A new model is presented, which considers the surface-complexation equilibrium between oil surface (amine and carboxylic groups) and rock surface (carbonate and calcite sites) with the brine solution. Effect of rock dissolution and oil composition on the number of available surface sites is taken into account. An in house finite volume solver, coupled with the geochemistry package PhreeqcRM, is utilized to model the multicomponent reactive flow of brine in chalk and the thermodynamic equilibrium between the oil and chalk surface. The equilibrium constants of the surface complexation reactions are tuned to the zeta potential measurements of chalk particles in different brines, and later adjusted to the chromatographic data for the flow of brine in the Stevns-Klint chalk cores. The effect of brine composition, temperature, and electrolyte models, i.e., (extended) Davies, Pitzer, and extended UNIQUAC on the solubility, and the results of the surface complexation model are studied and compared to a data set of the spontaneous imbibition experimental data for chalk. We found that the remaining oil saturation in the imbibition experiments is correlated with the number of bonds between the amine and carboxylate groups on the oil surface and the carbonate and protonated calcite on the chalk surface.@en

The surface complexation models (SCMs) are used successfully for describing the thermodynamic equilibrium between the pure calcite surface (carbonate and calcium sites) and brine solutions. In this work, we show that the model parameters that are reported for the calcite-brine system are not applicable to the natural carbonates. We adjust the SCM reaction equilibrium constants by fitting the model to the ζ potential data that are reported for the pulverized Stevns Klint chalk. Then, we use the model, implemented in the PhreeqcRM geochemistry package coupled with a finite volume solver, to predict the breakthrough composition of different ions in the chromatographic experiments on the intact Stevns Klint chalk cores. Again, the model falls short in predicting the reactive transport of brine in a natural carbonate, implying that ζ potential data is not enough for optimizing the SCM model parameters for the reactive transport applications. We propose an optimization procedure that fits the coupled SCM-transport model parameters to the chromatographic (single-phase core flooding) data. The ζ potential measurements are implemented in the optimization scheme as nonlinear constraints. We then use the optimized model to study the thermodynamic equilibrium between the oil and chalk surfaces in the presence of different brine compositions, including the dissolution and precipitation of minerals. We represent the chalk-oil interactions by acid-base equilibrium reactions between the calcium and carbonate sites on the chalk surface and carboxylic acids and amine bases on the oil surface, respectively. Comparing the model results to a data set of the spontaneous imbibition experiments for chalk shows that the remaining oil saturation in the imbibition experiments is correlated with the number of bonds between the amine and carboxylate groups on the oil surface and the carbonate and protonated calcium on the chalk surface.@en