The Preparation And Formation Mechanism Of Microemulsion Flooding System In Low And Medium Permeability Reservoirs

In order to achieve stable and increased production in oil fields,finding efficient post-water drive succession technology has been an important research topic in oil field extraction.Due to the characteristics of non-homogeneity,narrow pore throat and complex formation minerals in medium and low permeability reservoirs,a large amount of residual oil is often left in the formation during extraction,and the extraction effect of traditional chemical drive has been less than ideal,while the microemulsion system has a series of unique properties.For example,ultra-low interfacial tension,strong ability to solubilize water and oil,small particle size,etc.These properties are its good effect of reducing pressure and increasing wave efficiency when injecting into low permeability oil formations.In this thesis,sodium tetrapolyacrylate benzene sulfonate（ABS）and sodium fatty alcohol polyoxyethylene ether sulfate（AES）were preferably selected as the surfactant combination and sodium chloride as the salt to compound the mesophase microemulsion system;the effects of surfactant,salt,oil-water ratio,interfacial tension and other factors on the formation of the mesophase microemulsion system were investigated;the prepared mesophase microemulsion system was evaluated in terms of emulsification solubilization ability and particle size;the The repulsion experiments were carried out in different ways and different cores,and good repulsion effects were achieved.The details and results are as follows:In the preliminary screening,three types of surfactants:anionic surfactants,anionic-nonionic surfactants,and nonionic surfactants,were selected for compounding in different ratios and evaluated by measuring their interfacial tension.The results showed that for this crude oil,the applicable surfactant should have a low carbon chain.In addition,a formulation combination of an anionic surfactant and an anionic-nonionic surfactant was used for excellent performance,and the combination was found to achieve an ultra-low oil-water interfacial tension at a low salt concentration.Sodium tetrapolyacrylate benzene sulfonate（ABS）and sodium fatty alcohol ethoxylate sulfate（AES）were preferred as surfactant combinations;（1）the relationship between salt type and interfacial tension was investigated,and it was found that the mesophase system formed by Na₂CO₃as salt was superior to that formed by Na Cl as salt,but considering the problem that Na₂CO₃would scale the pore channels of the rock formation after injection,the final choice was Na Cl was chosen as the salt.（2）The specific combination selected was sodium tetrapolyacrylate benzene sulfonate（ABS）and sodium fatty alcohol polyoxyethylene ether sulfate（AES）,AES:ABS=1:1,and the relationship between surfactant concentration interfacial tension,salt concentration and interfacial tension were investigated respectively,and it was found that the optimal surfactant concentration was 0.3wt%and salt concentration was 0.5wt%to obtain ultra-low interfacial tension,and the microemulsion system interfacial（3）The relationship between surfactant concentration and salt concentration with phase state at different oil-water ratios and the relationship between the phase state of microemulsions with salt concentration at the same oil-water ratio were investigated,and it was found that medium-phase microemulsions could be formed in the narrower oil-water ratio interval,and the optimal oil-water ratio was 5:5,and the emulsification rate increased with increasing surfactant concentration.A very obvious phase change was observed,Winsor I type transformed to Winsor III type and finally to Winsor II type;（4）Microphase and particle size analysis of microemulsions was performed,and it was found that the size of particle size was mainly distributed in the range of 0.03μm to 0.1μm.（5）Determine the best repellent combination:the best surfactant concentration is 0.3 wt%,the best salt concentration is 0.5 wt%,and the best oil-water ratio is 5:5In the oil drive experiments,different replacement methods as well as different cores were used for replacement,and it was found that when the negative salinity gradient replacement method was used,it was more favorable for recovery improvement.When the replacement core was artificial beryl core,the medium-phase microemulsion system with0.3wt%concentration improved the recovery rate by 44.2%on the basis of 46.7%in water drive,and the total recovery rate reached 90.9%;the water content decreased significantly in the chemical drive process,down to 25%at the lowest,and the final residual oil saturation decreased to6.76%.When the replacement core is natural core,the 0.3%concentration of medium-phase microemulsion system increases the recovery rate by 26.19%based on 53.98%of water drive,and the total recovery rate reaches 80.18%;the water content in chemical drive process decreases not significantly,at least to 72%,and the final residual oil saturation decreases to 19.92%.Overall,the oil drive effect was satisfactory.