2
and after the first panel mined by the measurement site.
The previously developed methodologies were used, and
the mining was modeled using a geomechanical model
constructed in 3DEC software (Itasca, 2016). The model-
ing results show the permeability calculated in the model
agrees with the field measurements after the first panel
mine-by. The measurements will continue until after the
second panel mines by the test boreholes in Nov 2023. The
modeling results reported here will be compared with the
field measurements in a future paper.
DESCRIPTION OF MINE SITE
A longwall mine under 352-m cover in southwestern
Pennsylvania in the Pittsburgh coal bed is selected for this
study. The Marcellus shale and Pittsburgh coal seam are
1,200–2,100 m apart in the strata but share much of the
same areas within Pennsylvania and West Virginia. The
selected mine site is located above the Marcellus shale so
that to enable shale gas production, gas wells are positioned
in longwall pillars used to protect the casing from subsur-
face deformation. The longwall panel is 456-m wide with a
mining height of 2.13 m within a three-entry gateroad sys-
tem (Figure 1). Overburden geology to the mining depth of
352 m was interpreted by correlating a test site gamma log
and a nearby core hole (Van Dyke et al., 2022).
The rock types in the overburden are shale, sandstone,
sandy shale, limestone, coal, and shaley limestone with
the field-scale geomechanical properties listed in Table 1
(P. Zhang et al., 2020).
The slug permeability tests are conducted in two bore-
holes drilled above the abutment pillar (43.7 m width)
between the second and third panels in the district. The
perforated interval of the first borehole targeted the
Uniontown horizon at the depth of 290 m. The second
borehole was perforated at the depth of 327 m, targeting
the Sewickley horizon. Figure 2 shows the overall overbur-
den geology of the area.
FIELD PERMEABILITY MEASUREMENTS
Two monitoring boreholes were drilled in the overburden
to conduct slug permeability tests as the first panel and sec-
ond panels mine by the test site. Falling-head slug tests were
conducted by the research team at regular intervals dur-
ing the first panel mine-by. The second panel is currently
approaching the site, so the data collection is ongoing. The
predicted values by the model in this paper will be com-
pared with the measurements once the second panel mines
by the test site by November 2023.
Water head pressures were measured at the Uniontown
and Sewickley horizons (Figure 2). Permeability values
were calculated based on the falling water slug test method
detailed in previous works (Harris et al., 2023). An INW
PT2X (SeametricsTM) piezometer tracked the long-term
equilibrium water height and water slug height.
The data was recorded using the Aqua4TM software
package. For the falling-head slug tests, a water slug height
of up to 3 m was added to the boreholes. A previous study
conducted under shallow cover (127 m to the Sewickley
horizon and 76 m to the Uniontown horizon) (Watkins
et al., 2021) recorded the fall of water head at 5, 30, or
60-s intervals, depending on the expected drainage rate of
the water. Compared to the site described by Watkins et
al. (2021), the new site was at a greater overburden depth.
Consequently, fracture permeabilities were lower, produc-
ing a slower rate of water loss during testing. Therefore,
Table 1. Geomechanical properties applied to the model for
each lithology
Rock Type E ν C φ° T
Coal 2.1 0.3 1.9 28 0.3
Shale 11.6 0.25 11.7 35 4.5
Sandy
Shale
11.6 0.25 11.7 35 4.5
Sandstone 11.6 0.22 17.9 35 6.9
Limestone 17.4 0.25 15.9 35 6.1
E: Elastic modulus (GPa), ν: Poisson ratio, C: Cohesion (MPa),
φ: internal friction angle, T: Tension (MPa)
Figure 1. Surface topographical and top-of-coal contours
and location of the boreholes for permeability measurements
and after the first panel mined by the measurement site.
The previously developed methodologies were used, and
the mining was modeled using a geomechanical model
constructed in 3DEC software (Itasca, 2016). The model-
ing results show the permeability calculated in the model
agrees with the field measurements after the first panel
mine-by. The measurements will continue until after the
second panel mines by the test boreholes in Nov 2023. The
modeling results reported here will be compared with the
field measurements in a future paper.
DESCRIPTION OF MINE SITE
A longwall mine under 352-m cover in southwestern
Pennsylvania in the Pittsburgh coal bed is selected for this
study. The Marcellus shale and Pittsburgh coal seam are
1,200–2,100 m apart in the strata but share much of the
same areas within Pennsylvania and West Virginia. The
selected mine site is located above the Marcellus shale so
that to enable shale gas production, gas wells are positioned
in longwall pillars used to protect the casing from subsur-
face deformation. The longwall panel is 456-m wide with a
mining height of 2.13 m within a three-entry gateroad sys-
tem (Figure 1). Overburden geology to the mining depth of
352 m was interpreted by correlating a test site gamma log
and a nearby core hole (Van Dyke et al., 2022).
The rock types in the overburden are shale, sandstone,
sandy shale, limestone, coal, and shaley limestone with
the field-scale geomechanical properties listed in Table 1
(P. Zhang et al., 2020).
The slug permeability tests are conducted in two bore-
holes drilled above the abutment pillar (43.7 m width)
between the second and third panels in the district. The
perforated interval of the first borehole targeted the
Uniontown horizon at the depth of 290 m. The second
borehole was perforated at the depth of 327 m, targeting
the Sewickley horizon. Figure 2 shows the overall overbur-
den geology of the area.
FIELD PERMEABILITY MEASUREMENTS
Two monitoring boreholes were drilled in the overburden
to conduct slug permeability tests as the first panel and sec-
ond panels mine by the test site. Falling-head slug tests were
conducted by the research team at regular intervals dur-
ing the first panel mine-by. The second panel is currently
approaching the site, so the data collection is ongoing. The
predicted values by the model in this paper will be com-
pared with the measurements once the second panel mines
by the test site by November 2023.
Water head pressures were measured at the Uniontown
and Sewickley horizons (Figure 2). Permeability values
were calculated based on the falling water slug test method
detailed in previous works (Harris et al., 2023). An INW
PT2X (SeametricsTM) piezometer tracked the long-term
equilibrium water height and water slug height.
The data was recorded using the Aqua4TM software
package. For the falling-head slug tests, a water slug height
of up to 3 m was added to the boreholes. A previous study
conducted under shallow cover (127 m to the Sewickley
horizon and 76 m to the Uniontown horizon) (Watkins
et al., 2021) recorded the fall of water head at 5, 30, or
60-s intervals, depending on the expected drainage rate of
the water. Compared to the site described by Watkins et
al. (2021), the new site was at a greater overburden depth.
Consequently, fracture permeabilities were lower, produc-
ing a slower rate of water loss during testing. Therefore,
Table 1. Geomechanical properties applied to the model for
each lithology
Rock Type E ν C φ° T
Coal 2.1 0.3 1.9 28 0.3
Shale 11.6 0.25 11.7 35 4.5
Sandy
Shale
11.6 0.25 11.7 35 4.5
Sandstone 11.6 0.22 17.9 35 6.9
Limestone 17.4 0.25 15.9 35 6.1
E: Elastic modulus (GPa), ν: Poisson ratio, C: Cohesion (MPa),
φ: internal friction angle, T: Tension (MPa)
Figure 1. Surface topographical and top-of-coal contours
and location of the boreholes for permeability measurements