ABSTRACT
We have developed a massively parallel reservoir simulator for modeling thermal-hydrologicmechanical processes associated with CO2 sequestration in brine aquifers. Our simulator formulation is based on the TOUGH2-MP one, a massively parallel version of TOUGH2. TOUGH2 is a well known numerical simulator of multi-component, multiphase fluid and heat flow in porous and fractured media. In the TOUGH2 formulation, fluid advection is described with a multiphase extension of Darcy’s law, heat flow occurs by conduction and convection and phases are in local equilibrium. Physical properties are calculated using modules such as ECO2N, which is designed for CO2 sequestration in saline aquifers. TOUGH2 solves mass and energy balances over the simulation domain using the integral finite difference method on an unstructured grid. We fully couple geomechanics to reservoir flow with a conservation equation relating mean
stress, pore pressure and temperature, derived from the fundamental equations describing deformation of thermo-multi-poroelastic media, and incorporate this equation alongside the mass and energy conservation equations of TOUGH2-MP. In addition, rock properties, namely permeability and porosity, are functions of pore pressure and effective stress, which are obtained from poroelasticity theories and correlations from the literature. The simulator formulation and numerical implementation are verified using analytical solutions
and example problems from the literature. We simulated a double porosity one-dimensional consolidation problem and the Mandel-Cryer effect, both of which have analytical solutions. We then used a problem from the literature as the basis for a comparison of our simulator to a conventional reservoir simulator, highlighting the differences between a formulation that includes geomechanical effects and one that does not. Finally, we compared our results to those from two coupled computer codes, one that simulates fluid flow and heat transport, and the other that simulates rock deformation. We obtained a good match of surface uplift after three years of CO2 injection into the water leg of a depleting gas field and a good match of temperature and gas saturation profiles and surface uplift after injection of hot fluid into a model of a caldera structure. This agreement indicates that our formulation is able to capture THM effects modeled by a coupled simulation with a more detailed handling of rock mechanics.
