Molecular simulation of quartz wetting in crude oil/brine system at reservoir conditions using a novel protocol for contact angle calculation.

Abstract

The paper presents a comprehensive experimentally informed molecular simulations study of contact angles at the quartz–oil–brine interface under reservoir conditions. The wettability is simulated at various temperatures, pressures, oil composition and brine salinity. Crude oil is modeled as a real-component mixture of alkanes and arenes fitted to chromatographic data and distillation curves. The forcefield is quantitatively validated against experimental data on quartz–hydrocarbon–water contact angles. Special attention is paid to the role of light alkanes dissolved in the oil. The contact angles are calculated by a novel robust and easily adjustable protocol specifically tailored to mineral–fluid–fluid interfaces. The protocol includes parameterization of solid—fluid interaction parameters from ambient-conditions experimental data and transferring the models to reservoir conditions. Contact angle simulations are carried out in a slit-shaped pore formed by a quartz plane. Contact angles are calculated with a new fast algorithm for contact angle calculation that is based on the detection of “boundary cells”, through the centers of which the momentary interface is drawn. The algorithm accounts for asymmetry of the interface and is easily adjustable to any fluid—fluid—solid three-phase contact line. In agreement with experimental data, quartz is water wet, and no wettability reversal is found at any set of conditions and composition. The dependence of the contact angle on temperature for reservoir oil is found to differ qualitatively from that for decane: water contact angle increases with temperature at quartz–decane–brine system and decreases at quarts–crude oil–brine system. Significant influence of the methane content and brine salinity is also observed, while the aromatic content and pressure show a very weak effect on the wettability. Quantitative agreement with select available experiments is obtained. The simulation results are approximated by multivariate linear regression that describes the dependence of the contact angle on temperature, pressure, gas content and brine salinity. The results obtained will help engineers to adjust filtration strategies based on oil–water wettability in the reservoir, depending on the oil composition and external conditions.