Bureau of Mines Report of Investigations/ 1973 

The Direct Method of Determining 

Methane Content of Coalbeds 

for Ventilation Design 

UNITED STATES DEPARTMENT OF THE INTERIOR 
Report of Investigations 7767 

The Direct Method of Determining 

Methane Content of Coalbeds 

for Ventilation Design 

by F. N. Kissell, C. M. McCulloch, and C. H. Elder 

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 
This publication has been cataloged as follows: 

Kissell, Fred N 

The direct method of determining methane content of coalbeds for ventilation design, by F. N. Kissell, C. M. McCulloch, 

and C. H. Elder. [Washington] U.S. Bureau of Mines [I9731 

17 p. illus,, table. (US. Bureau of Mines. Report of investigations 7767) 

Includes bibliography. 

1. Mine gases. 2. Mine explosions. 3. Mine ventilation. I. U.S. 

Bureau of Mines. 11. McCulloch, Charles M., jt. auth. 111. Elder, 

Curtis H., jt. auth. IV. Title. (Series) 

TN23.U7 no. 7767 622.06173 

U.S. Dept. of the Int. Library 

. .L 
CONTENTS 

Page 

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

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

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

Laboratory feasibility test of the direct method for vertical 

borehole cores ........................................................ 2 

Field tests of the direct method ........................................ 4 

Results from the direct method compared with the indirect method ........ 6 

Direct method gas quantity compared with emissions from nearby mines .... 8 

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

References ......................................................... 10 

Appendix A...Measuring technique ........................................ 11 

Appendix B...Vertical boreholes ......................................... 14 

ILLUSTRATIONS 

1 . Desorption rate curves for Pittsburgh and Pocahontas No . 3 coals. 

114- to 112-inch size ........................................... 3 

2. Sample container .................................................. 4 

3 . Emission rate curve ............................................... 5 

4 . Equilibrium adsorption isotherms .................................. 7 

5 . Coalbed gas amount via the direct method versus actual mine 

emission ........................................................ 9 

A-1 . Emission rate curves: Cores from Loveridge. Howe. and Beatrice 

sites ........................................................... 12 

A-2 . Emission rate curves: Cores from Inland. Kepler. and 

Price sites ..................................................... 13 

TABLE 

1 . Methane amounts by the direct and indirect methods ................ 
THE DIRECT METHOD OF DETERMINING METHANE CONTENT 

OF COALBEDS FOR VENTILATION DESIGN 

by 

F. N. Kissell,' C. M. McCulloch,2 and C. H. Elder2 

ABSTRACT 

The applicability of the "direct method" for determining the methane content of virgin coalbeds was tested. Preliminary results indicate that the 

direct method, when applied to exploration cores, can be successfully used to 

estimate coalbed gas content and also approximately predict the total gas emission from a prospective mine located in the coalbed at the exploration site. 

INTRODUCTION 

One of the unknowns faced by a mine operator planning a new coal mine is 

the amount of methane that will be released. It is not uncommon to find that 

a mine is much gassier than was anticipated, necessitating additional ventilation which may increase the cost substantially, especially if additional air 

shafts must be dug. 

One way to estimate mine methane output is to use the correlation established by M. C. Irani (3).3 Irani has shown that, for a given coalbed, the 

methane output of a mine correlated with a factor [depth x production]. However, these correlations are only presented for four major coalbeds 

(Pittsburgh, Pocahontas No. 3, Illinois 5 and 6), and they are not much help 

in estimating methane emission from other coals. 

Possibly the best technique for measuring the gas in coal is the socalled direct method, which has been used in France for some years (1). The 

direct method has not been applied to virgin coalbeds but has only been used 

to estimate the gas in coal just ahead of a working face. Typically, a 

horizontal hole is drilled into the coalbed from a working face and the 

cuttings from the hole are collected and enclosed in a sealed container. 

The volume of gas emitted from the container is then measured. Later, the 

coal is taken from the container and crushed to a fine powder (at least 

200 mesh), releasing the remainder of the gas. 

lPhysica1 research scientist. 

2Geologist. 

