Impact of time-dependent deformation on geomechanical risk for geologic carbon storage

This paper investigates the consequences of time-dependent deformation on the stress changes and resulting geomechanical risks from injection of CO2 into geologic reservoirs. Using 3D fully coupled fluid flow-geomechanics simulations, it is shown that when time-dependent deformation occurs in the caprock, the shear stress decreases in the caprock but increases in the reservoir. The magnitude of this transfer of shear stress from caprock to reservoir is affected by the characteristic time scale of the time-dependent deformation of the adjacent formations. Compared to an elastic response, viscoelastic deformation of the caprock produces a higher possibility of fault failure within the reservoir during and after CO2 injection. The implication is that if the time-dependent deformation of the caprock is neglected by assuming the purely elastic behavior of the caprock, the geomechanical risk will be underestimated.