Numerical experiments on oil sands shear dilation and permeability enhancement in a multiphase thermoporoelastoplasticity framework

Abstract

Oil sands exhibit substantial shear dilation during thermal oil recovery processes. Shear dilation is the result of increasing effective horizontal stresses induced by inhomogeneous thermal expansion; shear dilation is irreversible and in quartzose sands leads to porosity, permeability and compressibility increases. Hence, shear dilation has been considered a major and positive geomechanics factor in thermal enhanced oil recovery. In this paper we extend a fully-coupled thermal reservoir model in the multiphase thermoporoelastic framework to a multiphase thermoporoelastoplastic framework, in order to account for shear dilation. In a series of numerical experiments we explore how the stiffness and Poisson's ratio of overburden rocks and the initial stress state in the reservoir affect the reservoir stress path, thus directing changes in the magnitude of shear dilation, porosity change and permeability enhancement. Numerical results indicate that a stiffer overburden rock leads to a smaller magnitude of shear dilation and permeability enhancement; a smaller Poisson's ratio of the overburden rock has only a slightly positive contribution; a larger initial lateral stress ratio corresponds to a larger magnitude of shear dilation and permeability enhancement; and a larger dilation angle of oil sands leads to a larger magnitude of shear dilation and permeability enhancement.