Chemoporoelastic model for transversely isotropic shale

This paper presents a linear chemo-poroelastic model for analyzing borehole stability in transversely isotropic shales. The theory couples mechanical, hydraulic and chemical processes in fluid-saturated porous media. In particular, the model couples stresses and pore pressure to hydraulic conduction, chemical osmosis, and solute diffusion. Field equations are obtained by requiring the rock constitutive and transport models to satisfy the momentum, fluid mass, and solute mass balance equations. The field equations are solved analytically for the problem of vertical and inclined boreholes in shales to yield the distributions of the solute mass fraction, pore pressure, and the stresses around the borehole. The analytical solution is used to demonstrate the impact of the degree of anisotropy, chemical osmosis, solute diffusion and reflection, swelling, and chemical properties of shales on the pore pressure and the stress fields around a borehole drilled in anisotropic shale.