分子动力学模拟表面活性剂降黏效果

Molecularr Dynamics Simulation on Viscosity Reduction Effect of Surfactants

目前应用于原油降黏方面的表面活性剂种类众多,宏观实验方法无法全面准确地描述降黏机理。利用计算机模拟实验过程及结果,对油田自主研发的三种表面活性剂PS-30、BS-12以及复配型表面活性剂FP1进行降黏效果对比,以分子动力学方法按照油水混相模拟分析并得到以下结论:三种加剂油水体系中,BS-12油水体系的界面生成能为-615.04kJ/mol,PS-30油水体系为-2312.42kJ/mol,FP1复配油水体系为-4156.32kJ/mol。界面生成能的绝对值越大,说明其降低油水界面张力的能力越强,降低界面张力的能力为:FP1>PS-30>BS-12。分子模拟中各表面活性剂加入体系后,FP1、PS-30和BS-12油水体系模型的密度分别降低至0.84g/cm^(3)、0.85g/cm^(3)和0.87g/cm^(3)左右,降黏效果的排序为:FP1>PS-30>BS-12。根据各原油体系石油分子的径向分布函数显示,BS-12、PS-30、FP1原油体系的峰值依次为9.784、9.202、8.347,峰值越低,油水黏附力越小,故FP1的降黏效果最佳。

At present there are various kinds of surfactants applied to viscosity reduction of crude oil,and the macroscopic experimental method cannot fully and accurately describe the viscosity reduction mechanism of the surfactants.Computer is applied to the simulation on experiment process and results,the viscosity reduction effect of three kinds of surfactants PS-30,BS-12 and combined FP1 with independent development by oilfield is compared,and the conclusion are drawn as follows by the molecular dynamics method according to the oil-water miscible simulation analysis.Among the oil-water systems of three surfactants,the interfacial formation energy(IFE)value of oil-water system in BS-12,PS-30 and combined FP1 is-615.04kJ/mol,-2312.42kJ/mol,and-4156.32kJ/mol respectively.Larger absolute value of the IFE indicates stronger ability on reducing oil-water interfacial tension.FP1 has the strongest ability on reducing the oil-water interfacial tension,PS-30 has stronger ability and BS-12 has strong ability.During the molecular simulation,the density of each oil-water system model of FP1,PS-30 and BS-12 reduced to 0.84g/cm^(3),0.85g/cm^(3)and 0.87g/cm^(3)or so respectively after adding surfactants.The order of the ability on reducing the viscosity of crude oil from large to small is:FP1>PS-30>BS-12.According to the radial distribution function of petroleum molecules in each crude oil system,the peak values of BS-12,PS-30,and FP1 crude oil systems are 9.784,9.202 and 8.347 respectively.The lower the peak value,the smaller the oil-water adhesion,so FP1 has the best effect on viscosity reduction.