Control Syst 

*iJ, srnvrr@a +' U.S. DEPARTMENT OF HEALTH UMAN SERVICES 

Public Health Service 

Centers for D~sease Control and Prevent~on 

Narional Irist~tute for Occupational Safety and Health CENTERS AND FL< PREVENTION [, ~ASE CONTROL 
This document is the public domain and may bepeely copied or reprinted. 

Disclaimer: Mention of any company or product does not constitute endorsement by NIOSH. 

DHHS (NIOSH) Publication No. 99-150 

October 1999 
Report of Investigations 9649 

Prediction of Longwall Methane Emissions: 

An Evaluation of the Influence of Mining 

Practices on Gas Emissions and Methane 

Control Systems 

William P. Diamond and Fred Garcia 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Public Health Service 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 

Pittsburgh Research Laboratory 

Pittsburgh, PA 
1 Piugh Remarch Laboratory Library #( 

International Standard Serial Number 

ISSN 1066-5552 
CONTENTS 

Page 

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

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

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

Instrumentation and monitoring strategy ............................................................. 2 

Longwall pass methane emission data ............................................................... 5 

VP-1 Mine study results ....................................................................... 5 

VP-3 Mine study results ....................................................................... 11 

Prediction of methane emissions for 305-m (1.00 0.ft) longwall faces ...................................... 18 

VP-1Mine .................................................................................. 18 

VP-3Mine .................................................................................. 18 

Bleeder system methane flow rates ................................................................. 19 

VP-1 Mine .................................................................................. 19 

VP-3Mine .................................................................................. 20 

Methanedrainage ............................................................................... 22 

Horizontal boreholes: VP- 1 Mine study panel ...................................................... 22 

Horizontal boreholes: VP-3 Mine study panel ...................................................... 24 

Gob gas ventholes: VP-I Mine study panel ........................................................ 26 

Gob gas ventholes: VP-3 Mine study panel ........................................................ 27 

Discussionofresults ............................................................................. 29 

Variation in longwall pass methane emission levels .................................................. 29 

Significance of ventilation and gas drainage for methane control ....................................... 30 

Summary ..................................................................................... 31 

Acknowledgments .............................................................................. 32 

References .................................................................................... 32 

ILLUSTRATIONS 

MapoftheVPMinecomplex ................................................................. 3 

Map of VP-1 and VP-3 Mine study areas ........................................................ 4 

Plan view of longwall face divided into equal-length segments for analysis and prediction of methane emission 

trends .................................................................................. 4 

Longwall face methane emissions for the baseline and days 1 and 2. VP-I Mine ......................... 6 

Average methane emissions by pass segment. VP- I Mine ........................................... 7 

Average daily methane emissions. all passes with data basis. VP-1 Mine ............................... 8 

Methane emissions associated with floor gas bleeder. pass 8. day 2. VP-I Mine ......................... 9 

Methane emissions and delays. pass 5. day 2. VP-1 Mine ........................................... 9 

Longwall face methane emissions for days 3-5. VP-I Mine ......................................... 10 

Longwall face methane emission intervals exhibiting a possible "staircase" effect. day 1. VP-1 Mine ......... 10 

Longwall face methane emission intervals exhibiting a possible "staircase" effect. day 4. VP-1 Mine ......... 11 

Longwall face methane emissions for the baseline and day 1. VP-3 Mine .............................. 12 

Longwall face methane emissions for days 2 and 3. VP-3 Mine ...................................... 12 

Average methane emissions by pass segment. VP-3 Mine ........................................... 13 

Average daily methane emissions. all passes with data basis. VP-3 Mine ............................... 14 

Longwall face methane emission intervals exhibiting a possible "staircase" effect. day 1. VP-3 Mine ......... 14 

Longwall face methane emission intervals exhibiting a possible "staircase" effect. days 2 and 3. VP-3 Mine ... 15 

Methane emissions. pass 3. day 1. VP-3 Mine .................................................... 16 

Methane emissions. pass 7. day 1. VP-3 Mine .................................................... 17 

Methane emissions. pass 5. day 2. VP-3 Mine .................................................... 17 

Methane emissions. pass 10. day 3. VP-3 Mine ................................................... 18 

Methane emission prediction curves for 305-m (1.00 0-ft) longwall faces. VP-I and VP-3 Mines ............ 19 
Page 

Detailed map of VP- 1 Mine study area .......................................................... 20 

Methane flows and emissions during mining of the VP-1 Mine study site .............................. 21 

Methane flows and emissions during mining of the VP-3 Mine study site .............................. 21 

Detailed map of VP-3 Mine study area .......................................................... 22 

Location of horizontal methane drainage boreholes. VP-1 Mine study panel ............................ 23 

Horizontal methane drainage borehole production. VP-1 Mine study panel .............................. 24 

Location of horizontal methane drainage boreholes. VP-3 Mine study panel ............................ 25 

Horizontal methane drainage borehole production. VP-3 Mine study panel ............................. 25 

Daily total gob gas venthole methane production. VP-1 Mine study panel .............................. 26 

Cumulative gob gas venthole methane production. VP-I Mine study panel ............................. 27 

Daily total gob gas venthole methane production. VP-3 Mine study panel .............................. 28 

Cumulative gob gas venthole methane production. VP-3 Mine study panel ............................. 28 

TABLES 

Average longwall pass methane emission summary. VP-1 Mine ...................................... 6 

Average direction of pass mining and delay time summary. VP-1 Mine ................................ 8 

Average longwall pass mining and delay time summary. VP-1 Mine .................................. 8 

Average daily longwall pass methane emission summary. all passes with data basis. VP-1 Mine ............ 9 

Average longwall pass methane emission summary. VP-3 Mine ...................................... 13 

Average daily longwall pass methane emission summary. all passes with data basis. VP-3 Mine ............ 13 

Average longwall pass mining and delay time summary. VP-3 Mine .................................. 16 

Average direction of pass mining and delay time summary. VP-3 Mine ................................ 16 

Bleeder system methane flows during VP-1 and VP-3 Mine emission studies ........................... 19 

Horizontal borehole methane production. VP-1 and VP-3 Mines ..................................... 24 

Gob gas venthole methane production. VP-1 and VP-3 Mines ....................................... 27 

Ventilation system and borehole methane flows during VP-1 and VP-3 Mine emission studies .............. 30 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

cfm cubic foot (feet) per minute m3/mo cubic meter (s) per month 

cm3/g cubic centimeter(s) per gram m3/sec cubic meter(s) per second 

ft foot (feet) min minute(s) 

ft3/st cubic foot (feet) per short ton MMcf million cubic feet 

h r hour(s) MMcfd million cubic feet per day 

m meter(s) MMcfImo million cubic feet per month 

m3 cubic meter(s) YO percent 

m3/d cubic meter(s) per day 
PREDICTION OF LONGWALL METHANE EMISSIONS: AN EVALUATION 

OF THE INFLUENCE OF MINING PRACTICES ON GAS EMISSIONS 

AND METHANE CONTROL SYSTEMS 

By William P. ~iamond' and Fred Garcia2 

ABSTRACT 

As part of its mine safety and health research program, the National Institute for Occupational Safety and 

Health, Pittsburgh Research Laboratory, has been investigating the geologic and mining factors influencing 

methane gas emissions associated with longwall mining. A primary focus of this research has been the 

consequences of increasing longwall panel dimensions, particularly face width, in gassy coalbeds. Continuous 

longwall face emission monitoring studies were conducted at two adjacent mines operating in the Pocahontas 

No. 3 Coalbed, where longwall faces were to be extended from 229 to 305 m (750 to 1,000 ft). Average 

longwall pass methane emission rates for 229-m (750-ft) wide faces were 61 % (0.072 m31sec (153 cfm)) higher 

at the VP-3 Mine than at the VP-1 Mine. It was predicted by regression analysis of methane emissions data 

from 229-m (750-ft) wide faces that extending faces to 305 m (1,000 ft) would increase methane emission rates 

by only 7%, or 0.009 m3/sec (20 cfm), to 0.144 mysec (304 cfm) at the VP-1 Mine. In contrast, it was 

predicted that extending faces to 305 m (1,000 ft) at the VP-3 Mine would increase methane emissions by as 

much as 13%, or 0.029 mysec (65 cfm), to 0.268 dlsec (567 cfm). 

'~esearch geologist. 

'~ining engineer. 

Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA 
INTRODUCTION 

The explosion or ignition of methane gas has been a major 

cause of multiple fatalities in U.S. underground coal mines. As 

part of its mine safety and health research program, the National 

Institute for Occupational Safety and Health (NIOSH), 

Pittsburgh Research Laboratory (PRL), has been investigating 

methane emissions associated with longwall mining [Diamond 

et al. 1992; Diamond et al. 1994; McCall et al. 1993; Schatzel 

et al. 19921. The fundamental goals of this research program 

are to develop an understanding of the influence of mining 

practices and geology on the release and migration of methane 

gas during longwall mining. With this knowledge, techniques 

can be developed to (1) predict underground methane emission 

levels and (2) improve methane control strategies designed to 

cope with the increased levels of methane emissions sometimes 

resulting from the use of high-productivity, advanced mining 

technology [Diamond et al. 19941. 

To remain competitive in domestic and foreign markets, 

today's mining industry continually strives for higher 

production and greater recovery of valuable coal reserves. One 

means of reaching these goals is to increase the size of longwall 

panels. Unfortunately, along with the increase in coal 

production, mining larger panels can also intensify various 

mining problems, including methane emissions. In some 

instances, the productivity gains anticipated from increasing 

panel size and utilizing advanced mining technology are limited 

by mining delays caused by increased methane emissions. This 

potential for increased methane emissions is of particular 

concern in mines that are already nearing the statutory limits for 

methane concentrations underground. 

The primary purpose of this field study was to predict the 

methane emission consequences of mining longwall panels of 

greater face width in the Pocahontas No. 3 Coalbed in Virginia. 

