Abstract A deep understanding of rock wettability is essential for elucidating multiphase flow dynamics in porous rocks and for applications such as hydrocarbon reservoir prediction and the safety assessment of subsurface carbon or hydrogen storage. However, wettability alterations driven by the formation of electrical double layers (EDL) at rock–brine interfaces remain poorly understood, highlighting the need for a clear theoretical framework. In this study, we develop a simplified and explicit model for rock wettability based on EDL free‐energy, capturing the effects of interfacial electrostatics and brine compositions. Analysis of existing experimental data shows that the proposed model delivers superior accuracy, robustness, and practical applicability compared with the DLVO model. The model further reveals that nonpolar gas/brine/rock wettability depends on the square of the surface charge, surface potential, and pH, whereas oil/brine/rock contact angles are governed primarily by the absolute sum of the brine/oil and rock/brine zeta potentials. We also find that EDL compression plays a more dominant role in wettability alteration than interfacial tension under low‐salinity conditions. The non‐monotonic tendency of contact angle with salinity is divided into three regimes governed by the Jones‐Ray effect, EDL compression and changes in interfacial tension, respectively. By incorporating the Hofmeister effect, our framework further explains ion‐specific differences in wettability behavior. These findings provide a physics‐based understanding of rock wettability and offer new insights into multiphase flow through porous rocks, low‐salinity waterflooding, and CO 2 /H 2 geo‐storage.
Zhang et al. (Mon,) studied this question.