Improvements on modelling wettability alteration by Engineered water injection: Surface complexation at the oil/brine/rock contact

Several laboratory experiments demonstrated that different water compositions cause rocks to change from oil- to water-wet state. Although it is a consensus that wettability alteration is the main recovery process, modeling the underlying mechanism is still a major challenge. Our main goal is to improve and validate a physically based model to predict contact angles from zeta-potential measurements. We hypothesize that, if rock and oil surface are sufficiently close as consequence of thin water layer, then the charge development of one surface will be affected by the other. We propose a new mass-action formulation for surface complexation modelling that includes the energy interface of two interacting double layers. Currently, surface complexation models consider rock and oil as completely isolated surfaces. Additionally, we develop a method of determining surface complexation equilibrium constants to honor several zeta-potential measurements for different ion concentrations (Na+, Ca2+, Mg2+, SO42- and H+). Finally, we estimate contact angles using disjoining pressure calculations and compare them with experimental ones reported in the literature. For the proposed parallel surface model, the system of equations' solution is very distinct to isolated surface approach when the interaction between surfaces are close (spacing approximately bellow 2 nm) at high salinity. Regarding zeta-potential prediction for calcite-brine system, we argue that Na+ might not be an indifferent ion as suggested previously. Our simulation results indicate that, besides the renowned potential-determining ions, sodium adsorption on calcite can play an important role in electrostatic interactions, switching surface charge polarity. Thus, we only honor zeta-potential measurements when Na+ is considered in the surface complexation reactions. Finally, contact angle estimation using proposed surface complexation modelling and disjoining pressure theory provide good predictions of seven different cases reported in the literature. We validate our method on a total of 66 and 163 contact angle and zeta-potential measurements, respectively. The present work is a novel approach to represent how electrostatic interactions among rock, brine and oil modify the rock surface charge and the rock wetting state.

Automated summary

The study aims to improve and validate a physically based model for predicting rock contact angles; a new surface complexation model is proposed considering the charge interactions among rock, oil, and brine; contact angles are estimated using disjoining pressure calculations and validated against experimental data in the literature.