3~nderlined numbers in parentheses refer to items in the list of references. 
Most of the gas is accounted for in this way; however, the gas which 

escaped the coal cuttings as they emerged from the hole must be accounted 

for. Five minutes may elapse between the instant the coal is cut by the 

drill and the time it is enclosed in the sample container, and in this 

interval a quarter of the gas may be lost, depending on the size of the 

cuttings. This "lost" gas is accounted for in the following way: It is 

known that the volume of gas emitted froni-a fine coal particle is proportional to the square roof of time, V a 0, where V is the volume emitted and 

Q is the time measured from the instant the emission began (6). From this, 

a simple equation can be derived which relates the "lost" gas to part of the 

gas given off from the coal while in the sample container (1). 

We reasoned that if the direct method could be applied to the coal cores 

extracted from vertical boreholes, then the amount of methane in a virgin 

coalbed could be readily estimated. Ruu~ine cvre drilling ahtad of mining i~ 

standard practice to measure coalbed thickness and assess the quality of the 

coal, and it would be a simple matter to add a methane test. 

The usefulness of the direct method depends on accurately estimating the 

lost gas, which in turn depends on the accuracy of V a 6 . This proportionality holds for fine coal (60 mesh and smaller) if 8 is not too large. This 

is why the direct method works with short horizontal holes drilled into the 

coalbed from the mine face. However, that is no guarantee that V a fi holds 

for the coal cores extracted from vertical boreholes. For one thing, the 

coal lumps are many inches across instead of 60 mesh. For another, the time 

8 is typically several hours instead of just a few minutes. 

ACKNOWLEDGMENTS 

The cooperation of Bureau of Mines geologists James R. White and Paul W. 

Jeran is greatly appreciated. James I. Joubert of the Bureau of Mines 

Pittsburgh Energy Research Center supplied us with all of the isotherm 

curves. The core at the Kepler location was loaned to us by Sam Schrader 

of the Pocahontas Fuel Co. 

LABORATORY FEASIBILITY TEST OF THE DIRECT METHOD 

FOR VERTICAL BOREHOLE CORES 

To find out whether V a !.m holds for coal cores at large values of 8, 

we initiated some laboratory desorption experiments on lump coal from the 

Pittsburgh and Pocahontas No. 3 coalbeds. Desorption curves for these coals 

are shown in figure 1. The size range was 114- to 1/2-inch. The coal was 

pressured to 200 psi and allowed at least a month to equilibrate. Then the 

pressure was released to atmospheric, and the emission from the coal was 

measured (appendix A). Figure 1 indicates that the V a fi proportionality 

holds up to approximately fi = 25 min1'" (or 8 2 10 hours). The 114- to 

112-inch size range was the largest coal that could be tested conveniently in 

the laboratory. However, it is probable that larger lumps would exhibit a 

similar emission behavior. The reason for this is that coal has a natural 

fracture network, and lumps that are much larger than the network spacing 

have about the same emission characteristics as lumps that are about the same 
Jr (min b2) 

80 - 

FIGURE 1. - Desorption rate curves for Pittsburgh and Pocahontas No. 3 coa Is, 1 /4- to 

1/2-inch size. 

70 

I I I I 

0 

- - 

Pocahontas No. 3 

60 - - 

50 - 

40 - - 

- 

- 

- 

10 20 30 40 50 60 
dimensions as the network spacing (1). In other words, if the network spacing 

is 112 inch, then a 6-inch lump will have the same emission characteristics as 

a 112-inch lump. Bielicki, Perkins, and Kissell (2) have found that the 

fracture spacing in Pocahontas No. 3 coal is about-1/16 inch and that of 

Pittsburgh coal is about 112 inch. The coal we tested was at least this 

large, and so we felt it correctly represented the emission behavior of larger 

lumps. This then indicated that the "direct method" could possibly be applied 

to cores from vertical boreholes. 

FIELD TESTS OF THE DIRECT METHOD 

The Bureau of Mines is conducting an extensive methane drainage research 

program, one phase of which involves drilling vertical boreholes from the 

surface into coalbeds in various parts of the country. Drill stem tests on 

these boreholes are used to measure the methane gas pressure and the cvalbecl 

permeability. Later, these are opened to drain methane from the coal. In 

the course of this work, coal cores were brought to the surface, which could 

be used to measure the coalbed methane content by the direct method. 

The boreholes were drilled 9 inches in diameter to within about 2 to 

3 feet of the coalbed. After logging, 7-inchcasingwithaguideand floatshoe 

FIGURE 2. - Sample container. Gas emission is measured by displacement of water. 
was run to the bottom and 

then cementedtothe surface. 

