UNITED STATES DEPA 
U.S. Department of the Interior 

Mzssion Statement 

As the Nation's principal conservation agency, the Department of 

the Interior has responsibility for most of our nationally-owned 

public lands and natural resources. This includes fostering 

sound use of our land and water resources; protecting our fish, 

wildlife, and biological diversity; preserving the environmental 

and cultural values of our national parks and historical places; and 

providing for the enjoyment of life through outdoor recreation. 

The Department assesses our energy and mineral resources and 

works to ensure that their development is in the best interests of 

all our people by encouraging stewardship and citizen participation in their care. The Department also has a major responsibility 

for American Indian reservation communities and for people who 

live in island territories under U.S. administration. 
Information Circular 9395 

Methane Control for Underground 

Coal Mines 

By William P. Diamond 

UNITED STATES DEPARTMENT QF THE INTERIOR 

Bruce Babbitt, Secretary 

BUREAU OF MINES 
Library of Congress Cataloging in Publication Data: 

I, 

Diamond, W. P. (William P.) 

Methane control for underground coal mines / by William P. Diamond. 

p. cm. - (Information circular; 9395) 

Includes bibliographical references @. 41). 

1. Coalbed methane drainage-United States. 2. Coal mines and miningqafety 

measures. I. Title. 11. Series: Information circular (United States. Bureau of 

Mines); 9395. 

TN295.U4 [TN305] 622 S-4~20 1622' .82] 93-46850 CIP 
CONTENTS 

Page 

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

Introduction ........................................................................ 2 

History of methane drainage ............................................................ 2 

Establishing the need for methane drainage ................................................. 4 

Establishingageologicframework ........................................................ 5 

General mapping requirements ........................................................ 6 

Coalbed discontinuities .............................................................. 6 

Multiplegasreservoirs .............................................................. 7 

Fractureanalysis .................................................................. 7 

Methane drainage technology ........................................................... 9 

Underground methane drainage ....................................................... 9 

Horizontal boreholes - in-mine ...................................................... 9 

Horizontal boreholes - from shaft bottoms ............................................. 17 

Horizontal boreholes - water infusion ................................................. 17 

Vertical boreholes into the mine roof ................................................. 20 

Cross-measure boreholes .......................................................... 21 

Horizontal boreholes drilled to other horizons ........................................... 22 

Surface methane drainage ............................................................ 26 

Stimulated vertical wells in virgin coalbeds ............................................. 27 

Directionally drilled boreholes ...................................................... 33 

Longwall gob gas ventholes ......................................................... 35 

Summary .......................................................................... 41 

References ......................................................................... 41 

ILLUSTRATIONS 

Daily U.S. gas emissions and number of contributing mines. 1971-88 ........................... Gas content versus depth and coal rank. Black Warrior Basin. Alabama ........................ Schematic section view of effect of coalbed discontinuities on vertical methane drainage wells ........ Schematic section view of effect of coalbed discontinuities on horizontal methane drainage boreholes ... Schematic section view of longwall mining with gob gas conduits and plan view of longwall panel ...... Schematic plan view of desorption of methane from coal micropore. diffusion through coal matrix, and 

Darcyflowthroughcleat .......................................................... Schematic section view of typical European coal basin and mining method ....................... Schematic plan view of horizontal methane drainage boreholes drilled to preferentially intercept face 

cleat ......................................................................... Plan view of horizontal methane drainage boreholes. Sunnyside Coalbed. Utah ................... Plan view of horizontal methane drainage boreholes. Pittsburgh Coalbed. Pennsylvania ............. Daily gas and water flow rates from horizontal methane drainage boreholes. Pittsburgh Coalbed. 

Pennsylvania ................................................................... Plan view of horizontal methane drainage borehole and gas flow in relation to mine advance. Mary Lee 

Coalbed. Alabama ............................................................... Schematic plan view of long horizontal boreholes for methane drainage in longwall mining .......... Schematic plan view of short horizontal boreholes for methane drainage from longwall panels ........ Schematic section view of typical horizontal methane drainage borehole gas collection system with failsafe pneumatic shut off valve ....................................................... Schematic section view of large-diameter vertical borehole for drilling horizontal methane drainage 

boreholes. Pittsburgh Coalbed. West Virginia ........................................... Plan view of horizontal methane drainage boreholes drilled from large-diam eter vertical borehole. 

Pittsburgh Coalbed. West Virginia ................................................... 
ILLUSTRATIONS 

Page 

Decline in methane emissions at the face as mining approached horizontal methane drainage boreholes 

drilled from a shaft bottom. Pittsburgh Coalbed. West Virginia .............................. Schematic section view of typical water infusion horizontal borehole completion ................... Schematic plan view of elliptical water fronts developed from water infusion of coalbed with face cleat 

perpendicular to section advance .................................................... Schematic plan view of elliptical water fronts developed from incomplete water infusion of coalbed with 

face cleat parallel to section advance ................................................. Perspective view of vertical in-mine boreholes for methane drainage of overlying Pocahontas No . 4 

Coalbed from mined Pocahontas No . 3 Coalbed. Virginia .................................. Plan view of cross-measure boreholes on advancing European longwall ......................... Plan view of cross-measure boreholes on retreating U.S. longwall ............................. Schematic section view of a typical cross-measure borehole completion with gas-water separator ...... Schematic section view of a typical gas-gathering system for cross-measure boreholes ............... Schematic pian and section views of methane drainage borehoies ciriiieci from roadway driven dong 

strike in rock below mined coalbed. Japan ............................................. Schematic plan and section views of methane drainage boreholes drilled from crosscut driven 

perpendicular to strike to intercept coalbed. Japan ....................................... Schematic plan and section views of methane drainage boreholes drilled from gate roads driven along 

strike in coalbed to outline longwall panels. Japan ....................................... Plan and section views of long horizontal methane drainage borehole drilled in strata above longwall 

panel. Japan ................................................................... Section view of methane drainage borehole drilled into an underlying coalbed. Australia ............ Schematic section view of gas drainage from sealed entries and/or gob ......................... Schematic section view of sand proppant from hydraulic stimulation. Lower Kittanning Coalbed. 

WestVirginia .................................................................. Schematic section view of sand proppant from hydraulic stimulation. Pittsburgh Coalbed. Pennsylvania . . Schematic plan view of relationship of mine entry orientation and interception of vertical fracture from 

hydraulic stimulation preferentially oriented in face cleat direction ............................ Schematic view of open hole and cased hole completions for vertical methane drainage well .......... Schematic section view of water pump installed in vertical methane drainage well ................. Plan view of elliptical placement of fluids in the Blue Creek Coalbed. Alabama. from a stimulated 

vertical methane drainage well ...................................................... Schematic plan view of vertical methane drainage wells placed to shield mine workings from migrating 

gas .......................................................................... Schematic plan view of location of two near-mine experimental stimulated vertical methane drainage 

wells. Blue Creek Coalbed. Alabama ................................................. Comparison of cumulative methane emissions in entries developed into areas with and without stimulated 

vertical methane drainage wells. Blue Creek Coalbed. Alabama .............................. Section view of long-radius directionally drilled well path to intercept the Pittsburgh Coalbed horizontally 

from the surface. Pennsylvania ...................................................... Plan view of multiple horizontal methane drainage boreholes drilled from a directional surface borehole. 

Pittsburgh Coalbed. Pennsylvania .................................................... Schematic section view of available directional hole drilling radiuses ........................... Schematic section view of short-radius directional methane drainage borehole equipped with downhole 

pumpfordewatering ............................................................. Schematic section view of various longwall gob gas venthole completion designs ................... Schematic section view of complete longwall gob gas venthole system .......................... Daily methane flow rate. gob gas venthole 178. Lower Kittanning Coalbed. Pennsylvania ............ Daily methane flow rate. gob gas venthole 176. Lower Kittanning Coalbed. Pennsylvania ............ Daily methane percent of produced gas. gob gas venthole 178. Lower Kittanning Coalbed. Pennsylvania 
ILLUSTRATIONS 

Page 

51. Combined daily methane production from 13 gob gas ventholes on a longwall panel in the Lower 

Kit tanning Coalbed, Pennsylvania .................................................... 38 

52. Histograms of methane production from individual gob gas ventholes, Lower Kittanning Coalbed, 

Pennsylvania ................................................................... 39 

53. Schematic perspective view of subsidence trough developed over an extracted longwall panel ......... 40 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

bbl/min barrel per minute m meter 

B cf billion cubic feet m2 square meter 

cfd/ft cubic foot per day per foot 

(of hole length) 

m3 cubic meter 

Mcf thousand cubic feet 

cm centimeter 

cm3/g cubic centimeter per gram 

Mcfd thousand cubic feet 

per day 

ft foot m3/d cubic meter per day 

cubic foot per minute 

cubic foot per short ton 

gallon 

gallon per minute 

hour 

inch 

kilogram 

kilo pascal 

pound 

(m3/d)/m cubic meter per day per meter 

(of hole length) 

MMcf 

MMcfd 

m3/min 

m3/s 

pet 

psi 

psig 

million cubic feet 

million cubic feet per day 

cubic meter per minute 

cubic meter per second 

percent 

pound per square inch 

pound per square inch, gauge 
METHANE CONTROL FOR UNDERGROUND COAL MINES 

By William P. ~iamond' 

Ventilation has long been the primary means of controlling methane emissions in underground coal 

mines. However, as mining has progressed into gassier areas of U.S. coal basins, supplemental means 

of methane control have become of interest, if not a necessity, for continued safe and productive mining 

operations. This paper describes the history and technology of methane drainage in the United States 

and other countries. The methane drainage technology developed in European countries is a valuable 

resource since their longer history of mining has already forced mine operators to deal with methane 

emission problems only now being experienced in the United States. Methods for assessing the need 

for methane drainage and the data required for planning and implementing an appropriate system are 

reviewed. The effectiveness of the various technologies for reducing methane emissions underground 

and/or the in-place gas content of individual coalbeds is illustrated with case studies. In addition to the 

safety and productivity gains to be realized from methane drainage systems, the potential for 

commercialization of coalbed methane is discussed. 

'~eolo~ist, Pittsburgh Research Center. U.S. Bureau of Mines, Pittsburgh, PA. 
INTRODUCTION 

Methane emissions can adversely affect both the safety 

and the productivity of underground coal mines. Since the 

first documented major U.S. coal mine explosion in Virginia in 1839, several thousand fatalities have occurred 

owing to explosions where methane was a contributing 

factor (91).2 Ventilation has been the primary means of 

controhg methane in coal mines for many years. 

However, as mines began operating in deeper and gassier 

coalbeds, supplemental means of methane control became 

of interest to mine operators. 

The shift to mining gassier coalbeds is quite evident in 

figure 1, which charts the gas emissions from coal mine 

ventilation systems from 1971 to 1988. The volume of 

methane and the number of operating mines remained .-tnl%ln +l.*n.,"l. +l.n -,,*I.. in -:AAln ln7n'P {AA AA\ IPLULI ~L~IJIL uu uup UL ~aly LU ULUULL 12 I u J \w, TWJ, 

technology, especially in the Black Wamor Basin of Alabama. Methane emissions from Alabama coal mines decreased by 17 pct, from 2.3 to 1.9 x 106 m3/d (82.4 to 

68.4 MMcfd), between 1985 and 1988 (10). During this 

same time, the annual production and capture of coalbed 

methane for commercial sale increased 130 pct, from 245 

to 563 x lo6 m3 (8,648 to 19,865 MMcf) (62). Approximately 90 pct of this commercial production was from 

methane drainage installations located on mine property. 

This paper describes the various methane control technologies available to the coal industry. Methodology and 

data requirements necessary to select and design optimum 

methane drainage systems are discussed, along with the ~rlxr~nt~npc ~nrl rl;r~rlxr~nt~npr nf tho c~rctomc Cv~mmloc nf UU I LILILUbVJ UU UIJUU I LILILUbV3 VA LUV 3J3LClAllJ. LX%UAAI~IClJ VA 

but as of the 1980 and 1985 surveys (35-36), methane gas production rates and the effects of the various methemissions increased substantially, while the number of ane drainage technologies on mine emissions from experimines declined in 1985. mental and larger scale programs are included. 

The decline of methane emissions in 1988 (fig. 1) is at 

least partly due to the increased use of methane drainage 

HISTORY OF METHANE DRAINAGE 

Bromilow and Jones (6) reported on the early history 

of methane drainage in Europe, where coal mining has a 

much longer history than in the United States. The first 

attempts to isolate and pipe gas from a coal mine in Great 

Britain occurred in 1733 at the Haig Pit, Whitehaven, 

England. In 1844, following an explosion at another colliery, investigators concluded that gas accumulations in 

the gob (caved and fractured zone above an extracted 

longwall panel) had caused the explosion. The investigators recommended that pipes should be used to drain 

the gob and carry the gas up the shaft to the surface. The 

recommendations were reviewed by a committee of mining 

engineers, but were dismissed as impractical. 

In-mine cross-measure holes were used in North Wales 

in the late 1800's to drain gas from overlying virgin coalbeds. The first successful large-scale use of cross-measure 

holes took place in the early 1940's at the Mansfield Colliery, Ruhr, Germany. The first recorded successful use of 

a vertical borehole to drain gas from virgin coal occurred 

at this same mine in 1943 (79, 104). 

In the United States, the potential for using boreholes 

(horizontal and vertical) to drain gas from coal in advance 

of mining was recognized in the early 1900's (13). Lawall 

and Morris (56) reported on an attempt to drain gas from 

the Pocahontas No. 4 Coalbed, West Virginia, by drilling 

short (4.6- to 31.1-m [15- to 102-ft]) horizontal holes into 

the ribs. Measured gas pressures and flow rates were variable, but generally low. The maximum flow measured was 

about 453 m3/d (16 Mcfd) from a 8.9-cm (3.5-in) diarneter, 21.6-m (71-ft) long hole. The hole had a maximum 

shut-in pressure of 207 kPa (30 psi). Ranney (86) reported on the "sorption" of gas in coal and the need to "upset" 

the equilibrium conditions by reducing the pressure to release the gas. He proposed that, for mine safety, a vacuum could be applied to a coalbed by drilling long horizontal holes spaced 244 m (800 ft) apart. He further stated 

that it was possible to drill horizontal holes 1,219 to 

1,524 m (4,000 to 5,000 ft), control the elevation of the 

'italic numbers in parentheses refer to items in the list of references Figure 1.--Daily U.S. gas emissions and number of contributat the end of this report. ing mines, 1971-88 (10. 
hole at any depth, and follow the contours of the coalbed. 

Unfortunately, he did not offer research results and details 

about the drilling equipment and procedures that could accomplish his claims. He stated, however, that it was the 

same technology used to drill horizontal oil wells. 

The first attempt to remove gas produced from underground methane drainage systems to the surface by use of 

pipelines is reported to have occurred in Great Britain 

about 200 years ago, and the practice became widely used 

throughout the coalfields of Europe in the 1940's (6). The 

first known similar system in the United States was a component of a cross-measure methane drainage system designed to drain gas from the gob at an advancing longwall 

mine in Colorado (87). 

In the early 19307s, in the United States, a 26-m (85-ft) 

deep, 7.6-cm (3-in) diameter corehole was used to suc- ----L.11.. A-n:.. ulalu gas frzm "brcker! sandstorrc" .hove 2 

mined-out section in the Pocahontas No. 5 Coalbed, Virginia (12). The coalbed was at a depth of approximately 

52 m (170 ft). Four similar coreholes were eventually 

completed and were estimated to have produced at a combined rate of nearly 25 x 103 m3/d (900 Mcfd). The holes 

reduced in-mine methane concentrations on the continuous 

miner sections from 1.5 to 0.3 pct. These holes were 

similar in concept to the gob gas ventholes used today to 

drain gas from Iongwall mining operations. 

