Study On Dynamic And Equilibrium Adsorption Properties Of Surfactants At Oil-water Interface

The adsorption properties of surfactants on the oil-water interface are one of the important factors affecting the chemical flooding process.At present,the influence of surfactant on oil-water interface is relatively perfect,but the dynamic and balanced adsorption behavior of surfactant in oil-water interface is relatively few.In order to get closer to the actual situation of reservoir,it is of great practical significance to study the influence of high temperature and high pressure on surfactant adsorption.This paper mainly includes two parts.In the first part,the adsorption model and law of surfactant on oil-water interface were deduced based on the adsorption theory of surfactant.Then the surface tension and the interfacial tension with n-heptane of SDS solution,HDPS solution and their mixtures were measured by hanging drop method at room temperature and pressure,and the interfacial rheological parameters were also measured.Finally,the dynamic interfacial tension was fitted by numerical method and finite difference method to obtain the relevant adsorption kinetic parameters.In the second part,the influence of high temperature and high pressure on the interfacial tension of distilled water-n-heptane was studied through the interfacial tension of rotating droplets at high temperature and high pressure.Then the influence of high temperature and high pressure on the two kinds of ultra-low interfacial tension was investigated.The experimental results at room temperature and pressure showed that:(1)There was a strong electrostatic repulsion between SDS and HDPS,but the repulsion between HDPS and HDPS was smaller and there was electrostatic attraction partly.Therefor,the maximum adsorption capacity of HDPS was larger than SDS,and the interface expansion modulus of HDPS was also larger.The equilibrium and dynamic interface adsorption properties of the mixed system were between them,which indicated that there was no obvious interaction between SDS and HDPS.(2)By fitting the dynamic interfacial tension of HDPS with numerical solution method,the apparent diffusion coefficient D decreased with the increase of bulk concentration.It was found that the adsorption capacity increased with time,and the higher the bulk concentration,the faster the increase rate.Before the maximum adsorption amount is reached,the decrease of interfacial tension was mainly due to the increase of cumulative adsorption amount.When the adsorption amount was basically unchanged,the factor affecting interfacial tension was the activity of surfactant at the sub-interface.From the volume concentration distribution calculated by the finite difference method,it was concluded that the adsorption rate in the early stage of adsorption is controlled by the diffusion of HDPS molecules.The experimental results at high temperature and high pressure showed that:(1)For distilled water-n-heptane system,the higher the temperature,the lower the interfacial tension.When the temperature was less than 90 ^oC,the interfacial tension decreased with the increase of pressure,but when the temperature reached 120 ^oC,the interfacial tension increased with the increase of pressure.(2)The interfacial tension of two ultra-low interfacial tension systems,CTAB/SDBS-n-tetradecane and mesophase microemulsion-water phase,were measured.The results showed that the interfacial tension of CTAB/SDBS-n-tetradecane could be reduced to ultra-low interfacial tension at 2 MPa and 60 ^oC,while at 120 ^oC,the interfacial tension would rise to more than 1 m N.m^-1.The lowest value in the latter's measurement process increased with the increase of temperature,which was caused by material exchange due to the change of total components.