Af ter the cement hardened, 

the cement plug and floatshoe at the bottom of the 

casingweredrilled out, and 

a core barrel inserted. The 

last few feet of overlying 

strata and the coal were 

then cored. The core. 

4 inches in diameter, was 

brought to the surface. 

Part ofthecoreobtained 

in this way was broken off and 

inserted into a sample container (fig. 2). Generally 

the container was filled to 

the top. After the lid was 

sealed, the valve was opened 

and the volume of gas emitted was continuously 

recorded. The valve was 

then closed and the sample 

brought to the laboratory 

where the emission was monitored for several weeks, or 

until it diminished to a 

negligible rate. The coal 

was then crushed to at least 

200 mesh, and the gas given 

.> off during the crushing was 

measured (appendix A). 

The technique used to 

determine theamount of "lost" 

gas was slightly different 

from that of Bertard (I). 

Rathcr than calculating the 

lost gas by means of an 

equation (which uses only 

one data point), we felt a 

500 

Ir) 

E " 400- 

a? 

W 

Z 

2 

z 2 300- 

W 

-I 

a 

v, 200- 

5 

o 

LT 

L 

100- 

~3 

to 

100 

Ir) 

E " 200- 

vi 

a 

0 

IVJ 800 S 

900, 

I,OOOA 

0 

graphical technique would be 

./t+150(rnin&) more accurate. The volume 

of gas first given off from 

FIGURE 3. - Emission rate curve. Core from Vesta No. 5 the sample container was 

site, Pittsburgh coalbed, plotted versus J8, where 8 

is the time since themethane 

pressure on the core was 

released. We assumed that this coincided with the coring of the coal in those 

cases where the coal was cored with air as a drilling medium. In cases where 

1 I 1 

o - 

o 

- 

o 

- 

- 

.---- - 

1 

1 

- 1 - I 

1 

I' 

I - 

I 

I 

P 

- 1 I - I 

/ 

1 

I - 

I 

1 I 

5 10 15 20 25 
the coring was done with water, we assumed that the methane pressure was 

released and emission began when the core was halfway out of the hole. 

As an example, the Vesta No. 5 coal (fig. 3) was air-cored. Here, 

t is the time measured from the instant the coal was inserted in the sample 

container. The time alapsed between this instant and the coring of the coal 

was 150 minutes. Then 8 = t + 150. By extrapolating the linear portion of 

the emission curve back to 8 = 0, the "lost" gas is obtained. For the Vesta 

No. 5 example (fig. 3)) it is 960 cm3. The total gas by the direct method is 

the "lost" gas, plus all the gas emitted from the coal while in the sample 

container, plus the gas released during crushing. Occasionally the extrapolation for the lost gas may be quite rough; however, the lost gas is generally only about a fourth of the total, and so the error in the total is 

reduced correspondingly. 

It must be pointed out that it is not necessary to adhere exactly to the 

procedure as outlined above. In drilling the borehole, all that is necessary 

is to bring a coal core promptly to the surface and place it immediately in 

the sample container. For example, the borehole at the Kepler location was a 

company explorationholewhichwas cored all the way from the surface and never 

cased. Similarly, it is not necessary to wait several weeks before crushing 

the coal. The detailed history of each core sample is given in appendix B. 

RESULTS FROM THE DIRECT METHOD COMPARED 

WITH THE INDIRECT METHOD 

Another possible way to estimate the amount of methane in a virgin coalbed would be to use what is called the indirect method (&). In this method, 

a vertical borehole is drilled into the coal from the surface. A packer is 

set just above the coal for a formation test (drill stem test), and the 

pressure of the methane gas is measured. This pressure is then related to 

the gas amount by means of an empirical curve which is determined experimentally in the laboratory. However, there is some doubt as to whether the gas 

amount measured in this fashion is correct, for two reasons: 

1. Coalbeds generally contain water along with the gas, and the pressure 

that is measured may be the hydrostatic head of water (4). - 

2. Most of the gas in coal is adsorbed under pressure on the internal 

surface rather than compressed in the pore space as it would be for a sandstone. The laboratory relation between the amount of gas adsorbed and the 

pressure is called the equilibrium adsorption isotherm. Typically, the 

isotherm is determined for powdered coal, and it has always been assumed that 

the same isotherm curves hold for coal underground. However there is no conclusive proof that this is so. 