Longwall panel face widths at the VP- I and VP-3 Mines were 

to be increased from 229 to 305 m (750 to 1,000 ft). However, 

since historically high methane emissions from the longwall 

face and gobs were already being experienced, there was a 

concern for further increases in methane emission rates. If 

higher emission rates were encountered on wider faces, it was 

preferable from a safety perspective to be prepared in advance, 

either with increased ventilation airflow, or with additional 

methane drainage. 

The bleeder and methane drainage systems associated with 

the two study panels were also evaluated to fully characterize 

the methane liberation patterns and control system performance 

for each study area. Methane drainage, including vertical gob 

gas ventholes and underground horizontal boreholes drilled into 

the panel prior to longwall mining, has been practiced 

extensively at this mining complex for many years [Aul and 

Ray 1991 ; Kline et al. 19871. 

STUDY AREA 

The longwall methane emission studies were conducted in 485 m (1,590 ft) at the VP-1 site to 668 m (2,190 ft) at the VP-3 

the VP-I Mine and the adjoining VP-3 Mine located in site. As can be seen in figure 2, the sites for both studies were 

Buchanan County, VA (figure 1). Additional mines in this near the startup end of the panels, and were beyond the first gob 

complex, both active and inactive, are located to the east and gas ventholes on each panel. Coal thickness ranged from 1.5 to 

south. The two study panels are approximately 1,600 m (1 1.9 m (5.0 to 6.3 ft) at the VP-1 study site and 1.7 to 2.0 m (5.5 

mile) apart. The depth of cover ranged from approximately to 6.5 ft) at the VP-3 site. 

INSTRUMENTATION AND MONITORING STRATEGY 

Instrumentation for the gas emission monitoring system 

consisted of a sensor to measure methane concentration and an 

electronic data logger to continuously collect and store 

information. Methane concentrations were automatically 

measured and recorded every 30 sec during the monitoring of 

production shifts. Airflow quantities were periodically 

measured with a handheld anemometer at the methane 

monitoring locations. With these data, the methane emission 

rate (m3/sec (cfm)) was calculated for each 30-sec measurement 

point. Methane emission volumes per unit time were calculated 

by applying the numerical integration version of the trapezoidal 

rule to the calculated 30-sec methane emission rate data. 

Average emission rate for specific time intervals was then 

correlated to the production time study data. The time study 

data included a detailed account of the longwall operations, 

including direction of pass, shearer location (relative to shield 

number) with time, specific operation (cutting or delay), the 

reason for any delays, and any other operational information 

that could influence the interpretation of the methane 

emission data. 

Methane concentrations were monitored at two locations on 

the face at each mine site (figure 3). One instrument was 

attached to a shield over the pan line, close to the headgate side 

of each panel, to monitor the methane concentration in the 

intake air before it swept the longwall face. A second 

instrument was located near the tailgate side of each panel. 

Any methane in the intake air would have to be subtracted from 

the methane levels in the return air to determine the amount of 
methane released from the longwall face. However, no additional locations were monitored in the bleeders to determine 

significant methane was measured in the intake air at either the total methane volume liberated into the ventilation airflow 

study site; therefore, the data from the monitoring location on from each panel, as well as the adjacent mined areas. 

the tailgate side of the panels did not have to be corrected. Two 

VP-3 

MINE 

VP- 1 

MINE 

VP-5 

MINE 

Legend 

Scale P77 Mined-out 

0 longwall panel 750 1,500 m 

VP-6 

MINE r7 i I 

Figure 1.-Map of the VP Mine complex. 
i Extended i 

longwall face, - 305 rn (1,000 ftl 

L ,,,,,,J H 

- Key Ventilation airflow direction 

Methane sensor 

+l-- 76 m (250 ft) longwall pass segment 

Figure 3.-Plan view of longwall face divided into equal-length segments for analysis and 

prediction of methane emission trends. 
LONGWALL PASS METHANE EMISSION DATA 

To predict the methane emission consequences of mining 

longwall panels of greater width, it was first necessary to 

determine if a cumulative increase in methane emission levels 

occurs with time (staircase effect), both during a longwall pass, 

and from pass-to-pass or day-to-day. Any differences in 

methane emissions related to direction of cutting, i.e., head-totail or tail-to-head, were also investigated. Characterizing the 

rate of methane gas emissions across the longwall face was 

facilitated by dividing each pass on the 229-m (750-ft) wide 

faces into three equal length segments of 76 m (250 ft) 

(figure 3). To evaluate emission rate trends during the mining 

of an individual pass, average methane emission rates of the 

second and third segments of a pass were compared to the 

respective rates of the previous segment. Emission trends 

established by this methodology were then extended to forecast 

the expected methane emission rate of an additional 76-m 

(250-ft) longwall pass segment, i .e., a 305-m (1,000-ft) face. 

Baseline emission data were collected over the weekend 

prior to the start of production shifts on Monday. Three full 

days and two partial days of monitoring (three production shifts 

per day) were completed at the VP-I Mine. During this time 

the face was advanced approximately 79 m (260 ft). Methane 

emission monitoring data and time study data were collected on 

83 individual passes. 

Two full days and one partial day (two production shifts per 

day) were monitored at the VP-3 Mine site. During this time, 

the face was advanced 37 m (1 20 ft). A total of only 38 passes 

were monitored due to a substantial number of delays. In fact, 

on average during the VP-3 study, delays accounted for 42.0% 

of the time necessary to complete a pass. In contrast, delays 

accounted for only 13.1 % of the time needed to complete apass 

during the VP-I study. Because of the influence of delay time 

on emission rates, this marked difference in delay time made 

comparisons between the two mines more difficult. 

It should be noted that the first segment of each longwall 

pass also included the "snake" or cutting-in of the shearer to 

begin the face pass. This procedure, which could involve as 

much as 30 m (1 00 ft) of the first 76-m (250-ft) pass segment, 

generally increased the time needed to mine this segment as 

compared to the remaining two pass segments. The summary 

tables in this report include emission results for the first pass of 

a segment both with and without the snake for completeness 

and general interest. Due to the longer time needed to mine the 

snake as part of the first segment of a pass, the emission rates 

are generally (but not always) slightly less for this segment 

when the snake portion is included in the calculation. Since the 

snake is part of the mining process, the emission results 

discussed throughout this report include the mining of 

the snake. 

The longwall pass methane emission data for this study were 

generally evaluated on three bases related to the relative amount 

of delay time. Delay time, when used as a data evaluation basis 

in this report, refers only to delay times occurring during apass. 

Delay times occurring between passes (generally most of the 

longer delays) are not included. The first evaluation basis (all 

passes with data) included all the passes with complete methane 

emission and time study data, regardless of the amount of delay 

time during a pass. The second evaluation basis (40% delay 

time) included only those complete data passes where active 

mining constituted at least 50% of the total time required to 

complete a pass, i.e., any pass where the delay time was 250% 

of the total time needed to complete the pass was eliminated. 

Also, any pass that had a delay >15 min on any one-third of the 

pass, or that experienced a reported methane delay, was also 

eliminated. 

The third basis (<25% delay time) for evaluating the 

emission results was the most stringent, essentially cutting the 

previous criteria in half. This basis included only those passes 

whose active mining time constituted at least 75% of the total 

time required to complete a pass, i.e., all passes with a delay 

time 225% of the total time needed to complete a pass were 

eliminated. This basis also eliminated any pass from evaluation 

that had a delay 27.5 min on any segment and any pass that 

experienced a methane delay. 

Passes with extended delays were eliminated from the 

second and third evaluation bases to support the concept of 

comparing the average methane emission results of the second 

and third segments of each pass to the previous segment in 

order to establish an emission trend that would estimate the 

emissions for a 305-m (1,000-ft) face. If a particular pass 

segment had an extended delay that caused a lower methane 

emission value, then comparing that result to a previous 

segment would yield a lower than "typical" increase in 

emissions from one segment to the next. Comparing the results 

from the pass segment with a delay to the next segment 

(without a delay) would result in a higher than "typical" 

increase in emissions from one segment to the next. A similar 

bias would occur when one segment of a pass includes a delay 

due to high methane emissions. Comparing that segment to 

other segments of the pass would again yield "atypical" results. 

The emission valves obtained by eliminating passes with 

various levels of delay time should be considered a 

representation of methane emission levels for an "ideal pass" 

with optimum mining rates, but not a "worst-case" emission 

scenario for mine planning purposes. 

VP-1 MINE STUDY RESULTS 

Baseline methane emissions for the VP-I Mine study panel 

were approximately 0.024 mysec (50 cfm). The start of mining 

can be seen in figure 4 as an increase in emissions shortly after 

midnight (beginning of day 1). Time study data were not 
-- 

Baseline D& I ~a; 2 

TIME OF DAY, h:min 

Figure 4.-Longwall face methane emissions for the baseline and days 1 and 2, VP-1 Mine. 

collected until the start of the day shift on day 1; therefore, no 

analysis was made of passes completed for the first shift. 

Methane emission monitoring and time study data were 

collected essentially around-the-clock for all three production 

shifts through Friday morning. Data were collected for a total 

of 83 passes. However, occasional instrumentation problems 

and the loss of time study data due to logistical problems, 

primarily during shift changes, resulted in incomplete data sets 

for six passes. A total of 77 passes with complete data sets 

were evaluated for the VP-I study site (table 1). 

Although delay time was not excessive during the passes 

monitored for the VP-1 Mine emission study, it was still ideal 

to evaluate the emissions on as much of a delay-free basis as 

possible. This would also facilitate comparison of results to the 

VP-3 Mine, where delay time was considerably greater. Sixtynine of the seventy-seven passes with complete data were 

evaluated for the 40% delay time basis for the VP-1 study 

(table I). Sixty of the seventy-seven passes with complete data 

met the more stringent criteria of the ~25% delay time 

evaluation basis. 

