Study On Solid/Liquid Interface Properties At Different Wettability Reservoir Conditions

Enhanced oil recovery(EOR)plays a vital role in enhancing oilfield recovery at present,Among various measures,the chemical enhanced oil recovery occupies an important position.Exploring the law of EOR involves the interaction of various components including reservoir,crude oil,water,and oil displacement agent.Traditional experimental methods are limited in studying these interactions from a microscopic perspective.Thanks to the advancement of modern computer technology and the development of chemical theory,the use of molecular simulation methods can conduct more in-depth research on the displacement mechanism from a microscopic perspective,which provides a strong theoretical guide for the selection of oil displacement methods in different reservoir environments.In this thesis,the adsorption behavior and oil displacement laws of crude oil on solid surfaces with different wettability were studied.The means of molecular dynamics were used to explore the properties of solid/liquid interface between solid surface,crude oil and surfactant and the micro mechanism in the process This thesis consists of the following four parts:Section Ⅰ:It is mainly introduced the development of enhanced oil recovery,the mechanism of surfactant flooding and the theory of the interaction between reservoir medium and reservoir.Besides,the research progress in the field of oil displacement law and mechanism by the means of molecular dynamics simulation was introduced.Section Ⅱ:Three solid silica surfaces modified by different proportions of methyl were established to simulate the adsorption of oil molecules in reservoir water environmnent and the effect of surfactant addition on interfacial tension was also considered.It was found that the contact angle decreased with the addition of surfactant on the hydrophilic surface with strong polarity,but it was opposite on the hydrophobic surface with more methyl coverage.Then,the results of contact angle were used to calculate the interfacial tension between the oil phase and different solid surfaces by the Young’s equation.These results provide a method to evaluate the difficulty of oil droplet peeling from solid surface based on interfacial tension and adhesion work.Section Ⅲ:Non-equilibrium molecular dynamics(NEMD)model was built to study the migration process of oil droplets in reservoir pores at micro scale was simulated,and the oil displacement results of surfactant under different wettability reservoir conditions were obtained.By analyzing and comparing the microstructure of oil droplet separation from the pore wall,it was confirmed that the water diffusion on the solid surface and the formation of water channel are the key steps of oil droplet stripping in the process of oil displacement under the effect of water flow.It was found that the relative size of solid/liquid interfacial tension γswand γso is the key factor to determine whether oil droplets can be separated from the wall in the pore during oil displacement by comparing the results of simulated oil displacement and the calculation results of interfacial tension.Section Ⅳ:This part summarized the main work and conclusions of this paper,including the innovation and shortcomings of this research and looked forward to further research space.