Flow‐Deformation Response of Dual‐Porosity Media

Abstract

A constitutive model is presented to define the linear poroelastic response of fissured media to determine the influence of dual porosity effects. A stress‐strain relationship and two equations representing conservation of mass in the porous and fractured material are required. The behavior is defined in terms of the hydraulic and mechanical parameters for the intact porous matrix and the surrounding fracture system, allowing generated fluid pressure magnitudes and equilibration rates to be determined. Under undrained hydrostatic loading, the pore pressure‐generation coefficients B, may exceed unity in either of the porous media or the fracture, representing a form of piston effect. Pressures generated within the fracture system equilibrate with time by reverse flow into the porous blocks. The equilibration time appears negligible for permeable sandstones, but it is significant for low‐permeability geologic media. The constitutive model is represented in finite element format to allow solution for general boundary conditions where the influence of dual‐porosity behavior may be examined in a global context.