Simulation of Advanced Waterflooding in Carbonates Using a Surface Complexation-Based Multiphase Transport Model

Abstract Understanding the injection water chemistry effect, in terms of both salinity and ionic composition, is becoming crucial to increase oil recovery from waterflooding in carbonate reservoirs. Various studies have shown that that surface charge alteration is the main mechanism behind favorable wettability changes toward water-wet conditions observed during the injection of controlled ionic composition water in carbonates. Therefore, the synergistic coupling between multiphase transport and electrokinetics of brine/calcite and brine/crude oil interfaces becomes important to optimize injection water compositions for enhanced oil recovery in carbonates. In this investigation, the electrokinetic interactions of brine and crude oil in carbonates are accounted for and coupled with the multiphase Darcy flow model. The electrokinetic interactions are parametrized by the zeta-potential values of brine/calcite and crude-oil/brine interfaces, which are determined using a Surface Complexation Model (SCM). The SCM zeta-potential parameters are computed based on the local concentration of aqueous ions that follow the transport equation. The relative permeability and capillary pressure curves are altered based on zeta potential shifts, which resembles the wettability alteration process. The SCM zeta potentials are compared with the experimental zeta-potential measurements, while the multiphase transport model coupled with geochemistry is validated through a comparative coreflood experimental data reported in the literature. The SCM results governed by specified surface geochemical reactions agreed well with zeta-potential measurements obtained at both calcite/brine and crude-oil/brine interfaces. The coupled geochemical SCM with multiphase transport model accurately matched both recovery and pressure drop data from forced imbibition tests reported by Yousef et al. (2011) in both secondary and tertiary modes. The generated relative permeability curves followed Craig's rules in shifting the wettability from oil-wet toward water-wet conditions for advanced waterflooding processes in carbonates. These results confirm the robustness of proposed model based on validated SCM electrokinetic interactions. The development of such a coupled geochemistry based multiphase transport model is an important step to simulate advanced waterflooding processes in carbonates at reservoir scale by taking into account of more representative physicochemical effects. The novelty of this work is that it validates the SCM results with experimental zeta-potential data for different injection water compositions. Also, the applicability of coupled SCM with a multiphase transport model is successfully demonstrated by history matching the experimental coreflood data. The developed model and new findings shed some light on the importance of lower salinity and controlled ionic composition during fluid flow and oil recovery in complex carbonate formations.