Interfacial tension at CO2/Water interfaces under aquifer storage: A review of characterizations and regulation strategies

Saline aquifers are promising targets for CO 2 sequestration, where interfacial tension (IFT) plays a critical role in determining both injectivity and long-term storage security. Understanding IFT characteristics and regulation strategies is therefore essential for CO 2 saline aquifer storage. This review systematically summarizes recent advances in IFT studies from the perspectives of influencing factors, experimental characterization, prediction approaches, and regulation technologies, with a particular focus on the controllability and characteristic evaluation of IFT. The results are summarized from 3 aspects: (1) IFT decreases exponentially with increasing pressure until reaching a plateau, followed by a slow and nonlinear increase under ultrahigh pressure. It increases with salinity, whereas its variation with temperature is non-monotonic. CH 4 , H 2 , N 2 , and Ar as impurity gases generally increase IFT, whereas SO 2 and H 2 S reduce it. CO 2 dissolution induces a two-stage IFT reduction, characterized by an initial rapid decline followed by a slower reduction stage. (2) Experimentally, IFT is predominantly measured using the pendant drop method, whose accuracy is strongly influenced by accuracy of density determination and droplet-profile fitting. Empirical correlations and machine learning models enable IFT prediction within specific parameter ranges but are constrained by data quality. Molecular dynamics simulations extend IFT prediction beyond experimental equipment constraints and provide microscopic insights into CO 2 -water interactions. (3) From an engineering perspective, IFT regulation strategies are systematically evaluated and compared in terms of controllability and technology readiness. Regulation through pressure adjustment is limited by reservoir conditions, whereas modifying injection gas composition offers greater flexibility but remains technologically immature. Chemical regulation using surfactants is relatively mature, and specialized surfactants, such as CO 2 -soluble and CO 2 -reactive surfactants, have demonstrated promise in IFT regulation and CO 2 mobility control. Nanoparticle technologies, although still immature, are considered valuable auxiliary additives for enhancing IFT regulation. Overall, this review establishes a unified framework that links IFT characteristics, evaluation approaches, and regulation technologies, providing a technology readiness level perspective for guiding controllable IFT management and engineering implementation in CO 2 saline aquifer storage.