Anisotropic Diffusive-Advective Porochemoelasticity Modeling for Inclined Boreholes

Abstract

In chemically active rocks, pore pressure and stress state are not the only parameters that are governed by hydromechanical processes. Chemical osmosis is also responsible for changes in the effective stress caused by the presence of chemical potential between the reservoir and the borehole filled with drilling fluid. Subsurface rocks such as shales are highly anisotropic, and assuming an isotropic model will fail to provide an accurate depiction of the in situ stress state. In this work, governing equations for a fully coupled anisotropic nonlinear porochemoelasticity are developed. A numerical model using the FEM is constructed to simulate the drilling of an inclined borehole problem in an anisotropic and chemically active medium. The model accounts for solute transport contributed by diffusion and advection. Several sensitivity analyses are conducted to highlight different features of the chemohydromechanical model. Solute concentration, membrane efficiency, solute-diffusion coefficient, and advection are investigated. Results of this study show that the rock elastic anisotropy significantly enhances the stresses induced by the borehole excavation. Moreover, the presence of chemical potential has been shown to have a large bearing on the near wellbore stress state and pore pressure. It was demonstrated that this effect cannot be generalized and should be studied carefully on a case-by-case basis. Last, the model is used to analyze borehole stability for inclined boreholes under chemical, hydraulic, and mechanical loading.