Integrated In Situ Conversion and CO2 Flooding–Sequestration for Low- to Medium-Maturity Shale Oil: A Review and Perspectives

Abstract Shale oil with low to medium thermal maturity (Ro = 0.5–0.9%) contains substantial residual hydrocarbon-generation potential but is difficult to exploit because of incomplete kerogen conversion, heavy hydrocarbon components, and restricted transport within nanoporous reservoirs. This review examines the integration of in situ conversion (ICP) with CO2-enhanced oil recovery and geological sequestration as a coordinated strategy for resource conversion, fluid mobilization, and carbon storage. ICP promotes kerogen pyrolysis and heavy-component cracking while inducing pore expansion, microfracture development, and changes in rock–fluid interfacial properties. These thermally reconstructed reservoir conditions subsequently regulate CO2 transport, phase behavior, oil displacement, and geological retention. CO2 enhances hydrocarbon recovery through oil swelling, viscosity reduction, compositional extraction, competitive adsorption, and diffusion-driven mass transfer, while geological storage occurs through adsorption, residual, dissolution, and mineral trapping. The coupled ICP–CO2 process is therefore interpreted within a thermo–hydro–mechanical–chemical (THMC) framework linking thermal conversion, pore-fracture evolution, multiphase transport, and long-term carbon sequestration. Published laboratory and core-scale studies indicate representative ICP heating temperatures of 300–450 °C, CO2 injection pressures of approximately 10–30 MPa, incremental oil recovery of 3–15%, and CO2 retention capacities of approximately 1–45 kg CO2 per ton of shale, although these values are strongly reservoir- and scale-dependent. Major uncertainties remain in nanoconfined CO2–oil phase behavior, cross-scale parameter upscaling, long-term reservoir integrity, and field validation. Future research should therefore integrate in situ experiments, multiscale THMC modeling, pilot testing, and full-cycle energy-carbon assessment to establish technically viable and low-carbon ICP–CO2 development strategies.