A novel computational framework for thermal-hydrological-mechanical-chemical processes of CO2 geological sequestration into a layered saline aquifer and a naturally fractured enhanced geothermal system

CO2 geo-sequestration into saline aquifers and an enhanced geothermal system (EGS) are two of the most effective solutions to reduce CO2 emissions into the atmosphere. The significance of thermal-hydrological-mechanical-chemical (THMC) interactions is well identified in these two processes: fluid and heat flow, solute transport within a three-phase mixture; stresses and displacements related to geomechanical effects; non-isothermal effects on fluid properties and reaction processes; and equilibrium and kinetics of fluid-rock and gas-rock chemical interactions. In this paper, a novel numerical model is developed to describe the THMC processes mathematically. One mean stress formulation, which is simplified from the geomechanical equations with full stress tensor, is employed to solve mean stresses and displacements. Chemical equilibrium and kinetics are considered to quantitatively simulate geochemical reaction associated with solute transport. A sequentially coupled computational framework is proposed and used to solve reactive transport of water, gas components, and chemical species in subsurface formation with geomechanics. It is designed to keep a generalized computational structure for different THMC processes. A practical case with complex chemical compositions is presented to analyze the THMC processes quantitatively on the coupled effects of geochemistry and geomechanics during CO2 geo-sequestration. In addition, a practical EGS case is presented to address the mutual effects of each THMC process quantitatively, especially the mutual effects of stress and chemical reaction. Heat transfer affects mean stress and geochemical reactions; mean stress impacts the solute transport and successive chemical reactions; and geochemical reactions are shown to have significant impact on the mean stress, pressure, or temperature.