Tilton (100) noted the production of gas from vertical 

~vells penetrating the Pittsburgh Coalbed in West Virginia. 

The initial well was completed in 1905 to gas resenoirs 

below the Pittsburgh Coalbed. In 1931, prior to abandonment of the well, gas was "discovered" in the Pittsburgh 

Coalbed, and the well was recompleted to that zone. In 

1949, 22 additional wells were drilled to the coalbed, with 

31 x lo6 m3 (1,217 MMcf) of gas produced through 1984 

(1 01). 

The first vertical wells in the United States designed 

specifically to remove gas directly from a coalbed were 

drilled in 1952 at a mine on the Pennsylvania-West Virginia border (92). The first well was a dual completion in 

the Sewickley Coalbed at a depth of about 113 m, (370 ft) 

and the Pittsburgh Coalbed at a depth of 140 m (458 ft). 

The well was completed so that gas could be produced and 

monitored separately from each coalbed. The Pittsburgh 

Coalbed produced up to 1.1 x 103 m3/d (40 Mcfd) of gas 

when the water level was kept low by bailing through the 

tubing string. No measurable gas was produced from the 

Sewickley Coalbed owing to the completion design, which 

precluded removing water from the zone. 

A second well at the same mine site was equipped with 

a downhole water pump and a vacuum pump on the surface to draw gas from the coal. Maximum gas production 

reached 453 m3/d (16 Mcfd). After 10 months of low gas 

production, an attempt was made to increase production 

by "shooting" the well with nitroglycerin. This was the 

first documented attempt to stimulate a coalbed gas drainage well. The stimulation was unsuccessful with poststimulation production reaching only 85 m3/d (3 Mcfd). 

The first known hydraulic stimulation of a coalbed occurred at this same mine in 1959 (92). Prior to stimulation, maximum gas production was 28 m3/d (1 Mcfd) from 

the Pittsburgh Coalbed at a depth of 140 m (460 ft). The 

coalbed was stimulated with 38 m3 (10,000 gal) of water. 

Fluorescein dye was added as a tracer for future underground evaluation of the stimulation. Treatment rate was 

0.5 to 0.8 m3jmin (3 to 5 bbijminj, and a maximum pressure of 4,137 kPa (600 psig) was reached. The pressure of 

4,137 kPa (600 psig) remained constant throughout the 

treatment; this was interpreted to suggest that a "true" 

fracture had not been created, but existing fractures had 

been "washed-out" or "flushed." Maximum gas production 

after stimulation was 4.2 x lo3 m3/d (150 Mcfd). Average 

production for 50 days after stimulation was 1.4 x 103 

m3/d (50 Mcfd). 

The potential value of coalbed methane as a recoverable resource was recognized many years ago. In 1934, 

Lawall and Morris (56) calculated that two mines operating in the Pocahontas No. 4 Coalbed, West Virginia, were 

liberating approximately 0.37 x 106 m3/d (13 MMcfd) of 

gas; based on a price of $0.10/28.3 m3 (1 Mcf), its value 

was $1,300/d. Burke and Parry (7) in 1936 noted that the 

presence of gas in coal mines required the use of "costly 

ventilation," but that the gas may have "considerable intrinsic value, and its recovery might conceivably be a profitable undertaking." Ranney (86) estimated in 1941 that 

approximately 14.2 x 106 m3/d (500 MMcfd) of natural gas 

was being "wasted" from U.S. coal mines. He thought it 

surprising that, in view of the 275 miner deaths in 1940, no 

thought was given to recovering the gas from coal in advance of mining to enhance mine safety. He recognized, 

however, that anyone suggesting that this gas be recovered 

and used would be considered "visionary or crazy." In 

1943, Price and Headlee (83) concluded that technology 

developed by the petroleum and gas industry could be 

adapted for the economic recovery of coalbed gas. 
ESTABLISHING THE NEED FOR METHANE DRAINAGE 

A mine-safety-related methane drainage program requires substantial capital expenditure and certainly should 

not be undertaken if it is not needed to maintain a safe 

and productive underground working environment. At an 

existing mine, the most obvious indicator of need is difficulty in maintaining methane concentrations at the working face or in the return air below the maximum level 

allowed by the requisite regulatory authority. An example 

that illustrates the effect of high methane concentrations 

on mine operations was reported by Kline (51). A mine 

operating in the Pocahontas No. 3 Coalbed, Virginia, lost 

over 333 h of production time owing to gas delays on a 

longwall panel. The capital cost of installing larger capacity fans or additional ventilation shafts to increase the 

volume of ventilation air made methane drainage an attractive and cost-effective alternative. Kline (51) reported 

that if the gas removed by the various methane drainage 

techniques were added to the volume emitted into the 

mine, the resulting methane volume would be "well beyond 

our capacity for dilution." 

Ideally, a property should be evaluated for its methane 

emission potential during the preliminary exploration and 

mine planning phase of mine development (15-16, 85). 

This approach offers a distinct advantage over the common practice of waiting until a methane emission problem 

has become acute before methane drainage is considered. 

If a premining course of action is taken, the necessary 

geologic, engineering, and reservoir data can be obtained 

early so that various methane drainage options can be 

evaluated for their effectiveness relative to the site-specific 

conditions (MI). This allows the inclusion of a methane 

drainage system, if it is needed, into the original mine 

design. 

Retrofitting a methane drainage system into existing 

mining operations, while feasible, generally limits options, 

especially if the methane problem has already become 

acute. This course of action will probably result in higher 

costs for the system itself, in addition to the cost of any 

loss of coal production. Methane drainage prior to mining has the additional advantage of potentially providing 

revenue to the mine at a time when no revenue is being 

generated from coal production. The primary advantage 

to the mine, however, would be the mining of coal with a 

reduced gas content, which over the long run allows for 

safer and more productive mining conditions. 

Assessment of the need for methane drainage prior to 

mine development generally requires both an empirical 

and a theoretical approach. If there are active mines in 

the general area with similar geologic conditions and coal 

characteristics, a review of gas problems in those mines 

provides the best insight into the level of gas emissions to 

be expected at the new location. 

A direct measurement of the site-specific gas in place 

for the coalbed to be mined can be helpful for assessing 

the relative gassiness of the coalbed. The gas content of 

surrounding strata, including other coalbeds, should also 

be measured to determine the number, location, and possible influence on mining of these additional gas-bearing 

zones. The gas content values are an important variable 

required for gas production simulations using the various 

available coalbed gas reservoir models. Gas content testing is a relatively simple procedure that utilizes samples of 

coal from exploration coal cores (20). The direct-method 

procedure requires that the coai sample to be tested be 

sealed in a desorption canister as soon as it is retrieved 

from the corehole to minimize the amount of gas lost before gas content testing begins. Gas is periodically bled 

from the container and measured, after which the results 

are corrected to standard temperature and pressure. After 

a period of desorption that may last several months, the 

total cumulative volume of gas desorbed is determined. 

Properly conducted direct-method testing of coal cores 

provides relatively accurate estimates of in-place gas contents for most mine planning purposes at a reasonably low 

cost. A modified-direct-method (MDM) procedure provides an increased level of accuracy, but at a higher level 

of instrumentation sophistication, procedural complexity, 

and cost (103). This methodology measures the pressure 

of the gas desorption in the sealed container and uses the 

ideal gas law to calculate the volume of gas desorbed from 

the coal sample. The MDM is particularly useful for samples (both coal and other rock types) with low gas contents 

and for samples with unusually high percentages of other 

gases besides methane. 

Gas content values can be compared with any available 

data from surrounding mine properties, or other areas of 

similar geologic conditions and mining methods. The severity of mining problems associated with known levels 

of in-place gas contents can then be compared with the 

test results from the new area of interest. A listing of 

gas content values for approximately 1,500 coal samples 

from more than 250 coalbeds in 17 States is included in 

Diamond (20). 

Gas content data on individual coal samples can be 

used along with auxiliary data on coal rank and/or depth 

to construct curves for estimating in-place gas contents 

(16, 19, 23, 42-43, 49, 67-68, 94). These curves can be used 

to estimate gas content values only if the rank and/or 
depth are known for a particular coalbed of interest 

(fig. 2). The curves are best used for estimating in-place 

gas volumes in regional studies. They should be used with 

caution for a relative small, mine-size area, where "abnormal" conditions may exist. The curves may be used in 

preliminary assessments of small areas but should not be 

considered a substitute for site-specific gas content 

determinations. 

Unfortunately, it is not possible to cite a definitive 

threshold in-place gas content value above which methane 

drainage would be required or recommended. Numerous 

geologic and mining factors in addition to the in-place gas 

content influence methane emissions into a mine. Methane drainage has been practiced by coal companies in the 

low-volatile, Pocahontas No. 3 Coalbed, Virginia, at depths 

of 380 to 790 m (1,250 to 2,600 ft), where gas contents 

appro*& 18.8 zix3/g (5% 23/~t) (52). /, -"- 2nd the highvolatile A, Pittsburgh Coalbed, Pennsylvania and West Virginia, at depths up to 305 m (1,000 ft) (61, 85, 99), where 

gas contents are commonly only about 4.7 to 6.3 cm3/g 

(150 to 200 ft3/st) (20). Large patterns of vertical boreholes have been successfully used for methane drainage in 

advance of mining in the medium- to low-volatile Mary 

Lee-Blue Creek Coalbeds, Alabama, where gas contents 

are approximately 14.0 to 19.0 cm3/g (450 to 600 ft3/st) at 

depths ranging from 305 to 610 m (1,000 to 2,000 ft) (17). 

Insight into the selection and configuration of appropriate methane drainage techniques can be gained from simulations using computer-based reservoir and production 

models. The models can best be used to evaluate the potential effectiveness of the various technologies available, 

alternate configurations of well patterns, and the time 

factor between when holes are put on production versus 

mine development. Most of the available models are designed to simulate the production of gas from vertical wells 

drilled into virgin coal reserves (50). However, several of 

the models have been adapted to include horizontal holes 

drilled from underground workings, as well as the influence of adjacent mine workings (41, 60, 88, 90, 97). 

A comprehensive mine simulator, combining the variables of mining operations and coalbed reservoir and 

production simulators, that could predict minewide ventilation and/or methane drainage requirements does not 

DEPTH, rn 

0 200 400 600 800 1.000 1.200 

Figure 2.4as content versus depth and coal rank, Black Warrior Basin, Alabama (67). 

currently exist. It is, therefore, not possible to predict the 

need for methane drainage by utilizing a theoretical analytical technique. Most mining companies wait until methane emission problems are encountered before methane 

drainage is considered owing to the difficulty in predicting 

the need for methane drainage. 

Another aspect of methane drainage to consider when 

evaluating the need for such technology is the potential for 

on-site utilization or commercial sale of the produced gas. 

The capture and utilization of coalbed gas does require 

additional effort beyond venting the produced gas at the 

surface. Gas gathering and metering systems and, depending on the ultimate use and quality of the gas, compression 

and gas treatment facilities may have to be constructed. 

Gas sales contracts and perhaps gas ownership and/or 

royalty agreements must be negotiated. In spite of the 

extra effort required, gas utilization or sales can offset the 

cost of methane drainage and perhaps produce a profit 

(27, 105). To illustrate the production potential, coalbed 

methane wells in the Black Warrior Basin of Alabama 

produced 2.6 x lo9 m3 (91.8 Bcf) of gas in 1992 (38). 

Cumulative production from coalbed methane wells in the 

basin was nearly 8.2 x lo9 m3 (290 Bcf) through 1992, with 

about 55 pct of the production being located on mine 

property. 

ESTABLISHING A GEOLOGIC FRAMEWORK 

Once the need for methane drainage has been deter- and designing the drilling and completion programs for inmined, a geologic framework must be established for the dividual methane drainage holes. Additionally, the mine 

site. A site-specific (minewide) geologic framework is development plan must be taken into account when finalessential to help provide a basis for picking drilling sites izing drilling locations. 
GENERAL MAPPING REQUIREMENTS 

Two basic types of maps are required for methane 

drainage planning: isopach and structure. Coal isopach 

maps should be constructed for all coalbeds (and any 

other gas-bearing strata) that may contribute gas to the 

mining operation and which may be considered for methane drainage. Coal thickness is a critical consideration. In 

vertical wells, maximum coal thickness or surface area exposed to the wellbore is advantageous for optimum gas 

and water production. In horizontal holes, the thicker the 

coalbed and the more uniform the structural dip, as determined from a structure map, the easier it is to keep the 

well path in the coalbed. Structure maps that depict 

changes in elevation of individual stratigraphic units, such 

as coalbeds, are also used in conjunction with surface 

eievation (topographic mapsj to provide an estimate of 

depth to the coalbed and other relevant strata for the 

design of the drilling and completion programs of vertical 

methane drainage wells. 

COALBED DISCONTINUITIES 

The data and trends portrayed on the geologic maps 

can be used to delineate or forecast the presence of coalbed discontinuities, in particular "wants," sand channels, 

and structural faults that can disrupt the continuity of the 

coalbed. Coalbed discontinuities should be avoided since 

they commonly cause drilling and production problems. If 

a vertical methane drainage well, such as well A, figure 3, 

penetrates a sand channel, the well may not produce appreciable gas. Well B, figure 3, has encountered the targeted coalbed, but has been drilled into an area between 

a clay vein and a fault. If the clay vein and fault are 

impermeable and their boundaries define a small drainage 

area, well B may only influence that small area, thus reducing the benefit for the cost expended. Well C, figure 3, has penetrated a fault plane that has displaced the 

targeted coalbed. Unless the fault plane is a conduit for 

gas migration, well C will probably not be productive. 

Well D, figure 3, encountered a mine void in an overlying 

coalbed. Technically not a coalbed discontinuity, the void, 

however, disrupts the continuity of the strata. The mine 

void will most likely result in drilling problems and may 

cause abandonment of the well before the target coalbed 

is reached. 

Coalbed discontinuities also adversely affect the drilling 

and production of gas from horizontal boreholes. Hole A 

in figure 4 has encountered a "roll" that will probably 

cause drilling problems when the harder, noncoal material 

is penetrated. Production of gas from this hole will most 

likely be adversely affected owing to the reduction in hole 

length caused by encountering splits and the eventual 

pinch-out of the gas reservoir. Hole B, figure 4, has 

encountered a sand channel and a fault that has displaced 

the coalbed, resulting in similar drilling and production 

problems. 

Well A Well B Well C Well D 

I mine 

' Fault A 

Figure 3.--Schematic section view of effect of coalbed discontinuities on vertical methane drainage wells (16). 
The occurrence of coalbed discontinuities obviously 

presents potential mining problems, in addition to being a 

concern for the most advantageous placement of coalbed 

gas drainage wells. If mine workings are available for 

underground mapping, geologic trends, including faults, 

clay veins, and sand channels, may be projected into adjoining unmined areas. A geologic and statistical methodology has been developed that uses data from mined-out 

areas to estimate the probability of encountering coalbed 

discontinuities with vertical drilling grids of various 

spacings (39). 

the gob or to the mine through the roof near the face 

(fig. 5). Diamond, (25) found that coalbeds as much as 

61 m (200 ft) above an extracted longwall panel contributed gas to the gob. Gas also migrates into mine workings 

developed in room-and-pillar sections through fractures in 

the roof and floor that connect to other gassy coalbeds. 

