(93d) Understanding the Wetting Behavior of Water-Octane-Silica Systems Using Monte Carlo Simulation

Understanding the interfacial properties of the hydrocarbon-water system is important for the design of many industrial applications, including enhanced oil recovery processes. Oil reservoirs consist of porous rock (minerals) in intimate contact with aqueous and oil phases. Reservoirs are often characterized by the phase that has a greater affinity for the rock surface. In the so-called "water-wet" case, water preferentially wets the mineral surface and oil is displaced from the interior of pores. For the "oil-wet" scenario, this relative preference is reversed. From an oil recovery perspective, one generally prefers the water-wet case, as oil is the more mobile phase and is driven to the surface as pressure is applied to the well. Under oil-wet conditions, the water needs to overcome a capillary pressure, which depends on two key interfacial properties: (1) the tension between the hydrocarbon-rich and water-rich phases and (2) the contact angle that a water-rich droplet forms on a mineral surface in a mother alkane-rich background. We discuss here the use of Monte Carlo (MC) molecular simulation to measure these properties for hydrocarbon/water mixtures in the presence of an atomistically detailed mineral surface. We focus on the evolution of the water contact angle on a silica surface in a mother n-octane phase. We find that the contact angle exhibits a minimum upon increasing the substrate hydrophilicity. At a molecular level, this minimum is connected to the manner in which water organizes at the silica-water interface.