A study of caprock hydromechanical changes associated with CO₂-injection into a brine formation

Abstract.

A numerical study of hydromechanical changes during a deep underground injection of supercritical CO₂ in a hypothetical brine aquifer/caprock system is conducted. The injection process is simulated using a newly developed computer model for multi-phase analysis of CO₂ and brine water flow, coupled with heat transfer and rock deformations. In this modeling, CO₂ is injected at a constant rate over a 10-year period at a depth of 1,300–1,500 m. The injection zone is overlain by a 100-m-thick caprock, located at 1,200–1,300 m, which in one of the studied cases is intersected by a vertical fault. The hydraulic, mechanical as well as hydromechanical responses caused by the injection are studied. This includes the spread of the CO₂ plume, effective stress changes, ground surface uplift, stress-induced permeability changes, and mechanical failure analysis. The analysis shows that most hydromechanical changes are induced in the lower part of the caprock near its contact with the injection zone, whereas the sealing mechanism of the upper part may remain intact, despite an injection pressure close to the lithostratic stress value.