An effective methane drainage strategy for multiple gasbearing coalbed reservoirs may require several gas drainage techniques. This could include multiple-zone completions in vertical wells drilled in advance of mining, as well 

as postmining gob gas drainage. 

MULTIPLE GAS RESERVOIRS FRACTURE ANALYSIS 

A geologic consideration that should be addressed early 

in the planning stages of a methane drainage program is 

an evaluation of additional gassy coalbeds surrounding the 

coalbed to be mined. Gas from overlying coalbeds can be 

a particular problem, especially if the beds occur in strata 

over a longwall panel. As the longwall panel is extracted, 

unsupported overburden collapses behind the temporary 

roof support of the shields. Gas enters the mine atmosphere from overlying coalbeds exposed directly to the 

caved zone (gob), or may migrate through fractures into 

Fractures, both in the coalbed (cleat) and in surrounding strata ('joints), can have a si&icant influence on the 

flow of gas to methane drainage boreholes and mine 

entries. Once gas has desorbed from the micropore structure of coal, its flow to a wellbore or mine entry is first 

governed by Fick's law of diffusion (concentration gradients) until the gas molecules reach the cleat, at which 

point Darcy flow is the controlling influence (fig. 6). In 

water-saturated coalbeds, the Darcy flow of gas through 

the cleat system is controlled by the degree of pressure 
orientations from mines in other coalbeds or from surface 

outcrops. In some cases, subsurface cleat orientations can 

be interpreted from fracture trends in other rocks exposed 

at the surface, or lineaments from areal photography (21, 

66). Where no other data are available, an oriented core 

sample can be used to determine cleat direction (4). 

The presence, orientation, and frequency of fracturing 

as measured at the surface may be indicative of similar 

fracture characteristics in the subsurface. Attempts have 

been made in several producing areas to place vertical 

coalbed gas drainage wells near fracture zones to take 

advantage of the expected increased permeability. Briscoe 

(5) reported that a significant increase in gas production 

was achieved in the Black Warrior Basin of Alabama when 

vertical wells were drilled near fracture systems. Wells 

located within 61 m (200 ft) of fracture zones obtained 

25 pct greater gas production and 50 pct greater water 

production than wells in unfractured areas. Additionally, 

Briscoe (5) showed that the position of wells relative to 

the regional dip of the coalbed influenced production. 

Updip wells dewatered and produced gas before the downdip wells. A similar relationship was found in West Virginia, where wells drilled on structural highs that - encounrigur 6.d.emaac phn ,,,w of desorption of mdane horn tered the Pittsburgh Coalbed above the gas-water contact 

coal micropore (A), diffusion through coal matrix (9, and Darcy produced gas. Wells drilled below the gas-water contact 

flow through cleat (0. were not productive (78). 
gy p

The various methane control technologies can be 

grouped in several ways for discussion purposes. In this 

paper, they are generally grouped as either underground 

or surface technologies. 

1- 

Crosscut 

Crosscut 

Horizontal methane 

.. . - F--J n a 1 direction gas flow 

- .. 1.' - .: .., vi.,?.....!:: ..,:; -... :,;:: 4.: .:*, :,'.; '>...-; ',. . .. 

Figure 7.-Schematic section view of typical European coal Figure 8.-Schematic plan view of horizontal methane drainbasin and mining method (9). age boreholes drilled to preferentially intercept face cleat 
environment. Commonly, the size of the working area can 

be quite small, transporting people and materials to the 

drill site can be cumbersome, and stringent safety regulations must be obeyed. The successful use of horizontal 

boreholes underground also requires close coordination 

between the mining plan and the methane drainage plan. 

Neither operation must hinder the other, in terms of logistics and in completing their respective activities so as to 

not impede the other's progress. 

Underground horizontal boreholes can be used to control methane emissions in two general ways: draining gas 

from a block of coal to be mined, or shielding active mining areas from migrating gas. The drainage of gas can be 

either in advance of mining or during mining as part of 

the mining cycle. Shielding can be accomplished either by 

intercepting the gas before it enters the mine atmosphere 

or by diverting the migrating gas from the active face area. 

Optimum placement of the holes can also provide a combination of control functions. 

Horizontal boreholes drilled from existing underground 

mine workings can be used for long-term methane drainage in advance of mining. In the mid-1970's, two horizontal boreholes were drilled in the Upper Sunnyside Coalbed, Utah, from a set of entries abandoned for more than 

a year due to high methane emissions (fig. 9). The two 

holes were drilled 131 and 137 m (430 and 450 ft) into 

the coalbed. Combined production from the two holes 

averaged over 4.0 x lo3 m3/d (140 Mcfd), or 15 (m3/d)/m 

Return air Intake 

and pipeline Beit I 

Intake 

air 

LEGEND 

D Stopping with door 

% Stopping 

Hole 1 

(430ft) 

- 

Face cleat 

Hole 2 

137 rn 

(450 ft) 

Scale 

Figure 9.--Plan view of horizontal methane drainage boreholes, Sunnyside Coalbed, Utah (80). 
(160 cfd/ft) of hole, for 6 months. In 9 months, the two 

holes produced over 0.99 x lo6 m3 (35 MMcf) of gas, and 

face emissions were reduced by 40 pct. This enabled mining to resume in the area (80). 

In the late 1970's, four long horizontal boreholes were 

drilled into the Pittsburgh Coalbed, Pennsylvania, from a 

section of a mine that had been abandoned for 2.5 years 

due to high gas emissions. The length of the holes ranged 

from 299 to 764 m (982 to 2,505 ft) (fig. 10). The combined initial flow rate of each hole was 16.4 x 103 m3/d 

(580 Mcfd), or 9.3 (m3/d)/m (100 cfd/ft) of hole. Production decreased to 6.6 x 103 m3/d (234 Mcfd), or 

3.7 (m3/d)/m (40 cfd/ft) of hole, after 2.7 years of production (fig. 11) (84). Cumulative production for the four 

holes was 7.2 x lo6 m3 (255 MMcf). Gas production from 

the holes was lower than expected for the Pittsburgh 

Coaibed, apparentiy owing to the presence of a sandstone 

channel and clay veins that effectively isolated this area 

from the rest of the gas reservoir. The 2.5-year idle 

period prior to the drilling of the holes also allowed gas 

from this isolated area to drain into the mine workings, 

lowering the volume of gas to be drained. 

This project in the Pittsburgh Coalbed was unique at 

the time for the United States for two reasons. In previous horizontal drilling projects, the primary gas problem 

was emissions at the active face. Gas produced by horizontal boreholes drilled near the face was vented underground to an area where sufficient air was available to 

dilute the methane concentration below the allowable 

limit. In this case, a 15.2-cm (6-in) diameter steel underground pipeline was included in the methane drainage system to carry the produced gas to the surface through a 

vertical borehole drilled into the mine. Also unique to this 

installation was a demonstration project to utilize some of 

the gas production to produce electricity from a turbine 

generator to power a ventilation fan (84). 

In the late 1970's, a 308-111 (1,010-ft) horizontal borehole was drilled to drain gas from the Mary Lee Coalbed, 

Alabama (81). The hole was drilled from a set of old 

workings into an adjacent area that was to be mined in the 

next year (fig. 12). The hole initially produced gas at 

a rate of 5.7 x 103 m3/d (200 Mcfd), or 18.6 (m3/d)/m 

(200 cfd/ft) of hole, and declined to 1.8 x 103 m3/d 

(65 Mcfd), or 6 (m3/d)/m (65 cfd/ft) of hole, a year later 

just prior to being mined through. Total gas production 

from the hole was 1.1 x 106 m3 (40 MMcf). Methane 

emissions at the face were reduced by as much as 60 pct 

after the initiation of methane drainage (fig. 12). 

Probably the most si&icant advance in underground 

horizontal drilling was the shift from rotary drilling equipment to the use of in-hole motors. In the first controlled 

direct comparison of the drilling techniques, Kravits (53) 

found that the in-hole motor provided greater control of 

the horizontal and vertical trajectory of the hole and at the 

same time increased drilling productivity and lowered the 

drilling cost per foot of hole. Another improvement in 

horizontal drilling technology has been the development of 

downhole directional surveying systems to replace the 

time-consuming single-shot survey tools that must be 

pumped down the hole and retrieved for each survey (52, 

98-99). 

With the increased use of longwall mining in the United 

States, many mines are experiencing unprecedented methane emission problems. Methane emissions associated 

with longwall mining are of particular concern because 

they can occur at any time in the mining cycle. Methane 

emissions can be encountered during the driving of development entries with continuous miners, progressing to 

emissions at the active longwall face, and continuing 

ihrough the acc-uiiiii~aiion of methae iii ;he gob 5- 

nally into the bleeder entries. These potential methane 

emission problems may require the use of several types of 

methane drainage systems, including several applications 

of horizontal boreholes. 

Long ( > 305-111 [ > 1,000 ft]) horizontal boreholes drilled 

in advance of driving the development entries for longwall 

panels can be utilized to drain methane as discussed 

previously, and/or they can be used to shield development 

entries from the flow of gas from the surrounding virgin 

coal reserves. Figure 13 illustrates an application of long 

horizontal boreholes (A) placed for general methane reduction in virgin blocks of coal prior to mining, and which 

also (B) provide a shielding benefit to development entries 

as they are advanced, as well as after completion. 

If sufficient time is available, a developed panel in a 

gassy coalbed may degas~fy naturally into the surrounding 

entries prior to longwall mining. However, in many mining operations, continuous miner sections for the driving 

of development entries are barely able to keep pace with 

the longwall. Consequently, sufficient time may not be 

available to provide a ~i~cant reduction in the gas 

volume within the longwall panel. This situation has become increasingly serious over the past several years, as 

more efficient longwall equipment and larger panels have 

been utilized to increase productivity. Aul and Ray (2) 

observed that between 1983 and 1990, longwall productivity 

increased by 200 to 400 pct, accompanied by a 200- to 

300-pct increase in methane emissions at several mines operating in the Pocahontas No. 3 Coalbed, Virginia. The 

mines are operating at depths ranging from 366 to 732 m 

(1,200 to 2,400 ft), with gas contents as high as 18.8 cm3/g 

(600 ft3/st). Methane emission rates at these mines averaged between 0.48 and 0.68 x 106 m3/d (17 to 24 MMcfd) 

in 1990. 

Owing to the increase in methane emissions, methane 

control systems at these mines had to evolve to keep pace 
Hole 2 

Hor 

d 

izontal methane 

rainaae hole 

-Projected 1 

clay veinsn 

1 

Hole 

Figure 10.--Plan view of horizontal methane drainage boreholes, Pittsburgh Coalbed, Pennsylvania (84). 

I I I 1 1 I 1 

4 hole: 

, 

- 

2 holes 

fi, - / 

I 

/ 

/ 

- / 

I - 

I 

-1 r - 

hole / Water flow 

I 

1 I I 1 I 1 I 1 i 

400 500 

TIME, days 

Figure 11.--Daily gas and water flow rates from horizontal methane drainage boreholes, Pittsburgh Coalbed, 

Dashed portions of curves represent interval when holes were shut in. 

Pennsylvania (84). 
N Horizontal methane 

\ drainage hole, 

ION 

Scale 

DISTANCE OF FACES FROM METHANE DRAINAGE, m 

300 200 100 0 100 200 

240 Z 

200 6 g': 

160 4 3E 

120 9ui 

80 LLW 

2 0 

40 - $2 

1,000 800 600 400 200 0 200 400 600 800 C3 

DISTANCE OF FACES FROM METHANE DRAINAGE, ft 

Figure 12.--Plan view of horizontal methane drainage borehole (A) and gas flow in relation to mine advance (9, 

Mary Lee Coalbed, Alabama (81). 
KEY 

Gas flow 

,, 

-b 

Figure 13.Schematic plan view of long horizontal boreholes for methane drainage in longwall mining in advance of mining (A) and for shielding (B). 

with the improvements in mining technology. At the lower 

longwall mining rates, sufficient time was available for the 

outline panel to effectively drain gas naturally, especially 

the middle and completion end of the panels, which have 

the longest time to drain gas. Initially, face emissions 

were effectively controlled by ventilation, and gob gas was 

drained using vertical ventholes. However, as productivity 

increased, these systems gradually reached their limit of 

effectiveness, and it became necessary to drain gas from 

the longwall panel prior to mining to help reduce emissions at the face. 

In the initial attempts to drain gas from the panel, 

short, 7.6-cm (3-in) diameter, horizontal boreholes were 

drilled from the advancing entries on the headgate side, 

beginning at the completion end of the panel as illustrated 

in figure 14 (holes A). The holes were drilled perpendicular to the rib on 61-m (200-ft) centers to within about 

46 m (150 ft) of the opposite side of the panel. Aul and 
Ray (2) reported that this drilling program removed a substantial amount of gas from the middle and the completion 

end of the longwall panel, since the area drilled first was 

the last to be mined. However, gas-related mining delays 

were encountered at the startup end of the panel because 

the horizontal methane drainage boreholes were only on 

production for a short time prior to mining of the panel. 

Three strategies can be employed to overcome this 

problem. Development sections can be advanced earlier 

to allow additional time for the headgate holes to drain 

gas. The horizontal boreholes at the startup end of the 

panel can be placed closer together to drain more gas in 

a shorter time. Alternatively, the holes can be drilled from 

the tailgate side into the developing panel (fig. 14, holes B) 

and/or from advancing entries into the virgin coal beyond 

the developing panel (fig. 14, holes C). Drilling from the 

tailgate side is the strategy generally adopted by most mine 

operators (2, 71). 

The importance of drainage time for reducing the inplace gas content of coal in a developed longwall panel 

was found by Aul and Ray (2) to be significant in the 

Pocahontas No. 3 Coalbed. Only 30 pct of the gas could 

be removed from the coal if drainage time was less 

than 2 months. Horizontal boreholes that produced for 

10 months were able to drain 80 pct of the gas from the 

coal. It was concluded that at least 6 months is required 

Active panel 

Horizontal 1r hole 

B Advance 

dri lling with 

B development 

Retreat 

drilling with 

adjacent 

longwal l 

I Developing I 

Main entried 

Figure 14.--Schematic plan view of short horizontal boreholes for methane drainage from longwall panels on active panel in advance 

of face (A), on developing panel adjacent to active panel (9, and from advancing development entries (C). 
to drain a sufficient volume of gas from the Pocahontas 

No. 3 Coalbed with the holes drilled on 61-m (200-ft) 

centers. Horizontal boreholes that were drilled from the 

tadgate side increased the time available for drainage to 

12 months and resulted in significantly higher gas production rates because the holes were drilled into the virgin 

coal away from mining (fig. 14, holes C). 

Mining conditions in the Pocahontas No. 3 Coalbed 

were slrmlficantly improved as the result of the horizontal 

methane drainage program (2). Ventilation air volume at 

the longwall face was reduced from a high of 57 m3/s 

(120,000 cfm) to only 12 m3/s (25,000 cfm). The tailgate 

methane drainage boreholes also benefit the subsequent 

development entries for the next panel by reducing inplace gas volume in that area. 

Similar conclusions were reached by Mills and Stevens== (71) frcm, th_& _t~_t~g~~e G-th m~o D nn~rntinnc -r-------- 

the Blue Creek Coalbed, Alabama. Short horizontal methane drainage boreholes drilled from the tailgate entries 

(fig. 14, holes B and C) were preferred because drainage 

time from the panel was maximized and the holes provided relief during drivage of the development entries. In 

one panel, 43 pct of the in-place gas was removed by the 

short horizontal boreholes in advance of mining. In a 

comparison of two longwall panels cited by Mills and 

Stevenson (71), downtime was reduced from 146 h on one 

panel without horizontal methane drainage boreholes to no 

downtime on the adjacent panel that utilized the holes. 

