4
2012, Zhang et al., 2023, Tanguturi et al., 2017). In this
study, researchers are using COMSOL Multiphysics for
CFD modeling to model airflow and gob gas distribution
for the collaborating longwall mine.
Gas extraction and gas in place results
The evaluation of methane control systems at the site
included a review of pre-mining frack wells in the Pocahontas
3 coal bed. Figure 4 shows on panel 31 Right and the frack
wells completed over the panel. For the six wells completed
over the panel, four showed less optimal completion data.
The data suggest any vertical fractures formed would be of
limited extent, reducing the surface area and effectiveness
of the well in extracting gas. This panel experienced high
rates of gas emissions shortly after the beginning of mining
and sub optimal frack well performance was one potential
contributor to these circumstances. potential contributing
factor.
A review of frack well data was conducted for bore-
holes drilled over the 1 South panel for completion quality.
Figure 5 shows the panel is in two halves with the beginning
of the longwall on the right side and the completion end of
the panel on the left side. Eight boreholes were positioned
over the longwall panel or gateroads. The evaluation of the
frack wells for completions for panel 1 South produced
three tiers of success at the Pocahontas No. 3 horizon. For
this group of wells, three boreholes produced good qual-
ity fractures. For the remaining five wells, three resulted in
sub optimal completions and two produced mixed qual-
ity results with expected horizontal and vertical fractures of
limited extent.
Another phase of the methane control used by the
operator at the mine site is the gob gas ventholes (GGVs).
The boreholes are configured to extract gas that would oth-
erwise enter the ventilation system from the longwall gob.
These boreholes utilize an exhauster on the surface near the
collar which is powered by electric motors. This process
continues during the mining of the active panel and poten-
tially after the panel is completed dependent on the panel
configuration. Gas produced from the GGVs at the study
site is sold commercially and piped to grids for distribution
following processing.
Figure 6 shows coal quantities being mined and the gas
flows being extracted from GGVs while panel 31 right was
advancing during a one-month period. During this month,
Figure 3. The cross-section view of the model with topography and geology
Table 1. Overburden strata rock properties used in the model
Rock Type Elastic Modulus (psi) v Cohesion (psi) Friction Angle Tensile Strength (psi)
Coal 250,000 0.3 270 28 41
Claystone 630,000 0.3 187 28 49
Limey shale 1,050,000 0.25 984 35 377
Shale 840,000 0.25 850 35 326
Sandy shale 840,000 0.25 850 35 326
Sandstone 840,000 0.25 1300 35 500
Shaley limestone 1,260,000 0.22 1050 38 431
Shaley sandstone 1,050,000 0.22 850 38 348
Silty shale 840,000 0.25 850 32 306
2012, Zhang et al., 2023, Tanguturi et al., 2017). In this
study, researchers are using COMSOL Multiphysics for
CFD modeling to model airflow and gob gas distribution
for the collaborating longwall mine.
Gas extraction and gas in place results
The evaluation of methane control systems at the site
included a review of pre-mining frack wells in the Pocahontas
3 coal bed. Figure 4 shows on panel 31 Right and the frack
wells completed over the panel. For the six wells completed
over the panel, four showed less optimal completion data.
The data suggest any vertical fractures formed would be of
limited extent, reducing the surface area and effectiveness
of the well in extracting gas. This panel experienced high
rates of gas emissions shortly after the beginning of mining
and sub optimal frack well performance was one potential
contributor to these circumstances. potential contributing
factor.
A review of frack well data was conducted for bore-
holes drilled over the 1 South panel for completion quality.
Figure 5 shows the panel is in two halves with the beginning
of the longwall on the right side and the completion end of
the panel on the left side. Eight boreholes were positioned
over the longwall panel or gateroads. The evaluation of the
frack wells for completions for panel 1 South produced
three tiers of success at the Pocahontas No. 3 horizon. For
this group of wells, three boreholes produced good qual-
ity fractures. For the remaining five wells, three resulted in
sub optimal completions and two produced mixed qual-
ity results with expected horizontal and vertical fractures of
limited extent.
Another phase of the methane control used by the
operator at the mine site is the gob gas ventholes (GGVs).
The boreholes are configured to extract gas that would oth-
erwise enter the ventilation system from the longwall gob.
These boreholes utilize an exhauster on the surface near the
collar which is powered by electric motors. This process
continues during the mining of the active panel and poten-
tially after the panel is completed dependent on the panel
configuration. Gas produced from the GGVs at the study
site is sold commercially and piped to grids for distribution
following processing.
Figure 6 shows coal quantities being mined and the gas
flows being extracted from GGVs while panel 31 right was
advancing during a one-month period. During this month,
Figure 3. The cross-section view of the model with topography and geology
Table 1. Overburden strata rock properties used in the model
Rock Type Elastic Modulus (psi) v Cohesion (psi) Friction Angle Tensile Strength (psi)
Coal 250,000 0.3 270 28 41
Claystone 630,000 0.3 187 28 49
Limey shale 1,050,000 0.25 984 35 377
Shale 840,000 0.25 850 35 326
Sandy shale 840,000 0.25 850 35 326
Sandstone 840,000 0.25 1300 35 500
Shaley limestone 1,260,000 0.22 1050 38 431
Shaley sandstone 1,050,000 0.22 850 38 348
Silty shale 840,000 0.25 850 32 306