Geomechanical insights into CO2 sequestration with water extraction: Surface deformation and sand production

Water extraction can enhance CO2 sequestration capacity and alleviate formation overpressure in saline aquifers. However, its effects on formation deformation and sand production—critical for risk assessment—remain unexplored. To address these gaps, we developed a fully coupled multiphysical computer model for simulating sand production and stratum deformation during water extraction, well validated against experimental and field data. Using the Junggar Basin as a study case, we evaluated the long-term sequestration capacity and associated risks during water extraction. The results show that water extraction significantly reduces pore pressure within the saline aquifer, partially offsetting the abrupt pressure rise in the near wellbore area caused by CO2 injection and reducing local surface uplift. Additionally, it lowers the pressure below the initial hydrostatic pressure in the main water-extraction affected area, increasing effective stress applied to rock skeleton, and causing rapid stratum subsidence and surface collapse (within 30 days). The low-permeability caprock and basement constrain pressure propagation and flowing-fluid interaction of the saline aquifer with the outside, elevating the hydraulic gradient in the caprock base and basement top, providing sufficient erosion force for particle detachment. Despite rapid occurrence of particle detachment in the early stage (<50 days), detached particles slowly migrate towards the production well, resulting in that persistent sand production only occurs after 400 days. Sand production and stratum deformation have minimal effect on CO2 storage capacity, and more attention should be paid to reduce associated risks. Increasing the well spacing can be recommended to weaken fluid mobility and alleviate sand production.