Interfacial competitive behavior of water/oil/surfactant systems in ultra-deep tight reservoir – Insights from dissipative particle dynamics

Abstract

The high-temperature and high-pressure characteristics of ultra-deep reservoirs pose significant challenges to studying their efficient development mechanisms, and conventional experimental research struggles to unravel the complex interaction mechanisms between oil, water, and chemicals at the molecular and interfacial levels. To address this, Dissipative particle dynamics (DPD) simulations were employed to delve into oil/water interfacial adsorption behaviors and influencing factors of ultra-deep tight reservoir. Initially, the interfacial dynamics, adsorption characteristics of crude oil components, and interfacial properties were studied. Further, the competitive adsorption dynamics at interface of surfactants and active crude oil components were analyzed. This comprehensive analysis encompasses interfacial dynamics, competitive adsorption characteristics, and interfacial properties, shedding light on the factors modulating these properties. In oil-water systems, resin and asphaltene migrate towards the interface under the influence of hydrogen bonding and heteroatoms, forming a stable interfacial film. The interfacial activity of crude oil components follows a specific order: asphaltene > resin > aromatic > saturated. As temperature increase, molecular thermal motion intensifies, extending interfacial stability time but also enhancing adsorption capacity of resin and asphaltene. This results in increased adsorption density, expanded interface thickness, and reduced Interfacial Tension (IFT). Moreover, this study finds that increasing the oil-water ratio prolongs the time to interfacial stability, yet IFT remains stable. In contrast to crude oil components, surfactants preferentially occupy the oil-water interface. However, resin and asphaltene also demonstrate a degree of competitive adsorption. As surfactant concentration increases, adsorption density rises, leading to decreased IFT. Upon reaching adsorption saturation, the interface undergoes structural changes to accommodate additional adsorption sites. Elevated temperatures further intensify molecular thermal motion, amplifying competitive interfacial adsorption and extending interfacial stability. Conversely, decreasing the oil-water ratio enhances the proportion of surfactant molecules at interface, resulting in reduced interfacial stability time and IFT.