Poroelastoplastic Borehole Modeling by Tangent Stiffness Matrix Method

Abstract

The stability of borehole is a major concern in petroleum and geotechnical engineering. Subsurface fossil fuel and thermal energy extraction, deep geologic carbon/energy storage, and waste disposal require sophisticated borehole modeling. In many instances in deep well drilling, rock exhibits a plastic behavior rather than a pure linear elastic behavior. Rock is a porous material consisting of a compressible solid matrix and number of compressible fluids occupying the pore space, so numerical analysis of complex borehole problems based on nonlinear poromechanics is indispensable. In computer methods for nonlinear poromechanics, it is expected that the tangent stiffness method is more efficient than the constant stiffness method because the number of iterations can be reduced; however, the speculation has not been corroborated, especially when applied in borehole engineering. To investigate the computational efficiency of the two methods, fully coupled poroelastoplastic borehole modeling was implemented by both the tangent stiffness and initial (or constant) stiffness methods. Results showed that the two calculation methods are consistent, and the computational performance of the tangent stiffness method is superior to the initial stiffness method based on borehole modeling, reflected in the significantly reduced number of iterations and total running time required.