Wettability alteration of CO2-water-shale system: state of the art and future directions

Wettability serves as a fundamental petrophysical property governing hydrocarbon recovery efficiency and determining the geological storage security of injected CO 2 within shale formations. This work systematically reviews the recent advances in wettability alteration (WA) of shale induced by CO 2 flooding. First, the classification criteria of reservoir wettability are summarized, and the respective merits and limitations of prevailing experimental and numerical characterization approaches for wettability quantification are critically discussed. Thereafter, key controlling factors encompassing in-situ reservoir conditions, formation water salinity, inherent mineralogy, total organic carbon (TOC) content and geochemical interactions are elaborated, with detailed assessment on how these variables modulate the WA behaviors of CO 2 -brine-shale ternary systems. On this basis, the urgent research demands toward multi-scale quantitative characterization and in-depth mechanistic exploration of WA are highlighted. Additionally, the pivotal role of WA in guiding CO 2 storage site screening and long-term geological safety evaluation is emphasized. This comprehensive review clarifies current research bottlenecks and delivers instructive references for preferential formation optimization and subsequent feasibility evaluation of field-scale CO 2 geological sequestration projects in shale reservoirs.