At each borehole where a direct method test was performed on the core, 

an "indirect method" test was also performed, as follows: After the coal 

was withdrawn, a well testing tool was inserted and the gas pressure in the 

coalbed was measured in a conventional drill stem test. A portion of the 

core was analyzed to obtain the coal moisture content (7). The gas pressure - 
PRESSURE, absolute atmospheres 

- 

Temperature 30" C 

- 

- 

- 

- 

pct 

Pocahontas No.3 0.7 

Pocahontas No.3 1.1 

- 

-x-Castlegate 2.2 

(subseam No. 3) 

++Illinois No.6 8 .O 

0 

10 20 30 40 

FIGURE 4. - Equilibrium adsorption isotherms. Coal type 

and moisture levels se lected to correspond 

to the cores extracted from the vertical 

boreholes. 

and the moisture content 

were used to determine the 

amount of gas adsorbed at 

coalbed pressure from the 

equilibrium adsorption 

isotherms in figure 44 (5). 

The methane released is 

the difference between the 

methane adsorbed at coalbed 

pressure (absolute, not 

gage) and the methane 

adsorbed at 1 atm. For 

instance, at the Vesta No. 5 

site the drill stem test 

gave 6.4 atm abs and the 

moisture content of the coal 

core was 1.4 percent. 

According to figure 4 

(Pittsburgh coalbed) the 

amount of methane adsorbed 

is 4.4 cIT? (sTP)/~. At 

1 atm 1.0 cm3/g is absorbed. 

Thus, if the pressure is 

reduced from 5.8 to 1 atm 

abs, the indirect method 

indicates 3.4 cIT? (SSP) /g 

of methane will be released. 

This value may be compared 

with 2.6 c$ (STP) /g obtained 

by the direct method 

(appendix B) . 

Methane amounts obtained 

by the indirect method and 

by the direct method for 

several vertical borehole 

sites are compared in 

table 1. There is reason50 ably close agreement in 

every instance, except 

for the Price site. 

4The isotherms were obtained from James I. Joubert, Pittsburgh Energy Research 

Center, Bureau of Mines, Pittsburgh, Pa. 
8 

TABLE 1. - Methane amounts by the direct and indirect methods 

DIRECT METHOD GAS QUANTITY COMPARED WITH EMISSIONS FROM NEARBY MINES 

The main purpose of determining the gas content of virgin coalbeds is in 

forecasting the methane emission from a prospective mine. Of the two methods, 

direct and indirect, the direct method is by far the most convenient and less 

expensive. Since routine core drilling ahead of mining is standard practice, 

adding a "direct method" test to assess the methane content of the core would 

be a simple matter. 

Direct method, 

cm3 (STp)/g 

2.6 

5.8,5.8 

11.1 

12.1 

1.7 

.9 

7.9 

4.2 

Most sites shown in table 1 were located within a mile of an operating 

coal mine. In figure 5 the methane emission from the mine (ft3 /ton of coal 

mined) is plotted against the amount of methane in the coalbed measured by 

the direct method (C~~(STP)/~.~ If methane came only from the coal that is 

removed from the mine, then these amounts should be equal. For instance at 

the Loveridge site (table 1) the direct method gives 5.8 cm3lg of methane in 

the coalbed. Since 1cm3/gis equivalent to 32 ft3/ton, then the emission from 

the mine would be 5.8 X 32 = 186 ft3/ton. However, figure 5 shows the actual 

emission from the mine is about 1,700 ff?/ton, which is a factor of 9 higher 

than the gas in the removed coal. This is not surprising, for methane is 

emitted not only by the coal being removed, but by all the coal that is left 

behind as ribs and pillars, as well as by the adjacent strata. 

Indirect method 

cm3 (STP) /g 

3.4 

5.2 

10.5 

13.5 

2.7 

.5 

7.8 

6.2,5.0 

Location 

Vesta No. 5.. 

Lover idge. ... Howe...... ... Beatrice.. ... Inland. ...... Do........ 

Kepler ....... Price.... .... 

The interesting feature of figure 5 is that, for all except the least 

Coalbed 

Pittsburgh ................. .... do.. ................... Hartshorne ................. Pocahontas No. 3........... 

Illinois No. 6............. 

