Effect of CO2 Injection Temperature on Caprock Stability

Abstract

Deep saline aquifers are promising candidates for long-term CO2 storage, provided they don’t leak. However, injection of CO2 causes pressure buildup and affects the geomechanical stresses in the caprock. If CO2 is injected at a temperature different from the temperature in the aquifer, additional stresses develop due to thermal expansion/contraction. Our work addresses the question whether these stresses are capable of fracturing the caprock and causing leakage. Using a fully coupled thermo-poromechanical model we simulate 10 years of continuous injection of CO2 at different temperatures. We use the geomechanical parameters for aquifer on Krechba (In Salah, Algeria) including recently published data on initial in situ stresses. We found that when CO2 is injected at temperature 40-50°C the stresses in the caprock become tensile and even overcome the tensile strength causing fracturing of the caprock. After initiation the fractures begin to propagate, driven by high fluid pressure in the reservoir. We estimate the fracture length to be 50 m within the first 10 years of propagation.