Aul and Ray (2) reported that in 1990, 28.3 x lo6 m3 

(1 Bcf) of methane was removed from the Pocahontas 

No. 3 Coalbed, Virginia, using underground horizontal 

methane drainage boreholes. Mills and Stevenson (71) 

reported that approximately 12 pct of the 0.99 to 1.1 x lo6 

m3/d (35 to 40 MMcfd) of commercial gas production at 

their mining operation in the Mary Lee-Blue Creek Coalbed, Alabama, is produced from horizontal methane drainage boreholes, while about 80 pct is from vertical gob gas 

ventholes and 8 pct from stimulated vertical wells. These 

high volumes of methane that have been captured and removed from the mine workings before entering the mine 

atmosphere are very simcant since they will never have 

to be confronted underground. This has resulted in significant benefits, in both increased mining safety and 

productivity. 

The optimization of the horizontal methane drainage 

system in the Pocahontas No. 3 Coalbed (as well as most 

other mines) includes the use of an underground gas pipe- 

-- line - (2). The pipeline gathers the gas from the individual 

holes and transports it to the surface through a vertical 

borehole. To aid the flow of gas through the pipeline, it 

is necessary to use exhausters on the surface to create a 

negative pressure on the system. 

Underground pipeline safety is critical, especially protection from a rupture that could dump large volumes of 

methane into the mine atmosphere. A fail-safe system developed by the U.S. Bureau of Mines (45, 84) to shut in 

the individual holes and the pipeline has been utilized by 

most mine operators in the United States. The system 

uses a thin-walled, small-diameter (1.9-cm [0.75-in]) polyvinyl chloride (PVC) pipe that is either strapped to the 

top of the pipeline or suspended directly above it, along 

its entire length (fig. 15). The PVC pipe is connected to 

Methane 20.3-cm (8-in) 

/detector pipe to surface 4 

ads* 

, 

Control 

\ 

\ panel 

- 

, - -.., I--I-' separaror 

Water a 

Figure 15.--Schematic &on view of typical horizontal methane drainage borehole gas collection system with fail-safe pneumatic 

shut off vatve (81). 
pneumatic valves which are installed on each hole at completion. The valves are spring-loaded and held open by air 

pressure supplied by a small air compressor. If a roof fall 

hits the pipeline, it will break the small-diameter pipe on 

top, releasing the pressure holding the pneumatic valves 

open, which shuts in the holes. 

The system also includes methane sensors spaced along 

the pipeline, typically every 152 to 305 m (500 to 1,000 ft), 

to provide additional protection. The sensors are wired 

into a control panel that can activate the pneumatic valves 

by venting the compressed air in the system. The system 

can be designed so that at any predetermined methane 

concentration (typically 1 pct), at any of the sensors, the 

holes will be shut in. The system is configured so that if 

any sensor stops functioning, or if the electrical line to the 

sensor is broken, the holes will also automatically be shut 

in. 

Horizontal Boreholes - From Shaft Bottoms 

One way to drain gas in advance of mining, perhaps 

even before development mining has started, is to drill 

long horizontal boreholes into the coalbed to be mined 

from the bottom of a shaft or slope. This application 

would, of course, require the construction of one or more 

shafts or a slope prior to their actual need in the mining 

operation. The expenditure of funds for such shaft sinking 

years in advance, at projected locations where the shafts 

may ultimately not be needed, is a financial risk that most 

coal companies will not accept. There is, however, the 

possibility that the cost of sinking a shaft will be less if the 

shaft is put in place sooner; also, the sale of the produced 

gas would to some extent offset the cost of sinking the 

shaft early. 

Two experimental installations of this type were completed in the early and mid-1970's at a West Virginia mine 

operating in the Pittsburgh Coalbed. The first installation 

(fig. 16) was a large borehole (1.2-m [4-ft] diameter casing), with a 4.3-m (14-ft) diameter room in the coalbed 

(30-31). From the bottom of this simulated shaft, seven 

horizontal boreholes ranging in length from 152 to 259 m 

(500 to 850 ft) were drilled into the coalbed (fig. 17). In 

the 8 years this installation was on production, 33.4 x lo6 

m3 (1,178 MMcf) of gas was drained from the coalbed, 

15.2 x lo6 m3 (538 MMcf) of which was sold to a gas 

pipeline. 

In a second experimental installation at this same 

mine, a 5.5-m (18-ft) diameter shaft was used to drill 

five long horizontal boreholes to depths of 204 to 648 m 

(670 to 2,126 ft) into the Pittsburgh Coalbed (29). This 

installation was on production for 3.7 years prior to interception by mining; and during that time 25.2 x lo6 m3 

(889 MMcf) of gas was drained from the coalbed, 3.4 

x lo6 m3 (121 MMcf) of which was sold. Periodic underground ventilation surveys revealed that methane emissions 

at the face decreased 70 pct as the installation was approached by mining (fig. 18) (14). 

A final consideration relative to horizontal methane 

drainage boreholes is their safe interception by mining. 

Since the holes are a conduit for gas flow, mining through 

a hole that is still producing gas could be a hazard. Depending on site-specific circumstances and regulatory requirements, the holes may have to be plugged prior to 

interception (1, 74). 

Horizontal Boreholes - Water Infusion 

Horizontal boreholes can be used for methane control 

in other ways in addition to the drainage of gas. They can 

be used to block and/or divert the flow of gas by pumping 

water into the coalbed to form a barrier to gas flow. This 

process, generally referred to as water infusion, was developed in South Wales in the early 1940's (48). Water infusion using short horizontal boreholes was actually first 

used to control dust generation during coal cutting by 

wetting the coal ahead of the face just prior to mining. It 

was also observed that the process of infusing the water at 

the face reduced the rate of gas emissions (37 47). 

In water-saturated coalbeds, the flow of methane is 

controlled by a reduction in pressure in the cleat system 

that results from dewatering. Dewatering and associated 

pressure reduction are natural consequences of mining into 

a coalbed. Water infusion takes advantage of the reservoir 

properties of coal in a way directly opposed to that of the 

various methane drainage techniques. Water infusion puts 

water back into the coalbed to saturate the cleat, thereby 

hindering the flow of gas in the infused area. 

A typical configuration for a water infusion hole is 

shown in figure 19. To form an effective water block at 

the face of a set of advancing entries, it is necessary to 

drill several horizontal boreholes, so that the water fronts 

from each infusion hole overlap. The distance between 

holes is dependent upon site-specific conditions, including 

cleat orientation (10). If the coalbed has a dominant permeability direction due to a well-developed face cleat and 

less developed butt cleat, the infusion water front will be 

an ellipse. When the advancing entries are perpendicular 

to the face cleat, as shown in figure 20, the horizontal 

infusion holes can be spaced farther apart. If the entries 

are advancing parallel to the face cleat, the holes must be 

spaced closer together to form a complete block. If a 

complete block is not formed, gas can still enter the face 

area (fig. 21). 
Figure 16.4chematIc section view of largediameter vertical borehole for drilling horizontal methane drainage 

boreholes, Pittsburgh Coalbed, West Virginia (30). 
I 

- 

1,524 m (5,000 ft) 

to nearest mine work~ngs I 

No 2 hole, 259 m 

Figure 17.--Pbn view of horizontal methane drainage borehdes drilled from laqmhmdor vWkd bomhok, Phbbwgh COdbd, 

West Virginla (36). (There is no hd. 3.) 

DISTANCE BETWEEN COAL FACE AND HONEY RUN SHAFT, m 

DISTANCE BETWEEN COAL FACE AND HONEY RUN SHAFT, ft 

O i 

Figure 18.--Decline in methane emissions at the face as mining approached horizontal methane drainage 

boreholes drilled from a shaft bottom, Pittsburgh Coalbed, West Virginia (91). 

0 

t5 

W 

-5 a 

LL 

0 

cn 

W 

-4 ; 

z 0 .C 

IY E 

-3 z E 

0 

v, 

C" 

Z 

W * 

Z 

a 

x 

IW 

I 

z c 

2'- 

o roocn !c 

Z 3,500 3,000 2,500 2,000 1,500 1,000 500 0 = 

2 80 

W 

W 

60 

a 

x 

Iw 40 

- 

Sepl. 16, 1976 - - Auq. 25, 1976 L 1 I I I I I I I 1 1 1 I 1 
gas was blocked and diverted from the active face. 

Vertical Boreholes Into the Mine Roof 

~:FI Butt cleat rl[ 

direction 

It is common to have methane bleeders into the work- Figure 2O.Schematic plan view of elliptical water fronts developed from water infusion of coalbed with face cleat perpen- ings of the mined coalbed from the overlying or underlying dicular to uction advance strata. A unique method of methane drainage designed to 

address this problem was successfully tested in the Pocahontas No. 3 Coalbed, Virginia (32). On initial development of a new mine, high methane emissions were causing 

methane levels to approach 1 pct. In this area of the 

mine, the Pocahontas No. 3 Coalbed was separated from 

the overlying, gassy Pocahontas No. 4 Coalbed by 2.7 to 

4 m (9 to 13 ft) of sandstone. 

Shortly after an entry was advanced, the sandstone roof 

would fracture, releasing methane into the entry, apparently from the overlying Pocahontas No. 4 Coalbed. To alleviate the problem, a series of small-diameter (4.1-cm 

[1.6-in]) methane drainage boreholes were drilled up 

through the overlying coalbed from the mine (fig. 22). 

After a series of test holes were drilled and evaluated, it infusion hole 

was determined that holes should be spaced a maximum Figure 21.--Schematic plan vlew of elliptical water fronts 

15 m (50 ft) apart for optimum drainage. The holes were developed from incomplete water infusion of coalbed with face 

drilled along the center entries to drain gas from the strata cleat parallel to section advance (la). 
Figure 22.4erspective view of vertical in-mine boreholes for methane drainage of overlying Pocahontas No. 4 Coalbed from mined 

Pocahontas No. 3 Coalbed, Virginia (32). 

directly overlying the new development. Additional holes 

were drilled along the outside entries to intercept gas 

flowing from the surrounding virgin area. Because of the 

high methane levels in the returns, the drainage boreholes 

were connected to a pipeline to the surface. 

In the first month of operation, the flow rate from these 

holes averaged 4.2 x lo3 m3/d (150 Mcfd), and methane 

emissions into the mine were reduced by 47 pct. Over the 

96-day life of the 37 holes, 0.34 x lo6 m3 (12 MMcf) of 

methane was drained from the overlying Pocahontas No. 4 

Codbed. As mining progressed away from this area, 

methane emissions from the overlying strata decreased, 

and additional drainage boreholes were not required. This 

was probably due to both an increase in the interval between the Pocahontas Nos. 3 and 4 Coalbeds and a thinning of the Pocahontas No. 4 Coalbed. 

Cross-Measure Boreholes 

Longwall mining has been the most common coal 

mining technique outside the United States for many 

years. It has increasingly become the method of choice in 

the United States because of the high coal production 

rates longwalls can achieve (3). Since the total extraction 

of a large block of coal leaves no support to hold up the 

roof, the overlying strata cave into the mine void (fig. 9, 

in many cases releasing large volumes of gas into the mine 

atmosphere. Additional gas may also enter the mine from 

fractures that develop in the floor strata. 

A common practice in Europe is to drill methane drainage holes underground into the strata that will cave and 

fracture above the extracted longwall panel. Crossmeasure boreholes are preferred owing to the greater 
margin of the panel. One disadvantage is that the holes 

must be drilled a greater length to reach the gob. 

In the original experimental programs (8, 89), the 

4.8-cm (1.9-in) diameter cross-measure boreholes were oriented toward the longwall face in an attempt to capture 

gas as early as possible from the gob near the face (fig. 24, 

panel A, holes 1-12). The experimental work, however, 

showed that most holes did not produce gas until the face 

passed 23 to 30 m (75 to 100 ft) beyond the end of the 

hole, but before the face reached the drilling location. It 

was also found that an exhauster had to be used on the 

vertical borehole to the surface to aid the flow of gas from 

the cross-measure boreholes to which it was connected. 

Detailed engineering drawings of a typical cross-measure 

methane drainage system are shown in figures 25-26. 

In subsequent work at the same mine, Garcia and 

Cervik (33) and Goodman and Cervik (34) confirmed that 

it was not necessary to drill the holes at an angle towards 

the face (fig. 24, panel B, holes 1-13). Their analysis 

indicated that most of the gas production came from near 

the pillar line, and the extra length of hole beyond 

contributed little gas. This may be due to an increase in 

Methane flow rates from the refined cross-measure 

boreholes generally averaged from 0.14 to 0.24 m3/s (300 

to 500 cfm) through the central part of the panels; they 

were slightly less at the begi~ing and greater at the completion end. Approximately 70 pct of the methane liberated during the mining of the panels was captured by the 

cross-measure boreholes and was transported out of the 

mine by a pipeline. Final recommendations for crossmeasure borehole spacing at this mine in the Lower 

Kittanning Coalbed, Pennsylvania, were 61 m (200 ft), 

except on the first 183 m (600 ft) of the panel, where the 

spacing was 30 m (100 ft). The holes are spaced closer at 

the beginning of the panel to capture the large quantities 

of methane that are released when the initial large roof 

fall occurs. 

Horizontal Boreholes Drilled to Other Horizons 

In many of the longwall coal mines in Japan, coalbeds 

are steeply dipping and are at depths of about 700 m 

(2,300 ft). As mining depth has increased, methane emissions have also increased. It has become common practice 
Figure 24.--Plan view of cross-measure boreholes on retreating U.S. longwall (31). 

to predrain gas from both the coalbed to be mined and the 

surrounding strata, including other coalbeds, using a variation of the cross-measure technique. To reach the steeply 

dipping coalbeds, "roadways" are frrst driven along strike 

in the rock below the coalbed to be mined. The roadways 

are driven in rock instead of the coalbed itself for enhanced stability of the main haulage. The initial premining 

methane drainage is conducted in a manner similar to the 

cross-measure borehole technique described previously, by 

drilling holes at an angle up into the virgin coalbed 

(fig. 27). Methane drainage boreholes are drilled about 10 

to 15 m (33 to 49 ft) apart in the coalbed and are allowed 

to drain gas for 6 to 12 months prior to the drivage of 

crosscuts to the coalbed. 

Crosscuts are driven perpendicular to the main roadway 

to intercept the coalbed for the development of the 

longwall panels. Additional cross-measure-type predrainage boreholes are drilled into the coalbed from "boring 

stations" along the crosscuts (fig. 28). Once the coalbed is 

intercepted by the crosscuts, gate roads are driven along 

strike to connect adjacent crosscuts. A third series of 

horizontal boreholes drilled into the coalbed to be mined 

may be necessary to further reduce methane emissions in 

advance of the drivage and in the longwall block in general 

(fig. 29). Finally, the crosscuts or adjacent gate roads may 

be used to drill the more traditional cross-measure boreholes into the gob for postmining methane drainage. 

