Numerical simulation of the coupled thermal-hydro-mechanical fields for evaluating CO2 geo-sequestration storage in deep saline aquifers of Hainan Fushan Sag, China

Injecting CO2 into deep saline aquifers, referred to as CO2 geological sequestration (CGS), is considered to be a promising method to reduce the emission of anthropogenic CO2 to atmosphere. CGS involves coupled thermal-hydrodynamic-mechanical (THM) processes, which are important for predicting migration and transformation of injected CO2, evaluating the reservoir performance, and assessing the risk associated. Based on the Terzaghi consolidation theory, a coupled mechanical module is developed that is incorporated into the existing simulator TOUGH2, which is a well-established code for TH processes in subsurface flow systems. Based on the geological and hydrogeological conditions of the Ordos CCS Demonstration Project, the new THM simulator is used to numerically analyze the spatial and temporal distribution of the temperature, pressure, CO2 saturation, vertical displacement, and effective stress. The results show that 10(5) metric tons of CO2 per year can be finished under the injection condition of wellhead pressure 8 MPa and 35 degrees C. The lateral distance with pressure buildup is more than that of CO2 plume and that of temperature decrease. They are 10 km, 620 m and 100 m, respectively after 20 years' injection. The vertical displacement and change of the effective stress are mainly related to the change of the pressure. The maximum surface uplift is about 0.14 m. The effective stress change is more significant in the horizontal direction than that in the vertical direction near the injection well, while it's in the opposite away from the injection well. Injection induces an obvious decrease in the effective stress but enhances the porosity and permeability, this, in turn increases the CO2 injectivity ultimately.