Hydro-thermo-mechanical analysis during injection of cold fluid into a geologic formation

We conducted in-depth investigations of pore-pressure buildup, temperature, and stress changes under isothermal or nonisothermal injection scenarios, using numerical simulations. The numerical simulation method combines fluid flow, poroelasticity, thermal diffusion, and thermal stress, and is based on the single-phase fluid flow condition. We also examined temporal evolutions of stress states and mobilized friction angles across base, injection zone, and caprock layers for two different stress regimes, normal-faulting and reverse-faulting. Results show that injecting cold fluid shifts an area in which the mobilized friction angle becomes maximum, which is where induced-seismic events are likely to be triggered first, for both stress regimes. We also tested a hypothetical stepwise injection of cold fluid; results show that this injection helps to improve the stability of the injection zone to some extent. Finally, we suggest using dimensionless parameters to determine a prevalence of the thermal-stress effect in the injection zone, and discuss the impact of the initial stress regime and implications of using the single-phase fluid flow condition.