Effects of thermal stresses on caprock integrity during CO2 storage

Abstract

Subsurface fluid injection results in a pore pressure increase, which induces geomechanical stresses. Additionally, if there exists a difference between the ambient formation temperature and the temperature of injected fluid, thermal stresses can develop. Herein we study the effect of CO2 injection temperature on caprock integrity using coupled thermo-poromechanical multi-phase simulations. Calculations show that when CO2 is injected within several years at a temperature below the ambient value in the formation, the stresses above the horizontal injection well lead to tensile or shear failure of the caprock. We study the sensitivity of resulting stresses to the injection temperature, caprock density and initial in situ stresses. We also show that the caprock failure can lead to propagating fractures, which may serve as pathways for CO2 leakage. Based on the results of our simulations we estimate the rate of fracture propagation and study the effect of caprock permeability on this rate. Our results show that injection of CO2 at temperature close to the ambient value in the aquifer significantly reduces the risk of caprock fracturing and, therefore, of possible leakage.