Table 1 .-Average longwall pass methane emission summary, VP-1 Mine 

Averaae pass seament methane flow rate, m3/sec (cfm) No. of Calculation basis passes used 1 st third Difference, Difference, 

Without snake With snake 2nd third Pnd/lst 3rd third 3rd/2nd. % 

TOTAL 

All with data . . . 77 of 83 0.1 12 (236) 0.1 10 (233) 0.123 (262) +12.4 0.1 30 (276) +5.3 0.1 18 (250) 

<50% delay . . . . 69 of 77 0.111 (236) 0.110 (232) 0.128 (271) +16.8 0.133 (281) +3.7 0.120 (254) 

<25% delay . . . . 60 of 77 0.1 13 (239) 0.1 1 1 (235) 0.130 (276) + 17.4 0.1 34 (284) +2.9 0.121 (257) 

HEAD-TO-TAIL -- 

All with data . . . 37 of 41 0.1 08 (230) 0.1 08 (230) 0.1 19 (252) +9.5 0.125 (266) +5.6 0.1 15 (244) 

<50% delay . . . . 30 of 37 0.107 (226) 0.1 08 (228) 0.123 (261) +14.4 0.1 29 (273) +4.7 0.1 17 (248) 

<25% delay . . . . 25 of 37 0.109 (232) 0.1 11 (236) 0.128 (272) +15.4 0.131 (277) +2.0 0.121 (255) 

TAI L-TO-H EAD 

All with data . . . 40 of 42 0.1 15 (243) 0.1 12 (236) 0.129 (274) + 15.9 0.136 (287) +4.9 0.122 (258) 

<50% delay . . . . 39 of 40 0.115(244) 0.111(236) 0.133(281) +15.5 0.136 (289) +2.8 0.1 23 (260) 

<25% delay . . . . 35 of 40 0.115 (244) 0.110 (234) 0.131 (279) +19.1 0.137 (290) +4.0 0.122 (258) 

'With snake. 

Base VP-1 flow rate = 0.024 m3/sec (50 cfm). 
Methane emissions increased 12.4% and 17.4% (depending 

on the evaluation basis) from the first to second pass segment 

during the VP-1 study (figure 5, table 1). As would be 

expected, the evaluation basis with the least amount of delay 

time (~25%) generally had the highest methane emission levels. 

Except where noted, the following discussions of the VP-1 

emission study data refers to the ~25% delay time evaluation 

basis. Emission rates were 0.1 1 1 and 0.1 30 mvsec (235 and 

276 cfm) respectively for the first and second pass segments. 

Emissions increased only slightly from the second to third pass 

segment, averaging 2.9% higher on the final third of the pass as 

compared to the second third. This observation seems to 

indicate that the emission rate was leveling-off during the final 

third of a pass, and that mining a wider face might not be 

expected to result in significantly higher methane emission 

levels. The average methane emission rate for the final pass 

segment was 0.134 m3/sec (284 cfm) and the average methane 

emission rate for a complete pass was 0.121 m31sec (257 cfrn). 

In addition to evaluating the average methane emissions for 

all passes, it was of interest to determine if there was any 

significant difference in the level of emissions related to the 

direction of mining. As can be seen in table 1, methane 

emissions were slightly higher for the tail-to-head mining 

direction. Table 2 presents time study data for head-to-tail and 

tail-to-head passes, respectively. Head-to-tail passes took 

several minutes longer to mine than tail-to-head passes, due to 

higher delay times (not methane-related) on the head-to-tail 

passes. The longer mining times for the head-to-tail passes, 

which allowed more time for gas to bleedoff, probably account 

for the slightly lower methane emission rate for this mining 

direction (table 1 ). 

Table 3 is a summary of average mining and delay times by 

pass segment for the three bases by which the longwall pass 

methane emission rates were analyzed for the VP- 1 Mine study 

site. Time needed to mine a complete pass (including the 

snake) averaged 39.9 min, with 1.0 min (2.5%) of delay time 

for the ~25% delay time basis. 

Average daily methane emissions by pass segment for all 

passes with data during the VP- 1 study are presented in figure 6 

and in table 4. The average total longwall pass methane 

emission rate for day 1 was 0.096 m3/sec (203 cfrn). Day 2 

showed a marked increase in methane emission rates, to an 

average of 0.142 m3/sec (300 cfm) due to a floor gas bleeder 

(figures 4 and 7). Reported methane delays of 1 min and 13 

min occurred on day 2 (pass 5, figure 8) before the floor gas 

bleeder was observed (figure 4). Methane levels actually began 

to rise earlier on day 2 (figure 4), from an emission rate of 

about 0.1 18 to 0.142 m3/sec (250 to 300 cfm) to >0.236 m3/sec 

(500 cfrn). During pass 5, when the first methane delay 

occurred, the emission rate exceeded 0.307 m3/sec (650 cfrn), 

and reached over 0.330 m3/sec (700 cfm) at the end of the pass. 

Methane levels on the next pass (pass 6) were about 

0.283 m3/sec (600 cfm) for most of the pass and spiked to 

0.330 m3/sec (700 cfm) near the end; however, no mining delay 

was noted. It took several passes for the methane emission 

rates to decline to more typical levels. 

After the steep rise in longwall pass methane emission rates 

on day 2, average daily emission rates declined on days 3 and 

4 (figure 6, table 4). This decline is probably due to a 

diminishing influence of the floor gas bleeder, which occurred 

on day 2, and a 16-hr delay for mechanical reasons early on 

day 3, which allowed additional time for gas bleedoff before 

I st Third 2nd Third 3rd Third 

LONGWALL PASS SEGMENT 

0.1 5 I 

Figure 5.-Average methane emissions by pass segment, VP-1 Mine. 

- 300 

260 

220 

180 

140 

-_,,- w-----------+ .*-• 

- 

Key 

0.10 

0.05 

*-* All with data - - 

- -.- - c50 pct delay - c25 pct delay - 

Baseline emissions = 0.02 m3/sec (50 cfm) - 

.. I 
Table 2.-Average direction of pass mining and delay time summary, VP-1 Mine 

kin -4 Averaqe pass segment time IYU. UI 

Calculation basis passes 1 st third Total 

used With snake 2nd third 3rd third 

snake With snake snake 

HEAD-TO-TAIL TOTAL MINING TIME, min 

All with data ....... 37 of 41 11.0 26.6 13.4 12.3 36.7 52.3 

40% delay ........ 30 of 37 10.4 22.0 12.1 11.5 34.1 45.7 

<25% delay ........ 25 of 37 10.6 20.7 11.1 10.7 32.3 42.4 

HEAD-TO-TAIL DELAY TIME, min (%) 

All with data ....... 37 of 41 1. (9.1) 5.6 (21.1) 2.8 (20.9) 1.5 (12.2) 5.3 (14.4) 10.0 (Klj 

<50%delay ........ 30of37 0.4(3.9) 1.3(5.9) l.S(l2.4) 0.7(6.1) 2.6 (7.6) 3.5 (7.7) 

<25% delay ........ 25 of 37 0.3 (2.8) 0.9 (4.4) 0.4 (3.6) 0.1 (0.9) 0.8 (2.5) 1.3 (3.1) 

TAIL-TO-HEAD TOTAL MINING TIME, min 

All with data ....... 40 of 42 10.3 20.1 10.1 9.5 29.9 39.8 

<SO% delay ........ 39 of 40 10.3 20.2 9.7 9.5 29.6 39.4 

<25% delay ........ 35 of 40 10.0 19.6 9.7 8.9 28.5 38.2 

TAIL-TO-HEAD DELAY TIME, min (%) 

All with data ....... 40 of 42 0.6 (5.8) 5.6 (27.9) 0.7 (6.9) 0.7 (7.4) 2.0 (6.7) 2.3 (5.8) 

<50%delay ........ 39of40 0.6(5.8) 0.9(4.5) 0.3(3.1) 0.7(7.4) 1.7 (5.7) 1.9 (4.8) 

<25% delav ........ 35 of 40 0.4 (4.0) 0.5 (2.6) 0.2 (2.1 ) 0.1 (1.1) 0.7 (2.5) 0.7 (1.8) 

Table 3.-Average longwall pass mining and delay time summary, VP-1 Mine 

Averase pass seqment time No. of 

Calculation basis passes 

1 st third Total 

Without With snake 2nd third used 3rd third 

snake With snake snake 

TOTAL MINING TIME, min 

All with data ...... 77 of 83 10.7 23.2 11.7 10.9 33.2 45.8 

<SO% delay ....... 69 of 77 10.4 21 .O 10.8 10.4 31.5 42.1 

<25% delay ....... 60 of 77 10.2 20.1 10.2 9.6 30.1 39.9 

DELAY TIME, min (%) 

All with data ...... 77 of 83 0.8 (7.5) 3.2 (13.8) 1.7 (14.5) 1.1 (10.1) 3.6 (10.8) 6.0 (13.1) 

<SO% delay ....... 69 of 77 0.5 (4.8) 1.1 (5.2) 0.8 (7.4) 0.7 (6.7) 2.0 (6.4) 2.6 (6.2) 

<25% delav ....... 60 of 77 0.4 (3.9) 0.6 (3.0) 0.3 (2.9) 0.1 (1.0) 0.8 (2.7) 1 .O (2.5) 

1st Third 2nd Third 3rd Third 

LONGWALL PASS SEGMENT 

Figure 6.-Average daily methane emissions, all passes with data basis, VP-1 Mine. 

