4
sampling protocol and test duration are designed to col-
lect samples throughout each test scenario until no gas is
detected in any of the samples.
Ventsim Model for a Typical Longwall Mine with Gob
Grids
Ventilation network models have become an indispensable
tool in mine operations, aiding in not only the planning
and management of ventilation systems but also in simulat-
ing gas migration, assessing potential hazards, and formu-
lating responses to emergencies such as fires or gas leaks.
VentSim, a mine ventilation simulation software from
Howden, is used in this study to conduct the ventilation
and gas simulation.
A well-established longwall mine ventilation network
from a partner coal mine located in the Pittsburgh coal
seam is selected for this case study. Figure 3 displays the
layout and ventilation of the studied longwall panels, which
includes two mined-out panels and one active longwall
face. A bleeder ventilation is applied to the longwall face,
which is intended to draw explosive methane accumula-
tions directly towards a dedicated bleeder fan (located in
the upright corner in Figure 3), and a gas well pad, includ-
ing ten gas wells, is located in the coal pillar between the
active longwall panel and the adjacent gob with the face
just mine by.
In typical ventilation simulations for mine design and
planning using network-based mine ventilation software,
the gob area is often excluded from consideration because
its airflow typically impacts only localized regions with-
out significantly influencing the overall mine ventilation
system. However, in this study, the gob area plays a critical
role in gas migration and ventilation dynamics, making it
impossible to overlook. To accurately simulate the airflow
and gas distribution in and around the gob, we introduced
gob grids to the gob areas of the active and adjacent long-
wall panels. The gob grids were created using a grid with
branches of 33 ft by 33 ft (10 m by 10 m). The perme-
ability of the gob is simulated by assigning varying levels
of resistance: lower resistance in the outer layers, indicating
higher permeability, and the highest resistance at the center,
reflecting lower permeability.
In this study case, the gas wells are in the abutment
coal pillar at the tailgate side of the active longwall panel
with the longwall just mined by (as shown in Figure 4). In
the worst-case scenario, if longwall-induced stress deforms
the gas well casing and causes breaches, the leaked gas will
enter the mine and be carried into the ventilation system.
In the VentSim model, the breached gas was added into
the mine with ten short branches connecting the surface.
The branches were set as fixed flow with 100% methane
introduced into the mine surrounding the gas wells. The
combined flow from the 10 short branches represents the
total gas inflow from the breached well.
RESULTS FROM LIAM PHYSICAL MODEL
Samples for GC analysis were collected from critical loca-
tions, including the longwall face, tailgate entries, tailgate
corner gob, tailgate mid gob, BEP, and bleeder entries.
These locations were chosen because they are where power
is energized at the longwall face, at approved monitoring
points in the ventilation plan, and areas where miners are
Figure 3. Layout of longwall face, gobs, and gas wells
sampling protocol and test duration are designed to col-
lect samples throughout each test scenario until no gas is
detected in any of the samples.
Ventsim Model for a Typical Longwall Mine with Gob
Grids
Ventilation network models have become an indispensable
tool in mine operations, aiding in not only the planning
and management of ventilation systems but also in simulat-
ing gas migration, assessing potential hazards, and formu-
lating responses to emergencies such as fires or gas leaks.
VentSim, a mine ventilation simulation software from
Howden, is used in this study to conduct the ventilation
and gas simulation.
A well-established longwall mine ventilation network
from a partner coal mine located in the Pittsburgh coal
seam is selected for this case study. Figure 3 displays the
layout and ventilation of the studied longwall panels, which
includes two mined-out panels and one active longwall
face. A bleeder ventilation is applied to the longwall face,
which is intended to draw explosive methane accumula-
tions directly towards a dedicated bleeder fan (located in
the upright corner in Figure 3), and a gas well pad, includ-
ing ten gas wells, is located in the coal pillar between the
active longwall panel and the adjacent gob with the face
just mine by.
In typical ventilation simulations for mine design and
planning using network-based mine ventilation software,
the gob area is often excluded from consideration because
its airflow typically impacts only localized regions with-
out significantly influencing the overall mine ventilation
system. However, in this study, the gob area plays a critical
role in gas migration and ventilation dynamics, making it
impossible to overlook. To accurately simulate the airflow
and gas distribution in and around the gob, we introduced
gob grids to the gob areas of the active and adjacent long-
wall panels. The gob grids were created using a grid with
branches of 33 ft by 33 ft (10 m by 10 m). The perme-
ability of the gob is simulated by assigning varying levels
of resistance: lower resistance in the outer layers, indicating
higher permeability, and the highest resistance at the center,
reflecting lower permeability.
In this study case, the gas wells are in the abutment
coal pillar at the tailgate side of the active longwall panel
with the longwall just mined by (as shown in Figure 4). In
the worst-case scenario, if longwall-induced stress deforms
the gas well casing and causes breaches, the leaked gas will
enter the mine and be carried into the ventilation system.
In the VentSim model, the breached gas was added into
the mine with ten short branches connecting the surface.
The branches were set as fixed flow with 100% methane
introduced into the mine surrounding the gas wells. The
combined flow from the 10 short branches represents the
total gas inflow from the breached well.
RESULTS FROM LIAM PHYSICAL MODEL
Samples for GC analysis were collected from critical loca-
tions, including the longwall face, tailgate entries, tailgate
corner gob, tailgate mid gob, BEP, and bleeder entries.
These locations were chosen because they are where power
is energized at the longwall face, at approved monitoring
points in the ventilation plan, and areas where miners are
Figure 3. Layout of longwall face, gobs, and gas wells