Study on Geological Deformation of Supercritical CO2 Sequestration in Oil Shale after In Situ Pyrolysis

After the completion of in situ pyrolysis, oil shale can be used as a natural place for CO2 sequestration. However, the effects of chemical action and formation stress-state changes on the deformation of oil shale should be considered when CO2 is injected into oil shale after pyrolysis. In this study, combined with statistical damage mechanics, a transverse isotropic model of oil shale with coupled damage mechanisms was established by considering the decreased mechanical properties and the chemical damage caused by CO2 injection. The process of injecting supercritical CO2 into oil shale after pyrolysis was simulated by COMSOL6.0. The volume distribution of CO2 and the stress evolution in oil shale were analyzed. It is found that CO2 injection into oil shale after pyrolysis will not produce new force damage, and the force damage caused by the decrease in the mechanical properties of oil shale after pyrolysis can offset the ground uplift caused by CO2 injection to a certain extent. Under the combined action of chemical damage and mechanical damage, the uplift of a formation with a thickness of 200 m is only 10 cm. The injection of supercritical CO2 is beneficial for maintaining the stability of oil shale after in situ pyrolysis.