Phenomenological Correlation of Pressurization/Depressurization Hysteresis of Stress-Dependent Porosity and Permeability of Shale Reservoirs

Abstract

Abstract This paper presents a theoretically rigorous correlation of the effect of poroelasticity on pressurization/depressurization hysteresis of stress-dependent porosity and permeability of shale reservoirs. Naturally fractured shale formations are characterized as a matrix-fracture system. The constituents of this model are individually described by their own stress-dependent properties which are then coupled to determine the overall stress-dependent response of the shale system. This model accounts for the deformation, transformation, deterioration, and collapse of the shale pore structure during pressurization and depressurization processes and their effect on the porosity and permeability of shale reservoirs. The comprehensive model developed in this study is then validated by means of the experimental data gathered by testing of samples from various shale and sandstone reservoirs. The phenomenological parameters of the shale and sandstone samples are determined for best match of the experimental data. The data analyzed in this study indicates that pressurization/depressurization hysteresis has a significant effect on the stress-dependent porosity and permeability of shale reservoirs. The model developed in this paper can describe the stress-dependent porosity and permeability of shale rock more accurately than the commonly used empirical correlations.