Fluid Behavior in Clay-Hosted Nanopores with Varying Salinity: Insights into Molecular Dynamics

Abstract

Summary Clays, with their charged surfaces, are characterized by strong interactions with dissolved ions in brines and injected water. While there is a considerable body of research devoted to clay swelling, little to no progress has been made on fluid distributions and their impact on transport through clay pores when exposed to fluids of varying salinity. In this work, we use a molecular dynamics (MD) approach to characterize fluid distributions when oil and brine with varying salinities are present in clay-hosted pores. This promises to provide a rationale for optimizing salinities in fracturing fluid salinity (or low-salinity waterflooding applications). Our results indicate that at high salinities, unabsorbed Na+ and Cl− ions appear as aggregates while at low salinities, water forms bridges across the pore width. Both of these phenomena impede the diffusion of oil molecules through the clay nanopores. At intermediate values of salinity, in the absence of either ionic aggregates or water bridges, we observe the highest mobility of the oil phase. This modeling-based work provides a first look into optimal salinity values that promote oil mobility for fracturing fluids (or low-salinity waterflooding applications) for formations where clays may be present.