Illinois No. 5. ............ Pocahontas No. 3......... .. Castlegate (subseam No. 3). 

gassy Inland mine, the ratio mine emission is relatively fixed; it varies 

direct amount 

between about 6 and 9. This is despite the fact that these mines are in 

widely different coalbeds with different kinds of adjacent strata. The mines 

themselves do have similarities: All are fairly large, deep mines with a 

sustained and constant coal production of at least several thousand tons a 

day; virtually all have been in operation for many years and have extensive 

old workings and gob areas. 

Data are available for only six mines, so the correlation shown in 

figure 5 must be regarded as tentative. However, in coalbeds for which data 

50ne mine is included (Federal No. 2) for which only the indirect test was 

per formed. , 
/ Loveridge@ Federal No.2 / 

3,000 

2,800 

u 2 4 6 8 10 12 14 16 18 20 

DIRECT METHOD, cm3/g 

FIGURE 5. - Coalbed gas amount via the direct method 

versus actual mine emission. 

I /I 1 

- Beatrice / 

/ 

800 

=0°- 

400- 

similar to that used by 

Irani are not available, 

the direct method combined 

with figure 5 should provide 

an approximate long-range 

forecast for any coal mine 

on the drawing board. 

- / - 

a/ Vest a NO. 5 

/ - 

/ 

/ - 

/ 

CONCLUSIONS 

200 

Inland 

1 I I n 

These preliminary 

studies have indicated that 

the methane output of an 

entire mine can be estimated 

by a direct gas measurement 

on an exploration core in 

conjunction with the correlation in figure 5. The 

method seems to work even 

if the drill bit has cut 

into the coalbed by mistake 

(as in Loveridge boreholel), 

or even if the coalbed is 

missed and just a few lumps 

of rider coal are obtained 

(as in the Beatrice site 

borehole). 

The technique appears 

to fit where the mines are 

large and deep, have a 

sustained coal production 

of at least several thousand 

tons a day, and have been in 

operation for many years. 

This means that it is a 

long-range forecast. 

In new mines--those which have been in operation only a few years--the 

emission in cubic feet per ton is much lower than emission from older mines 

which have extensive old workings and gob areas that are still bleeding gas. 

Hence the factor of 6 to 9 from figure 5 will be on the conservative side. 

Nevertheless, after the mine has been worked for some time, the emission 

may approach the relationship given in figure 5. 
1. Bertard, C., B. Bruyet, and J. Gunther. Determination of Desorbable Gas 

Concentration of Coal (Direct Method). Internat. J. Rock Mech. and Min. 

Sci., v. 7, 1970, pp. 43-65. 

2. Bielicki, R. J., J. H. Perkins, and F. N. Kissell. Diffusion From Coal 

Fragments--A Measuring Apparatus and Some Preliminary Results. BuMines 

RI 7697, 1972, 12 pp. 

3. Irani, M. C., E. D. Thimons, T. G. Bobick, M. Deul, and M. G. Zabetakis.. 

Methane hission From U.S. Coal Mines, A Survey. BuMines IC 8558, 1972, 

58 PP* 

4. Paul, L. Mesures de pressions de gae et de concentrations de gaz les 

couches de charbon (methode indirect) [Measurements of Gas Pressures and 

Concentrations in Coalbeds (Indirect ~ethod)]. Conference on Control of 

Firedamp Emission, Improvement of Mine Atmospheres. Published by the 

European Coal and Steel Community Information and Documentation Center, 

Luxembourg, October 1971, 537 pp. 

5. Ruppel, T. C., C. T. Grein, and D. Beinstock. Adsorption of Methane/Ethane 

Mixtures on Dry Coal at Elevated Pressure. Fuel, v. 51, 1972, 

pp. 297-303. 

6. Sevenster, P. G. Diffusion of Gases Through Coal. Fuel, v. 38, 1959, 

p. 403. 

7. U.S. Bureau of Mines. Methods of Analyzing and Testing Coal and Coke. 

Bull. 638, 1967, 85 pp. 

6Titles enclosed in brackets are translations from the language in which the 

item was published. 
APPENDIX A. --MEASURING TECHNIQUE 

The most convenient way to measure methane emission from the sample 

container is to displace water in an inverted graduated cylinder (fig. 2). 

