An Asperity-Deformation Model for Effectivity Pressure

The variations of the mechanical and transport properties of cracked and/or porous rocks under isotropic stress depend upon both the confining pressure (Pc) and the pore-fluid pressure (Pp). To a first approximation these rock properties vary with differential pressure, Pd = Pc - Pp; at least for low differential pressures. However, at higher differential pressures. the properties vary in a more complicated, way upon the two pressures. The concept of effective pressure, Pe, is used to denote this variation; that is, the rock properties are constant for constant effective pressure even though the confining and pore pressures change.