A unique combination of the cross-measure borehole 

technique combined with long horizontal boreholes is 

reported by Ohga and Higuchi (73). At one mine in Japan, the coalbeds are relatively flatlying, but the overlying 

coalbed was reported to be of low permeability, which 
Plasl 

6.35-cm (2.5-in) ID 

Plastic pipe, 

3.18-cm (1.25-in 

Plastic pipe (standpipe 1, 

6.35-cm (2.5-in) ID 

5.2-cm (6-in) main 

Not to scale 

Figure 26.--Schematic don view of a typlcal gasgathering system for cross-measure boreholes (33). 
//I\+ I Methane drainage 

Plan view 

Coal bed 

hole 

~oadw/a~ in rock 

Section view 

Figure 27.Schematic plan and section views of methane 

drainage boreholes drilled from roadway driven along strike in 

rock below mined coalbed, Japan (modified from Ohga and 

Higuchi (73)). 

Section view Coal bed 

Methane drainage 

7?

Plan view 

Figure 29.-Schematic plan and section views of methane 

drainage boreholes drilled from gate roads driven along strike in 

coalbed to outline longwail panels, Japan (modified from Ohga 

and Higuchi (73)). 
gob, the flow of gas from the old workings to the active 

mining area can be minimized. However, since the buildup of gas pressure behind the seals can eventually force 

gas into the active workings, the gas must be drained using 

pipes installed through the seals (fig. 32) (9). This gas is 

then removed from the mine by pipeline. 

SURFACE METHANE DRAINAGE 

Methane drainage techniques undertaken from the surface have the distinct advantage of not being conducted in 

the restrictive underground environment. They can be 

utilized far in advance of mining for maximum gas reduction (and commercial production) before mining, or they 

can be used during and after mining to drain gas from 

longwall gobs. However, methane drainage wells drilled 

from the surface are not without limitations. A primary 

requirement for these technologies is a surface site from 

which the drilling operations can be conducted. Topography, lakes, rivers, wetlands, cultural development, adverse ownership, archeological sites, and environmental 

and oil and gas regulations are factors that can hinder the 

development of surface sites. Gas production from most 

in-mine systems begins quickly because the mine provides 

an efficient pressure sink to initiate the desorption of gas. 

Wells drilled from the surface into virgin, water-saturated 

Upper Wongawilli Coalbed 

-*...., .. .. .". . . ,, .. ., , ''..... , . . 

Lower Wongawlll~ Coalbed 

Not to scale 

Figure 31 .-Section view of methane drainage borehole drilled 

into an underlying coalbed, Australia (modifled from Hungerford 

('0)). 

Methane-drainage pipe 

/ c rout pipe, I I to3m 

* 

Pressure- ) rnonltorlng pipe Grout pipe ' 

Figure 32.Schematic section view of gas drainage from 

sealed entries and/or gob (9). 
coalbeds must be dewatered to lower the reservoir pressure and initiate gas desorption and flow. This can result 

in a considerable time lag before gas is actually produced 

and in additional expense to dispose of the water according to State and Federal regulations. 

Despite the drawbacks, vertical wells drilled into virgin 

coalbeds are a viable alternative to in-mine methane drainage systems. Vertical gob gas ventholes are the method of 

choice in the United States, after ventilation, to control gas 

emissions from longwalls. The majority of gas produced 

commercially from coalbeds in the United States has been 

from methane drainage systems drilled from the surface. 

This is in contrast to other countries, where holes drilled 

from the surface are less common, but where utilization of 

the gas produced from the underground systems has long 

been a standard practice. 

Stimulated Vertical Wells in Virgin Coalbeds 

The use and effectiveness of stimulated vertical wells to 

drain gas from virgin coalbeds, specifically related to mining operations, has been well documented (17, 27, 55, 93, 

96). Vertical coalbed methane drainage wells are currently 

being used extensively in only two coal basins in the 

United States: the San Juan Basin in southern Colorado 

and northern New Mexico, and the Black Warrior Basin 

of Alabama. Only the wells in Alabama, at depths of 305 

to 610 m (1,000 to 2,000 ft), are generally associated with 

mining operations. The wells in the San Juan Basin, at 

depths generally greater than 610 m (2,000 ft), have been 

developed solely for commercial purposes and are not associated with mining. Programs to use vertical wells associated with mining operations have also been implemented 

in the Central Appalachian Basin of Virginia and West 

Virginia, and activity in this area has been increasing (63). 

Even though stimulated vertical wells have been shown 

to be an effective means of draining gas from virgin coalbeds, the technology has not been universally accepted in 

the mining industry. The reasons are varied, but lack of 

acceptance is related to questions of coalbed gas ownership, as well as a concern that the stimulation treatments 

required to enhance the generally low permeability of the 

coalbed may adversely affect the integrity of the mine roof, 

resulting in future mining problems. 

Coal mine operators in the United States are obligated 

under Federal and State law to control the concentration 

of methane underground. The primary means to comply 

with methane concentration regulations is ventilation. 

However, methane drainage is also an allowable option. 

It is generally recognized that as long as the gas is produced as part of the mining operations and is not captured 

for commercial purposes, the coal leaseholder may dispose 

of it by venting to the atmosphere (69). However, when 

the gas is captured for commercial sale, legal issues as to 

its ownership may arise if the coal and gas rights are not 

owned by the same party (57). 

Coalbed gas ownership has generally been an issue primarily in the Northern Appalachian Basin of the United 

States, where a potential commercial methane drainage 

site may involve multiple oil and gas leases and separate 

and multiple coal leaseholders and surface owners. Because many of the leases and deeds were conveyed prior 

to the recognition of the potential value of coalbed methane, this resource was not addressed in deed descriptions 

of mineral rights ownership. Consequently, when commercial production is planned, multiple claims to the 

produced gas may ensue, resulting in protracted legal 

proceedings. Concern over the potential for adverse ownership issues and/or unwillingness to make the effort to 

negotiate agreements with all parties that may have some 

claim to the gas has slowed commercial development. 

Another concern expressed by mining companies, particularly in the Northern Appalachian Basin, is the potential for mine roof damage resulting from the hydraulic 

stimulation of coalbeds. There is direct evidence and 

experience that addresses this issue. Coalbeds as gas 

reservoirs are unique production horizons in that access to 

the reservoir is made possible by mining. This allows for 

the direct observation of the results and consequences of 

the drilling, completion, and stimulation of the reservoir. 

The results of the underground observation and mapping of 22 stimulation treatments in U.S. coalbeds were 

presented by Diamond and Oyler (24). Their compilation covers the early history of stimulations from 1974 

to 1982 and includes data from several different coal basins. These treatments were generally of low fluid volume (189 m3 [50,000 gal] maximum) and low injection 

rates (1.1 to 2.5 m3/min [7 to 16 bbl/min]). Sand proppant weights were generally under 9,080 kg (20,000 Ib). 

The fluids were predominantly foam (16 of 22), with the 

rest being gelled water and water alone. 

The work by Steidl (95) covers 15 recent stimulations 

(1982 to 1986) exclusively in the Mary Lee-Blue Creek 

Coalbeds of the Black Warrior Basin of Alabama. This 

compilation updates the previous study because the treatment volumes were sidcantly larger and the injection 

rates were higher. All but one of these treatments used 

water as the stimulation fluid. Nine of the treatments used 

378 m3 (100,000 gal) or more of fluid, with a maximum of 

711 m3 (108,000 gal). Sand proppant weights were also 

higher, with most treatments using 18,160 kg (40,000 Ib) or 

more, with a maximum of 45,400 kg (100,000 lb). Injection rates were generally over 3.2 m3/min (20 bbllmin), 

with several at 6.4 m3/min (40 bbllmin). 
It is of particular significance that the Black Warrior 

Coal Basin has the highest incidence of roof penetrations 

and is also the mining area with the greatest number of 

stimulated vertical wells being used for methane drainage 

in the United States. Many of the wells drilled in the 

Black Warrior Basin are on mine property and are intended for commercial gas production. In addition to revenue 

from gas sales, the mines will benefit from the mining of 

coal with lower gas content. With the continued drilling 

and stimulation of vertical wells on mine property, it is 

quite evident that these mining companies have concluded 

that the roof penetrations have not been a problem, and 

any potential for adverse mining conditions is an acceptable risk. 

The reason for the more extensive roof penetrations in 

the Black Warrior Basin of Alabama is not conclusively 

known, but may be related to the complex structural history of the area. In situ state of stress (ISSOS) tests conducted in the vicinity of the underground observations indicate lower in situ stress values for the rocks surrounding 

the Mary Lee-Blue Creek Coalbeds than were measured 

in the coal (82). In the absence of a stress barrier or 

mechanical strength barrier, upward fracture breakout is 

more likely. Upward fracture breakout from this coal section was reported during the ISSOS testing. The presence 

--5-- -- --- - - - --I Floor - --- -. - 

Not to scale 

Figure 34.Schematic section view of sand proppant from hydraulic stimulation placed in face cleat, along inclined fracture in 

coal and shale parting, and along horizontal surfaces above and 

below shale parting, Pisburgh Coalbed, Pennsylvania (24). 

of naturally occurring roof joints coupled with lower or 

similar in situ stresses above the coal probably influenced 

the extent of roof penetrations observed. 

It would be advisable early in a methane drainage program to place one or more stimulated wells relatively close 

to mining, so that the effects of the stimulation treatment 

on the coalbed and surrounding strata can be determined. 

Roof penetrations that are observed can then be evaluated 

in conjunction with the prestimulation geologic mapping of 

the mine. If roof penetrations have occurred, and if they 

are preferentially oriented, such as along a minewide roof 

joint system parallel to the face cleat, it may be possible in 

room-and-pillar sections to place the vertical methane 
drainage wells so that the probable orientation of the roof 

penetrations cuts across the short dimension of an entry 

instead of the long dimension (fig. 35). Intercepting roof 

penetrations in this manner would expose the least length 

of such penetrations to the mine workings. 

Modifications to the stimulation design may also be 

made to minimize the penetration of the roof strata. 

Steidl (95) concluded that water stimulations at high injection rates (3.2 m3/min [20 bbl/min] or higher) had a 

greater propensity for creating thin fractures that more 

readily penetrated the strata overlying the coalbed stimulated. Foam and gel stimulation treatments with lower 

injection rates tended to result in shorter and wider 

fractures that stayed in the coalbed (24). 

Steidl(95) also pointed out that the general practice of 

using open-hole completions in coalbed gas wells that 

would eventually be mined through may also contribute to 

the increased occurrence of stimulations outside the coalbed. Steel pipe in the minable coal interval is generally 

unacceptable to the mining industry; therefore, the well 

casing is generally placed 0.3 m (1 ft) or more above the 

coalbed (fig. 36, coalbed A) to ensure that it does not 

extend into the coal. However, the exposure of a portion 

of the roof strata to the open-hole interval being stimulated may aid the fluids in penetrating these strata. 

When the stimulation interval is behind casing, communication to the desired gas-bearing zone can be controlled 

by the use of perforations or slots (fig. 36, coalbed B). 

This type of completion introduces the stimulation fluid 

into the desired zone at the wellbore but may not influence the ultimate placement of the stimulation treatment. 

Steidl (95) reports that fiberglass casing has been successfully used in mining-related applications and was an acceptable completion alternative for eventual mine-through. 

A recent development in enhancing the flow of gas 

from vertical wells without hydraulic stimulations has been 

the use of cavity completions. With this technique, a cavity 

is created in the coalbed by one of several methods, as 

described by Mavor (59). The creation of the cavity is 

thought to increase permeability by a process of stress 

relaxation and subsequent cleat aperture increase. This 

factor plus the minimizing of formation damage and the 

increase in wellbore diameter that more effectively links 

the well to the cleat system has in some cases resulted in 

higher gas production than that from comparison wells 

that were hydraulically stimulated. This completion technique may be a viable alternative for mining-related methane drainage in some cases where hydraulic stimulations 

are not acceptable. 

As with all methane drainage systems, it is essential that 

the drilling and placement of stimulated vertical wells be 

coordinated with both current mining operations and future development. It is even more important with the 

- 

Well 1 

, 1 t 

LEGEND 

- Vertical face cleat fracture 

-- Vertical bun cleat fracture 

Figure 35.--Schematic plan view of relationship of mine entry 

orientation and interception of vertical fracture from hydraulic 

stimulation preferentially oriented in face cleat direction (24). 

Casing 4 

Coal bed 

-Perforation 

Coal bed B 

Cement 

Water 

sand 

Coal bed A 

Figure 36.--Schematic view of open hole (A) and cased hole 

(9 completions for vertical methane drainage well. 
Figure 37.SchemaUc don view of water pump Installed In 

vertical msthane drainage well. 

y 

sand proppant preferentially penetrate and flow along the 

existing cleat, with the face cleat being the primary flow 

path (24). An example of the preference for the stimulation fluids to penetrate face cleat is shown in figure 38. 

The resulting drainage pattern for a stimulated well, such 

as that shown in figure 38, would be expected to be elliptical in shape, with the long axis of the ellipse parallel to the 

face cleat. This suggests that the wells should be drilled 

on a rectangular grid, with the wells spaced farther apart 

in the face cleat direction, and closer together in the butt 

cleat direction. 

Gas content testing of coal cores obtained prior to the 

start of methane drainage and additional cores obtained at 

the same locations as methane drainage progresses can be 

correlated to methane emission levels to determine the extent to which the in-place gas content must be reduced to 

sufficiently reduce the mine emissions. Pressure monitoring holes can be used in place of, or in addition to, the gas 

content data to monitor the progress of methane drainage 

(77). 

It is not generally necessary, or even possible, to remove all the gas from a coalbed to have a significant 

impact on mine emissions. Several examples of declining 
Cleat 

LEGEND 

/ Vertical fracture, paint-coated I: Horizontal fracture, paint-coated 

Figure 38.--Plan view of elliptical placement of fluids in the Blue Creek Coalbed, Alabama, from a stimulated vertical methane 

drainage well (24). 

methane emissions cited in this paper are associated with 

short-term methane drainage projects, where a substantial percentage of the in-place gas could not have been 

drained. It appears that most coalbeds have a certain percentage of their total gas content that is relatively mobile. 

This gas flows quite readily to either mine workings or 

methane drainage holes as the pressure is reduced in the 

coalbed, This gas will be produced from progressively 

greater distances from the wellbore in preference to that 

portion of the in-place gas that is more difficult to release 

from the coal, even though it may be closer to the wellbore (1722). With the gas content and/or pressure monitoring results and production data from the wells, the 

computer-based reservoir and production simulations can 

be updated to continually refine the well spacing and 

lead time required to provide the optimum impact on 

mine emissions. 

Another important factor to consider in the design of 

a vertical well methane drainage program is the need 

to shield the mine workings or property from gas migrating from the surrounding area. As methane drainage 

progresses, an expanding area of reduced pressure and gas 

desorption is created outside the perimeter of the pattern. A study in the Mary Lee-Blue Creek Coalbed, Alabama, showed that after 10 years of gas production from 

a 23-well pattern of vertical wells, the drainage radius extended as much as 1,524 m (5,000 ft) from the perimeter 

of the pattern (17). The gas desorbed from this reducedpressure area migrates to the production wells in the pattern. While this may be desirable from a commercial gas 

production perspective, it can be a problem from a mining 

perspective. 

If no shielding wells are drilled between the mine workings and the migrating gas (fig. 39), increased methane 

levels may be experienced in the mine, even though the 

gas content of the coal has been reduced by the vertical 

methane drainage wells. A line of wells could be drilled 

around the perimeter of a mine property to intercept migrating gas. However, it is more practical to position additional shielding wells just outside the actual mining area 

(fig. 39). It may also be possible to reinject water into 

wells near the mine workings to block the flow of gas, 

similar to underground water infusion. Reinjection of 

water may not be an option in some locations, depending 

on applicable oil and gas regulations. 
a distance of 180 m (590 ft). During that time, 1.7 x lo6 

m3 (61 MMcf) of gas was vented from the workings 

(fig. 41). The "west" entries, which were driven toward the 

two methane drainage wells, required only 63 days to mine 

180 m (590 ft), and only 1.0 x lo6 m3 (37 MMcf) of gas 

was encountered. This represents a 40-pct reduction in 

the amount of gas liberated into the mine atmosphere. 

