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Shale is featured by nanometer pores and ultralow permeability. Enhancing shale oil recovery after primary production is challenging as a result of the low injectivity of water. CO 2 could be a promising injection fluid to enhance shale oil recovery for its high mobility in porous media and mixability with hydrocarbons. Fluid behaviors in the nanometer pores of shale reservoirs deviate from those in the micrometer pores of conventional reservoirs. The previous understanding of CO 2 displacement and sequestration in conventional reservoirs is not completely applicable to shale reservoirs. In this review, we analyzed research advances in CO 2 interactions with reservoir fluids and shale rocks at the microscopic level. We delineated recent progress in interpreting phase behavior, mass transfer of the CO 2 −oil system confined in nanometer pores, and reshaping of CO 2 -induced mineralization in shale porous media. We also discussed limitations and future directions for studying CO 2 injection in shale reservoirs, from the experimental scope, theoretical analysis, and field application.

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