Evaluation Of Adsorption And Displacement Properties Of Anion-Cation Pair Surfactant System

Chemical flooding has been an important tertiary oil recovery method all over the world.Surfactant,a significant component in chemical flooding system,can improve oil recovery dramatically by reducing oil-water interfacial tension（IFT）and raising displacement efficiency.Among the various surfactants,anion-cation pair surfactant has got more and more attention and application due to its special properties.The adsorption and displacement performance of anion-cation pair surfactant in long-distance migration were evaluated by laboratory physical simulation experiment.Firstly,the IFT,temperature and salt resistance,and emulsifying stability of anion-cation pair surfactant system and ASP system were evaluated.Then,the crude oil recovery,pressure drop along the model and the residual oil distribution were studied using a 30 m ultra-long one-dimensional physical sand-packed model.During the flooding experiment,samples along the model were collected to test the component concentration,viscosity,IFT and emulsification effect.Finally,the displacement mechanism of anion-cation pair surfactant was studied according to the displacement efficiency.The experimental results show that anion-cation pair surfactant can reduce the IFT obviously.At a low concentration of 0.05 wt%,anion-cation pair surfactant can lower IFT to an ultra-low level of 10^-4m N/m in a short time.It also has good emulsion stability,temperature and salt resistance.In the 30 m ultra-long one-dimensional physical sand-packed model flooding experiment,the anion-cation pair surfactant can enhance oil recovery by 8.26%at a low concentration（0.2 wt%）.Its ASP system can enhance oil recovery by 16.64%in presence of 0.8 wt%Na₂CO₃.The concentration and viscosity of each component show an obvious ladder distribution from inlet to outlet.The ultra-low IFT of anion-cation pair surfactant system maintained nearly 1/3 of the model,stable emulsion formed between 6.38-13.98 m of the model.The ultra-low IFT of the ASP system maintained about 1/2 of the model,the stable emulsion formed between 6.38-21.63 m of the model.The ASP system has good performance of displacing oil due to its good emulsifying property and its ability of reducing IFT.The study can offer meaningful guidance for the composite system optimization as well as rational knowledge of flooding mechanism of anion-cation pair surfactant.