Impact of Sodium Dodecyl Benzene Sulfonate Concentration on the Stability of the Crude Oil–Mineral Water Interfacial Film: A Molecular Dynamics Simulation Study

Abstract

The interfacial behavior of surfactants exerts a considerable impact on the chemical flooding-produced liquid treatment project. For circumventing the limitations of model simplification and single-factor simulation of previous molecular dynamics (MD) studies, this paper based on the experimental results of crude oil-phase and water-phase composition constructed different simulation systems of “crude oil/SDBS/mineral water” considering the concentration of sodium dodecyl benzene sulfonate (SDBS). The impact of SDBS concentration on the stability of the crude oil–mineral water interfacial film was explored, and the simulation results were verified by comparing with the simulation system of “crude oil/SDBS/pure water” and interfacial tension experiments. The simulated results showed that the SDBS molecules in the system exist in the form of a monolayer film after dynamic relaxation equilibrium, and with the increase in concentration, the number of SDBS molecules per unit area of the film increases, and the molecular chain bending characteristics are weakened. The order of the effect of inorganic cations on the aggregation degree of SDBS is Ca2+ > Na+ > K+ > Mg2+. When the concentration of SDBS increased from 0.15 to 0.70 mol/L, the total oil water interfacial film thickness increased from 1.433 nm in the crude oil/SDBS/mineral water system and 1.272 nm in the crude oil/SDBS/pure water system to 2.125 nm in the crude oil/SDBS/mineral water system and 2.398 nm in the crude oil/SDBS/pure water system. The absolute value of interface formation energy increased from 1223.59 and 1236.32 to 2739.19 and 3033.64, respectively, which are also basically consistent with the experimental results of interface tension. Furthermore, inorganic ions will weaken the performance of the surfactant SDBS and detrimentally affect the structural strength and stability of interfacial films. These results offer useful insights into the stabilization mechanism of oil–water emulsions. In particular, they provide a basis for the design and optimization of new pathways for oil–water emulsion instability in oilfield development.