(677d) Wetting and Interfacial Properties of CO2/Brine/Illite System

Clays are important because of their association with oil and natural gas reservoirs. Knowledge of clay structure, porosity, interfacial tension and wettability has significant importance in the petroleum industry for better subsurface imaging and fluid flow modeling. Within gas shale, illite comprises up to 20% of the clay minerals, which themselves constitute up to 50% of the overall shale contents. Theoretically, there is an enormous potential for interactions between the clay surfaces and their environments, which makes shale a promising candidate for CO₂ transport and storage.

Wettability is a long-standing issue primarily addressed by looking at the angle of contact at the edge of the interface between a liquid and a solid. The value of the solid-liquid contact angle provides useful information about the interactions between the liquid and the solid. Due to the small particle size and the high humidity sensitivity, the contact angles of aluminosilicate clays are usually difficult to measure. Atomistic simulation provides valuable guidelines for their power to deal with the complexity of large assemblies of interacting components, and therefore becomes a practical approach for the prediction of clay wettability.

The present work focuses on determining the solid-liquid contact angles of fluid droplets on the illite surface using molecular dynamics simulation. In the simulation, the illite surface was built based on the structure obtained from the previous density functional theory (DFT) study. The clay-clay, clay-fluid and fluid-fluid interactions were described by the ClayFF empirical force field. Canonical (constant-NVT) molecular dynamics was utilized to obtain the equilibrium fluid density profiles and the solid-liquid contact angles. Two systems, 1) brine droplet on illite and 2) supercritical CO2 droplet on illite immersed in brine, were studied. The interfacial structure, the fluid concentration profiles, and the liquid-solid contact angles, as a function of brine concentration will be presented.