Numerical study on the geomechanical responses in the Jilin Oilfield CO2-EOR and CGS projects in China

Abstract

In order to overcome the limitation of low recovery in secondary recovery of oil fields, CO₂ is used as a reliable solvent to enhance oil recovery. The process also enables the storage of greenhouse gas. The CO₂-enhanced oil recovery (CO₂-EOR) and CO₂ geological storage (CGS) projects in the Jilin oilfield in China represent the largest carbon capture sequestration with EOR (CCS-EOR) demonstration project in Asia. A coupled model of Darcy seepage and solid mechanics was developed using extensive monitoring data from CO₂ injection and oil production in the H-59 block. Multiphysics simulations of the CO₂-EOR and CGS processes were conducted because large-scale CO₂ injection and storage projects were planned in the region. The simulations analyzed trends in CO₂ plume migration, pore pressure variations, formation deformation, and the mechanical stability of the caprock throughout the injection and production phases. The results indicated that the layer with the highest permeability retained the majority of the injected CO₂ (53.8 %). Pressure disturbances were significantly higher and widespread in areas with denser well spacing. Despite CO₂ storage in the reservoir during the CO₂-EOR project, the maximum surface subsidence in the dense well group was 5.02 mm after six years of CO₂ injection and oil production. In the CGS project, the maximum uplift rate was 2.88 mm/year, and a maximum surface uplift of 12.9 mm was observed after five years of large-scale CO₂ injection. These uplift amounts and rates adhered to international safety standards. The caprock exhibited no shear or tensile failure in CO₂-EOR project and CGS project. This study offered valuable insights into the geomechanical responses associated with CO₂-EOR and CGS in depleted oil and gas reservoirs.