9
panel. This explains the asymmetric horizontal extend of
the GEZ from both sides of the panel and shorter extend
on the headgate side of the panel.
A three-dimensional model focusing only on the work-
ing panel is developed and presented in Figure 11. The
model geometry is created based on an active longwall coal
mine. The headgate and tailgate are 18-ft wide and 7-ft
high. Airflow quantity at the headgate side is 110.5 kcfm
and at the tailgate side is 35 kcfm. There is also a stop-
ping at the headgate side to control the airflow (Figure 11).
In this model, we assumed different zones of permeabil-
ity and porosity with the inner most circle (middle part of
the geometry) having low permeability and porosity. The
permeability and porosity values increase in the subsequent
zones moving towards the gate roads. The permeability and
porosity values for different gob zones used for this study
are shown in Figure 12.
The turbulent model used is Realizable κ-ε with a non-
Darcian flow model for porous media. Figure 13 shows the
velocity profile at the mid-section of the model. The flow
direction in the model shows that air flows from the head-
gate and tailgate side and moves towards the return side
with very low velocity through the gob area. Figure 14 pres-
ents airflow velocity streamlines, revealing air leakage into
the gob area from the headgate side, with the airflow circu-
lating around the gob. Velocity streamlines of the airflow
is presented in Figure 14 and shows that there is a leakage
of air into the gob area from the headgate. Based on the
geomechanical modeling and work done by researchers in
the past (Karacan, 2010, Karacan et al., 2007, Esterhuizen
and Karacan, 2005), NIOSH researchers are currently in
the process of developing CFD models. Given the multi-
ple components of this project, interaction between geo-
mechanical modeling and gas transport simulations will
be needed for validation of the results (Karacan, 2010,
Karacan et al., 2007, Esterhuizen and Karacan, 2005).
SUMMARY AND CONCLUSIONS
The work presented in this report is part of a broader
research effort to provide scientific evidence for improving
ventilation controls in longwall mines producing relatively
high methane emission rates. A review of pre-mining frack
well completion data was done at the study site for wells
on the two panels. It is expected that the observed uneven
quality of fracking completions shared by the study pan-
els is not a major influence on the differences in gas emis-
sions during mining. The duration of methane extraction
is expected to be a contributing factor to the underground
emission histories.
An analysis was done of gob gas venthole production
(GGV) on the higher gas emission panel by comparing
coal production to cumulative gas production histories.
The GGV design and placement strategies were effective
in extracting gas from these boreholes as they were under-
mined, and coal and gas production showed a strong cor-
respondence with each other.
Gas content values for the mined seam vary greatly on
the mine property on the two study panels, from 300 to
600 cu ft per ton. Significant contributions to the overall
mine emissions during longwall mining are produced from
the overburden and underlying strata. The Gas Emissions
Zone (GEZ) has been used to describe the gas producing
horizons in this study through simulation of ground move-
ment affecting the gas bearing strata.
FLAC3D analysis of the overburden showed good
agreement between predicted and measured subsidence
for panels associated with the high gas emissions location Figure 13. Velocity profile at the mid-section of the model
Figure 14. Velocity streamlines plot showing air movement in
the model domain
panel. This explains the asymmetric horizontal extend of
the GEZ from both sides of the panel and shorter extend
on the headgate side of the panel.
A three-dimensional model focusing only on the work-
ing panel is developed and presented in Figure 11. The
model geometry is created based on an active longwall coal
mine. The headgate and tailgate are 18-ft wide and 7-ft
high. Airflow quantity at the headgate side is 110.5 kcfm
and at the tailgate side is 35 kcfm. There is also a stop-
ping at the headgate side to control the airflow (Figure 11).
In this model, we assumed different zones of permeabil-
ity and porosity with the inner most circle (middle part of
the geometry) having low permeability and porosity. The
permeability and porosity values increase in the subsequent
zones moving towards the gate roads. The permeability and
porosity values for different gob zones used for this study
are shown in Figure 12.
The turbulent model used is Realizable κ-ε with a non-
Darcian flow model for porous media. Figure 13 shows the
velocity profile at the mid-section of the model. The flow
direction in the model shows that air flows from the head-
gate and tailgate side and moves towards the return side
with very low velocity through the gob area. Figure 14 pres-
ents airflow velocity streamlines, revealing air leakage into
the gob area from the headgate side, with the airflow circu-
lating around the gob. Velocity streamlines of the airflow
is presented in Figure 14 and shows that there is a leakage
of air into the gob area from the headgate. Based on the
geomechanical modeling and work done by researchers in
the past (Karacan, 2010, Karacan et al., 2007, Esterhuizen
and Karacan, 2005), NIOSH researchers are currently in
the process of developing CFD models. Given the multi-
ple components of this project, interaction between geo-
mechanical modeling and gas transport simulations will
be needed for validation of the results (Karacan, 2010,
Karacan et al., 2007, Esterhuizen and Karacan, 2005).
SUMMARY AND CONCLUSIONS
The work presented in this report is part of a broader
research effort to provide scientific evidence for improving
ventilation controls in longwall mines producing relatively
high methane emission rates. A review of pre-mining frack
well completion data was done at the study site for wells
on the two panels. It is expected that the observed uneven
quality of fracking completions shared by the study pan-
els is not a major influence on the differences in gas emis-
sions during mining. The duration of methane extraction
is expected to be a contributing factor to the underground
emission histories.
An analysis was done of gob gas venthole production
(GGV) on the higher gas emission panel by comparing
coal production to cumulative gas production histories.
The GGV design and placement strategies were effective
in extracting gas from these boreholes as they were under-
mined, and coal and gas production showed a strong cor-
respondence with each other.
Gas content values for the mined seam vary greatly on
the mine property on the two study panels, from 300 to
600 cu ft per ton. Significant contributions to the overall
mine emissions during longwall mining are produced from
the overburden and underlying strata. The Gas Emissions
Zone (GEZ) has been used to describe the gas producing
horizons in this study through simulation of ground move-
ment affecting the gas bearing strata.
FLAC3D analysis of the overburden showed good
agreement between predicted and measured subsidence
for panels associated with the high gas emissions location Figure 13. Velocity profile at the mid-section of the model
Figure 14. Velocity streamlines plot showing air movement in
the model domain