undzrlined numbers in parentheses refer to the list of references at the end 

of this report. 
FIGURE 1. - Study area. 

Thomas Daniel, geologist, 

Geological Survey of Alabama , provided general geologic data . 

GEOLOGY 

Nomenclature 

The Mary Lee group is comprised of five coals which, in ascending order, 

are the Ream, Jagger, Blue Creek, Mary Lee, and New Castle. The most persistent. and economically important member of this group is the Mary Lee coal. It 

is composed of two predominant benches which split and coalesce in the northern part of the Warrior basin and are often mined as one bench. As the Mary 

Lee dips southwest into the basin, the bottom bench thickens, the interval. 

between the two main benches increases, and the bottom bench becomes the minable bed. The distance between these two main benches ranges from less than 

1 foot in the shallow parts of the basin to more than 9 feet in the deeper 

portion of the basin where, in places, the bottom bench has been named the 

Blue Creek coal. 
Structure and Overburden 

The Warrior basin dips to the southwest, and its major structures, the 

Warrior and Caalburg synclines and Sequatchie anticline, trend northeast to 

southwest (fig. 2). The major fault trends are nearly perpendicular to the 

structural axes and are generally oriented northwest to southeast. Thrust 

faults are present along and parallel to the southeastern flank of the basin. 

The overburden thickness trend follows the regional southwestern structural dip and ranges from 0 feet at outcrop to greater than 2,300 feet at the 

southern limit of the study area (fig. 3). The most rapid transition in overburden thickness, from 0 to 1,500 feet in approximately 1/2 mile, occurs in 

an east to west direction across the southeastern flank of the Warrior basin. 

The distribution of the various overburden intervals is given in table 1. 

TABLE 1. - Overburden distribution 

Coal Thickness 

Two isopachs of the original coalbed were constructed for use in calculating methane gas volumes. The publication of these isopachs has been withheld owing to the confidentiality of the data. The Mary Lee coal isopach 

Area, pct 

34 

33 

21 

9 

3 

100 

Overburden 

thickness, ft 

0- 500 .......................... 500-1,000 .......................... 1,000-1,500 .......................... 1,500-2,000 .......................... 2,000-2,500 .......................... Total... ...*.................... 

included the two predominant benches of coal that are of greatest interest to 

the mining industry, commonly known as the Mary Lee in the north and the Mary 

Lee and/or Blue Creek in the south. The total coal isopach included the coal 

of the first isopach and the New Castle, plus the Blue Creek coalbed where 

data is complete. The total coal isopach represented a conservative estimate 

of coal present in the Mary Lee group because most core holes were not drilled 

Area, mi2 

282 

277 

174 

79 

27 

839 

deep enough to intercept the lower members of the group. 
FlGUR E 2. - Structure map. 
FIGURE 3. - Overburden map. 
METHANE GAS 

C ONTE NT 

Method of 

Calculation 

Coal samples were 

obtained from seven core 

holes ranging in depth from 

600 to 2,200 feet. The 

methane content of a unit 

weight of coal was determined for the 12 samples by 

the direct method (3-4). - - 

A graph for estimation o.f 

gas content was constructed 

(fig. 4) by plotting the 

measured gas content versus - OVERBURDEN, ft depth for each sample and 

fitting a line to the points 

using least squares statis- FIGURE 4. - Depth of coalbed versus gas content. tical analysis. The overburden isopach was over laid 

on the coal isopachs to determine the amount of coal contained under each overburden interval. The methane content for each overburden interval was obtained 

by multiplying the volume of coal under an interval by the estimated methane 

content of the median depth of each interval. 

Results 

The methane gas content of the Mary Lee group, within the study area, is 

estimated to be approximately 1 trillion cubic feet. Approximately 700 

billion cubic feet of methane is contained within the Mary Lee coalbed alone. 

Table 2 lists the gas potentials of the Mary Lee and the Mary Lee group for 

each overburden interva 1. 

TABLE 2. - Methane potentials 
DISCUSS ION 

It is estimated that nearly 70 pct of the 1 trillion cubic feet of methane present in the Mary Lee group is contained within that portion likely to 

be encountered by mining operations. Based on the amount of coal known to 

have been previously removed, primarily from shallow (less than 500 feet) 

depths, and the expected low gas content of that coal, 98 pct of the calculated methane content probably remains. The calculated methane content is 

probably conservative because only the gas in the coal has 'been calculated 

and no assessment of that which may be contained in the roof and floor rocks 

has been included. 

Mining operations are gradually progressing to greater depths in the Mary 

Lee group, with mines now operating in excess of 1,000 feet. The data derived 

from coal samples obtained from various depths, as plotted on the graph 

(fig. 4), indicate an increase in gas content with increasing depth. Table 3 

indicates approximately 90 pct of the total methane content exists at depths 

greater than 1,000 feet. The Mary Lee group is at depths of greater than 

1,500 in less than 12 pct of the study area, yet more than half of the methane is estimated to be within that portion. 

TABLE 3. - Methane distribution 

The present study does not include the total extent of the Mary Lee group 

in the deeper part of the Warrior basin, owing to the lack of data. However, 

it should be noted that the methane potential of the Mary Lee group in the 

deeper part of the Warrior basin is enormous. Every additional square mile of 

coal 6 feet thick, at a depth of 2,000 feet, would contribute another 3.3 billion cubic feet of gas to the l-trillion-cubic-foot total. 

Experimental methods to remove methane in advance of mining have been 

conducted in the Mary Lee coalbed. Production from degasification boreholes 

at a depth of approximately 1,000 feet in Jefferson County, Ala., sustained a 

flow rate of 70,000 ft3 /day after hydraulic stimulation (2). The gas production averaged 93 pct methane, with H2 and CO, making up the greatest part of 

the remaining 7 pct. The British thermal unit value of the gas ranged from 

970 to 990. 

C ONCLUS LON AND RECOMMENDATIONS 

The Mary Lee coal group of the Warrior basin, Ala., contains substantial 

quantities of methane, estimated to be in excess of 1 trillion cubic feet. 

Most of this methane will be encountered in mining operations, with the 
greatest concentration being in the deeper portions of the basin. Bureau of 

Mines research (2) has shown that degasification in advance of mining is 

feasible in the Mary Lee coalbed and can produce commercial quantities of 

pipeline-quality methane. It is recommended that degasification in advance 

of mining be considered as part of a complete mine development plan for areas 

having greater than 1,000 feet of overburden. 
REFERENCE S 

1. Culbertson, W. Geology and Coal Resources of the Coal-Bearing Rocks of 

Alabama. U.S. Geol. Survey Bull. 1182-B, 1964, 79 pp. 

2. Elder , C. H. , and M. Deul. Degasification of the Mary Lee Coalbed Near 

Oak Grove, Jefferson County, Ala. , by Vertical Borehole in Advance of 

Mining. BuMines RI 7968, 1974, 21 pp. 

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

Determining Methane Content of Coalbeds for Ventilation Des ign. 

BuMines RI 7767, 1973, 19 pp. 

4. McCulloch, C. M., J. R. Levine, F. N. Kissell, and M. Deul. Measuring 

the Methane Content of Bituminous Coalbeds. BuMines RI 8043, 1975, 

22 PP