1
24-093
Validation of Modeled Rockmass Permeability Against Field
Measurements in a Longwall Mine
Zoheir Khademian
CDC NIOSH, Pittsburgh Mining Research Division,
Pittsburgh, PA
Marcia M. Harris
CDC NIOSH, Pittsburgh Mining Research Division,
Pittsburgh, PA
Steven J. Schatzel
CDC NIOSH, Pittsburgh Mining Research Division,
Pittsburgh, PA
Kayode M. Ajayi
CDC NIOSH, Pittsburgh Mining Research Division,
Pittsburgh, PA
ABSTRACT
Predicting rockmass permeability is critical in evaluating
various engineering designs, including estimating gas inflow
to a longwall mine in the case of a hypothetical breach in
the gas well. This study conducted field permeability mea-
surements to validate a geomechanical model capable of
predicting rockmass permeability during longwall min-
ing. A series of slug permeability tests were conducted in
an active mine in Pennsylvania. A model of the mine was
constructed in 3DEC numerical modeling software, and
permeabilities were calculated. The modeling results agreed
well with the pre- and post-mining permeability measure-
ments, showing the applicability of this tool to evaluate gas
well stability near mine workings.
INTRODUCTION
The intrinsic permeability of a rock or soil is a measure
of the rock or soil’s ability to transmit fluid as the fluid
moves through it (Schwartz and Zhang, 2003). Evaluation
of rockmass permeability is essential in various rock engi-
neering designs such as constructing dams (Thawatchai,
Bunpoat, &Warakorn, 2021), tunnels (K. Zhang et al.,
2021), geothermal reservoirs (Tomac &Sauter, 2018), oil
and gas reservoirs (Gehne &Benson, 2019), and waste
containment structures (Sasaki &Rutqvist, 2021). Another
application is the evaluation of permeabilities enhanced
by mining where shale gas reservoirs underlie active or
future longwall mining operations (PADEP, 2018). In the
Northern Appalachian Basin in the United States, some of
the production wells in shale gas reservoirs intersect with
minable coal seams and thus require specific design consid-
erations to allow both operations to coexist. In most cases,
the gas wells are positioned in the mine abutment pillars for
protection against mining-induced ground deformations.
However, one of the safety concerns is excessive ground
movement that might damage gas well production cas-
ing, leading to the leakage of explosive gas into the mine
working. Under such scenario, mining-induced rockmass
permeabilities and relevant changes induced by mining
becomes of main importance.
In previous work (Khademian, et al. 2021)(Khademian,
et al. 2021), a geomechanical modeling methodology was
developed based on the Discrete Fracture Network (DFN)
technique to calculate the permeability evolution during
mining of a shallow, 145-m-cover mine in the Pittsburgh
coal seam. In-situ measurements were used to constrain
and calibrate the range of DFN parameters in the model.
The methodology was then validated against field perme-
ability measurements in a deeper mine, at a 341-m-cover
site in the Pittsburgh seam (Khademian et al., 2022). In
this paper, another case is studied in a 352-m deep mine,
and field permeability measurements are conducted before
24-093
Validation of Modeled Rockmass Permeability Against Field
Measurements in a Longwall Mine
Zoheir Khademian
CDC NIOSH, Pittsburgh Mining Research Division,
Pittsburgh, PA
Marcia M. Harris
CDC NIOSH, Pittsburgh Mining Research Division,
Pittsburgh, PA
Steven J. Schatzel
CDC NIOSH, Pittsburgh Mining Research Division,
Pittsburgh, PA
Kayode M. Ajayi
CDC NIOSH, Pittsburgh Mining Research Division,
Pittsburgh, PA
ABSTRACT
Predicting rockmass permeability is critical in evaluating
various engineering designs, including estimating gas inflow
to a longwall mine in the case of a hypothetical breach in
the gas well. This study conducted field permeability mea-
surements to validate a geomechanical model capable of
predicting rockmass permeability during longwall min-
ing. A series of slug permeability tests were conducted in
an active mine in Pennsylvania. A model of the mine was
constructed in 3DEC numerical modeling software, and
permeabilities were calculated. The modeling results agreed
well with the pre- and post-mining permeability measure-
ments, showing the applicability of this tool to evaluate gas
well stability near mine workings.
INTRODUCTION
The intrinsic permeability of a rock or soil is a measure
of the rock or soil’s ability to transmit fluid as the fluid
moves through it (Schwartz and Zhang, 2003). Evaluation
of rockmass permeability is essential in various rock engi-
neering designs such as constructing dams (Thawatchai,
Bunpoat, &Warakorn, 2021), tunnels (K. Zhang et al.,
2021), geothermal reservoirs (Tomac &Sauter, 2018), oil
and gas reservoirs (Gehne &Benson, 2019), and waste
containment structures (Sasaki &Rutqvist, 2021). Another
application is the evaluation of permeabilities enhanced
by mining where shale gas reservoirs underlie active or
future longwall mining operations (PADEP, 2018). In the
Northern Appalachian Basin in the United States, some of
the production wells in shale gas reservoirs intersect with
minable coal seams and thus require specific design consid-
erations to allow both operations to coexist. In most cases,
the gas wells are positioned in the mine abutment pillars for
protection against mining-induced ground deformations.
However, one of the safety concerns is excessive ground
movement that might damage gas well production cas-
ing, leading to the leakage of explosive gas into the mine
working. Under such scenario, mining-induced rockmass
permeabilities and relevant changes induced by mining
becomes of main importance.
In previous work (Khademian, et al. 2021)(Khademian,
et al. 2021), a geomechanical modeling methodology was
developed based on the Discrete Fracture Network (DFN)
technique to calculate the permeability evolution during
mining of a shallow, 145-m-cover mine in the Pittsburgh
coal seam. In-situ measurements were used to constrain
and calibrate the range of DFN parameters in the model.
The methodology was then validated against field perme-
ability measurements in a deeper mine, at a 341-m-cover
site in the Pittsburgh seam (Khademian et al., 2022). In
this paper, another case is studied in a 352-m deep mine,
and field permeability measurements are conducted before