The Synergistic Impacts of Wormhole Length and Pressure-Depletion Rate on Cyclic Solvent Injection: An Experimental Study Utilizing Microfluidic Systems

Cold Heavy Oil Production with Sands (CHOPS) creates high-permeability wormhole networks that strongly influence post-CHOPS recovery performance. Although CSI is a promising post-CHOPS recovery method, the coupled effects of wormhole coverage and pressure depletion strategy on oil recovery remain insufficiently understood. In this study, microfluidic systems were employed to investigate the combined influence of wormhole length and pressure depletion strategy on CSI performance. Micromodels with varying wormhole lengths were used under different pressure-depletion strategies to examine oil production behavior over multiple CSI cycles. Macroscopic recovery trends were analyzed alongside microscopic observations of oil displacement, gas nucleation, and foamy oil development. The results show that increasing wormhole length enhances reservoir connectivity and solvent access, resulting in a 19% improvement in the total recovery factor by 19%. Lower depletion rates favor early cycles and capillary-driven recovery, whereas higher depletion rates become more effective in later cycles as gas expansion and foamy oil-assisted mechanisms intensify. An incremental pressure-depletion strategy that exploits this transition yielded the highest cumulative recovery rate at 46.3%. These findings show that wormholes amplify the impact of pressure depletion rate during CSI by enhancing reservoir connectivity and pressure communication, thereby increasing the effectiveness of adaptive depletion strategies in post-CHOPS reservoirs.