I 

.*******... .......... -350 

- - - - 0 A0---.7*7.:.T 

€ 

'4- 

-300 

4 > i 

0 - 

,250 $ 

- *-*-0-*-• t W 

t ./ ./*- - 200 w 

W Key Z 

W 

Z 

6 

I 

b 2 0.05 

.-A-. 6 

Day 7 I 

-6- Day2 b 

Baseline emissions = 0.02 m3/sec (50 cfm) -, Day 3 2 

- 1-1 Day 4 - ......... Day 5 100 

I 
TlME OF DAY, h:min 

Figure 7.-Methane emissions associated wlth floor gas bleeder, pass 8, day 2. VP-1 Mine. 

o 150 Shield No. (shearer location) a, 

PASS 5 (TAIL-HEAD) 

2:20 2:30 2:40 2: 50 3:OO 3:lO 3:20 

TlME OF DAY, h:min 

Figure 8.-Methane emissions and delays, pass 5, day 2, VP-1 Mine. 
mining resumed (figure 9). Three additional major (>60 min) 

delays during production passes on day 3, as well as numerous 

shorter delays on day 4, also contributed to the observed decline 

in emission rates after day 2. Days 3 and 4, in general, 

experienced the most delay time during the VP-I study. 

The evaluation of emission trends with time, i.e., a day-today "staircase effect," was essentially lost for the VP-I study 

site due to the impact of the floor gas event and major delays on 

days 2 and 3, which interrupted any longer term trends 

developing early in the study. However, a visual inspection of 

the methane emission curve (figure 10) suggests several time 

intervals prior to the floor gas event where the general emission 

rates were trending upward. A similar upward trend in 

emission rates occurs at the end of day 4 (figure 11). The only 

increase in average daily longwall pass methane emission rates 

after day 2 occurred on day 5 (figure 6, table 4). However, the 

high emission rates on day 5 were not attributed to any 

observable gas event and should probably not be considered 

indicative of the emission trend for that day, since only four 

passes were actually evaluated. 

TlME OF DAY, h:min 

Figure 9.-Longwall face methane emissions for days 3-5, VP-1 Mine. 

0.4 I I I I I I I I - 800 

0 

Q) Reported gas delay 0 

18:OO 

A\ 

0 6:OO 12:OO 18:OO 0 6:OO 12:OO 18:OO 0 /\ / v v 

Baseline Day 1 Day 2 

TlME OF DAY, h:min 

Figure 10.-Longwall face methane emission intervals exhibiting a possible "staircase" effect, day 1, VP-1 Mine. 
Major delay 

/Baseline emissions -- -I---- 

0 6:OO 12:OO 18:OO 0 6:OO 12:OO 18:OO 0 

\ / \ v v 'b 

Day 3 Day 4 Day 5 

TIME OF DAY, h:min 

Figure 11.-Longwall face methane emission intervals exhibiting a possible "staircase" effect, day 4, VP-1 

Mine. 

VP-3 MINE STUDY RESULTS 

Baseline methane emissions for the VP-3 study panel 

(figure 12) were approximately 0.071 m3/sec (1 50 cfrn), 

0.047 m3/sec (100 cfm) higher than those of the VP-1 study. 

The time study did not begin until the second pass of the 

day shift on Monday. Methane emission monitoring data were 

collected 24 hr per day, even though only two production shifts 

(day and night) were mining coal during the VP-3 study. Data 

were collected on 38 passes mined during the 3 days of the 

study (figures 12-1 3). The study was terminated after only 

3 days due to the high proportion of mining delays (not 

methane-related) being experienced. The extended mining 

delays, when combined with fewer production shifts per 

day and logistical problems similar to those noted for the VP-1 

study, resulted in only 27 passes with complete data sets being 

available for analysis of longwall pass methane emission trends. 

This is substantially fewer passes than the 77 passes evaluated 

for the VP- I study . 

Mining delays during the 27 passes with complete data sets 

were substantially more frequent than those experienced during 

the VP-1 study. Utilizing the same evaluation bases criteria 

(percent delay time) for determining average methane emissions 

as in the VP-1 study, only 11 passes were analyzed for the 

40% delay time basis and 5 passes for the <25% delay time 

basis. The 40% delay time basis data were used to establish 

trends for average total emissions and average emissions by 

pass segment (table 5). Due to the small number of passes 

available for evaluation, only data on the "all passes with data" 

basis were considered for establishing day-to-day average daily 

emissions (table 6) and head-to-tail versus tail-to-head emission 

trends (table 5). 

Longwall pass methane emissions increased by about 17.4% 

from the first to the second pass segment during the VP-3 study 

(figure 14, table 5). This increase in emission levels is quite 

similar to the 1 6.8% increase measured for the VP- I study site 

(table 1) on the same delay time basis (40%). However, the 

actual VP-3 average emission rate for the second pass segment 

was substantially higher-0.207 m7/sec (438 cfm) versus 

0.1 28 m7/sec (27 1 cfm) for VP- I. 

There is one significant difference in the emission trends 

between the two mine sites. The emission rate at the VP-3 

study site continued to increase (14.6%) from the second to 

third pass segment. This level of increase is in marked contrast 

to the 3.7% average increase observed at VP-I for the same 

basis (40% delay time). For the VP-3 study site, the average 

methane emission rate for the third pass segment reached 

0.237 m'lsec (502 cfrn), while the average emission rate for all 

VP-3 passes was 0.202 m7/sec (427 cfrn). The observed steady 

increase in average methane emission rates during mining of a 

pass may be an indication that levels would increase even 

further if wider panels were mined, potentially resulting in an 

increase in methane-related mining delays. 

Table 6 summarizes the VP-3 average daily and pass 

direction methane emission results for the "all passes with data" 

basis. Average daily longwall pass methane emission rates 

progressively increased from 0.176 to 0.207 m7/sec (373 to 

438 cfm) over the 3 days of the study, indicating that a general 

"staircase effect" was present (figure 15). A visual inspection 

of the face emission curves for the VP-3 study (figures 16-1 7) 
Baseline Day 2 

TlME OF DAY, h:min 

Figure 12.-Longwall face methane emissions for the baseline and day 1, VP-3 Mine. 

\ v / \ v 

Day 1 Day 2 

TlME OF DAY, h:min 

Figure 13.-Longwall face emissions for days 2 and 3, VP-3 Mine. 
Table 5.-Average longwall pass methane emission summary, VP-3 Mine 

Averaae Dass seament methane flow rate, m3/sec (cfm) No. of Calculation basis passes used 1 st third Difference, Difference, 

Without snake With snake 2nd third Pnd/1 st %I 3rd third 3rdI2nd. % Total1 

All with data . . . . 27 of 38 0.172(365) 0.169(359) 0.196(415) +15.6 0.233 (494) +19.2 0.190 (403) 

~50% delay . . . . . 11 of 27 0.177 (376) 0.176 (374) 0.207 (438) + 17.4 0.237 (502) +14.6 0.202 (427) 

HEAD-TO-TAIL 

Allwithdata . . . . 140f 18 0.1 66 (352) 0.1 60 (339) 0.203 (431) +27.2 0.249 (528) +22.6 0.192 (407) 

TAIL-TO-HEAD 

All with data . . . . 13 of 20 0.1 77 (376) 0.1 77 (375) 0.1 91 (404) +7.8 0.21 6 (458) + 13.2 0.188 (399) 

'With snake. 

Base VP-3 flow rate = 0.071 m3/sec (1 50 cfm). 

Table 6.-Average daily longwall pass methane emission summary, all passes with data basis, VP-3 Mine 

Averaae pass seament methane flow rate, m3/sec (cfml No. of 

Day passes used 1 st third Difference, Difference, 

Without snake With snake 2nd third Pnd/1 st 3rd third 3rdI2nd. % 

1 . . . . . . . . . . . . 10of 13 0.164(348) 0.158(335) 0.180(381) +13.7 0.231 (490) +28.5 0.176 (373) 

2 ............ 9of12 0.172 (364) 0.1 80 (380) 0.194 (41 1) +8.0 0.230 (487) + 18.6 0.1 96 (415) 

3 ............ 8of13 0.1 78 (377) 0.181 (384) 0.225 (478) +24.5 0.238 (505) +5.6 0.207 (438) 

Total . . . . . . . . . 27 of 38 0.172 (365) 0.1 69 (359) 0.196 (41 5) +15.6 0.233 (494) +19.2 0.1 90 (403) 

'With snake. 

Base VP-3 flow rate = 0.071 m3/sec (1 50 cfm). 

1st Third 2nd Third 

LONGWALL PASS SEGMENT 

3rd Third 

Figure 14.-Average methane emissions by pass segment, VP-3 Mine. 
0.25- I 

0 

Q) 

V) 

\ 

C3 

€ 

Q 0.15- I 

Iw Baseline emissions = 0.07 m3/sec (1 50 cfm) - 300 

t - 275 

I 250 

I st Third 2nd Third 3rd Third 

LONGWALL PASS SEGMENT 

Figure 15.-Average daily methane emissions, all passes with data basis, VP-3 Mine. 

Figure 16.-Longwall face methane emission intervals exhibiting a possible "staircase" effect, 

day 1, VP-3 Mine. 
~ac 2 ~ai3 

TIME OF DAY, h:min 

Figure 17.-Longwall face methane emission intervals exhibiting a possible "staircase" effect, days 2 and 

3, VP-3 Mine. 

suggests several time intervals where cinissions wcl-e trending 

upward. Average mcthanc emission rates were higher on 

passes mined from hcad to tail than those mined from tail to 

head (table 5). This is in contrast to the slightly higher emission 

rates in the tail-to-head mining direction at VP-I. 

As mentioned previously, delays (not methane-related) 

during the VP-3 study were substantially higher in both 

frequency and duration. Average pass mining time at VP-3 was 

65.9 rnin (table 7), compared to only 45.8 rnin (table 3) for 

passcs at VP- I on thc same basis (all passes with data). Actual 

average pass delay time was 27.7 inin (42.0%) for VP-3 and 6.0 

rnin (1 3.1 %I) foi- VP- I. On a dircction of mining basis (table 8), 

tail-to-head passes cxpcricnccd significantly more total average 

delay time-35.1 inin versus 20.9 min. Total average pass 

mining time was 76.2 inin for tail-to-head passcs, compared to 

56.5 rnin for heaci-to-tail passcs. Thc longer mining time for 

tail-to-head passcs may explain the lower methane emission 

levels for this mining direction, as was speculated for the VP-I 

study for the hcad-to-tail passes. 

