Demulsification of Fluids Produced from Polymer Flooding in Oilfields: A Molecular Dynamics Simulation Study

In this study, a combined approach of molecular dynamics (MD) simulations and experimental bottle tests was employed to systematically investigate the demulsification performance and underlying mechanisms of two distinct demulsifiers—Demulsifier X (SP/BP series and alcohol-initiated polyethers) and Demulsifier Y (AP/AE series and amine-initiated polyethers)—targeting polymer-containing oil-in-water (O/W) emulsions derived from heavy oil polymer flooding. Molecular models for heavy oil, saline water, partially hydrolyzed polyacrylamide (HPAM), and demulsifiers were constructed using BIOVIA Materials Studio software. Their dynamic behaviors at the oil–water interface were simulated within three distinct saline systems containing NaCl, CaCl2, and MgCl2, respectively. Simulation results indicated that the demulsifiers effectively displaced interfacial HPAM molecules, increased interfacial tension, and reduced interfacial interaction energy. Experimental bottle tests, evaluating the effects of settling time, temperature, and concentration on dehydration rates and oil content, confirmed that Demulsifier Y outperformed Demulsifier X. Specifically, Demulsifier Y achieved superior dehydration rates with lower dosages, shorter settling times, and reduced temperature requirements under optimal conditions. This work provides both microscopic mechanistic insights and macroscopic experimental validation for the screening and application of high-efficiency demulsifiers.