Readings of the volume emi~ted should start as soon as the coal is in the 

sample container and be taken at least every 15 minutes for the next several 

hours. This initial monitoring is used to obtain the emission curves shown in 

figures 3, A-1, and A-2. During this initial period the container valve 

should be left open, to prevent back pressure from building up.l 

After the initial monitoring the valve was closed and the sample 

container was taken to the laboratory where the emission was monitored until 

it became negligible. Generally this was done by opening the sample container 

valve every day or so. 

When emission had virtually stopped, the coal was crushed to at least 

200 mesh in two stages--first to 8 mesh in a chipmunk crusher, and then to 

200 mesh in a rotary grinder. The crushing devices were both enclosed in a 

plexiglass box which was purged with nitrogen. The coal was then crushed and 

the methane content in the box was analyzed with a gas chromatograph. This 

procedure was adopted because all the equipment was on hand, but the crushing 

technique used by Bertard (1) is much simpler. 

The total gas by the direct method is the "lost" gas obtained by extrapolation from the initial measurement, plus all the gas emitted from the coal 

while in the sample container, plus the gas released during crushing. 

Any vessel capable of withstanding moderate pressures will do for the 

sample container. The ones used by the Bureau are fabricated from 4-inch 

aluminum pipe. The top lid is sealed with an O-ring and is equipped with a 

15-psi gage and a valve. 

lOccasionally, when it was not practical to monitor the volume emitted at the 

well site, the valve was closed while the cylinder was transported to a 

nearby motel. In such cases, we tried to avoid letting the pressure build 

up beyond a few psi, as then this would begin to affect the emission rate. 
FIGURE A-1 . - Emission rate curves: A, Core from Loveridge s ite-borehole 1, 

Pittsburgh coalbed; B, core from Loveridge site-borehole 2, 

Pittsburgh coalbed; C, core from Howe site-Lower Hartshorne 

coalbed; and D, core from Beatrice site-Pocahontas No. 3 

coa lbed. 
FIGURE A-2. - Emission rate curves: A, Core from Inland site 1-Illinois No. 6 coalbed; 

R, core from Inland site 2-Illinois No. 5 coalbed; C, core from Kepler 

s ite-Pocahontas No. 3 coa lbed; and n, core from Price site-Castlegate 

coalbed (subseam 3). 
APPENDIX Be--VERTICAL BOREHOLES 

The results from the vertical boreholes are discussed individually, to 

show how the values in table 1 were obtained and also to show how the circumstances of drilling may differ. 

Vesta No. 5 Site, Pittsburgh Coalbed 

By the evening of the first day the bit had penetrated to within a few 

feet of the coalbed. Seven-inch casing was set to the bottom of the hole and 

then cemented to the surface. On the second day the cement was drilled out, 

the bit was replaced with a core barrel, and coring (with air) began. At 

1:10 p.m. the drilling froth turned black, indicating that the coal had been 

reached. By 3:40 the coal was out and a portion of the core was in the sample 

container. Emission was carefully measured for the next 7 hours (fig. 3). 

Then, for the next month, the gas was vented off and measured every few days. 

The emission for the first 7 hours was used to plot figure 3. The total emission from the container after a month was 1,850 cm3. Another 960 cs is 

obtained from the extrapolation in figure 3. On the assunption that the core 

began to release gas at 1:10 p.m., the extrapolation was for 150 minutes. The 

amount released in crushing was 1,790 cm3. When these volumes are added, 

converted to STP, and divided by the sample weight of 1,570 grams, the total 

by the direct method was 2.60 cm3(s~p)/g. 

The extrapolation in figure 3 is a long one (as are many of the others), 

and it is quite likely that considerable errors may creep in. However, the 

lost gas (960 c1-8) is less than a fourth of the total, and so any errors will 

be reduced by at least a factor of four. 

A portion of the original core was analyzed for moisture, which was found 

to be 1.4 percent. A drill stem test performed immediately after the core was 

taken from the borehole showed that the methane pressure in the coalbed was 

6.37 atm abs. The isotherm in figure 4 shows that, for Pittsburgh coal at 

6.37 atm and 1.4 percent moisture, 4.4 cm3 (STP)/g of methane is adsorbed. At 

1 atm and 1.4 percent moisture about 1.0 cm3/g is adsorbed. According to the 

indirect method 3.4 c~~(sTP)/~ would be released. The amount by the direct 

measurement was 2.6 cm3 (sTP)/~. 

