Integrated Experimental and Numerical Investigation on CO 2 -Based Cyclic Solvent Injection Enhanced by Water and Nanoparticle Flooding for Heavy Oil Recovery and CO 2 Sequestration

Cyclic solvent injection (CSI) with CO 2 is a promising non-thermal enhanced oil recovery (EOR) method for heavy oil reservoirs that also supports CO 2 sequestration. However, its effectiveness is limited by short foamy oil flow durations and low CO 2 utilization. This study explores how waterflooding and nanoparticle-assisted flooding can enhance CO 2 -CSI performance through experimental and numerical approaches. Three sandpack experiments were conducted: (1) a baseline CO 2 -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 CO 2 foam. The CO 2 -CSI process achieved a maximum CO 2 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 CO 2 sequestration efficiency. This work demonstrates that combining waterflooding and nanoparticle injection with CO 2 -CSI can enhance both oil recovery and CO 2 sequestration, offering a framework for optimizing low-carbon EOR processes.