Insights into the effect of water content on asphaltene aggregation behavior and crude oil rheology: A molecular dynamics simulation study

In the production and transportation of crude oils, the interaction between asphaltene components and water is inevitable, significantly impacting asphaltene aggregation, deposition behaviors, emulsion stability, and rheological properties of crude oils. However, the comprehension of the oil-water interaction mechanisms and corresponding viscosity responses remains unclear. Hence, we performed molecular dynamics (MD) simulations to investigate the effect of varying water content on distinct asphaltene aggregation states and the rheological behavior of crude oils. The microscopic mechanisms underlying the aggregation and rheological properties were elucidated. Our MD results show that with the continuous introduction of water, the original bulk phase aggregation of asphaltenes undergoes a transition towards interfacial adsorption behavior, culminating in the formation of water-in-crude oil emulsions. The strength and driving forces of this interfacial adsorption are influenced by different polar functional groups of asphaltene. Besides, by elucidating the contributions of external molecular friction and internal structural deformation to the viscosity, two viscosity-influencing mechanisms are revealed. Furthermore, we delineate a physical viscosity scheme. These intriguing discoveries hold promise for advancing the comprehension of rheological behavior in crude oils with distinct aggregation states, providing theoretical guidance for efficient development of crude oils.