Loveridpe Site--Borehole 1, Pittsburgh Coalbed 

This borehole was completed on the first day, when the d r i l l b i t 

accidentally cut into the first foot of coal. The borehole was then cased and 

cemented and left standing that night. Air coring began on the morning of the 

second day. By 9 a.m. the core barrel had cut through the cement plug and was 

cutting the coal. The coal was out and in the sample container by 2:25 p.m. 

Emission was measured for the next few days (fig. A-14). A total of 6,420 cm3 

was given off from the container over the next 2 months. Extrapolation for 

325 minutes (9 a.m. to 2:25 p.m.) gave 855 cm3, and crushing released 

4,850 cm3. The sample weight was 1,864 grams, and the total released 

(corrected to STP) was 5.8 cm3 (STP) /g . 
A drill stem test gave a coalbed methane pressure of 12.0 atm abs. Moisture analysis on part of the remaining core gave 1.5 percent water. The 

isotherm indicated that 6.2 cm3Ig is adsorbed under these conditions. If 

1.0 c~~(sTP)/~ is adsorbed at atmospheric pressure, the amount released should 

be 5.2 cm3Ig. The direct method gave 5.8 cm3(s~p)Ig. 

Loveridge Site--Borehole 2, Pittsburgh Coalbed 

This borehole was completed soon after the first one. Coring of the coal 

began at 11 a.m., and the core was in the sample container by 4:30 p.m. 

Emission from the container was measured carefully for the next 24 hours 

(fig. A-1g). The total given off for the next 6 weeks was 4,730 cm3. Extrapolation of figure A-1g for 330 min (11 a.m. to 4:30 p.m.) gave 700 cm3 and 

crushing gave 3,550 cm3. Dividing hy the sample weight of 1,366 grams and 

correcting to STP, the total released was 5.8 cm3 (sTP)/~. This was exactly 

the amount released from the core at borehole 1, a short distance away. 

Howe Site--Oklahoma (Lower) Hartshorne Coalbed 

This borehole was drilled in the usual fashion, but it was cored with 

water whereas the previous ones were cored with air. We assumed that the 

methane release from the core began when the core was halfway out of the hole, 

and so the time to the sample container was only 30 minutes. The extrapolation from figure A-1s gives 1,150 cm3, and 8,010 cm3 was given from the sample 

container in the next 3 weeks. Crushing yielded a negligible amount of gas 

because this particular coal is very friable, so that gas escapes more quickly 

from it (2). By the end of 3 weeks, emission was essentially complete. The 

sample weight was 725 grams, and so the total emission after correcting to STP 

was 11.1 

The drill stem test was not successful, so the pressure was deduced by 

measuring the water level height in the cased borehole. It was 17.2 atm abs. 

The core contained 1.3 percent moisture. The isotherm in figure 4 gives 

12 cm3 (STP)/g for 17.2 atm and 1.3 percent moisture. At 1 atm, 1.5 cm3Ig is 

adsorbed, and so the indirect method indicates 10.5 cm3(s~p)/g should be 

released. 

Beatrice Site--Pocahontas No. 3 Coalbed 

This borehole was drilled with a cable tool and cored with water as a 

drilling medium. Coring began at 3 p.m. of the first day, and by 7:17 p.m. 

the core was out. It contained no coal. On the next day, another core was 

taken. This was started at 8:30 a.m. and was out of the hole by 1:30 p.m. 

The core was 3 feet long and had 2 inches of coal at the very top and 3 inches 

at the very bottom. The rest was rock. Despite the poor quality of the 

sample, the coal was placed in the sample container at 3 p.m. It was assumed 

that emission began at 1 p.m. The extrapolation from figure A-12 gives 

2,100 cm3 of lost gas, and a total of 5,230 cm3 was given off from the sample 

container over a period of 8 weeks. Only 54 cm3 was given off in the crushing, 

as the coal is very friable. The sample weight was 542 grams, so the total by 

the direct method was 12.1 c~~(sTP)/~. The pressure was not measured at this 
hole; however, a drill stem test in a nearby hole gave a pressure of 40.4 atrn 

abs. The coal moisture content was 0.7 percent. Figure 4 gives 15 cm3Ig at 

40.4 atrn and 1.5 cm3Ig at 1 atm, so the indirect method indicates 

13.5 cm3 (STP)/g should be released. 

