3
the data during the longwall mine-by was recorded with
a 15-minute interval, and the falling rate was later deter-
mined from the downloaded data. Later, after the longwall
panel passed the abutment pillar and the permeability val-
ues returned to pre-mine-by values, the data was collected
every 60 minutes.
The initial H0 and current Hw water slug heights were
recorded by the piezometer and then converted to Hw/
H0 values. Hw/H0 values were plotted on a semi-log graph
to determine the T37 time which is the time (minutes) in
which the water slug drained to 37% of the initial water
slug height. Equation 1 can be used to obtain the absolute
permeability of the screened section from T37 (Istok, 1992).
ln`
k L g T
r R
L
120
37
2
t
n
=
j (1)
where r is the radius of well casing, L is the length of the
well screen, R is the radius of the well screen (the same
as well casing in this case), r is density of the fluid, µ is
the dynamic viscosity of the fluid in kg/ms, and g is the
gravitational acceleration. Multiple assumptions are made
when calculating permeabilities from slug test head drop
or from 3DEC aperture calculations. For the slug test, the
permeability is obtained from Hvorsley method with the
assumptions that flow in the ground is radially outward and
follows Darcy’s law. The aquifer is assumed significantly
larger than the borehole diameter with an incompressible,
homogeneous, and isotropic matrix that is vertically con-
fined by aquicludes.
Figure 3 displays the permeability measurements
before, during, and directly after the first panel mine-by.
Figure 2. Generalized stratigraphic profile for the monitoring boreholes (not to scale) (Harris et al., 2023)
Figure 3. Measured permeability values for the Uniontown
(VEP-U) and the Sewickley (VEP-S) horizons under deep
cover are shown during the mine-by of the first longwall panel
the data during the longwall mine-by was recorded with
a 15-minute interval, and the falling rate was later deter-
mined from the downloaded data. Later, after the longwall
panel passed the abutment pillar and the permeability val-
ues returned to pre-mine-by values, the data was collected
every 60 minutes.
The initial H0 and current Hw water slug heights were
recorded by the piezometer and then converted to Hw/
H0 values. Hw/H0 values were plotted on a semi-log graph
to determine the T37 time which is the time (minutes) in
which the water slug drained to 37% of the initial water
slug height. Equation 1 can be used to obtain the absolute
permeability of the screened section from T37 (Istok, 1992).
ln`
k L g T
r R
L
120
37
2
t
n
=
j (1)
where r is the radius of well casing, L is the length of the
well screen, R is the radius of the well screen (the same
as well casing in this case), r is density of the fluid, µ is
the dynamic viscosity of the fluid in kg/ms, and g is the
gravitational acceleration. Multiple assumptions are made
when calculating permeabilities from slug test head drop
or from 3DEC aperture calculations. For the slug test, the
permeability is obtained from Hvorsley method with the
assumptions that flow in the ground is radially outward and
follows Darcy’s law. The aquifer is assumed significantly
larger than the borehole diameter with an incompressible,
homogeneous, and isotropic matrix that is vertically con-
fined by aquicludes.
Figure 3 displays the permeability measurements
before, during, and directly after the first panel mine-by.
Figure 2. Generalized stratigraphic profile for the monitoring boreholes (not to scale) (Harris et al., 2023)
Figure 3. Measured permeability values for the Uniontown
(VEP-U) and the Sewickley (VEP-S) horizons under deep
cover are shown during the mine-by of the first longwall panel