Cooling-induced aggregation in SARA-Modeled crude oils near oil-water interfaces: Molecular mechanisms of interplay among wax, asphaltene, and resin.

Waxy crude oils under high water cut, low temperature pipeline transport conditions undergo complex gelation upon cooling, yet the interplay between asphaltene, resin, and wax in confined oil layers near oil-water interfaces remain poorly understood. Through molecular dynamics simulations of model crude oil systems with systematically varied SARA compositions, this study reveals the cooperative and competitive mechanisms among these three components. Asphaltene initiates wax crystallization by serving as heterogeneous nucleation sites, whereas resin promotes subsequent crystal growth and enhances structural ordering, increasing the nematic order parameter by up to 23.5% under high wax and low asphaltene conditions. In addition, wax confines asphaltene movement, leading to denser asphaltene aggregates, while resin adsorbs onto asphaltene surfaces and disperses aggregates through steric hindrance. Analysis of density profiles confirms that asphaltene preferentially accumulates at the oil-water interface, wax concentrates in the oil-layer interior, and resin bridges the two. These complex interactions drive the formation of a multicomponent network that integrates interfacial stabilization by asphaltene, molecular bridging by resin, and crystalline ordering by wax. Sensitivity analysis confirms that asphaltene and wax jointly suppress molecular diffusion, while resin substantially mitigates this effect, reducing the cooling-induced decline in diffusivity by approximately 91%. The present work provides a molecular-level understanding of multicomponent aggregation in confined oil-water interfacial systems during cooling, offering both mechanistic insights and practical guidance for flow assurance in high water cut pipelines.