Inland Site--Illinois 5 and 6 Coalbeds 

These coalbeds are only 60 feet apart. At this site the No. 5 coalbed 

was the deeper at 793 feet, while the No. 6 coalbed was at 733 feet. It might 

be expected that the methane amounts would be similar; however, a drill stem 

test in the No. 6 coalbed gave 9.3 atrn abs (or 122 psig), while a test in a 

separate borehole drilled into the No. 5 coalbed gave 2.4 atrn abs (or 21 psig). 

The corresponding amounts, using figure 4 and subtracting 0.5 cm3/g as the 

1 atrn value, are 2.7 cm3(s~p)/g for the Illinois No. 6 and 0.5 c~~(sTP)/~ for 

the Illinois No. 5 coalbed. The core moisture values were high--about 

8 percent. 

The direct method results were as follows: For the No. 6 coalbed the 

extrapolated amount from figure A-2A was 1,120 cm3, 1,730 cm3 were given off 

while in the sample container, and crushing yielded 180 cm3. The sample 

weight was 1,568 grams, and so the direct method gave 1.7 c~~(sTP)/~. For the 

No. 5 coalbed the extrapolated amount from figure A-2g was 360 cm3, 943 cm3 

were given off while in the sample container, and crushing yielded 310 cm3. 

The sample weight was 1,644 grams, and so the direct method gave 

0.9 cm3(s~p)Ig. In both cases the extrapolation had to be made using two 

points . 

The direct amounts from both coalbeds are plotted in figure 5, although 

the mine is in the No. 6 coalbed. These are proportionally quite high when 

compared with the mine emission. For the No. 6 coalbed the ratio 

mine emission = 2.2, whereas for gassier coalbeds it varied between 6 and 9. 

direct amount 

There are two possible reasons for this: First, the total amount of gas 

released is quite small and so errors in the absolute amount can lead to very 

large proportional errors. Second, both cores were not recovered quickly 

enough, and not enough data points were taken in the first hour. It follows 

that the lost gas may be incorrectly estimated, and this may be especially 

true in the case of the No. 6 coalbed, where the lost gas was unusually high 

compared with that from the No. 5 coalbed (figs. A-2A - and A-2g). 

Kepler Site--Pocahontas No. 3 Coalbed 

This was a company exploration hole, which was cored all the way from the 

surface and never cased. The hole was water-cored, and only 28 minutes 

elapsed before the coal was enclosed in the sample container. The emission 

curve and extrapolation are shown in figure A-2C. Comparison with figure A-1D 

shows the advantages of water coring and enclosing the coal in the sample 

container as quickly as possible. The data are much more likely to be in a 

linear portion of the emission curve, and the "lost" gas is a much smaller 

percentage of the total, especially when the coal is friable. Here, the lost 

gas was 560 cm3, the amount given off while in the sample container for 4 weeks 
was 12,300 cm3, and the amount from crushing was 3,010 cm3. The sample weight 

was 1,783 grams, and so the total corrected to STP, is 7.9 cm3 (STP)/g. The 

core contained 1.1 percent moisture, and the methane pressure, measured at a 

nearby borehole, was 11.8 atm abs. Figure 4 indicates 9.3 cm3Ig is adsorbed 

under these conditions. If 1.5 cm3Ig is substracted as the 1-atm value, then 

7.8 cm3 (STP) Ig should have been released. 

Price, Utah Site--Castlegate Coalbed 

(Subseam 3) 

This borehole was air cored and so the elapsed time since emission began 

was 165 minutes. The extrapolation of the emission curve is shown in 

figure A-2D. The lost gas amounted to 545 cm3, the amount released while in 

the sample container was 4,720 cm3, and the amount released upon crushing was 

1,430 cd. The sample weight was 1,427 grams, and the total amount of gas by 

the direct method was 4.2 cm3(s~P)Ig. 

A drill stem test in the borehole from which the core was taken gave a 

pressure of 24.4 atm abs. Figure 4 shows 7 crn3(s~P)Ig is adsorbed at this 

pressure and 0.8 cm3(s~P)Ig is adsorbed at 1 atm abs. This indicates 

6.2 cm3(s~P)Ig should be released, which is somewhat higher than the 4.2 from 

the direct method. The moisture content of the core was 2.2 percent. 

However, the borehole pressures were not consistent. A drill stem test 

in a nearby (1,500 feet away) borehole gave 16.6 atm abs, and this indicates 

about 5 cm3 (STP) /g should be released.