There were four short methane delays noted during the VP-3 

longwall emission study. Methane delays of 4 min and 1 rnin 

occurred during passes three and seven on day 1 (figures 18- 

19). Additional methane delays of 4 min and 8 rnin were 

reported on day 2 (figure 20) and day 3 (figure 21), 

respectively. Emission rates associated with the delays were 

approximately 0.283 to 0.307 m7/sec (600 to 650 cfm), similar 

to the rates associated with methane delays during the VP-1 

study. However, emission rates prior to the methane delays 

were approximately 0.165 to 0.189 m3/sec (350 to 400 cfm), or 

about 0.047 mg/sec (1 00 cfm) higher than those during the VP- 1 

study. This figure reflects the same difference (0.047 m7/sec 

(100 cfm)) between the measured baseline emissions of the two 

study sites. Since methane delays were observed at about the 

same emission rate at each mine, less margin existed for 

methane emission increases at the VP-3 site. On several other 

occasions during the study at VP-3, the methane emission rate 

exceeded 0.283 mg/sec (600 cfm) (figures 1 2- 1 3); however, no 

methane delays were indicated in the time study data. 
8:50 9:OO 9:10 9:20 9:30 9:40 9:50 

TIME OF DAY, h:rnin 

Figure 18.-Methane emissions, pass 3, day 1, VP-3 Mine. 
W 

k, I 

2 I 

Pass 4 I PASS 5 (HEAD-TAIL) 

0 

I 

I I I 1 I I 0 

12:30 12:40 12:50 13:OO 13:lO 13:20 13:30 

TlME OF DAY, h:min 

Figure 20.-Methane emissions, pass 5, day 2, VP-3 Mine. 
() 

mine. The predicted average emission values for the additional 

76 m (250 ft) of face length are not necessarily the "worst-case" 

scenarios, which would include sporadic high-methane 

emission events such as the floor gas bleeder observed at the 

VP-1 Mine. 

VP-1 MlNE 

Longwall pass segment methane emission data for the<25% 

delay time basis (table I) were selected for regression analysis 

for the prediction of emissions for an additional 76 m (250 ft) 

of face length at the VP-1 Mine. A power curve (figure 22) in 

the form Y = 236.89Xo.''', where Y = average pass segment 

methane emission rate and X = individual 76-m (250-ft) pass 

segment number, fit the measured data best (R' = 0.95). 

Extending the regression curve to a fourth 76-m (250-ft) 

longwall pass segment (figure 22), i.e., to a face length of 

305 m (1,000 ft), yields an average methane emission rate of 

0.144 mR/sec (304 cfm) for an additional 76 m (250 ft) of face 

width. The predicted value is a 7% (0.009 m3/sec (20 cfrn)) 

increase over the average measured methane emission value of 

0.134 m3/sec (284 cfm) for the third 76-m (250-ft) segment of 

the 229-m (750-ft) wide faces at the VP-1 Mine. At this 

relatively low predicted increase in methane emissions at the 

gpg

delay time basis (table 5) were selected for regression analysis 

for the prediction of emissions for an additional 76-m (250-ft) 

longwall pass segment at the VP-3 Mine. The small number of 

passes (five) meeting the more restrictive <25% delay time 

basis for the VP-3 Mine study was not considered sufficient to 

characterize existing emission trends for prediction purposes. 

A linear regression curve (figure 22) in the form Y = 309.6 + 

64.25X. where Y = average pass segment methane emission 

rate and X = individual 76-m (250-ft) pass segment number, fit 

the measured data best (R' = 0.99). 

Extending the regression curve to a longwall face length of 

305 m (1,000 ft) yields an average methane emission rate of 

0.268 m3/sec (567 cfm) for the additional 76-m (250-ft) pass 

segment (figure 22). This predicted value is a 13% 

(0.029 m3/sec (65 cfrn)) increase over the average measured 

methane emission value of 0.237 mR/sec (502 cfm) for the third 

76-m (250-ft) pass segment of the 229-111 (750-ft) wide 

longwall faces at the VP-3 Mine. Face emissions in the 0.283 

to 0.330 mvsec (600 to 700 cfm) range at the VP-3 Mine 

occasionally resulted in short delays during the study. To 

ensure a safe underground workplace, methane emission rates 

at the levels predicted may require additional ventilation airflow 

on the face, or increased levels of methane drainage in 

advanceof longwall mining. 
- 

Key 

I I I 

I Measured 

- Predicted, VP-3 Mine I 

- - - - Predicted, VP- 1 Mine 

- 

Y = 309.6 + 64.25X - = 0.99 

- li 

__.--me .- - - Y = 236.89~~"~ - = 0.95 

I - 

I I I A 

1 2 3 

76.2 m (250 ft) LONGWALL PASS SEGMENT 

Figure 22.-Methane emission prediction curves for 305-m (1,000-ft) longwall faces, VP-1 and VP-3 

Mines. 

BLEEDER SYSTEM METHANE FLOW RATES 

In addition to the longwall face emission studies, the bleeder 

system associated with each mine site was monitored. The 

bleeder system methane flow data were used to obtain a more 

comprehensive evaluation of how much ofthe methane in each 

mine's ventilation system was attributable to active mining on 

the study panel (table 9). As with the face emission portion of 

the study, the bleeder systems were monitored over the idle 

weekend to establish a methane flow baseline. Methane 

volumes above the baseline could then be attributed to the 

active study panel. 

Table 9.-Bleeder system methane flows during VP-1 

and VP-3 Mine emission studies 

Methane flow rate, 1 o3 m 3/d 

(MMcfd) 

VP-1 Mine VP-3 Mine 

Minimum (base) ................ 104.8 (3.7) 133.1 (4.7) 

Maximum ..................... 184.1 (6.5) 175.6 (6.2) 

Average ...................... 141.6 (5.0) 152.9 (5.4) 

Differential' (maximum-minimum) ... 79.3 (2.8) 42.5 (1.5) 

Average' ...................... 36.8 (1.3) 22.7 (0.8) 

'Methane flow attributable to active mining on study panel. 

study panel as well as from the gobs associated with the two 

previously mined panels. A true baseline was not actually 

established, since the methane flow rate was still declining at 

the time mining resumed on Monday morning (figure 24). The 

minimum flow rate was about 104.8 x lo3 m3/d (3.7 MMcfd). 

As soon as mining began on the study panel, the methane 

flow rate in the bleeders began to rise, and generally continued 

to rise throughout the 5 days of the emission study (figure 24). 

Methane flow in the bleeders averaged 141.6 x lo3 m3/d 

(5.0 MMcfd) after the base level (minimum flow rate) was 

established (table 9). The maximum methane flow rate of about 

184.1 x lo3 m3/d (6.5 MMcfd) was measured in the bleeder 

system on the final day of the study. The 79.3 x lo3 m3/d 

(2.8 MMcfd) differential between the maximum and minimum 

bleeder system methane flow rates is inferred to be an estimate 

of the maximum methane liberation into the mine's bleeder 

ventilation system as a result of active mining during the face 

emission study. The average methane liberation rate into the 

bleeders as a result of mining on the active study panel was 

36.8 x 1 O3 m3/d (1.3 MMcfd). 

At the end of the emission study, methane concentrations in 

the bleeders were approaching their allowable limit. By this 

time, the longwall face had advanced far enough away from the 

VP-1 MINE previously intercepted gob gas venthole (239) that its influence 

on methane levels in the bleeders was diminishing, and the next 

The VP-1 bleeder system monitoring location is shown on gob gas venthole (240) was not yet on production (figure 23). 

the study area map (figure 23). The monitoring location During the week ofthe study, a larger centrifugal exhauster was 

included methane contributions from the face and gob of the installed on venthole 239, which stabilized methane flow in the 
Scale 

0 250 500 m 

Legend 

A Instrumentation location 

P77 Mined-out longwall panel 

'240 Completed gob gas venthole 

'24f Gob gas venthole to be drilled 

Figure 23.-Detailed map of VP-1 Mine study area. 

bleeders at approximately 161.4 x lo3 m3/d (5.7 MMcfd) for 

about 12 hr during the first half of day 4, before the methane 

flow climbed once again, as shown in figure 24. 

VP-3 MINE 

In addition to the study panel, 10 other previously mined 

panels to the north were also part of the VP-3 bleeder system 

(figure 1); this significantly complicated meaningful analysis of 

the data and comparisons to the VP-1 study. Baseline 

monitoring (figure 25) indicated a minimum methane flow rate 

of about 1 33.1 x 1 O3 m3/d (4.7 MMcfd), approximately 28.3 x 

lo3 m3/d (1.0 MMcfd) greater than that for the VP-1 study 

(table 9). The bleeder system monitoring location was on the 

western end of the No. 1 Development entries, seven panels 

north of the area shown in figure 26. One reason for the 

relatively high methane flow rates during baseline monitoring 

is the larger associated gob area compared to VP- 1. Barometric 

pressure changes also may have influenced the outgassing ofthe 

large gob area [Garcia et al. 19951. Finally, higher in situ 

methane contents associated with the mined coalbed, as well as 

the surrounding strata in this area, may have contributed to the 

high bleeder baseline methane flow rates. 