The effectiveness of a large-scale pattern of stimulated 

vertical wells in reducing the gas content of coalbeds has 

been shown by Diamond (17). In 1976, a pattern of 23 

methane drainage wells was drilled and stimulated in the 

Blue Creek Coalbed on mine property. The wells were 

drilled on a 305-m (1,000-ft) square grid (approximately 

100 x I@-m2 [25-acre] spacing). After 10 years, the wells 

had produced a total of 90.6 x 106 m"3.2 Bcf) of methane 

that will never have to be controlled in the underground 

mine environment. 

Coal samples obtained from coreholes in and around 

the 23-well pattern after 10 years of gas production were 

tested for gas content and compared with samples obtained from the same area prior to the start of methane 

drainage. Inside the pattern, 73 pct of the original gas in 

place had been drained from the Blue Creek Coalbed, the 

only coalbed that had been completed for production. 

Figure 39.Schematic plan view of vertical methane drainage 

wells placed to shield mine workings from migrating gas. 

7 

WEST ENTRIES 

Figure 40.Schematic plan view of location of two near-mine 

experimental stimulated vertical methane drainage wells, Blue 

Creek Coalbed, Alabama (55). 
LENGTH OF VIRGIN RIB EXPOSED, m 

0 50 100 150 200 250 300 

w -- 

-- 

100 200 300 400 500 600 700 800 900 1,000 1,100- 

LENGTH OF VIRGIN RIB EXPOSED, ft 

Figure 41.--Comparison of cumulative methane emissions in entries developed into areas with and 

without stimulated vertical methane drainage wells, Blue Creek Coalbed, Alabama (55). 

The early success of the vertical methane drainage program at this mine led to the drilling of a large number of 

additional commercial wells on the property. Total production through 1992 was 1.75 x lo9 m3 (62 Bcf) of gas. 

At a nearby mine operating in the same coal interval, Mills 

and Stevenson (70) reported a decrease of about 50 pct in 

methane emissions in the mining of longwall development 

entries in an area where 31 stimulated vertical wells had 

drained gas for at least 5 years prior to mining. 

Directionally Drilled Boreholes 

Boreholes directionally drilled from the surface are a 

unique methane drainage technology that combines the 

best attributes of the underground horizontal boreholes 

and the stimulated vertical wells. These holes can be 

drilled from the less restrictive surface environment, but by 

deviating the well path from the vertical, the hole can be 

turned to intercept horizontally the coalbed to be degasified. Once the well path has intercepted the coalbed, 

the hole can be continued in the coalbed to drain gas in 

the same manner as the horizontal boreholes drilled 

underground. Directional boreholes can also be oriented 

to preferentially intercept perpendicularly the greater permeability of the face cleat. Drilling long horizontal boreholes into virgin coalbeds also eliminates the need for the 

stimulation treatments required in the vertical methane 

drainage wells. 

The first experimental directional boreholes drilled 

for coalbed methane drainage were long radius, turning 

from vertical to horizontal at a rate of about 6" per 30 m 

(100 ft) (76). These well paths required about 305 m 

(1,000 ft) of depth to intercept the target coalbed horizontally (fig. 42). Downhole motors and various configurations of drilling assemblies were used to drill the directional boreholes and control the well path. A directional well 

methane drainage system into the Pittsburgh Coalbed, 

Pennsylvania, included three long horizontal boreholes 

(539 m, 912 m, and 977 m [1,767 ft, 2,993 ft, and 3,207 ft]) 

drilled from the bottom of the single well path to the 

coalbed (fig. 43) (75). Sloughing of the bottom portion of 

the uncased part of the hole in the roof shale above the 

Pittsburgh Coalbed and dewatering problems severely limited the gas production from this hole. 
900 800 700 600 500 400 300 200 100 0 

Feet 

300 2 50 200 150 100 50 0 

200 - Meters 

50 - HORIZONTAL DISTANCE 

Figure 42.-sedon view of long-radius directionally drilled well path to intercept the Pittsburgh Coalbed horizontally from the 

surface, Pennsytvania (75). 

Alternative to the long-radius directional drilling system 

are the medium- and short-radius systems that have been 

developed in the oil industry over the past few years (58, 

72) (fig. 44). Medium-radius systems are turned at a rate 

of 8" to 200 per 30 m (100 ft), requiring 91 to 213 m (300 

to 700 ft) of vertical section. Short-radius systems can be 

deviated at a rate of 1.5" to 3" per 0.3 m (1 ft), which requires only 6.1 to 12.2 m (20 to 40 ft) of vertical section to 

make the turn from vertical to horizontal. Nazzal (72) 

reports that holes can be drilled up to 305 m (1,000 ft) 

horizontally using the short-radius system. 

This new technology in directional drilling, especially 

the short-radius boreholes, may have significant applications to coalbed methane drainage. Shorter radius drilling reduces the length of unproductive directional hole in 

the overlying rock, thus reducing drilling time and costs. 

Also, with the short-radius systems, a pump can be installed in the bottom of the vertical well section below the 

kickoff point of the directional hole (fig. 45). This pump 

configuration may provide for more effective dewatering 

than was possible in the long-radius wells. This proven 

directional drilling technology, which uses off-the-shelf 
0 Horizontal drill path 

Vertical monitoring hole 0 400 800 1,200 ft 

a Air shaft 

 

Figure 43.--Plan view of murtiple horizontal methane drainage boreholes drilled from a directional surface borehole, Pittsburgh 

Coalbed, Pennsylvania (75). 

components, has a greater potential for successful implementation in coalbed methane drainage than the experi- 

, mental directional boreholes drilled in the 1970's, which 

required in-the-field development of prototype tools and 

drilling procedures. 

Longwall Gob Gas Ventholes 

Vertical gob gas ventholes are drilled over longwall 

panels to drain gas from the gob that results from the 

complete extraction of the large block of coal. As the coal 

is extracted, the roof strata are allowed to cave in behind 

the movable supports that protect the men and equipment 

on the face. Gas-bearing strata, particularly overlying gasbearing coalbeds, either are directly exposed to the caved 

zone, or are connected by fractures that extend into the 

caved zone. This allows gas to enter the mine atmosphere 

from above (fig. 5). Gas-bearing strata below the mined 

bed may also contribute gas to the mine atmosphere. It 

is not uncommon for longwall sections to be shut down 

for a shift or more while excessive volumes of gas emitted after a large roof fall behind the longwall supports 
Figure 45.4chematic section view of short-radius directional methane drainage borehole equipped with downhole pump for 

dewatering. 

dissipate from the working area. Gas-related mining delays are becoming an increasingly common occurrence, 

even with the use of vertical gob gas ventholes. This is 

due to the coal industry's use of advanced mining technology and progressively larger panels to increase coal 

production. 

The use of vertical gob gas ventholes is most common 

in the United States, probably owing to the greater ease of 

obtaining surface drill sites than in the more mature mining districts of Europe. The relatively shallow depth of the 

pp(g

), 

the hole is only drilled and cased to within about 30 m 

(100 ft) or more of the coalbed, and then a smaller diameter open hole is drilled through the bottom of casing to 

the coalbed (fig. 46, hole 175-B). Numerous variations on 

these basic designs are possible, as illustrated in figure 46, 

which represents the trial-and-error process to find a more 

productive venthole completion technique on a single longwall panel in the Lower Kittanning Coalbed, Pennsylvania. 

The distance between the gob gas ventholes, like the 

basic drilling and completion design, is determined by experience and site-specific mining conditions. When conditions are stable from panel to panel, the holes may be 

drilled several months in advance. However, when conditions are not stable, the sites for the holes are based on 

inc~easing mine emissions as the panel progresses. The 

holes are drilled only a few days in advance of interception 

by mining under these circumstances, occasionally resulting 

in mining delays due to high methane emissions. The time 

required to drill and complete a gob gas venthole to a 

typical depth of 229 m (750 ft) is only a few days. The 

gob gas ventholes will usually produce only a small volume 

of gas under natural flow conditions. The holes are 

typically equipped with exhausters on the surface to draw 

gas from the gob (fig. 47). The installation of the surface 

equipment requires about 1 day. In most cases, a gob gas 
Fiame 

arrester 

KEY 

Fractures 

Slotted caslng -c"d Coal bed 

or open hole -1 

Figure 47.--Schematic section view of complete longwall gob 

gas venthole system. 

venthole can be drilled and put in operation in less than 

1 week. 

An individual gob gas venthole over a longwall in the 

Lower Kittanning Coalbed, Pennsylvania, produced over 

10.0 x lo6 m3 (357 MMcf) of methane (18). A hole in the 

Pocahontas No. 3 Coalbed, Virginia, produced nearly 

17 x lo6 m3 (600 MMcf) of methane during mining of that 

coalbed (64). Maximum daily methane production generally occurs within the first several days after a hole is 

intercepted by the longwall. Relatively high production 

rates are usually sustained for only a few weeks (fig. 48), 

or in some cases for a few months (fig. 49). In most circumstances, no effort is made on the part of the mine operator to control the methane concentration in the produced gas. The initial methane concentration in the gas 

stream is generally high (>80 pct) and remains relatively high for several months after mine-through (fig. 50). 

The methane concentration usually declines gradually 

with time. Commonly, when the methane concentration 

reaches 25 pct, the exhausters are turned off as a safety 

precaution, because the explosive range of methane in air 

is 5 to 15 pct. The holes are generally allowed to free flow 

after the exhausters are turned off. 

Gob gas ventholes are an effective technology to drain 

gas from longwall gobs. Mills and Stevenson (70) reported 
that approximately 30 to 40 pct of the total gas liberated 

from several mines operating in the Mary Lee-Blue Creek 

coal interval, Alabama, was produced by gob gas ventholes. Dixon (26) stated that the mines could not operate 

Panel 2 

. 

4.0 

u r 

0 3.5 I 

3.0 W 

2.5 a 

3 2.0 

S 

LL 1.5 

W 5 1.0 I 

IW .5 r 0 

Mar. 

w 

r 

CI 

Apr. May June July Aug. 

1990 

Figure 48.4aily methane flow rate, gob gas venthole 178, 

Lower Kittanning Coalbed, Pennsylvania. 

6ct. Dec. Feb. Apr. June Aug. Oct. ~ec:- 

1989 1990 

Figure 49.4aily methane flow rate, gob gas venthole 176, 

Lower Kmanning Coalbed, Pennsylvania. 

100 

Panel 2 

Mar. Apr. June July Aug. 

at economic levels without gob gas drainage. Dixon (26) 

also reported that the methane level in the mine bleeder 

entries can be reduced by as much as 80 pct using the gob 

gas ventholes. 

In some cases, the methane produced from the gob gas 

ventholes is sold to commercial gas pipelines. Under these 

circumstances, it is desirable to maintain pipeline-quality 

gas for maximum revenue. This is accomplished by closely 

monitoring the methane concentration at the holes and 

adjusting the amount of vacuum to minimize the volume 

of mine air drawn into the gob. Mills and Stevenson (70) 

reported that 0.48 to 0.65 x 106 m3/d (17 to 23 MMcfd) of 

methane from gob gas ventholes at two mines in the Mary 

Lee-Blue Creek coal interval, Alabama, was sold to a commercial gas pipeline. 

Figure 51 shows the total methane production for all --L -- - - .-- &L guv gaa ~CIILIIO:~~ ~ii a panel in ihc Lower Kiiiaruiirig 

Coalbed, Pennsylvania (including holes 176 and 178, 

figs. 48-49). The numerous peaks above the base level 

production of about 0.11 x 106 m3/d (4 MMcfd) represent 

the successive interception of each of the 13 gob gas ventholes drilled on this panel. The holes produced 29.4 x 106 

m3 (1,039 MMcf) of methane through 12 months after the 

panel was completed. 

Methane production rates of 0.11 x 106 m3/d 

(4 MMcfd) for Lower Kittanning gob gas ventholes, Pennsylvania (It?), 0.17 x 106 m3/d (6 MMcfd) for the Mary 

Lee-Blue Creek coal interval, Alabama (70), and 0.26 x 

106 m3/d (9.1 MMcfd) for the Pocahontas No. 3 Coalbed, 

Virginia (64) have been reported. Note that these maximum values do not necessarily represent typical or average 

production rates. In fact, the production of gas from gob 

holes can be quite variable (fig. 52). Some of the variability (low gas production) can be due to completion 

problems, such as inadvertently cementing fractures during 

the setting of casing in holes drilled after mining 

" 

Dee. Jan. Feb. Mar. Apr May June July 

1989 1990 

1990 Figure 51.--Combined daily methane production from 13 gob C 

Figure 50.4aily methane percent of produced gas, gob gas gas ventholes on a longwall panel in the Lower Kittanning 

venthole 178, Lower Kittanning Coalbed, Pennsylvania. Coalbed, Pennsylvania. 
KEY 

Before mining 0 

-After mining 9 

l? 

4 

- Direction of mining 

Panel 1 200 Total 

3 26.3 x 106d 

loo (929 MMcf) 

0 

1,265 m E (4,150 ft) 

BOREHOLE DESIGNATION 

9 - ' 300 - 6 - - Panel 2 - 200 Total + - 29.42~ 106m3 2 

3 - 

I - 100 (1,039 MMcf E - 0. I 1. 1 I 1 I 0 z- * 93 c;, m F:eX o ZXL, C! t1,301 m 2 cD (D (D UC rL (4,270 f t) I- $$ $ $$ $ $$ $$$ 0 

BOREHOLE DESIGNATION I) 

0 

9 300 

0 

a 

- a 

6 - - Panel 3 - 200 Total 

- W 

3 2- 

31.21 X lo6 m3 5 

I I I 

- 100 (1,102 MMcf) I - 0 1 I 0 I- 

? 9 * * * W 

4 - 0-1 ma m 6, '1.31 1 m I 

?a, g 8 k$$ $. $ (4,300 ft w BOREHOLE DESIGNATION 2 

I 

o 260 460 6b0 860 l,&o 1.2bo 1,400 m 

Scale 

9 .- - 300 a 

J - Panel 4 J 

3 I) 

2 6: Tota I I 3 - - 

200 29.93 x106m3 2 

3- I - 100 (1,057 MMcf) 

- 

0 . I I I I I. 

9??4? ? oma 

2 % ? a, 5 (4,190ft) 

BOREHOLE DESIGNATION 

9 300 

Figure 52.--Histograms of methane production from individual gob gas ventholes through 12 months 

(panels 1-4) and 9 months (panel 5) after panel completion, Lower Kittanning Coalbed, Pennsylvania (18). 

6 

3 

- 1 

Panel 5 - 200 Total 

27.58 X lo6 m3 

- 

0 1 I ,I 

o o ma 0 

9 7 OP? 9 7 * c c (D (D Z (D (D Ah &Am'l,30lm aD 2 a3 $? E aD E s E 5 E s ?E?(4,270ft) 

BOREHOLE DESIGNATION 

- 100 (974 MMcf ) 

I I. . 1 
(frg. 52, panel 1, hole 174-C). Another problem is setting 

casing above water-bearing zones that flow water into the 

open hole and restrict the flow of gas. If the casing is 

crushed or sheared off when the overburden collapses into 

the mine void, gas production will cease or be restricted. 

