表面活性剂修饰SiO_2纳米颗粒增强油/水界面活性分子动力学模拟

Molecular dynamics simulation for oil/water interfacial activity enhancement of surfactant modified SiO_2 nano-particles

中高渗透率老油田进入高含水开采期后,剩余油分布零散,提高采收率难度大。纳米颗粒在老油田提高采收率方面优势明显:它在水中形成纳米尺度的小颗粒,大幅降低油水界面张力,使孔隙中的原油易于被驱替出来;同时,纳米颗粒对小孔道有暂时堵塞作用,通过扩大波及提高采收率。采用分子动力学模拟方法,研究了SiO_2纳米颗粒接枝各类表面活性剂的溶液分散性和界面活性。首先筛选得到羧酸链修饰的SiO_2体系,考察了降低油水界面张力的能力(从50.880 m N/m降低至37.956 mN/m)。引入Janus结构(双子结构),设计了烷烃和羧酸表面活性剂混合修饰的SiO_2纳米颗粒。研究结果表明,该结构能够进一步降低油/水界面张力(从37.956 mN/m降低至32.028 mN/m),表明了纳米颗粒表面修饰表面活性剂体系与界面活性之间的构效关系,为高效纳米驱油剂的设计与实验合成提供了一定的理论依据。

After the old oilfield with medium and high permeability enters high water cut developing period,its remaining oil is scatteredly distributed and it is very difficult to enhance oil recovery.Nano-particles have obvious superiority over enhanced oil recovery for old oilfield.The formation of small particles at nanometer scale in water greatly reduces oil-water interfacial tension and makes the oil in the pores easy to be displaced.Meanwhile,nano-particles possess the temporary blocking effect for the small channels and the recovery factor can be improved by spreading sweeping area.Therefore,the dispersity of the solution and interfacial activity with SiO2 nano-particles grafted with various surfactants were researched on by using molecular dynamics simulation method.First,SiO2 system modified by carboxylic acid line was obtained through screening and the ability of reducing oil-water interfacial tension(from 50.880 mN/m to 37.956 mN/m)was investigated.Then,SiO2 nano-particles modified with alkane and carboxylic acid surfactant mixture were designed with the introduction of Janus structure(Gemini structure).The research results indicate that this structure can further reduce oil-water interfacial tension(from 37.956 mN/m to 32.028 mN/m)and show the structure-activity relationship between nano-particles modified with surfactant system at surface and interfacial activity.It also provides certain theoretical basis for the design and experimental synthesis of high-efficiency nanometer oil displacement agents.