Methane flow rates in the VP-3 bleeder system peaked at 

about 175.6 x lo3 m3/d (6.2 MMcfd), late on day 3 of the study 

(figure 25), then declined into day 4 due to an extended mining 

delay (not methane-related). Methane flow in the bleeders 

averaged 152.9 x 1 O3 m3/d (5.4 MMcfd) after the base level was 

established (table 9). The peak flow rate in the VP-3 bleeder 

system was 8.5 x lo3 m3/d (0.3 MMcfd) lower than the peak 

flow rate observed at the VP-1 Mine. 
The 42.5 x 1 O3 m3/d (1.5 MMcfd) differential between the 

minimum and maximum bleeder system methane flow rate for 

the VP-3 site is 36.8 x 1 O3 m3/d (1.3 MMcfd) less than the 

79.3 x lo3 m3/d (2.8 MMcfd) differential for the VP-1 study 

panel (table 9). However, the average methane flow rate of 

152.9 x lo3 m3/d (5.4 MMcfd) is 1 1.3 x lo3 m3/d (0.4 MMcfd) 

higher than the average rate for the VP-1 site. The difference 

of 42.5 x lo3 m3/d (1.5 MMcfd) between the maximum and 

minimum methane levels in the bleeders is inferred to be an 

estimate of the maximum methane liberation rate into the 

bleeders as a result of mining on the active study panel at the 

VP-3 Mine (table 9). The average methane liberation rate into 

the bleeders as a result of mining on the active study panel was 

22.7 x lo3 m3/d (0.8 MMcfd). 

The reason for the lower maximum methane flow rate in the 

VP-3 bleeders, in spite of the higher face emissions, is not 

conclusively known, but may be related to the higher amount of 

delay time (42.0% versus 13.1%) andlor fewer monitoring days 

(3 days versus 5 days) at the VP-3 site, as compared with the 

VP- 1 study site. The lower differential between the minimum 

and maximum bleeder system methane flow rate at the VP-3 

site, as compared to the VP- 1 site, may be related to the higher 

base level bleeder flow rate at VP-3 site, which in turn, may be 

related to the larger gob area. 

------ 

Baseline Day I Day 2 Day 3 Day 4 Day 5 

TlME OF DAY, h:min 

Figure 24.-Methane flows and emissions during mining of the VP-1 Mine study site. 

--- - 

~aieline ~a; I Day 2 D,; 3 D& 4 

TlME OF DAY, h:min 

Figure 25.-Methane flows and emissions during mining of the VP-3 Mine study site. 
Legend 

Scale 

0 - 250 500 m 

0 800 1.600 ft 

Instrumentation location 

Mined-out longwall panel 

.z08 Completed gob gas venthole 

O226 Gob gas venthole to be drilled 

Figure 26.-Detailed map of VP-3 Mine study area. 

METHANE DRAINAGE 

To completely investigate the methane emission characteristics of each study site, it was necessary to evaluate all 

methane control systems in use prior to and during the face 

emission studies. Methane drainage has generally been 

necessary to effectively control underground methane levels in 

deep mines operating in the Pocahontas No. 3 Coalbed [Aul and 

Ray 199 1; Kline et al. 1987; Schatzel et al. 19921. 

Methane drainage practices employed at the VP- I and VP-3 

Mine study sites included horizontal boreholes drilled into the 

outlined longwall panels to drain gas in advance of mining, and 

the use of postmining vertical gob gas ventholes. Horizontal 

methane drainage borehole drilling and gas production records 

were used to estimate the volume of gas removed from the 

study panels at each mine site. Gob gas venthole production 

records, supplemented with more detailed gas production 

monitoring during the face emission studies, were used to 

document this component of the methane control system. 

HORIZONTAL BOREHOLES: VP-1 MINE 

STUDY PANEL 

A total of 29 horizontal boreholes (7 on the tailgate and 

22 on the headgate) were drilled for gas drainage on the VP-1 

study panel (figure 27). The tailgate holes were drilled 

progressively from the startup (west) end of the study panel, 

and covered about one-third of the panel length. The holes 
----------- 

----------- 

---------- 

---------- 

i Key 

HG Headgate l?7"77 Mined-out 

TG Tailgate ---- Mine projections 

Scale 

Drilling order on panel - Completed holes 0 600 m ---- Holes drilled in Feb. 1 I, Emission study area -..- Pipeline 0 2,000 ft 

a Gob gas venthole 

Figure 27.-Location of horizontal methane drainage boreholes, VP-1 Mine study panel. 

were drilled 46 to 137 in (1 50 to 450 ft) apart, with the spacing 

generally increasing to the east, away from the startup end of 

the panel. These holes, and the holes drilled from the headgate 

side of the panel, were drilled to within about 69 m (225 ft) of 

the opposite side of the panel. The seven tailgate holes had a 

cumulative methane production of about 0.14 x lo6 m3 

(5.0 MMcf) over approximately 2 months (figure 28, table 10). 

Methane production from the tailgate horizontal holes ended 

approximately 5 months prior to the start of mining on the study 

panel and about 7 months prior to the mining of the study site. 

The first headgate horizontal methane drainage boreholes 

were drilled starting from the completion (east) end ofthe study 

panel, and new holes were progressively drilled closer to the 

startup end of the panel (figure 27). Drilling the holes in this 

sequence resulted in the last holes drilled being the first holes 

mined through by the longwall. If sufficient drainage time is 

not allowed before the start of mining, the methane control 

effectiveness of the holes at the startup end of the panel could 

potentially be reduced. However, in this case, there were also 

seven horizontal holes drilled from the tailgate side on the 

startup end of the study panel, which enhanced methane 

drainage in this area. 

The headgate horizontal holes were drilled approximately 

91 m (300 ft) apart on the startup end of the panel, where 

horizontal holes were also drilled from the tailgate side of the 

panel. Borehole spacing for the headgate holes was decreased 

to 61 m (200 ft) on the rest of the panel beyond the area of 

tailgate holes. The earliest drilled headgate holes began 

production approximately 6 months prior to the start of mining 

on the study panel and 8 months prior to mining of the study 

site (figure 28). The headgate holes drilled within the study site 

were completed and on production 5.5 months prior to the 

methane emission study. The total methane volume produced 

from the headgate horizontal holes was about 2.01 x lo6 m3 

(71.0 MMcf) through the end of the longwall face emission 

study (table 10). 

Gas production from the horizontal holes declined rapidly 

after peak production of 0.67 x 1 O6 m3/mo (23.5 MMcfImo) was 

reached, 4 months after the first headgate holes were drilled and 

2 months prior to the start of mining (figure 28). By the time 
m 4 I I I I I 1 I I I 

E 

- 1 

Start of 

- +- Tailgate holes 

Nov. Dec. Jan. Feb. Mar. April May June July Aug. 

MONTH 

Figure 28.-Horizontal methane drainage borehole production, VP-1 Mine study panel. 

Table 10.-Horizontal borehole methane production, VP-1 and VP-3 Mines 

Cumulative production, 1 06m3 (MMcf) Average 

Hole No. of production 

locations holes To start of To end of Total per hole, mining emission study 1 06m3 (MMcf) 

VP-1 Mine: 

Tailgate . . . 7 0.14 (5.0) 0.14 (5.0) 0.1 4 (5.0) 0.02 (0.7) 

Headgate . . 22 1.81 (64.0) 2.01 (71 .O) 2.06 (72.7) 0.09 (3.3) 

Total . . . . . . 29 1.95 (69.0) 2.15 (76.0) 2.20 (77.7) 0.08 (2.7) 

VP-3 Mine: 

Tailqate . . . 17 3.54 (125.0) 3.79 (134.0) 38.3 (135.2) 0.23 (8.0) 

longwall mining began, gas production from the headgate active face on the adjoining panel that was mining in the same 

horizontal holes was down to 0.1 1 x lo6 m3/mo (4.0 MMcfImo), directioq. This drilling sequence allowed for the maximum 

and the holes ceased production 3 months after the start of time for methane drainage before longwall mining began for the 

mining, 1 month after the face emission study was completed. holes closest to the startup end of the study panel. 

Total horizontal borehole methane production for the VP-I The first four holes, including those in the face emission 

study panel was 2.20 x lo6 m3 (77.7 MMcf) (table 10). study area, were drilled and producing gas 8.5 months prior to 

Average methane production for the VP-1 study panel was the start of mining, and 10 months prior to the emission study 

0.08 x 1 O6 m3/hole (2.7 Mmcflhole). (figure 30). At the time drilling of the horizontal holes began, 

the study panel was not yet completely outlined by development 

HORIZONTAL BOREHOLES: VP-3 MINE entries. In fact, the development entries on the headgate side of 

STUDY PANEL the panel were only completed about 3 months prior to the start 

of mining and 4.5 months prior to mining of the study site. The 

The first horizontal methane drainage boreholes drilled at the entries of the 12-Development section were advanced from the 

VP-3 Mine were on the panel investigated for longwall face completion end of the panel toward the startup end. At the time 

emissions during this study (figure 29). A total of 17 holes of the drilling and during initial production of methane from the 

were drilled on the tailgate side of the study panel holes on the startup end of the panel, including the study site, 

(1 1 Development), beginning at the startup (east) end of the the holes were producing gas from an unlimited, downdip virgin 

panel. The horizontal holes were drilled on approximately gas reservoir (figure I). The horizontal holes at the startup end 

91-m (300-ft) spacing, to within about 38 m (125 ft) of the of the study panel were on production for about 5 months 

headgate side ofthe panel. The holes were drilled progressively before the 12-Development entries were completed and the 

toward the completion (west) end of the panel, ahead of the panel completely outlined. 

Gas production rates from the horizontal holes on the VP-3 (2.5 MMcfd). Approximately 0.6 x lo6 m3 (20.5 MMcf) of 

study panel were high (>0.28 x 1 06m3/mo (>lo MMcfImo)) for methane at an average rate of 1 16.1 x lo3 m3/d (4.1 MMcfd) 

7 months (figure 30). In contrast, there were only 3 months of was exhausted by this venthole during the 5 days of the study. 

horizontal borehole methane production at that level on the Gob gas venthole 239 produced 5.6 x lo6 m3 (196 MMcf) of 

VP-1 study panel, where the area had been isolated from the methane during its 104 days of production. The bottom hole 

virgin coalbed gas reservoir for 18 months. Total methane location of gob gas venthole 240 was intercepted (or was close 

production from the horizontal drainage holes was 3.83 x lo6 to being intercepted) near the end of the emission study. 

m3 (1 35.2 MMcf) over 11 months of production, considerably 

more than the 2.20 x 1 O6 m3 (77.7 MMcf) over 10 months for 

the VP-1 study panel (table 10). Average methane production 

was 0.23 x lo6 m3/hole (8.0 MMcfIhole), also substantially 

higher than the 0.08 x lo6 m3/hole (2.7 MMcfIhole) average for 

the VP-1 study panel. Production from the horizontal methane 

drainage boreholes ended approximately 2 months after mining 

began on the VP-3 study panel. 

