Geomechanical analysis of the influence of CO2 injection location on fault stability

Large amounts of carbon dioxide (CO2) should be injected in deep saline formations to mitigate climate change, implying geomechanical challenges that require further understanding. Pressure build-up induced by CO2 injection will decrease the effective stresses and may affect fault stability. Geomechanical effects of overpressure induced by CO2 injection either in the hanging wall or in the foot wall on fault stability are investigated. CO2 injection in the presence of a low-permeable fault induces pressurization of the storage formation between the injection well and the fault. The low permeability of the fault hinders fluid flow across it and leads to smaller overpressure on the other side of the fault. This variability in the fluid pressure distribution gives rise to differential total stress changes around the fault that reduce its stability. Despite a significant pressure build-up induced by the fault, caprock stability around the injection well is not compromised and thus, CO2 leakage across the caprock is unlikely to happen. The decrease in fault stability is similar regardless of the side of the fault where CO2 is injected. Simulation results show that fault core permeability has a significant effect on fault stability, becoming less affected for high-permeable faults. An appropriate pressure management will allow storing large quantities of CO2 without inducing fault reactivation. © 2016 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences