Heating-Assisted CO₂ Huff-n-Puff for Improved CO₂ Utilization: Further Discussion of the EOR Mechanism and Enhancing Carbon Sequestration in Shale Reservoirs

To deal with the difficult development caused by the organically rich and ultratight shale reservoirs and the environmental problems caused by the excessive discharge of CO2, a storage-driven enhanced oil recovery (EOR) development method of heating-assisted CO2 huff-n-puff (HNP) is proposed in this paper. Through static reaction, diffusion, and HNP experiments, the effects of heating assistance on reservoir/fluid properties and CO(2 )diffusion behavior were studied. With the help of NMR, the migration law and utilization effect of crude oil in various pore throats were further clarified, the morphological changes of the displacement front were directly characterized by numerical simulation, and the EOR mechanism was revealed. Moreover, its feasibility in carbon sequestration was explored. The research showed that heating-assisted CO2 injection will aggravate the corrosion of primary pores on the shale surface, make the rock surface more prone to wetting inversion, and effectively reduce the viscosity of crude oil; the CO2 diffusion coefficient in the core is more than doubled after heating, effectively improving the pore throat properties and increasing the fluidity of crude oil. After heating, the utilization ratio of macropores increased from 37.56 to 44.86%, and the remaining oil in micropores and smallpores was displaced to mesopores for redistribution. Increasing the temperature makes the displacement front of the HNP gradually evolve from being arc-shaped to an overlying inclined plane, and the dimensionless displacement distance increases from 0.4 to 0.9. In addition, CO2 can indirectly separate the heavy components in crude oil and improve the displacement mobility ratio, but the overlapping effect of gas after heating will be more obvious, which will indirectly affect the CO2 HNP efficiency. The proportion of CO2 stored in the reservoir increased by 4.49%, indicating the potential of the heating-assisted CO2 HNP in carbon sequestration. This study provides valuable experimental and theoretical support for improving the utilization of CO2 in shale reservoirs.