Microfluidic insights into CO2 sequestration and enhanced oil recovery in laminated shale reservoirs: Post-fracturing interface dynamics and micro-scale mechanisms

Subsequent CO2 injection can enhance oil recovery and achieve carbon sequestration in shale reservoirs, which is crucial for energy sustainability and environmental protection. However, for continental sedimentary shale oil, the development process must consider the multiscale matrix-fracture structure and the impact of heterogeneous wettability on f luid-solid interactions. Moreover, the mechanisms of CO2 miscibility and interfacial behavior in post-fracturing reservoirs remain unclear. In this study, a laminated shale micro-model with fracture based on scanning electron microscopy observations was designed, and the process of fracturing fluid flowback and subsequent CO2 huff-n-puff were simulated. Results showed that forced imbibition primarily affects limestone layers, while spontaneous imbibition affects mudstone layers, contributing 89.3% and 10.7% to the affected area, respectively. The oil recovery mechanism of CO2 is mainly influenced by pressure, transfer from displacement-carry at low pressure to dissolution-extraction, and eventually to diffusion-extraction in the miscible state. Additionally, before reaching miscibility, Taylor dispersion, Kelvin-Helmholtz instability, Rayleigh-Taylor instability, and Marangoni effects occur at the oil-CO2 interface, leading to interfacial turbulent instability. Lastly, water huff-n-puff produces membrane and isolated droplet residual oil, while immiscible CO2 breaks cluster residual oil into columnar residual oil. Miscible CO2 enhances the recovery of various residual oils, improving oil recovery and facilitating CO2 storage. This study provides insights for post-fracturing CO2 huff-n-puff development of continental sedimentary shale oil and CO2 sequestration, promoting energy utilization and environmental improvement. Document Type: Original article Cited as: Li, L., Zhang, D., Su, Y., Zhang, X., Lu, M., Wang, H. Microfluidic insights into CO2 sequestration and enhanced oil recovery in laminated shale reservoirs: Post-fracturing interface dynamics and micro-scale mechanisms. Advances in Geo-Energy Research, 2024, 13(3): 203-217. https://doi.org/10.46690/ager.2024.09.06