Summary
In the context of carbon capture and storage (CCS) engineering, ensuring the stability of the caprock is paramount to mitigating CO2 leakage, thus constituting a pivotal engineering challenge in CO2 geological sequestration. With the injection of CO2, pore pressure accumulates within the reservoir, bringing forth risks including diminished effective stress within the formation, surface deformation, occurrence of microseismic events, and potential caprock failure. Therefore, it is necessary to explore the geomechanical issues in CCS projects. This study focuses on the Daqingzijing in the Jilin Oilfield as the study area, utilizing the small baseline subset (SBAS)-interferometric synthetic aperture radar (InSAR) method to conduct a deformation time-series analysis in the well group area under injection and production conditions. The results reveal variations in deformation sensitivity among the sites, with surface displacements correlated to fluid injection and production, demonstrating temporal delays. At the H79 North block, the time effect is relatively minimal, with rapid propagation of formation deformation. Surface displacement in the H46 block appeared 4 months later than behind cumulative fluid volume changes. By conducting triaxial creep tests on shallow mudstone samples from the Songliao Basin under various triaxial stress states, a constitutive creep equation for caprock rocks was obtained. The numerical models of elastic and creep constitutive equations were established. The results show that the creep model exhibits superior accuracy by comparing with InSAR monitoring data (the root mean square error values of elastic and creep constitutive geomechanical models were 6.7 mm and 1.7 mm, respectively). Additionally, based on the experimental and simulation results, this study explores the transfer mechanisms of formation deformation and the inverse relationship between deformation and pore pressure. This study provides theoretical support for the geomechanical safety analysis in corresponding CCS projects.
