Molecular Dynamics-Based Simulation on Chemical Flooding Produced Emulsion Formation and Stabilization: A Critical Review

Oil-water emulsions are commonly encountered at various stages of petroleum production. For example, the alkaline-surfactant-polymer flooding is extensively used to promote emulsion formation and thus enhance oil recovery. However, the chemicals (e.g., polymers and surfactants) involved in this process can also stabilize the produced emulsions to adversely affect the subsequent processes of oil field surface systems. Therefore, a deep understanding of oil-water emulsions formation and stabilization is required to guarantee and promote oil field production. This work summarizes the current knowledge on (1) the formation of oil-water emulsions, (2) the influence of crude oil components (e.g., asphaltenes and resins), and (3) the above-mentioned water phase components on emulsions stability on a macroscopic scale. Moreover, considering the importance of molecular dynamics (MD) simulation for revealing interphase interactions and its advantages of microstructure characterization, we also probe the mechanism of such simulations, discuss the obtained results, and reveal progress in the elucidation of the mechanism of oil-water interface stabilization. MD simulation is shown to shed light on oil-water emulsification and demulsification processes and is concluded to be well suited for exploring molecular adsorption, droplet coalescence, and droplet separation on a microscale. However, future researchers should aim to circumvent the limitations of model simplification and single-factor simulation, integrate the characteristics of internal and external phase components, and consider external factors like temperature and pressure to comprehensively analyze crude oil emulsification and demulsification behavior. Furthermore, the potential role of bubbles on produced emulsion structure should be considered in future simulations.