Behavior of fluids in clay-hosted nanopores: insights from molecular dynamics

Abstract

Our understanding of fluid behavior and transport in shales, especially in organic or kerogen pore systems, has grown rapidly over the last few years. Yet, given the prevalence of inorganic material that often hosts the organics in shales, little attention has been devoted to how fluids move and distribute themselves in clay-hosted pores. In this work, I use classical molecular dynamics simulations to investigate fluid behavior and transport in charged clay-hosted nanopores. I focus on mixtures of brines and hydrocarbon confined in clay slit pores and consider two different surface charges. A very important constraint I impose on the models is rigidity to avoid clay swelling behavior. My initial set of simulations focuses on oil-solvent mixtures in clay pores and the conditions under which they become miscible, and the impact of confinement on the self-diffusion of hydrocarbon as well as viscosity. At specific pore widths and water saturations, water is shown to bridge across the pore from one clay surface to the other, and not merely be adsorbed. My work discusses the conditions under which these bridges form and their impact on fluid movement. I show that increasing brine salinities can dissipate the water bridges which motivates me to discuss optimizing salinity for waterfloods or hydraulic fracturing fluids when clays are predominant. The final discussion is the effect of varying salinity on the shape and stability of surfactant-solvent microemulsions in clay pores.