When pore fluid is single liquid phase, the measured permeability is the

absolute permeability, which is an intrinsic property of the rock which depends upon the pore structure of the granite and the applied stress [26].

Levine, "Model study of the influence of matrix shrinkage on

absolute permeability of coal bed reservoirs," Geological Society, London, Special Publications, vol.

where k is the sample

absolute permeability, [nabla]pis the pore pressure gradient, g is the gravitational acceleration, and z is the vertical axis passing through the center of the sample and its direction is upward.

After the pressure and velocity fields are solved, Darcy's law (Equation 7) is used to evaluate the

absolute permeability for all three directions.

[A.sub.dent1] is the angular opening of a stator tooth, [[mu].sub.0] is the air

absolute permeability, [N.sub.sph] is the phase number of turns, [N.sub.dsp] is the number of main teeth of the stator, [L.sub.m] is the engine length, [H.sub.d] is the height of a main stator tooth, [L.sub.enc] is the slot width, [D.sub.st] is the bore diameter and [theta] is the rotor position.

Model study of the influence of matrix shrinkage on

absolute permeability of coal bed reservoirs, Geological Society, London, Special Publications, 109(1): 197-212.

During the production process, the effective stress of the coal reservoir and the shrinking of the coal matrix will influence the

absolute permeability of the reservoir (Durucan and Edwards, 1986; Laubach et al., 1998; Chen et al., 2010; Liu et al., 2010; Tao et al., 2012; Liu and Harpalani, 2013).

where K is the

absolute permeability, [10.sup.-3] [micro][m.sup.2]; [K.sub.rw] is the water relative permeability, f; [K.sub.ro] is the oil relative permeability, f; [[mu].sub.w] is the viscosity of water, mPa x s; [[mu].sub.o] is the viscosity of oil, mPa x s.

The laboratory observation of fluid flow behavior in Berea sandstone induced by low-frequency dynamic stress stimulation of Roberts (2005) indicates that during single-phase brine flow, stimulation increases the

absolute permeability of the rock by 10-20%.

Then the

absolute permeability will be calculated in the following term:

where K is the

absolute permeability tensor in the porous medium, g is the gravity acceleration, z is the depth, and [k.sub.r[alpha]], [[mu].sub.[alpha]], [p.sub.[alpha]], and [[rho].sub.[alpha]] are the relative permeability, viscosity, pressure, and density of each phase, respectively.

where k is the

absolute permeability, [k.sub.ro] is the relative permeability with respect to oil, g is the acceleration due to gravity, [[rho].sub.o] is the oil density, and [v.sub.o] is the oil kinematic viscosity.