Geologic and/or rock strength anomalies can also influence the production rates from gob gas ventholes (18). 

The position of the holes on the longwall panel may 

also influence gas production rates. In a study of five 

adjacent longwall panels in the Lower Kittanning Coalbed, 

Pennsylvania, gob gas ventholes drilled on either end of 

the panels tended to have the highest cumulative production (fig. 52) (18). The reason for this may be related to 

the subsidence mechanics of longwalls. At the ends of the 

panels, the overburden strata are partly supported on three 

sides by the surrounding pillars of the development entries (fig. 53). Siraia in ihib area are draped inio ihe 

subsidence trough and are under tension. This allows the 

mining-induced fractures at the ends of the panel to stay 

open longer than those in the center of the panel, where 

complete subsidence and recompaction occur relatively 

quickly. The longer the fracture permeability is maintained, the longer the gob gas ventholes remain on production, and hence, the higher the cumulative production. 

This, along with the gas released in the "first break" of the 

strata over the longwall, may also explain why higher gas 

emissions are commonly experienced at the beginning of 

panels (70). 

Strata along the margin of the panels are also draped 

into the subsidence trough and should have enhanced fracture permeability (fig. 53). It is possible that placing gob 

gas ventholes along the centerline of the panels, as is the 

customary practice, may not be the optimum approach for 

gas production. Holes placed along the margin of the panels may produce more gas for a longer time. In an experimental application of this concept in a Pennsylvania mine 

operating in the Lower Kittanning Coalbed, near-margin 

holes vented approximately 80 pct more gas than the centerline holes on the same panel (18). The optimum distance from the panel margin for hole placement must be 

determined by evaluating the subsidence mechanics of 

iongwaii overburden, combined with site-specific experimental evaluations. The holes must be placed close 

enough to the panel margin to be in the zone of tension, 

but not so close that excessive amounts of mine ventilation 

air are drawn into the system. Close monitoring of the 

methane concentration of the produced gas and of the 

magnitude of vacuum applied to the system is necessary 

for the holes to operate at maximum efficiency. 

1 Finish I 

Ma 

sub 

- - : Subsidence is exaggerated - - - - - -. - 

Figure 53.--Schematic perspective vlew of subsldence trough developed over an extracted longwall panel. 
Since gob gas ventholes are not stimulated, there is overlying coalbeds or other gas-bearing strata. By pregenerally only a small flow of gas, if any, from the holes draining gas for several months or longer before mining 

before they are intercepted by mining. The holes could be and converting the holes to gob gas ventholes, it may be 

drilled and stimulated far enough in advance of mining to possible to use fewer holes per panel, thereby offsetting 

produce gas from the coalbed being mined and/or from the added cost of the stimulation treatments. 

SUMMARY 

Control technology exists that addresses many of the 

current mining-related methane emission problems in underground coal mines. A combination of general research 

results, experience. trial-and-error methodology, and 

computer-based simulations can usually provide the information necessary to select or modify appropriate methane 

conir"l iecL-oiogj fGr sitz-spceifiz situa:ior;s. As is 

learned about the occurrence, storage, and migration of 

coalbed methane, more effective control technologies or 

modifications to existing technologies will be developed. 

The ability to more accurately measure coalbed reservoir properties, both in the laboratory and in the field, 

will improve the reliability of computer-based simulations. 

This will lessen the reliance on trial-and-error methods 

to design site-specific methane control systems and thus 

shorten the time required for implementation. 

There has been a tremendous increase over the past 

10 years in the use of stimulated vertical boreholes to produce gas from coalbeds for commercial purposes. The research and experience associated with these efforts are 

valuable assets that can be used to improve the applicability of the technology to the mining environment. 

An area of particular concern for methane control in 

the United States is the increase in methane emissions as 

larger longwall panels are mined to increase productivity. As panel size increases, larger volumes of gas in the 

roof and floor strata are exposed to the mine atmosphere 

on a daily basis. Mining delays are already being experienced on some of these larger panels owing to higherthan-expected methane emissions. Methane emission 

consequences must be taken into account if the mining 

industry is to take advantage of the potential for increased 

productivity from advanced mining technology. 

REFERENCES 

1. Aul, G. N., and J. CeMk. Grouting Horizontal Drainage Holes 

in Coalbeds. BuMines RI 8375, 1979, 16 pp. 

2. Aul, G. N., and R Ray. Optimizing Methane Drainage Systems 

To Reduce Mine Ventilation Requirements. Ch. 80 in Proceedings of 

the 5th U.S. Mine Ventilation Symposium, Morgantown, WV, June 3-5, 

1991. Min. Eng., 1991, pp. 638-656. 

3. Barnak, T. M. The History and Future of Longwall Mining in the 

United States. BuMines IC 9316, 1992, 26 pp. 

4. Boyer, C. M., 111, F. H. Briscoe, B. S. Camp, R A. Koenig, 

P. G. Malone, and P. B. Stubbs. Geologic and Reservoir Characterization for the Multiple Coal Seams Completion Project at Rock Creek. 

Gas Res. Inst. Topical Rep. GRI-8710083, v. 1, 1986, 120 pp. 

5. Briscoe, F. H., B. S. Camp, L. K Lottman, and P. G. Malone. A 

Study of Coal Bed Methane Production Trends Related to Geologic 

Features. Wamor Basin, Alabama. Paper in Geology and Coal-Bed 

Methane Resources of the Northern San Juan Basin, Colorado and New 

Mexico, ed. by J. E. Fassett. Rocky Mtn. Assoc. Geol., Denver, CO, 

1988, pp. 237-246. 

6. Bromilow, J. G., and J. M. Jones. Drainage and Utilization of 

Firedamp. Colliery Eng., v. 32, No. 6, 1955, pp. 222-232. 

7. Burke, S. P., and V. F. Parry. Flow of Gas Through Coal. Trans. 

AIME, v. 119, 1936, pp. 418-432. 

8. Campoli, A. A., J. Cervik, and S. J. Schatzel. Control of Longwall 

Gob Gas With Cross-Measure Boreholes (Upper Kittanning Coalbed). 

BuMines RI 8841, 1983, 17 pp. 

9. Cervik, J. Methane Control on Longwalls-European and U.S. 

Practices. Soc. Min. Eng. AIME preprint 79-100, 1979, 6 pp. 

10. Cervik, J., A. Sainato, and M. Deul. Water Infusion of Coalbeds 

for Methane and Dust Control. BuMines RI 8241, 1977, 27 pp. 

11. Cetinbas, A., R P. Vinson, J. CeMk, and M. G. Zabetakis. 

Methane and Dust Control by Water Infusion. BuMines RI 7640,1972. 

17 PP. 

12. Coal Age. Fans in Parallel and Core-Drill Gas Bleeding Feature 

Pocahontas Fuel Improvements. V. 43, No. 3, 1938, p. 68. 

13. Darton, N. H. Occurrence and Utilization of Firedamp. BuMines 

B 72, 1915, pp. 101-102. 

14. Deul, M., M. L. Skow, and A. G. IGm. Helping Finance New 

M~nes With Revenues From Coalbed Degasification. Paper in Proceedings of the 3rd Symposium on Underground Mining, Louisville, KY, 

Oct. 18-20, 1977. National Coal Association/Bituminous Coal Research. 

Inc., Coal Conference and Exposition IV, 1977, pp. 25-41. 

15. Diamond, W. P. Evaluation of the Methane Gas Content of Coalbeds: Part of a Complete Coal Fxploration Program for Health and 

Safety and Resource Evaluation. Paper in Coal Exploration, v. 2, ed. 

by G. 0. Argall (Proc. 2d Int. Coal Exploration Symp., Denver, CO, 

Oct. 1-4, 1978). Miller Freeman Publications, Inc., 1979, pp. 211-222. 

16. . Site-Specific and Regional Geologic Considerations for 

Coalbed Gas Drainage. BuMines IC 8898, 1982, 24 pp. 

17. Diamond, W. P., W. R Bodden, M. D. Zuber, and R A. 

Schraufnagel. Measuring the Extent of Coalbed Gas Drainage After 

10 Years of Production at the Oak Grove Pattern, Alabama. Paper 8961 

in Proceedings of the 1989 Coalbed Methane Symposium, Tuscaloosa, 

AL, Apr. 17-20, 1989. Univ. AL, Tuscaloosa, AL, 1989, pp. 185-193. 
18. Diamond, W. P., P. W. Jeran, and M. A. Trevits. An Analysis of 

Production Trends and the Potential for Increasing Gas Flow From 

Longwall Gob Gas Ventholes. Paper 9313 in Proceedings of the 1993 

International Coalbed Methane Symposium, v. 2, Birmingham, AL, 

May 17-21, 1993. Univ. AL, Tuscaloosa, AL, 1993, pp. 443-452. 

19. Diamond, W. P., J. R Kelafant, D. E. Wicks, P. Malone, and 

R Schraufnagel. Geologic and Economic Appraisal of Gas From Coalbeds in the Northern Appalachian Coal Basin. Pres. at Soc. Min. Eng. 

AIME, Eastern Regional Meeting, Pittsburgh, PA, Oct. 12-13, 1987, 

21 pp.; available from W. P. Diamond, U.S. Bureau of Mines, Pittsburgh, 

PA. 

20. Diamond, W. P., J. C. LaScola, and D. M. Hyman. Results of 

Direct Method Determination of the Gas Content of U.S. Coalbeds. 

BuMines IC 9067, 1986, 95 pp. 

21. Diamond, W. P., C. M. McCulloch, and B. M. Bench. Use of 

Surface Joint and Photolinear Data for Predicting Subsurface Coal Cleat 

Orientation. BuMines RI 8120, 1976, 13 pp. 

22. Diamond, W. P., and G. W. Mume. Methane Gas Content of the 

Pittsburgh Coalbed and Evaluation of Drilling Results at a Major 

Degasification Installation (abstr.). Abstracts With Programs, Geol. Soc. 

America, Northeastern Section, Binghamton, NY, v. 9, No. 3, 1977, 

p. 256. 

23. Diamond, W. P., G. W. Murrie, and C. M. McCulloch. Methane 

Gas Content of the Mary Lee Group, of Coalbeds, Jefferson, Tuscaloosa, and Walker Counties, Ala. BuMines RI 8117, 1976, 9 pp. 

24. Diamond, W. P., and D. C. Oyler. Effects of Stimulation Treatments on Coalbeds and Surrounding Strata - Evidence From Underground Observations. BuMines RI 9083, 1987, 19 pp. 

25. Diamond, W. P., J. P. Ulery, and S. J. Kravits. Determining the 

Source of Longwall Gob Gas: Lower Kittanning Coalbed, Cambria 

County, PA. BuMines RI 9430, 1992, 15 pp. 

26. Dixon, C. A. Coalbed Methane - A Miner's Viewpoint. Paper 

8704 in Proceedings of the 1987 Coalbed Methane Symposium, Tuscaloosa, AL, Nov. 16-19, 1987. Univ. AL, Tuscaloosa, AL, 1987, pp. 7-10. 

27. Dunn, B. W. Coal as a Conventional Source of Methane: A 

Review and Analysis of 50 Wells in Two Production Areas in the Black 

Wamor Basin of Alabama. Paper SPE/DOE/GRI 12875 in Proceedings 

of the Unconventional Gas Recovery Symposium, Pittsburgh, PA, 

May 13-15, 1984. Soc. Pet. Eng., Dallas, TX, 1984, pp. 407416. 

28. Elder, C. H. Use of Vertical Boreholes for Assisting Ventilation 

of Longwall Gob Areas. BuMines TPR 13, 1969, 6 pp. 

29. Fields, H. H., J. Cervik, and T. W. Goodman. Degasification and 

Production of Natural Gas From an Air Shaft in the Pittsburgh Coalbed. 

BuMines RI 8173, 1976, 23 pp. 

30. Fields, H. H., S. Krickovic, A. Sainato, and M. G. Zabetakis. Degasification of Virgin Pittsburgh Coalbed Through a Large Borehole. 

BuMines RI 7800, 1973, 27 pp. 

31. Fields, H. H., J. H. Peny, and M. Deul. Commercial-Quality Gas 

From a Multipurpose Borehole Located in the Pittsburgh Coalbed. BuMines RI 8025, 1975, 14 pp. 

32. Finfinger, G. L., and J. Cervik. Drainage of Methane From the 

Overlying Pocahontas No. 4 Coalbed From Workings in the Pocahontas 

No. 3 Coalbed. BuMines RI 8359, 1979, 15 pp. 

33. Garcia, F., and J. Cervik. Methane Control on Longwalls With 

Cross-Measure Boreholes (Lower Kittanning Coalbed). BuMines 

RI 8985, 1985, 17 pp. 

34. Goodman, T. W., and J. Cervik. Comparisons Between CrossMeasure Boreholes and Surface Gob Holes. BuMines RI 9013, 1986, 

14 PP. 

35. Grau, R H. An Overview of Methane Liberations From U.S. 

Coal Mines in the Last 15 Years. Ch. 38 in Proceedings of the 3rd U.S. 

Mine Ventilation Symposium, ed. by J. M. Mutmansky (University Park, 

PA, Oct. 12-14, 1987). Soc. Min. Eng. AIME, 1987, pp. 251-255. 

36. Grau, R H., and J. C. LaScola. Methane Emission From U.S. 

Coal Mines in 1980. BuMines IC 8987, 1984, 13 pp. 

37. Gregson, H. Deep Hole Infusion in the Kent Coalfield. Colliery 

Guardian, v. 212, 1966, pp. 599-604. 

38. Hill, D. G. (ed.). Basin Activities - Black Wamor Basin, AL, 

Quarterly Review of Methane From Coal Seams Technology. Gas Res. 

Inst., Chicago, IL, v. 10, No. 4, 1993, pp. 4-5. 

39. Houseknecht, D. W. Probability of Encountering Coalbed Discontinuities During Vertical and Horizontal Borehole Drilling. BuMines 

RI 8665, 1982, 21 pp. 

40. Hungerford, F., M. Kelly, A. Saghafi, and R J. Williams. LongHole Drilling for Gas Emission Control at Appin Colliery NSW, Australia. Paper in Proceedings of the Fourth International Mine Ventilation 

Congress, ed. by A.D.S. Gillies (Brisbane, Queensland, Australia, July 3- 

6, 1988). Aust. Inst. Min. and Metall., Melbourne, Victoria, Australia, 

1988, pp. 207-216. 

41. Hyman, D. M., and P. A. Stahl. A Computer-Implemented Coalbed Methane Model. Ch. 47 in Proceedings of the 2nd Conference on 

the Use of Computers in the Coal Industry, Tuscaloosa, AL, Apr. 15-17, 

1985. Soc. Min. Eng. AlME, 19K5; pp. 378-387. 

42. Iannacchione, A. T., C. A. Kertis, D. W. Houseknecht, and J. H. 

Perry. Problems Facing Coal Mining and Gas Production in the Hartshome Coalbeds of the Western Arkoma Basin, OK BuMines RI 8795, 

1983, 14 pp. 

43. Iannacchione, A. T., and D. G. Puglio. Methane Content and 

Geology of the Hartshorne Coalbed in Haskell and Leflore Counties, 

OK BuMines RI 8407, 1979, 35 pp. 

44. Irani, M. C., P. W. Jeran, and M. Deul. Methane Emission From 

U.S. Coal Mines in 1973, A Survey. BuMines IC 8659, 1974, 47 pp. 

45. Irani, M. C., F. F. Kapsch, P. W. Jeran, and S. J. Pepperney. A 

Fail-Safe Control System for a Mine Methane Pipeline. BuMines 

RI 8424, 1980, 11 pp. 

