2
NIOSH is conducting research with a cooperator
where the longwall panels being mined are classified as
subcritical, meaning the depth of cover is much greater
than the panel width. This configuration is very similar to
longwall mining in Europe that produced empirical models
used to describe the zone of emissions (Curl, 1978). One
such method frequently used was proposed by Flugge, and
another commonly used empirical model was developed by
Schultz (Curl, 1978, Qu et al., 2022).
Incorporating ground control simulations into this
research provides valuable insights into the specific strata
where deformation is concentrated and where gas release
occurs. Previous ground control studies have demon-
strated that deformation and fracture development in the
overburden, resulting from longwall mining, tend to be
concentrated in discrete zones characterized by a signifi-
cant contrast in bending strength (Su et al., 2019). The
researchers will assign a measured or extrapolated gas con-
tent to coal units in the zone of emissions. Transport rates
of the released gas volumes towards the working area of the
mine will be estimated using computational fluid dynam-
ics methods and the quantities of gas being emitted will be
predicted.
The current methane control system of the collaborat-
ing mine was evaluated as part of the research approach.
Performance-related parameters are being evaluated related
to gas extraction. Three levels of methane control are done
at this mine site which include pre-mining frack wells, pre-
mining in seam boreholes and gob gas ventholes which
extract gas during active mining on the panels.
An assessment of gas quantities in place is underway,
covering gas contents for the mined seam and adjacent coal
units within the gas emission zone. This includes a review
of borehole gas flows and may incorporate new experimen-
tal data on gas content and borehole gas flow rates. While a
ventilation analysis of the systems used is part of the broader
research project, it falls outside the scope of this paper.
Figure 1 shows the study site for this research. The cur-
rent focus of this effort is on two longwall panels. There are
significant differences between these two
panels in their panel design and ventilation configura-
tion. Panel 31 Right and adjacent panels in the section used
a 705-ft face, a four-entry system with yield and abutment
pillars positioned as shown. The multiple panel section was
open and ventilated until the section was completed when
it was sealed.
Beginning on panel 1 South the mine used a new panel
configuration. Figure 1 shows this panel configuration with
a 1,000-ft face, and a three-entry system. Each panel is
configured as a separate district and panels are successively
sealed after mining. Yield and abutment pillar positions are
shown with barrier pillars between panels.
Stratigraphy
The coal bed being mined at the study site is the Pocahontas
No. 3. It is of early Pennsylvanian age which began about
323 million years ago. At the study site, the coal rank is
primarily a low volatile bituminous coal. The primary use
of the extracted coal is in steel making. The Pocahontas No.
3 is classified as part of the Pocahontas Formation which
is overlain by the New River Formation that includes the
Pocahontas No. 7, No. 8, and No. 9 coal beds plus addi-
tional younger coal units in the sequence (Figure 2).
The Pocahontas and New River Formations contain
abundant siliclastic strata adjacent to the present coal seams
which can be structurally competent units. Shales and silt-
stones are also common. The Pocahontas No. 3 coal bed
is known to have a very close cleat spacing which makes
the coal unit mechanically weak over much of its thick-
ness. There is a middleman bench within the main seam
which includes bone and high mineral matter content. An
overlying P31 and an underlying P345 coal units are associ-
ated with the Pocahontas No. 3. These splits from the main
bench vary in their position to the main bench over the
mine property, reaching up to 20 ft to the P345.
FLAC 3D Analysis for Ground Movement
Considering the complex nature of the overburden geol-
ogy and longwall-mining-induced deformations/stresses,
NIOSH researchers have employed a calibrated numerical
modeling approach to investigate the potential gas emis-
sion zone within the overburden. The modelling approach
used in this study was originally developed for assessing
the influence of longwall-mining-induced gas well casing
Figure 1. Study site, mine location for cooperative research
project. Study panels 31 Right and 1 South are shown.
NIOSH is conducting research with a cooperator
where the longwall panels being mined are classified as
subcritical, meaning the depth of cover is much greater
than the panel width. This configuration is very similar to
longwall mining in Europe that produced empirical models
used to describe the zone of emissions (Curl, 1978). One
such method frequently used was proposed by Flugge, and
another commonly used empirical model was developed by
Schultz (Curl, 1978, Qu et al., 2022).
Incorporating ground control simulations into this
research provides valuable insights into the specific strata
where deformation is concentrated and where gas release
occurs. Previous ground control studies have demon-
strated that deformation and fracture development in the
overburden, resulting from longwall mining, tend to be
concentrated in discrete zones characterized by a signifi-
cant contrast in bending strength (Su et al., 2019). The
researchers will assign a measured or extrapolated gas con-
tent to coal units in the zone of emissions. Transport rates
of the released gas volumes towards the working area of the
mine will be estimated using computational fluid dynam-
ics methods and the quantities of gas being emitted will be
predicted.
The current methane control system of the collaborat-
ing mine was evaluated as part of the research approach.
Performance-related parameters are being evaluated related
to gas extraction. Three levels of methane control are done
at this mine site which include pre-mining frack wells, pre-
mining in seam boreholes and gob gas ventholes which
extract gas during active mining on the panels.
An assessment of gas quantities in place is underway,
covering gas contents for the mined seam and adjacent coal
units within the gas emission zone. This includes a review
of borehole gas flows and may incorporate new experimen-
tal data on gas content and borehole gas flow rates. While a
ventilation analysis of the systems used is part of the broader
research project, it falls outside the scope of this paper.
Figure 1 shows the study site for this research. The cur-
rent focus of this effort is on two longwall panels. There are
significant differences between these two
panels in their panel design and ventilation configura-
tion. Panel 31 Right and adjacent panels in the section used
a 705-ft face, a four-entry system with yield and abutment
pillars positioned as shown. The multiple panel section was
open and ventilated until the section was completed when
it was sealed.
Beginning on panel 1 South the mine used a new panel
configuration. Figure 1 shows this panel configuration with
a 1,000-ft face, and a three-entry system. Each panel is
configured as a separate district and panels are successively
sealed after mining. Yield and abutment pillar positions are
shown with barrier pillars between panels.
Stratigraphy
The coal bed being mined at the study site is the Pocahontas
No. 3. It is of early Pennsylvanian age which began about
323 million years ago. At the study site, the coal rank is
primarily a low volatile bituminous coal. The primary use
of the extracted coal is in steel making. The Pocahontas No.
3 is classified as part of the Pocahontas Formation which
is overlain by the New River Formation that includes the
Pocahontas No. 7, No. 8, and No. 9 coal beds plus addi-
tional younger coal units in the sequence (Figure 2).
The Pocahontas and New River Formations contain
abundant siliclastic strata adjacent to the present coal seams
which can be structurally competent units. Shales and silt-
stones are also common. The Pocahontas No. 3 coal bed
is known to have a very close cleat spacing which makes
the coal unit mechanically weak over much of its thick-
ness. There is a middleman bench within the main seam
which includes bone and high mineral matter content. An
overlying P31 and an underlying P345 coal units are associ-
ated with the Pocahontas No. 3. These splits from the main
bench vary in their position to the main bench over the
mine property, reaching up to 20 ft to the P345.
FLAC 3D Analysis for Ground Movement
Considering the complex nature of the overburden geol-
ogy and longwall-mining-induced deformations/stresses,
NIOSH researchers have employed a calibrated numerical
modeling approach to investigate the potential gas emis-
sion zone within the overburden. The modelling approach
used in this study was originally developed for assessing
the influence of longwall-mining-induced gas well casing
Figure 1. Study site, mine location for cooperative research
project. Study panels 31 Right and 1 South are shown.