CO2 Huff ’n’ Puff Performance in Shale Oil Reservoirs and Field Application

Summary Shale oil holds significant development potential but suffers from low oil recovery factor, even after fracturing. Carbon dioxide (CO2) huff ’n’ puff (HnP) has emerged as a promising solution, combining enhanced oil recovery (EOR) with carbon sequestration. However, this technology mainly remains in its exploratory phase for shale oil reservoirs, constrained by unclear CO2/brine/shale interaction mechanisms, CO2/shale oil interaction behavior, and limited understanding of CO2 HnP performance in shale oil reservoirs. With this work, we present the integration of experiment with simulation and field verification of CO2 HnP in shale oil reservoirs of the S Basin. We conducted static experiments to analyze mineralogical changes, element changes of formation water, and dissolution (e.g., calcite/pyrite) under high temperature/pressure based on shale samples. We also performed dynamic experiments to evaluate the effects of injected CO2 on oil properties and minimum miscibility pressure (MMP). We developed a dual-permeability numerical model with complex fracture networks to optimize HnP parameters and validate its practical feasibility. CO2/brine/shale interactions induced mineral dissolution, creating micropores and fractures. Dynamic experiments confirmed high-pressure CO2 miscibility with shale oil, resulting in reduced oil viscosity and volumetric expansion. Simulations predicted that five HnP cycles can improve oil recovery factor by 14.2% (3.97×10⁴ t oil) while ‌sequestrating 5.8×10⁴ t CO2. Field application indicates that CO2 HnP can effectively enhance shale oil recovery factor and achieve carbon neutrality, offering mechanistic insights and a technical framework for integrated CO2 EOR and sequestration in shale oil reservoirs.