Speaker
Description
Low-salinity waterflooding (LSW) has emerged as a promising enhanced oil recovery method in carbonate reservoirs, yet the pore-scale mechanisms by which brine composition alters rock wettability and mobilizes trapped oil remain incompletely understood. In this work, we develop a pore-scale numerical framework that couples multiphase flow, solute transport, and surface-complexation-based wettability alteration to quantify low-salinity effects in realistic carbonate pore geometries.
The model represents the carbonate surface using a multi-site surface complexation formulation that captures protonation–deprotonation and specific-ion adsorption reactions between brine species and mineral surface groups. The resulting surface charge and potential are mapped to spatially varying local contact angles through an empirical electrostatic–wettability relationship, allowing brine chemistry to dynamically modify wettability during flooding. These contact angles are embedded in a color-gradient lattice Boltzmann multiphase flow solver to simulate immiscible oil–brine displacement at the pore scale. Solute transport is described with an interfacial-partitioning lattice Boltzmann model that moves ions between bulk water and interfacial regions, enabling explicit treatment of transport to and from the three-phase contact line.
The framework is applied to synthetic channels and micro-CT-based carbonate pore structures initially saturated with oil and a high-salinity brine, followed by injection of low-salinity brine with systematically varied ionic strength and composition. Simulation results show that reducing brine salinity weakens specific adsorption of divalent cations, increases surface charge magnitude, and shifts the wettability toward more water-wet conditions. This transition promotes breakup and reconnection of oil ganglia, enhances snap-off in small throats, and increases oil recovery relative to high-salinity floods. Parametric studies indicate that the magnitude and spatial distribution of wettability alteration are sensitive to both the mineral surface site density and the detailed brine composition, including the relative concentrations of Na⁺, Ca²⁺, and SO₄²⁻. In more heterogeneous carbonate textures with mixed micro- and macro-porosity, low-salinity effects are amplified in smaller pores with larger surface-to-volume ratios, leading to improved sweep of previously by-passed oil.
By explicitly linking surface complexation, electrolyte chemistry, and multiphase displacement at the pore scale, this work provides a mechanistic basis for interpreting core-scale LSW experiments and for designing brine recipes tailored to specific carbonate reservoirs. The modeling framework is readily extensible to include mineral dissolution–precipitation and fines migration, and thus offers a versatile tool for integrating pore-scale wettability alteration into multiscale reservoir simulation workflows.
| Country | United States |
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