Study On The Performance Of Viscoelastic Surfactant For Oil Displacement

Surfactant flooding as an important method to enhance oil recovery,mainly by reducing the oil-water interfacial tension, improving the wettability of rock surface, and the formation of microemulsion enhance oil recovery. At present, the conventional surfactant can’t control mobility well,and binary system can not avoid chromatographic separation phenomenon effectively.At this time, Viscoelastic surfactant (VES) made up for its shortcomings, which has viscosity and the ability of reducing oil-water interfacial tension. and the oil displacement efficiency and swept efficiency increased.This thesis has determined two systems(VES04and VES05) based on anionic surfactant (AT) as the main agent respectively with cationic surfactants (CA), amphoteric ionic surfactants (BET) for distribution of screening.What’s more, the influence of concentration, salinity, temperature on the rheological property, aggregate behavior, the oil-water interfacial tension, the long-term stability and emulsifying properties has been studied based on two blocks.According to the principle of screening, when the mixture ratio were respectively3:7and27:73,the system compound with the system present excellent performance. Orthogonal experiment results showed that concentration and temperature influence respectively on VES04, VES05solution viscosity,and repetitive experiments has already verified.When the temperature was65℃,the viscosity was20mPa·s. In the study of shear stability, two kinds of solution form the shear-thinning phenomenon,and shear stress increased.In addition, the characteristic of system of viscoelasticity was obvious,and fluid types were pseudoplastic fluid. Relaxation time with the increase of the concentration increased and decreased, respectively. What’s more,two solution linked between overlapping with irregular reticular structure by ESEM,but its molecular structure present fragmentation distribution and low stereotacticity in the presence of inorganic salt. The critical micelle concentration CMC, surface tension and other performance parameters of two solutions were measured respectively at25℃by Wilhelmy-plate method. The parameters of surface properties(γCMC,pC2o,Amin and Γmax) have been calculated.Finally,the diameter of two solutions were respectively237.14nm,96.7nm in the absence of salt by DLS,while their diameter increased after adding salt.On the condition of reservoir temperature, the oil-water interfacial tension of different concentrations can reach the degree of10-2or10-3,which showed excellent ability to reduce the interfacial tension. Long-term resistance experiments of two solutions showed that:the viscosity of different concentrations decreased,then they remained unchanged with the increase of aging time, viscosity retention rate was over65%.The interfacial tension still remained in the degree of10-2at the concentration of4000mg/L(VES04),3000mg/L(VES05) in90days,which presented good ability of long-term resistance to temperature and salt. In the study of emulsification, the abeorption rate of VES04increased rapidly on the condition of two kinds of oil,in the oil/water ratio of3:7,2:8.When the concentration was4000mg/L, Emulsification rate and stability was higher.High concentration of VES04solution showed low abeorption rate,high emulsification rate and good emulsification stability.In addition,when the salinity was respectively5000mg/L,20000mg/L,the emulsification stability of two solutions were the best.Then the emulsification rate was the biggest in the oil/water ratio of1:1,3:7.Both of solutions presented good emulsification stability in the oil/water ratio of3:7.The research of this paper provides references of surfactant flooding for two blocks, and it applies to oil production with some guidance significance.