Impact of CO2 Injection on Geomechanical Response in THMC Simulation within the Chalk Reservoir: Thermal Considerations

Mechanical tests using supercritical CO2 have yielded contradictory results under both flow and no-flow conditions. Samples exposed to flowing CO2 for an extended period (four days) exhibit a notable strengthening of the yield stress, up to a factor of 2.5, attributed to mineral precipitation resulting from water evaporation in the presence of supercritical CO2. Conversely, other individual experiments indicate that the yield stress and compressional modulus of subsurface chalk flooded with supercritical CO2 can be reduced by up to 30% and 15%, respectively, with no observable impact on the creep rate. Consequently, in hot, depleted hydrocarbon chalk reservoirs, including all these complexes processes trigger thermo-hydro-mechanical-chemical (THMC) interactions. Accurately assessing stresses, pressures, and temperature changes associated with supercritical CO2 injection around injectors is crucial for injection design, thermal fracturing, and leakage prevention.

This paper explores coupled multiphysics simulations for cold CO2 injection in a depleted chalk reservoir, aiming to understand the THMC processes involved in CO2 storage in the Harald East depleted gas reservoir. Utilizing a 3D THM model, we investigate the impact on reservoir compaction, considering both the thermal and weakening effects induced by cold supercritical CO2.