GOB GAS VENTHOLES: VP-1 MINE 

STUDY PANEL 

Four gob gas ventholes were drilled on the VP-1 study panel. 

The first hole intercepted by the longwall (No. 239, figure 23) 

was located 122 m (400 ft) from the startup end of the panel and 

320 m (1,050 ft) from the face emission study site. This 

However, the first measured gas production from the venthole 

was on the fifth day (third working day), after the end of the 

emission study. 

Total methane production for the four gob gas ventholes on 

the study panel was 38.3 x lo6 m3 (1,35 1 MMcf) through 

19 months (566 days) of production (figure 32, table 11). Two 

holes (Nos. 240 and 242) were still on production through the 

end of the available production data, more than 13 months after 

panel completion. Figure 3 1 shows the combined total daily 

methane production for all gob gas ventholes on the study 

panel. The highest single-day gob gas production for the panel 

was 274.7 x lo3 m3/d (9.7 MMcfd). Methane production 

averaged approximately 226.5 x lo3 m3/d (8.0 MMcfd) for 

35 days when the last hole on the panel (No. 242) came on 

production. The highest daily methane production for 

individual holes ranged from 12 1.8 to 158.6 x 10' m3/d (4.3 to 

venthole was on production 40 days prior to the face emission 5.6 MMcfd). Cumulative methane production for individual 

study (figures 3 1 -32), producing a total of 2.8 x 1 O6 m3 holes ranged from 5.6 to 12.9 x 106m3 (196 to 456 MMcf). 

(98.9 MMcf) of methane at an average rate of 70.8 x 1 O3 m3/d 

10 

E 

r" 

82 

i 

0 

6 5 

3 

n 

0 

Holes 240 and 242 % 

W 

z 

a 

2 I 

L 

t 

0 

100 200 300 400 500 600 

PRODUCTION DAY 

Figure 31 .-Daily total gob gas venthole methane productions, VP-1 Mine study panel. 
- 0 100 200 300 400 500 600 

PRODUCTION DAY 

Figure 32.-Cumulative gob gas venthole methane production, VP-1 Mine safety panel. 

Table 11 .-Gob gas venthole methane production, VP-1 and VP-3 Mines 

Highest 

No. of Cumulative Average production, 1 o3 m3/d (MMcfd) single-day 

Hole No. production production, production, 

days 1 0' m3 (MMcf) 1 00 days 200 days 300 days 1 o3 m3/d 

(MMcfd) 

VP-1 Mine: 

239 ............... 

240 ............... 

241 ............... 

242 ............... 

Average per hole .... 

Panel total ......... 

VP-3 Mine: 

2248 .............. 

224 ............... 

225 ............... 

226 ............... 

227 ............... 

Average per hole .... 

55.2 (1.95) NAP NAp 158.6 (5.6) 

77.6 (2.74) 47.3 (1.67) 35.1 (1.24) 130.3 (4.6) 

49.6 (1.75) 32.3 (1.14) 24.1 (0.85) 121.8 (4.3) 

81.6 (2.88) 52.4 (1.85) 38.5 (1.36) 152.9 (5.4) 

66.0 (2.33) 44.0 (1 55) 32.6 (1.1 5) NAP 

103.9 (3.67) 133.9 (4.73) 107.3 (3.79) 274.7 (9.7) 

43.6 (1.54) 27.2 (0.96) 20.1 (0.71) 104.8 (3.7) 

42.8 (1.51) 25.5 (0.90) 18.7 (0.66) 79.3 (2.8) 

57.8 (2.04) 43.0 (1.52) 32.6 (1 .IS) 107.6 (3.8) 

93.4 (3.30) 69.9 (2.47) 56.6 (2.00) 135.9 (4.8) 

26.3 (0.93) 18.4 (0.65) NAp 59.5 (2.1) 

52.8 (1.86) 36.8 (1.30) 32.0 (1.13) NAP 

Panel total ......... '431 '44.9 (1,585) 130.3 (4.60) 144.4 (5.1 0) 127.1 (4.49) 220.9 (7.8) 

NAP Not applicable. 

'Production ongoing. 

GOB GAS VENTHOLES: VP-3 MINE 

STUDY PANEL 

Five gob gas ventholes were drilled on the VP-3 study panel 

(figure 26). The first two ventholes on the startup end of the 

panel (224B, 224) had been intercepted by the longwall and 

were both on production (28 days and 24 days, respectively) at 

the time of the longwall face emission study (figures 33-34). In 

comparison, venthole 239 on the VP-1 study panel had been on 

production 40 days at the start of the emission study at that 

mine. Combined methane production from the two VP-3 holes 

was 2.4 x lo6 m3 (86.4 MMcf) at an average rate of 87.8 x lo3 

m3/d (3.1 MMcfd) prior to the emission study. During the 

3 days of the emission study, 0.4 x lo6 m3 (12.6 MMcf) of 

methane was produced at an average rate of 11 8.9 x lo3 m3/d 

(4.2 MMcfd), a rate almost identical to the 116.1 x lo3 m3/d 

(4.1 MMcfd) for the VP- 1 emission study. 

The five gob gas ventholes on the VP-3 study panel 

produced 44.9 x 1 O6 m3 (1,585 MMcf) of methane during the 

43 1 days for which production data were available (table 11). 

Three holes were still on production at the end of the available 

data. The highest single-day methane production from gob gas 

ventholes on the VP-3 study panel was 220.9 x lo3 m3/d 

(7.8 MMcfd), 20% lower than the 274.7 x lo3 m3/d 
PRODUCTION DAY 

Figure 33.-Daily total gob gas venthole methane production, VP-3 Mine study panel. 

Holes 2248 and 224 

off production 

Hole 227 

on production I , ..I, 

Holes 225,226 and 227 

luction 

I - 

- 

Holes 2248 and 224 

- 

Hole 2248 

- 

- 

- 

- 

0 - 100 200 300 400 500 

PRODUCTION DAY 

Figure 34.-Cumulative gob gas venthole methane production, VP-3 Mine study panel. 

(9.7 MMcfd) recorded at the VP-1 site. The highest daily 618 MMcf). A comparison of the average daily methane 

production for individual holes ranged from 59.5 to 135.9 x lo3 production rate per venthole for the same time intervals for both 

m3/d (2.1 to 4.8 MMcfd), slightly lower than the production for study panels (table 1 1) shows a convergence to an almost 

VP-1. Cumulative production for individual holes on the VP-3 identical rate at 300 days. 

study panel ranged from 4.4 to 17.5 x lo6 m3 (155 to 
DISCUSSION OF RESULTS 

VARIATION IN LONGWALL PASS METHANE 

EMISSION LEVELS 

The methane emission characteristics were quite different at 

the two study sites. Baseline methane emission levels were 

0.047 m3/sec (100 cfm) higher, and average longwall pass 

emissions were approximately 0.072 m3/sec (1 53 cfm) higher 

(all passes with data basis) at the VP-3 site. Methane emission 

levels were higher at the VP-3 Mine even though there were 

only two daily production shifts compared to three at the VP-1 

Mine. There were also significantly more mining delays (not 

methane-related) at VP-3, which should have allowed for 

additional "natural" bleedoff of methane. Additionally, there 

was a floor gas bleeder at the VP-I Mine, which generally 

raised the average methane emission levels for about 2 days. 

Given these circumstances, lower methane emission rates might 

have been expected at the VP-3 Mine than at the VP-1 Mine. 

The observed variation in methane emission rates are 

perhaps unexpected for two mining operations located only 

about 1,600 m (1 mile) apart in the same coalbed. However, 

a closer look at the mine design factors associated with the sites 

helps to explain the observed differences. When comparing the 

two sites, probably the most significant mine design factors 

influencing the variation in methane emission levels at the face, 

as well as the gas production rates from the horizontal 

boreholes, are (1) proximity and relative exposure to the virgin 

coalbed gas reservoir, and (2) gas bleedoff time prior to 

horizontal borehole methane drainage and longwall mining. At 

the time of the studies, the VP-I study panel was the third in a 

series of five longwall panels that were progressively mined to 

the north (figure 23). This block of five panels in the southwest 

corner of the mine had been outlined by main entries 

3.5 months prior to the mining of the first panel. The area to the 

north of this five-panel block was mined 3 to 12 years prior to 

the outlining of the block. This part of the VP-I Mine is also 

bordered by the VP-5 Mine to the south and the VP-3 Mine to 

the west (figure 1). From these factors, it is inferred that the 

extensive mine development surrounding the VP- I study panel 

has very effectively isolated the area from methane migration 

from the downdip virgin coalbed gas reservoir. 

This mining sequence is optimum from a methane control 

viewpoint. In addition to the general isolation of the southwest 

corner of the VP-1 Mine from gas migration, the in situ gas 

volume within the five-panel block has had a substantial length 

of time to bleedoff into the surrounding entries. The first and 

the third (study) panels in the five-panel block were separated 

from the surrounding coalbed gas reservoir by development 

entries and bleeding off gas for about 6 months and 18 months, 

respectively, prior to mining. This relatively long period for 

in situ gas content reduction within the isolated five-panel 

block, in particular for the later mined panels, should result in 

progressively lower gas emissions at the face. 

Company engineering staff reported that the first panel 

mined in this isolated block was one of the gassiest at the VP-1 

Mine, and that supplemental horizontal methane drainage 

boreholes had to be drilled to control the higher emissions. 

