Simulation of geomechanical responses of reservoirs induced by CO2 multilayer injection in the Shenhua CCS project, China

Abstract

Shenhua CCS demonstration project, the first demonstration project for deep saline aquifer storage in China, used a multilayer injection technology to ensure CO2 injectivity. Using a coupled fluid flow and geomechanical modeling, we numerically simulated the CO2 injection and the geomechanical responses during 10-year injection with an injection rate of 100,000 tonnes/year. Simulation results indicate that, though multilayer reservoirs are considered potential storage layers, preferential injection occurs in relatively higher permeability layers because of heterogeneous permeability between injection layers. After 10-year CO2 injection, the highest permeability layer will store most of the injected CO2, which suggests that maximizing utilization of storage potential of a multilayered reservoir–caprock system needs artificially controlling CO2 injection rate according to permeability of each injection layer. The lateral propagation scale and velocity of the injection-induced pressure perturbation are different between the injection layers because of heterogeneous permeability. The significant pressure buildup is located in the radial range of about 3.5km during the 10-year injection, but the pressure perturbation can spread 10km in some injection layers of the Shenhua CCS project. The 10-year CO2 injection can induce a maximum vertical uplift of 2.22mm, which is located close to the injection well and on top of the topmost reservoir formation. Restricted by the overburden stiffness, this uplift gradually decays with depth decrease, inducing a maximum ground surface uplift of 1.49mm. In addition, the ground surface uplift in the first year is intensive, which can account for about 45% of the 10-year ground surface uplift. The injection-induced pressure buildup compresses low-permeability interlayers, inducing compressive deformation in the interlayers.