Multi-scale simulation of thermal pressurization of fault fluid under CO2 injection for storage and utilization purposes

We investigated the impact of thermal pressurization (TP) on temperature and pore pressure changes within the shear zone of a slipping fault under supercritical CO2 injection. As a weakening mechanism, TP of fault fluid during slip tends to reduce frictional resistance by increasing pore pressures along the fault shear zone. We employed a multi-scale modeling approach in which the CO2 injection was simulated in a large-scale model of reservoir and the results were then exported into a micro-scale model of the fault shear zone which incorporates the TP effect. A poroelasticity finite element model was created in the large-scale model to determine the stress and pressure changes in the reservoir and within the fault zone during CO2 injection. The fault slip, pressure, and stresses obtained from the large-scale model were fed into the small-scale model to define hydraulic and mechanical boundary conditions of the shear zone of the fault. Two small-scale models were developed to compare the response of the fault shear zone with and without considering the TP. For the model with the TP effect, a simple constitutive law was implemented to couple pore pressure changes with temperature rise due to frictional heating. The results indicated that, in general, TP can lead to a significant increase of pore pressure build up due to CO2 injection. The effects of hydraulic diffusivity, slip velocity, shear zone thickness as well as injection rate on pore pressure, temperature and fracture energy prediction were evaluated. It was found that temperature and pore pressure rise decrease significantly by decreasing the slip velocity and increasing the shear zone thickness. For the values which were examined, hydraulic diffusivity was found to have insignificant effect on pore pressure and temperature changes which can be attributed to high compressibility of CO2. Findings of this study can be used and further expanded in future studies for more accurate assessment of induced seismicity potential due to CO2 injection.