Assessment of CO₂ Injectivity in Highly Deformable Chalk Reservoirs: a Thermo-Hydro-Mechanical Analysis

Depleted hydrocarbon chalk reservoirs are attractive candidates for CO₂ storage in Denmark. However, their highly deformable nature presents challenges for CO₂ injectivity and storage. This study investigates the potential for thermal effects on reservoir and caprock integrity caused by a 16 year-long supercritical cold CO₂ injection in a depleted gas reservoir using a thermohydro-mechanical simulation. We focus on quantifying the additional stresses and strains induced by the thermal expansion and contraction of the rocks and examine whether these changes could trigger fracturing/fault reactivation in the chalk and/or the overlaying shale deposits. To address convergence issues in non-isothermal flow modeling, we assume that the density and viscosity of CO₂ remain constant with temperature change in the coupled simulation. Our results demonstrate that, with constant rate injection of CO₂, temperature propagation is limited to a short distance around the well, and CO₂ only cools down the temperature around the injection site. This study provides insights into the feasibility of cold CO₂ injection in hot depleted hydrocarbon reservoirs and highlights the importance of considering thermal effects on faults and fractures behavior.