Geomechanical Integrity and Non-Isothermal Effects in CO2 Storage

Carbon capture and storage (CCS) is an important component among several initiatives to reduce greenhouse gases emitted to the atmosphere. In Norway, a joint venture is underway between Equinor, Shell and Total to implement the world's first complete value chain (capture, shipping, transport and storage) offshore CCS demonstration project, in which the CO2 can come from many different sources. Here we investigate the thermal effect on a future candidate site for CO2 storage, Smeaheia, using numerical modelling. To do this, we compare results from hydro-mechanical (HM-model) and thermo-hydro-mechanical (THM model) CO2 injection simulations, including the equation of state for the fluids. The injected CO2 is colder than the storage reservoir, and as the CO2 migrates, it cools down the surrounding formations, mainly the reservoir and the overlying caprock. Increased pore pressure due to injection dissipates fast in the high-permeable reservoir in Smeaheia. However, in the caprock, the cooling causes the fluid to contract and the low-permeable caprock creates undrained conditions for the formation water which results in significant reduction in pore pressure. We observe that the thermal effect contributes to destabilizing the reservoir and stabilizing the caprock, which is seemingly fortuitous, but also potentially an unpredictable situation because of the large stress transients and gradients in a small area where the stability can be sensitive to small weaknesses and heterogeneities.