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

Zabetakis. Methane Emissions From U.S. Coal Mines, A Survey. 

BuMines IC 8558, 1972,58 pp. 

47. Jackson, E. O., and W. M. Memtts. Water Infusion of Coal 

Pillars Before Mining, Independent Coal and Coke Co., Kenilworth, UT. 

BuMines RI 4836, 1951, 25 pp. 

48. Jenkins, P. T. Suppression of Dust by System of Water Infusion 

in Coal Seams. Proc. South Wales Inst. Eng., v. 59, 1943, p. 306. 

49. Kelafant, J. R, D. E. Wicks, and V. A. Kuuskraa. A Geologic 

Assessment of Natural Gas From Coal Seams in the Northern Appalachian Coal Basin. Gas Res. Inst. Topical Rep. 88/0039, 1988, 84 pp. 

50. Kmg, G. R., and T. M. Ertekin. A Survey of Mathematical Models Related to Methane Production From Coal Seams: Part I - Empirical and Equilibrium Sorption Models; Part I1 - Non-Equilibrium Sorption Models. Paper 8951 in Proceedings of the 1989 Coalbed Methane 

Symposium, Tuscaloosa, AL, Apr. 17-20, 1989. Univ. AL, Tuscaloosa, 

AL, 1989, pp. 125-155. 

51. Kline, J. R., L. P. Mokwa, and P. W. Blankenship. Island Creek 

Corporation Experience With Methane Degasification. Paper 8755 in 

Proceedings of the 1987 Coalbed Methane Symposium, Tuscaloosa, AL, 

Nov. 16-19, 1987. Univ. AL, Tuscaloosa, AL, 1987, pp. 279-284. 

52. Kravits, S. J., and J. Millhiser. In-Mine Test of the Bureau of 

Mines Preproduction Wireless Survey System. BuMines RI 9291, 1990, 

22 PP. 

53. Kravits, S. J., A. Sainato, and G. L. Finfinger. Comparison of 

Rotary and In-Hole MotorTechniques for Drilling Horizontal Boreholes 

in Coal. BuMines RI 8933, 1985, 31 pp. 

54. Kravits, S. J., J. J. Schwoebel, and D. Chiari. Utilization of 

Horizontal In-Mine Gob Ventilation Boreholes at Cambria Slope No. 33 

Mine. Paper 9338 in Proceedings of the 1993 International Coalbed 

Methane Symposium, v. 2, Birmingham, AL, May 17-21,1993. Univ. AL, 

Tuscaloosa, AL, 1993, pp. 461469. 
55. Lambert, S. W., M. A. Trevits, and P. F. Steidl. Vertical Borehole 

Design and Completion Practices To Remove Methane Gas From Minable Coalbeds. U.S. Dep. Energy, CMTC/TR-80/2, 1980, 163 pp. 

56. Lawall, C. E., and L. M. Morris. Occurrence and Flow of Gas 

in the Pocahontas No. 4 Coalbed in Southern West Virginia. Trans. 

AIME, V. 108, 1934, pp. 11-30. 

57. Lewin, J. L., H. J. Siriwardane, S. Ameri, and S. S. Peng. Unlocking the Fire: A Proposal for Judicial or Legislative Determination of 

the Ownership of Coalbed Methane. WV Law Rev., v. 94, No. 3, 1992, 

pp. 563-691. 

58. Logan, T. L. Horizontal Drainhole Drilling Techniques Used in 

Rocky Mountain Coal Seams. Paper in Geology and Coalbed Methane 

Resources of the Northern San Juan Basin, Colorado and New Mexico, ed. by J. E. Fasset. Rocky Mtn. Assoc. Geol., Denver, CO, 1988, 

pp. 133-141. 

59. Mavor, M. J. Coal Gas Reservoir Cavity Completion Well Performance. Preprint 021, Int. Gas Res. Conf., Orlando, FL, 1992, 18 pp. 

60. Mavor, M. J., and J. J. Schwoebel. Simulation Based Selection of 

Underground Coal Mine Degasification Methods. Ch. 20 in Proceedings 

of the 5th U.S. Mine Ventilation Symposium, ed. by Y. J. Wange 

(Morgantown, WV, June 3-5, 1991). Soc. Min. Eng., 1991, pp. 144-162. 

61. Mazza, R L. Hydraulic Stimulation of the Pittsburgh Coal Seam: 

A Case Study. Paper in Proceedings of the Second Annual Methane 

Recovery From Coalbeds Symposium, ed. by R L. Wise (Pittsburgh, PA, 

Apr. 18-20,1979). U.S. Dep. Energy, METCISP-7919,1979, pp. 148-161. 

62. McBane, R A. (ed.). Basin Activities - Black Warrior Basin, Alabama, Quarterly Review of Methane From Coal Seams Technology. Gas 

Res. Inst., Chicago, IL, v. 6, Nos. 3 and 4, 1989, pp. 17-20. 

63. . Basin Activities - Northern and Central Appalachian 

Basins, Quarterly Review of Methane From Coal Seams Technology. 

Gas Res. Inst., Chicago, IL, v. 10, No. 1, 1992, p. 5. 

64. McCall, F. E., and I.'. Garcia. Case Study of the Influence of 

Longwall Panel Size on Methane Gas Emissions (abstr.). AAPG Bull., 

v. 75, No. 8, 1991, p. 1388. 

65. McCulloch, C. M., M. Deul, and P. W. Jeran. Cleat in Bituminous 

Coalbeds. BuMines RI 7910, 1974, 25 pp. 

66. McCulloch, C. M., S. W. Lambert, and J. R White. Determining 

Cleat Orientation of Deeper Coalbeds From Overlying Coals. BuMines 

RI 8116, 1976, 19 pp. 

67. McFall, K S., D. E. Wicks, and V. A. Kuuskraa. A Geolopc 

Assessment of Natural Gas From Coal Seams in the Warrior Basin of 

Alabama. Gas Res. Inst. Topical Rep. 8610272, 1986, 80 pp. 

68. McFall, K S., D. E. Wicks, V. A. Kuuskraa, and K B. Sedwick. 

A Geologic Assessment of Natural Gas From Coal Seams in the Piceance Basin, CO. Gas Res. Inst. Topical Rep. 8710060, 1986, 75 pp. 

69. McGinley, P. C. Legal Problems Relating to Ownership of Gas 

Found in Coal Deposits. WV Law Rev., v. 80, No. 4, 1978, 27 pp. 

70. Mills, R A., and J. W. Stevenson. History of Methane Drainage 

at Jim Walter Resources, Inc. Paper 9133 in Proceedings of the 1991 

Coalbed Methane Symposium, Tuscaloosa, AL, May 13-17, 1991. Univ. 

AL, Tuscaloosa, AL, 1991, pp. 143-151. 

71. . Improved Mine Safety and Productivity Through a Methane Drainage System. Ch. 58 in Proceedings of the 4th U.S. Mine 

Ventilation Symposium, ed. by M. J. McPherson (Berkeley, CA, June 5- 

7, 1989). Soc. for Min. Eng., 1989, pp. 477483. 

72. Nazzal, G. Planning Matches Drilling Equipment to Objectives: 

Horizontal Wells-2. Oil and Gas J., Oct. 8, 1990, pp. 110-118. 

73. Ohga, K, and K Higuchi. The Practice of Methane Drainage in 

Japan. Ch. 40 in Proceedings of the 3rd U.S. Mine Ventilation Symposium, ed. by J. M. Mutmansky (University Park, PA, Oct. 12-14,1987). 

Soc. Min. Eng. AIME, 1987, pp. 261-270. 

74. Oyler, D. C. Use of a Sodium Silicate Gel Grout for Plugging 

Horizontal Methane-Drainage Holes. BuMines RI 8843, 1984, 20 pp. 

75. Oyler, D. C., and W. P. Diamond. Drilling a Horizontal Coalbed 

Methane Drainage System From a Directional Surface Borehole. BuMines RI 8640, 1982,50 pp. 

76. Oyler, D. C., W. P. Diamond, and P. W. Jeran. Directional Drilling for Coalbed Degasification - Program Goals and Progress in 1978. 

BuMines RI 8380, 1979, 15 pp. 

77. Oyler, D. C., and P. B. Stubbs. Measuring Formation Pressures 

and the Degree of Gas Drainage in a Large Coalbed Gas Drainage 

Field. BuMines RI 8986, 1985, 15 pp. 

78. Patchen, D. G., J. F. Schwietering, T. E. Rapine, K. L. Avery, 

W. Grady, and K Timberlake. Geologic Controls on Gas Accumulations and Production. Northern West Virginia (abstr.). Abstracts With 

Programs, Geol. Soc. America, Annu. Meet., San Diego, CA, v. 23, 

No. 5, 1991, p. A38. 

79. Perry, H. Degasification of Coalbeds in Advance of Mining. Nat. 

Safety Congr. Trans., v. 7, 1959, pp. 21-34. 

80. Perry, J. H., G. N. Aul, and J. Cervik. Methane Drainage Study 

in the Sunnyside Coalbed, UT. BuMines RI 8323, 1978, 11 pp. 

81. Perry, J. H., L. J. Prosser, Jr., and J. Cervik. Degasification of the 

Mary Lee Coalbed, Brookwood, AL. BuMines RI 8669, 1982, 13 pp. 

82. Popovich, G. S. Multiple Coal Seam Project: Quarterly Review 

of Methane From Coal Seams Technology. Gas Res. Inst., v. 3, No. 2, 

1985, pp. 4347. 

83. Price, P. H., and A. J. W. Headlee. Natural Coal Gas in West Virginia. AAPG Bull., v. 27, No. 4, 1943, pp. 529-537. 

84. Prosser, L. J., Jr., G. L. Finfinger, and J. Cervik. Methane Drainage Study Using an Underground Pipeline, Marianna Mine 58. BuMines 

RI 8577, 1981, 29 pp. 

85. Puglio, D. G. Evaluating Geology, Mining Problems, and Methane 

Content of Coalbeds Through Exploration Programs in the Northern 

Appalachian Coalfield. Paper in Coal Exploration 3, ed. by G. 0. Argall 

(Proc. 3d Int. Coal Exploration Symp., Calgary, Alberta, Canada, 

Aug. 23-26, 1981). Miller Freeman Publications, Inc., 1981, pp. 148-161. 

86. Ranney, L. The Recovery of Natural Gas From Coal. OH State 

Univ. Eng. Exp. Station News, June 1941, pp. 6-8. 

87. Reeves, J. A., Jr. Advancing Longwall Mining at Mid-Continent. 

Am. Min. Congr. J., v. 64, No. 7, 1978, pp. 25-29. 

88. Saghafi, S. A Computer Simulation of Gas Flow in Coal Seam 

and Its Application to Long Borehole Drainage Pattern Design. Preprint, Computer Systems in the Australian Mining Industry, Univ. Wollongong, N.S.W., Sept. 1989, 9 pp. 

89. Schatzel, S. J., G. L. Finfinger, and J. Cervik. Underground Gob 

Gas Drainage During Longwall Mining. BuMines RI 8644,1982, 14 pp. 

90. Schwerer, F. C., E. R Bollinger, A. M. Pavone, and H. R Kokal. 

Methane Modeling - Predicting the Inflow of Methane Gas Into Coal 

Mines (contract 5033395). BuMines OFR 107-85, v. 1, 1984, 238 pp. 

91. Skow, M. L., A. G. IGm, and M. Deul. Creating a Safer Environment in U.S. Coal Mines. The Bureau of Mines Methane Control Program, 1964-79, A Bureau Impact Report. BuMines Spec. Publ., 1980, 

50 PP. 

92. Spindler, M. L., and W. N. Poundstone. Experimental Work in 

the Degasification of the Pittsburgh Coal Seam by Horizontal and 

Vertical Drilling. AIME, preprint 60F106, 1960, 28 pp. 

93. Steidl, P. F. Foam Stimulation To Enhance Production From Degasification Wells in the Pittsburgh Coalbed. BuMines RI 8286, 1978, 

10 PP. 

94. . Geology and Methane Content of the Upper Freeport 

Coalbed in Fayette County, PA. BuMines RI 8226, 1977, 17 pp. 

95. . Obse~vations of Induced Fractures Intercepted by Mining 

in the Wamor Basin, AL. Gas Res. Inst. Topical Rep. GRI-9110327, 

1991,39 pp. 
%. Stubbs, P. B., F. X. Dobscha, and J. V. Mahoney. Degasification 

of the Blue Creek Coal Seam at Oak Grove Mine. Paper in Proceeding 

of the Second Annual Methane Recovery From Coalbeds Symposium, 

ed. by R L. Wise (Pittsburgh, PA, Apr. 1&20,1979). U.S. Dep. Energy, 

METCISP-7919, 1979, pp. 96-113. 

W. Sung W., T. Ertekin, and R V. Ramani. Evaluation of the Impact of the Degasification Process on Inflow of Methane Gas Into Coal 

Mines: A Numerical Exercise. Ch. 49 in Proceedings of the 3rd U.S. 

Mine Ventilation Symposium, ed. by J. M. Mutmansky (University Park, 

PA, Oct. 12-14, 1987). Soc. Min. Eng. AIME, 1987, pp. 328-333. 

98. Thakur, P. C., D. A. Christopher, and R W. Bockhorst. Horizontal Drilling Technology for Coal Seam Methane Recovery. Paper in 

Proceedings of the Fourth International Mine Ventilation Congress, ed. 

by A.D.S. Gillies (Brisbane, Queensland, Australia, July 34, 1988). 

Aust. Inst. Min. and Metall., Melbourne, Victoria, Australia, 1988, 6 pp. 

99. Thakur, P. C., and W. N. Poundstone. Horizonal Drilling Technology of Advance Degasification. Min. Eng., v. 32, No. 6,1980, pp. 676- 

680. 

100. Tilton, J. G. Gas From Coal Deposits. Paper in Proceeding of 

the National Research Council Meeting, Washington, DC, Jan. 15,1976, 

30 PP. 

101. Trevits, M. A., and G. L. Finfinger. Case Studies of Long-Term 

Methane Extraction From Coal. Soc. Min. Eng. AIME preprint 85-333, 

1985, 7 pp. 

102. Trevits, M. A., G. L. Finfinger, and J. C. LaScola. Evaluation of 

U.S. Coal Mine Emissions. Ch. 23 in Proceeding of the 5th U.S. Mine 

Ventilation Symposium, ed. by Y. J. Wange (Morgantown, WV, June 3-5, 

1991). Soc. for Min. Eng., 1991, pp. 177-182. 

103. Ulery, J. P., and D. M. Hyman. The Modified-Direct-Method of 

Gas Content Determination: Applications and Results. Paper 9163 in 

Proceedings of the 1991 Coalbed Methane Symposium, Tuscaloosa, AL, 

May 13-17, 1991. Univ. AL, Tuscaloosa, AL, 1991, pp. 489-500. 

104. Venter, J., and P. Stassen. Drainage and Utilization of Firedamp. 

BuMines IC 7670, 1953, 22 pp. 

105. VonSchonfeldt, H., B. R Pothini, G. N. Aul, and R L. Henderson. Production and Utilization of Coalbed Methane Gas in Island 

Creek Coal Company Mines. Paper SPEIDOE 10817 in Proceeding of 

the Unconventional Gas Recovery Symposium, Pittsburgh, PA, May 16- 

18, 1982. Soc. Pet. Eng., Dallas, TX, 1982, pp. 235-244. 

+ U S GOVERNMENT PRINTING OFFICE 2000-509-307