Anisotropic poromechanics of the wellbore coupled with thermal and chemical gradients.

Abstract

A generalized anisotropic porothermoelastic formulation incorporating fully coupled thermo-hydro-mechanical response of saturated porous media is developed. Governing equations are tailored for transversely isotropic media and the solution for the inclined borehole problem is developed. The effect of material anisotropy on the stress, pore pressure and borehole stability is analyzed.

A comprehensive and systematic study of anisotropic poromechanics is undertaken with application to the problem of an inclined borehole in a saturated porous rock formation. The development is based on the theoretical approach in anisotropic poromechanics that accounts for the coupling characteristics between the fluid saturated porous rock and rock solid structure with emphasis on the thermal, chemical, hydraulic and mechanical coupled processes. The borehole is assumed to be deep, as in an oil recovery process, and inclined to the insitu three-dimensional state of stress. Analytical solutions for stress and pore pressure distributions in the vicinity of the borehole have been developed under the framework of the poromechanics models. It is envisaged that the theoretical formulations and solutions would aid in the understanding of complex coupled phenomena known to exist in fluid saturated porous media when subjected to stress and pressure perturbations. Further, these solutions developed would provide an accurate assessment of borehole stability that is critical to a successful drilling operation.

A generalized anisotropic porochemothermoelastic formulation is presented which is an extension of the porochemoelastic model and accounts for thermal effects in chemically active poroelastic media. Governing equations are specialized for transversely isotropic and isotropic cases and corresponding inclined borehole solutions are developed. As in the porochemoelastic case, the effect of chemical potential on borehole stability is studied.

Chemical effects are incorporated into the anisotropic poroelastic formulation and the resulting model is termed porochemoelastic. The model accounts for fully-coupled hydraulic, chemical and mechanical processes and, is applicable to chemically active anisotropic formations saturated with a pore fluid comprising of two species. Inclined borehole solutions applicable to transversely isotropic and isotropic media are developed. The effect of chemical potential of the fluid in the wellbore on its stability is also analyzed.

A generalized solution strategy for the inclined borehole problem, where the problem is sub-divided into simpler problems, is presented. The linearity of stress-strain relations assumed, allows a superposition of the solutions of the sub-problems.