Molecular Dynamics Simulation of Water-Based Fracturing Fluids in Kaolinite Slit Pores

Abstract

The adsorption behavior inside kaolinite mesopores of aqueous solutions of various salts and additives is investigated using Molecular Dynamics simulations. In particular, we examine the various combinations of water + salt, water + additive, and water + salt + additive mixtures, where the salts examined are NaCl, CsCl, SrCl2 and RaCl2 and the additives are methanol and citric acid.Citric acid is modeled in two forms, namely fully protonated (H3A) and fully deprotonated (A 3-), the latter being prevalent in neutral pH conditions, in accordance with the kaolinite structure employed. The force fields used for the individual system components include CLAYFF for the kaolinite mesopores, SPC/E for water, parameters optimized for the SPC/E water model based on hydration free energies (HFE) for ions and general Amber force field (GAFF) for the additives.The spatial distributions along the kaolinite pore are delineated and reveal the preferential adsorption behavior of the various species with respect to the gibbsite and siloxane surface, as well as the effect on this behavior of the interactions between the various species. Furthermore, we examine the hydrogen bonds formed between the kaolinite surfaces and water molecules as well as the additives. For the case of citric acid, which tends to aggregate, a cluster analysis is also carried out, in order to examine the effect of the various ions on the cluster formation. Finally, through the calculation of lateral diffusion coefficients and mean residence times, we provide insights on the mobility of the various species inside the kaolinite mesopores.

Long range ionic and short range hydration effects govern strongly anisotropic clay nanoparticle interactions

“…We show in Figure 3(c,d) the different behaviour of ions at the two kaolinite faces: the gibbsite face shows a pronounced peak of Cl − anions, and the siloxane face shows a quite smaller peak of the Na + cations and the absence of any Cl − anion in its proximity. Thus, ions distribute on the two kaolinite faces to counteract the intrinsic surface charge, screening the inter-particle Coulomb interaction, in agreement with literature [3,20,25]. This screening effect appears as the reason for the lack of long range interaction among the kaolinite particles in saline solution observed in Figure 3(a).…”

Wetting Behavior of Tight Rocks: From Core Scale to Pore Scale

“…Phyllosilicate kaolinite is composed of a single tetrahedral silicon‐oxygen (siloxane) and an octahedral aluminum‐oxygen (gibbsite) sheets. Several studies have been conducted to investigate the wettability of water/oil droplets on kaolinite surfaces (Papavasileiou et al, ; Siddiqui et al, ; Zhang et al, ). Šolc et al () conducted molecular dynamics simulations to study the wettability of the basal kaolinite.…”

Distribution and Mobility of Crude Oil–Brine in Clay Mesopores: Insights from Molecular Dynamics Simulations

“…Clay minerals (e.g., montmorillonite, illite, chlorite, and kaolinite) are ubiquitous and play important roles in both conventional and unconventional reservoirs . Over the last few decades, molecular dynamics (MD) simulations have been extensively employed to study the interactions between organics and clay minerals. − Using MD simulations, Underwood and co-workers observed that decane and decanoic acid aggregate together and separate from montmorillonite surfaces by the brine layer covering on montmorillonite surfaces. However, decane and decanoic acid droplets prefer to approach a near kaolinite silicate surface and completely withdraw from the kaolinite hydroxyl surface. , Our previous MD study indicates that the layer charge significantly dominates the wettability of 2:1-type clay .…”

“…Anvari and Choi revealed the distribution of water/cyclohexane confined in a 5 nm mesopore composed of kaolinite at different water amounts and salinity, and found that water first covered on the clay surface because of the screening effect of the adsorbed counterions.Papavasileiou et al used MD simulations to examine the adsorption behavior of various aqueous solutions in combination with methanol and citric acids confined in mesopores composed of kaolinite. They found that fully deprotonated citric A 3− tend to aggregate into large clusters driven by cation bridging .…”

“…They found that fully deprotonated citric A 3− tend to aggregate into large clusters driven by cation bridging. 21 They also investigated the distribution and mobility of n-octacosane-water mixture inside the titania nanopores. 22 Wang et al used octane as a shale oil model and found that the diffusion coefficient increases by several orders of magnitude as the pore width increases from 2.8 to 50 nm.…”