Numerical simulation for optimizing schemes and operational parameters of dual well asynchronous CO2 huff-and-puff practice in fractured shale reservoir of Jiangsu oilfield

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The efficient recovery of shale oil from naturally fractured reservoirs in Jiangsu Province, China, faces notable challenges due to the limitations of conventional CO2 huff-and-puff (H-n-P) techniques. To address these issues, this study developed a Multifunctional Coupled Numerical Model (MCNM) based on CMG’s GEM simulator, tailored for fractured shale oil and gas reservoirs. The model integrates relative permeability functions and gas state equations to evaluate and optimize dual-well asynchronous CO2 H-n-P schemes. A total of 31 simulation scenarios were conducted, varying operational parameters such as CO2 injection timing, volume, rate, soaking time, and cycle number, to assess their impacts on oil production, oil change rate, CO2 sweep efficiency, and distribution of the CO2 saturation. Results show that the dual-well asynchronous approach significantly outperforms traditional single-well H-n-P methods. A CO2 injection volume of 30,000 tons is effective in sustaining reservoir energy, while soaking time and the number of injection cycles have the most substantial influence on production performance. Injection timing showed a weaker impact during the early production phase. Overall, the dual-well asynchronous scheme improves CO2 sweep and recovery efficiency, offering a promising strategy for enhancing shale oil recovery in complex fractured reservoirs.