Integrated Experimental and Numerical Investigation on CO2-Based Cyclic Solvent Injection Enhanced by Water and Nanoparticle Flooding for Heavy Oil Recovery and CO2 Sequestration

Cyclic solvent injection (CSI) with CO2 is a promising non-thermal enhanced oil recovery (EOR) method for heavy oil reservoirs that also supports CO2 sequestration. However, its effectiveness is limited by short foamy oil flow durations and low CO2 utilization. This study explores how waterflooding and nanoparticle-assisted flooding can enhance CO2-CSI performance through experimental and numerical approaches. Three sandpack experiments were conducted: (1) a baseline CO2-CSI process, (2) a waterflood-assisted CSI process, and (3) a hybrid sequence integrating CSI, waterflooding, and nanoparticle flooding. The results show that waterflooding prior to CSI increased oil recovery from 30.9% to 38.9% under high-pressure conditions and from 26.9% to 28.8% under low pressure, while also extending production duration. When normalized to the oil saturation at the start of CSI, the Effective Recovery Index (ERI) increased significantly, confirming improved per-unit recovery efficiency, while nanoparticle flooding further contributed an additional 5.9% recovery by stabilizing CO2 foam. The CO2-CSI process achieved a maximum CO2 sequestration rate of up to 5.8% per cycle, which exhibited a positive correlation with oil production. Numerical simulation achieved satisfactory history matching and captured key trends such as changes in relative permeability and gas saturation. Overall, the integrated CSI strategy achieved a total oil recovery factor of approximately 70% and improved CO2 sequestration efficiency. This work demonstrates that combining waterflooding and nanoparticle injection with CO2-CSI can enhance both oil recovery and CO2 sequestration, offering a framework for optimizing low-carbon EOR processes.