An effective technique for simulation of low-salinity waterflooding with detailed ion tracking

Design and modeling of LSWF remain challenging for tracking detailed ion composition throughout the reservoir during flooding to capture ion-specific interactions effectively. To address this challenge, this work proposes a novel numerical approach that combines a fully implicit solution for calculation of pressure, water saturation, and total salinity with an explicit scheme for tracking individual ion species (in this study, Na⁺, Cl⁻, Ca²⁺, Mg²⁺, SO₄²⁻, HCO₃⁻). The implicit step follows formulations for mass conservation equations for three-dimensional three-phase black oil simulation, extended with a lumped salt pseudo-component, incorporating salinity-dependent fluid properties and two-point upstream weighting for mobilities. The explicit ion transport uses upstream-weighted fluxes with ion concentrations normalization to total salinity enabling efficient delumping (detailed tracking of ions) without compromising the stability of the implicit solution for a computationally efficient ion concentration tracking. The proposed method was validated against an existing simulator in 2D and 3D homogenous and heterogenous models and coreflooding experiment for low-salinity simulation, with close agreement in production performance behavior. The ion tracking module successfully captured the evolution of ion concentrations, breakthrough times for species and the development of mixing zones between formation and injection brines.