Effects of Surfactant Charge and Molecular Structure on Wettability Alteration of Calcite: Insights from Molecular Dynamics Simulations

Abstract

Wettability alteration of oil-wet calcite by surfactants was studied by means of molecular dynamics (MD) simulations. The simulations use the recently developed model for positively charged calcite surface, whose oil-wet state originates from binding of negatively charged carboxylate molecules contained in the oil, consistently with the bulk of the available experimental data. The ability to alter the surface wettability, which can be directly quantified by the release of the surface-bound carboxylates, is tested for nine different surfactants of all charge typescationic, anionic, nonionic, and zwitterionicand compared to that of brine. It was found that only the cationic surfactants are able to detach the organic carboxylates more efficiently than brine, while the neutral and anionic surfactants do not seem to have any measurable effect on the wettability. The outperformance of the cationic surfactants is generally consistent with the majority of previously published experimental observations. The data also point toward a consistently better performance of single-tailed cationic surfactants over the two-tailed structure. Molecular mechanism of the wettability alteration by different types of surfactants is discussed, along with the implications of the results for the design of new surfactant formulations for the enhanced oil recovery.

Computational Study on the Microscopic Adsorption Characteristics of Linear Alkylbenzene Sulfonates with Different Chain Lengths on Anthracite Surface

“…When m � 18, the influence of the hydrophobic interaction was dominant, causing the adsorption energy to decrease again. e components of adsorption energy were further analyzed [54,84,87]. van der Waals interaction played a leading role in adsorption process, and electrostatic interaction was so small that it can be ignored.…”

“…With the development of science and technology, it is becoming a reality to use computer simulations to explain the macroscopic properties from a microscopic point of view [51][52][53][54][55][56][57][58][59]. In particular, MD simulation has proven to be a useful tool for analyzing coal interface properties at the molecular level [60][61][62][63][64][65][66].…”

Microscopic Diffusion Characteristics of Linear Alkylbenzene Sulfonates on the Surface of Anthracite: The Influence of Different Attachment Sites of Benzene Ring in the Backbone

“…As the value of m is further increased, the flexibility of the short-chain branch increases, and the hydrophobic interaction force with the long-chain branch increases, which reduces the intermolecular interaction, resulting in a decrease in the adsorption strength [24,40]. To gain deeper insight into the adsorption mechanism of the collector, the components of interaction energy were analyzed [41,42]. The van der Waals interaction energy is far greater than the electrostatic interaction energy, and it plays a leading role in the adsorption of anthracite and surfactants.…”

Fast Evaluation Model of Surfactant Flooding Based on Modification Fractional Flow Theory

“…Rate   is defined as two similar component lines (direction): fast and slow lines. Fast line must pass the initial conditions (in the oil reservoir), whereas slow line has to pass the injection conditions [7][8]. The model first goes through two-phase flash calculation and fractional flow computation along the component lines.…”