Retention and Permeability Properties of Damaged Porous Rocks

Abstract

The objective of this research work is to model the influence of deformation and damage on the permeability and retention properties of cracked porous media. This is achieved thanks to the introduction of microscale information into a macroscopic damage model. To this end, the Pore Size Distribution (PSD) of the material is coupled to the mechanical behaviour of the rock. Changes to this distribution due to deformation and damage are modelled and then used to capture induced changes to the retention and permeability properties of partially saturated materials.

Rock microstructure is characterized by the size distributions of natural pores and cracks, which are used to update intrinsic permeability with Hagen–Poiseuille flow equation and Darcy’s law. The void space occupied by water is computed by integrating the pore size distributions of natural pores and cracks up to the capillary pore radius (rsat). Laplace equation is used to relate rsat to the capillary pressure.

The paper explains how to update PSD parameters with the macroscopic variables (such as deformation and damage), and then how to update permeability and retention properties with the PSD parameters. Conventional triaxial compression tests are simulated under controlled capillary pressure and under controlled water content. The proposed model captures well the intrinsic permeability decrease associated to the elastic compression of the natural pores, followed by the permeability jump due to crack opening. The modeling framework can be adapted to any rock constitutive model, including thermo-hydro-chemo-mechanical couplings. Applications may be found in energy production, ore exploitation and waste management.