Thermo-hydro-mechanical-chemical coupling effects on the integrated optimization of CO2-EOR and geological storage in a high water-cut reservoir in Xinjiang, China

Carbon dioxide-enhanced oil recovery (CO₂-EOR) and storage is recognized as an economically feasible technique if used in suitable reservoirs. The type or form and capacity of this CO₂ sequestration technique is synergistically affected by heat, flow, stress, and chemical reactions. Aimed at addressing the technological issues in applying CO₂-EOR and storage in a high water-cut reservoir in Xinjiang, China, this paper proposes a thermo-hydro-mechanical-chemical coupling method during CO₂ flooding. The potential of CO₂ sequestration and EOR in the target reservoir is discussed in combination with the surrogate optimization method. This method works better as it considers the evolution of structural trapping, capillary trapping, solubility trapping, and mineral trapping during CO₂ injection as well as the influence the physical field has on the sequestration capacity for different forms of CO₂ sequestration. The main mechanisms of CO₂ sequestration in the high water-cut reservoir is structural trapping, followed by capillary trapping. Solubility trapping and mineral trapping have less contribution to the total sequestration capacity of CO₂. After optimization, the cumulative oil production was 2.36 × 10⁶ m³, an increase of 0.25 × 10⁶ m³ or 11.9 % compared to the pre-optimization value. The CO₂ sequestration capacity after optimization was 1.39 $\times$ 10⁶ t, which is an increase of 0.23 $\times$ 10⁶ t compared to values obtained before optimization; this effectively increases the area affected by CO₂ by 24.4 %. Of the four trapping mechanisms, capillary trapping and structural trapping showed a high increase of 32.5 % and 17.28 %, respectively, while solubility trapping and mineral trapping only led to an increase of 5.1 % and 0.43 %, respectively. This research could provide theoretical support for fully utilizing the potential of CO₂-EOR and sequestration technology.