However, as each new panel in the block was mined, methane 

emissions generally decreased. Even with the additional 

bleedoff time prior to mining, it was still necessary to utilize 

horizontal methane drainage boreholes on the study panel to 

further control methane emissions. However, the increased 

panel isolation and natural gas bleedoff time at VP- I resulted in 

considerably lower horizontal borehole gas production rates and 

cumulative production than at VP-3. 

Mine design parameters for the area ofthe VP-3 Mine where 

the study panel was located were quite different, and less 

desirable, from a methane-control viewpoint. The study panel 

was the 1 1 th in a series of panels mined in the southeast corner 

of the mine (figure 1). Virgin coal reserves were adjacent to 

this area of the mine both to the west and south. Unlike the 

isolated block of five panels at the VP-1 study area, the series 

of panels in the VP-3 Mine had not been surrounded by main 

entries prior to mining of the panels. The panels in the VP-3 

study area were progressively developed and mined to the south 

(figure 26). Each successive panel in the series was 'therefore 

connected to the virgin coalbed gas reservoir until the 

development entries for the panel were completed. The VP-3 

study panel was surrounded by development entries and 

ventilation airflow just 3.5 months prior to the start of mining 

on the panel and less than 5 months prior to the emission study. 

Therefore, there was very little time for in situ gas content 

reduction by bleedoff into the mine's ventilation system prior to 

mining of the study panel. These conditions resulted in both 

higher gas emission rates on the face and higher horizontal 

borehole gas production than was observed at the VP-1 Mine 

study site. 

It is probable that at the time of the emission studies, the 

in situ gas content on the VP-3 study panel was significantly 

higher than that on the VP- 1 study panel due to the shorter time 

available for bleedoff of gas into the mine's ventilation system 

prior to mining. It is also possible that the virgin gas content 

may have been higher at the VP-3 mine site. The VP-3 Mine 

study panel lies under a depth of cover that is about 183 m 

(600 ft) greater than the VP- 1 Mine study panel. In general, the 

gas content of a coalbed increases with increasing depth 

[Diamond 19821. Based on limited available gas content data 

from the mine complex area, it is estimated that the virgin gas 

content of coal at the VP-3 study site could be about 1.3 cm3/g 

(40 ft3/st) higher than that at the VP- 1 study site. However, this 

is probably not a significant enough difference to account for 
the substantial differences in longwall face methane emissions 

or horizontal borehole production rates observed between the 

two mines. 

Another factor known to influence emission rates at this 

mine complex is the relative proximity of the overlying, gasbearing, Pocahontas No. 4 Coalbed. High emission rates are 

experienced when the interval between the two coalbeds is 

<7.6 m (25 ft). Other geologic factors identified by the mine 

engineering staff as influencing methane emissions andlor 

methane drainage rates include variations in the physical 

properties of the coal and proximity to geologic structures such 

as sand channels, faults, and rolls. Insufficient geologic data 

were available to evaluate the potential influence of these 

various geologic parameters on the observed methane emission 

rates at the two sites. 

SIGNIFICANCE OF VENTILATION AND GAS 

DRAINAGE FOR METHANE CONTROL 

Figures 24-25 and table 12 show the individual contributions 

of the ventilation and methane drainage components to the 

overall methane control system during the VP- 1 and VP-3 Mine 

longwall face emission studies, respectively. These data show 

that face emissions are a relatively small contributor to the total 

methane emissions resulting from the mining of the panels. 

Table 12.-Ventilation system and borehole methane 

flows during VP-1 and VP-3 Mine emission studies 

Average methane flow rate, 

Source 1 O3 m3/d (MMcfd) 

VP-1 Mine VP-3 Mine 

Bleeders ................. 141.6 (5.0) 152.9 (5.4) 

emission study, while horizontal boreholes (not shown in 

figure 24) were producing at an average rate of only 2.8 x 1 O3 

m3/d (0.10 MMcfd). The 9.6 x lo3 m3/d (0.34 MMcfd) of 

methane emissions from the face was only about 3.7% of the 

average of 260.5 x lo3 m3/d (9.20 MMcfd) total methane 

emissions/borehole production measured at the VP-1 Mine 

study site. However, the 9.6 x lo3 m3/d (0.34 MMcfd) of 

methane emissions from the face was about 6.2% of the average 

of 155.7 x lo3 m3/d (5.50 MMcfd) total methane emissions/ 

borehole production attributable to mining of the study panel. 

At the VP-3 Mine, where the study panel had been directly 

connected to the virgin coalbed gas reservoir until shortly 

before mining began, face emissions were a higher portion of 

the total methane emissionlborehole production (table 12). 

During the emission study, the average methane flow rate in the 

bleeders was 152.9 x 1 O3 m3/d (5.4 MMcfd). Gob gas ventholes 

were producing methane at an average rate of 1 18.9 x 1 O3 m3/d 

(4.2 MMcfd). Most of the horizontal borehole methane 

production occurred prior to mining of the panel, and the 

average production had declined to 3.4 x lo3 m3/d 

(0.12 MMcfd) during the study (not shown in figure 25). The 

16.4 x lo3 m3/d (0.58 MMcfd) of methane emissions from the 

face was 6.0% of the total of 275.2 x lo3 m3/d (9.72 MMcfd) 

methane emissionslborehole production measured at the VP-3 

study site. However, the 16.4 x lo3 m3/d (0.58 MMcfd) of 

methane emissions from the face was about 11.3% of the 

average of 145.0 x lo3 m3/d (5.12 MMcfd) total methane 

emissions/borehole production attributable to mining of the 

study panel. 

The importance of horizontal borehole methane drainage to 

supplement the ventilation system, especially given the 

conditions at the VP-3 Mine, can be demonstrated by 

Bleeders1 ................ 36.8 (1.3) 22.7 (0.8) converting the production volumes to a m3/sec (cfm) basis. 

Horizontal holes ........... 2.8 (0.10) 3.4 2, Horizontal boreholes at the VP-3 Mine produced methane at an Gobgasventholes ......... 116.1(4.1) 118.9(4.2) 

Total .................... 260.5 (9.20) 275.2 (9.72) average rate of about .6 O3 m3/d (0.4 MMcfd), Or 

Total1 .................... 155.7 (5.5) 145.0 (5.12) 0.135 m3/sec (285 cfm) over their 1 1 -month production life. 

Face .................... 9.6 (0.34) 16.4 (0.58) Adding this value to the 16.4 x 10' m3/d (0.58 MMcfd), or 

Face, % of total ............ 3.7 6.0 0.190 m3/sec (403 cfm) average face methane emission rate for 

Face, % of total1 ........... 6.2 11.3 the VP-3 ~ine during the study, yields a potential average face 'Methane flow attributable to active mining on study panel. emission rate of 0.325 m3/sec (688 cfm), if horizontal borehole 

methane drainage had not been utilized. This emission rate is Average methane flow in the bleeders during the VP-1 similar to those associated with reported methane-related delays emission study was 14 1.6 x lo3 m3/d (5.0 MMcfd). The active at this mine. gob gas ventholes on the study panel were producing methane - - 

at an average rate of 1 16.1 x 1 O3 m3/d (4.1 MMcfd) during the 
gas in advance of mining is credited with maintaining the 

methane emissions at a lower than predicted level. 

Methaneemission levels were significantly different between 

the two mine study sites even though the sites were only about 

1,600 m (I mile) apart. Baseline methane emission levels at the 

VP-3 Mine study site were 0.047 m3/sec (100 cfm) higher than 

those at the VP-1 Mine. Average longwall pass methane 

emission levels were 0.190 m3/sec (403 cfm) at the VP-3 Mine 

and only 0.1 18 m3/sec (250 cfin) at the VP- I Mine. Study 

panels at both mines utilized in-mine horizontal borehole and 

vertical gob gas venthole methane drainage to supplement the 

mine's ventilation system. The higher level of methane 

emissions at the VP-3 Mine study site is primarily attributed to 

(1) the closer proximity and longer exposure to the adjacent 

virgin coalbed gas reservoir and (2) the shorter time for in situ 

gas content reduction by horizontal methane drainage 

relatively small portion of the overall methane liberation from 

an active longwall section. At the VP-I Mine site, methane 

emissions from the active longwall face averaged only 3.7% of 

the 260.5 x 10' m3/d (9.20 MMcfd) total methane emissions/ 

borehole production measured during the emission study. 

However, methane emissions made up a higher portion of the 

total at the VP-3 Mine, where the study panel had been directly 

connected to the virgin coalbed gas reservoir until shortly 

before mining began. At this study site, methane emissions 

from the face averaged 6.0% of the 275.2 x lo3 m3/d 

(9.72 MMcfd) total methane emissions/borehole production. 

The importance of methane drainage in supplementing the 

face ventilation system is quite clear. If even a small fraction of 

the gas handled by the methane drainage systems were 

encountered in the face area, both mine safety and the expected 

increase in coal production could be adversely affected. 
ACKNOWLEDGMENTS 

This research was conducted in cooperation with the acknowledged. Richard E. Ray, Jr., Chief Ventilation Engineer 

Virginia Division of Island Creek Coal Co. (now Consolidation (now with Parsons Brinckerhoff), and George N. Aul, 

Coal Co.), Oakwood, VA. The day-to-day assistance of the Supervisor of Horizontal Methane Drainage (now with the Mine 

engineering staff to conduct the underground monitoring and Safety and Health Administration), are acknowledged for their 

time study data collection required for the successful assistance in project planning and data evaluation. 

completion of the original project goals is gratefully 

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Diamond WP [I 9821. Site-specific and regional geologic considerations 

for coalbed gas drainage. Pittsburgh, PA: U.S. Department of the Interior, 

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Diamond WP, Jeran PW, Trevits MA [1994]. Evaluation of alternative 

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Kline JR, Mokwa LP, Blankenship PW [1987]. Island Creek Corporation 

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Methane Symposium. Tuscaloosa, AL: University of Alabama, pp. 279-284. 

McCall FE, Garcia F, Trevits MA, Aul G [1993]. Methane gas emissions 

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