Grading Evaluation and Ranking of CO₂ Sequestration Capacity in Place (CSCIP) in China's Major Oil Basins: Theoretical, Effective, Practical and CCUS-EOR

Because it is necessary to focus on differences in regional oil reservoirs and determine the priority of the CCUS-EOR (Carbon capture, utilization, and storage-enhanced oil recovery) deployment under China's net-zero CO2 emission target, systematic and regional evaluations of CO2 sequestration capacity in major oil basins are needed considering the geofluid properties-carbon sequestration capacity in place (CSCIP)-where the 'in place' indicates actual geological formation conditions underground, e.g., formation temperature and pressure. Therefore, physical properties of geofluids at different depths with different geologic temperatures and pressure conditions are considered for the CO2 sequestration capacity evaluation in place, including shallow (800-2000 m), medium (2000-3500 m), deep (3500-4500 m) and ultra-deep (4500-8000 m) depth intervals. A modified evaluation model with four grading levels is proposed, combining the P-V-T equations of state (EOS) and evaluation equations of the Carbon Sequestration Leadership Forum (CSLF), including theoretical, effective, practical, and CCUS-EOR CSCIP, which is more consistent with geofluid physical properties underground, to make the grading evaluation and ranking of the CSCIP in China's major oil basins. Then, the grading CSCIP of 29 major oil basins in China was evaluated based on the petroleum resources evaluation results of the Ministry of Natural Resources of China (MNRC) during China's 13(th) Five-Year Plan period. According to the grading evaluation results, suggestions for China's CCUS-EOR prospective regions are given as follows: shallow oil fields of the Songliao Basin in Northeast China, shallow-medium oil fields of the Bohai Bay Basin in East China, medium oil fields of the Zhungeer Basin in West China, and medium oil fields of the Ordos Basin in Central China; all are potential areas for the CCUS-EOR geological sequestration in China's onshore oil basins. In addition, in China's offshore oil basins, shallow-medium oil fields of the Bohai Sea and shallow oil fields of the Pearl River Mouth Basin have potential for CCUS-EOR geological sequestration.