Innovative Zoning Control Techniques for Optimizing a Megaton-Scale CCUS-EOR Project with Large-Pore-Volume CO₂ Flooding

After water flooding development in ultralow permeability reservoirs, connected water channels formed under high injection pressure will reduce the effectiveness of oil recovery and CO2 storage. Based on the geological characteristics of the megaton-scale carbon capture, utilization, and storage (CCUS) project implemented in Changqing Oilfield, we propose an innovative method for characterizing breakthroughs based on the correlation between water and gas breakthrough. We also implement zoning control optimization to achieve the goal of significantly improving oil recovery and CO2 storage efficiency. Taking the HX block after water flooding development as an example, the production performance of the single well is first analyzed. The well groups with significant differences in average water cut are classified as Class I and Class II. Then, precise breakthrough characterization is completed based on the distribution of water saturation and flow rate multiple. We evaluated the feasibility and development effectiveness of the large PV (pore volume) CO2 flooding technology through well pattern adjustment, injection-production parameter optimization based on designed exploration and controlled evolution, parameter sensitivity analysis, and miscibility differences among different levels of well groups. According to statistics, over 60% of the well groups have entered the stage of medium-high water cut. After zoning optimization, the oil recovery of the two well groups under large PV CO2 flooding can increase by more than 25%, and the total storage amount of CO2 in the whole region is predicted to reach 3 million tons. It is found that high pressure CO2 injection under a linear infill pattern is more suitable for weak breakthrough well groups and can greatly improve the oil recovery and CO2 storage efficiency. The injection intensity should be reduced to ensure the effective utilization of CO2 for strong breakthrough groups. Sensitivity analysis shows that the gas-water slug ratio is the key factor affecting the CO2 storage effect, so accurate real-time control is needed in the development process. In addition, when water alternating injection is not sufficient to effectively control the CO2 breakthrough, gas-water gradient slug injection and gel plugging may be a better approach. These results are beneficial for large-scale CCUS engineering applications.