Classical Density Functional Theory for Surface Charge Regulation of Oil-Brine-Rock Systems

Low salinity water-flooding (LSW) can enhance oil recovery by modifying the interfacial properties of reservoir systems, but the underlying mechanism and potential adverse effect are not well understood. Existing models can explain wettability changes in LSW processes with only limited success. Herein we report a coarse-grained model for oil-brine-rock systems within the classical density functional theory (cDFT) framework. In addition to the phase behavor of reservoir fluids, the coarse-grained model allows us to capture ionic size effect and electrostatic correlations essential for predicting the interfacial properties of oil-brine-rock systems. We demonstrate that our model is able to make quantitative predictions of surface charge density and zeta potential at rock-brine interface as a function of important parameters such as temperature, pH and brine composition.