The slow kinetics of wettability alteration toward a more water-wetting state by low-salinity waterflooding (LSWF) in oil-brine-rock (OBR) systems is conjectured to be pertinent to the electrokinetic phenomena in the thin brine film. We hypothesize that the nanoscale physicochemical heterogeneities such as surface roughness and surface charge heterogeneity at the rock/brine interface control further the dynamics of electrodiffusion and electrostatic disjoining pressure (Π_el), thus the time-scale and the magnitude of the low salinity effect (LSE). In this regard, film-scale computational fluid dynamics (CFD) simulations were performed. The coupled Poisson-Nernst-Planck (PNP) equations were solved numerically in a thin water film confined between a solid surface and oil, both negatively charged. The solid surface is representative of sandstone (quartz/kaolinite) with patchwise physicochemical heterogeneity. The electrical properties of the oil are representative of a crude-oil sample. The OBR system was initially under chemical equilibrium with high salinity (HS) brine, then was exposed to low salinity (LS) brine. The time-scale of reaching chemical equilibrium under LS, and the spatio-temporal evolution of electric potential were investigated. We find that surface roughness (introduced by quartz patches on quartz surface) increases the diffusion time up to 3-fold due to increased tortuosity. However the effect of surface roughness and surface charge heterogeneity (introduced by kaolinite patches on quartz surface) on the effective diffusion coefficient (D_eff) is minor. While surface roughness and surface charge heterogeneity affect the disjoining pressure (Π_el) significantly, the influence of surface roughness on Π_el is more pronounced under HS than LS condition. In contrast, the effect of surface charge heterogeneity is more appreciable under LS than HS. Our findings imply that the LS effect can be enhanced in rough, heterogeneously charged systems like clayey sandstone, although its magnitude depends on the charge density of the roughness and its variation with salinity. We introduce two scaling factors, namely the effective diffusion coefficient (D_eff) and the retardation coefficient (ω), to upscale the nanoscale results to pore-scale and beyond.

据推测，油-盐水-岩石 (OBR) 系统中的低盐度注水 (LSWF) 导致润湿性向更亲水状态转变的缓慢动力学与盐水薄膜中的电动现象有关。我们假设岩石/盐水界面处的表面粗糙度和表面电荷异质性等纳米级物理化学异质性进一步控制了电扩散和静电分离压力的动力学（Π _el)，因此是低盐度效应 (LSE) 的时间尺度和幅度。在这方面，进行了薄膜级计算流体动力学 (CFD) 模拟。耦合的泊松-能斯特-普朗克 (PNP) 方程在数值上求解在固体表面和油之间的薄水膜中，两者都带负电。固体表面代表砂岩（石英/高岭石），具有片状物理化学非均质性。油的电特性代表原油样品。OBR 系统最初与高盐度 (HS) 盐水处于化学平衡状态，然后暴露于低盐度 (LS) 盐水中。研究了LS下达到化学平衡的时间尺度，以及电位的时空演变。我们发现，由于曲折度增加，表面粗糙度（由石英表面上的石英片引入）将扩散时间增加了 3 倍。然而，表面粗糙度和表面电荷不均匀性（由石英表面上的高岭石斑块引入）对有效扩散系数的影响（D _eff ) 是次要的。虽然表面粗糙度和表面电荷不均匀性会显着影响分离压力（Π _el），但表面粗糙度对Π _el的影响在 HS 条件下比在 LS 条件下更明显。相比之下，表面电荷异质性的影响在 LS 下比在 HS 下更明显。我们的研究结果表明，LS 效应可以在粗糙的非均质带电系统（如粘土砂岩）中增强，尽管其大小取决于粗糙度的电荷密度及其随盐度的变化。我们引入了两个比例因子，即有效扩散系数 ( D _eff ) 和延迟系数 ( ω），将纳米级结果升级到孔隙级及以上。