Preparation And Performance Study Of Microemulsion For Tight Oil And Gas Reservoirs

In recent years,due to lack of natural energy,high viscosity and poor fluidity of some reservoirs,oil and gas production capacity has declined.Therefore,it is necessary to carry out fracturing for ultra-low permeability and tight reservoirs.In the process of fracturing,the microemulsion is full of favorable parts,such as high porosity,high permeability zone,large pore throat or crack,and the oil and gas in the medium,small pore throat or matrix can be replaced by the oil and gas in the medium,small pore throat or matrix,which can lead to the redistribution of oil and water in the production layer.Because of the synergistic effect of surface active agents,the microemulsion is firmly combined with the core surface,and the surface of the hydrophilic core is improved to neutral weak hydrophilic(65°<?<90°),reducing the drag of the capillary,which is beneficial to the flow of water phase and the return of the working fluid.At the same time,reducing the interfacial tension of the oil and water surface of fracturing fluid and changing the wetting condition of the formation also contribute to the return of the working fluid,reduce the damage to the formation by the fracturing fluid and achieve the goal of increasing oil and gas production and stable production.In this paper,the adsorption of surface active agents S1,S2,S3,S4,S5,S6,S7,S8,S9,S10(among these,S1 is a cationic surfactant,S2 and S3 are nonionic surfactants,S4-S8 are betaine amphoteric surfactant,and S9 and S10 are the amines surfactants)on the solid surface,the improvement of the wettability of mica surface,the decrease of the surface tension and the properties of the compound microemulsion are studied.The results show that S1 improves the hydrophilic property of mica to the hydrophile property,and can also make the charge of the sandstone core surface positive.Under low concentration,the mica surface is monolayer on the mica surface,and the high concentration is mainly monolayer adsorption,accompanied by double adsorption.Low concentration of S2 and S3 mainly occurred monolayer adsorption on mica surface.At high concentration,S2 mainly occurred in double layer adsorption and monolayer adsorption occurred mainly in S3.S4 weak acid environment can make the core surface positively charged,low concentration is monolayer adsorption,high concentration is double-layer adsorption.At low concentration,the adsorption morphology of S5,S7,S8,S9 and S10 on the mica surface is mainly monolayer adsorption,and S6 is mainly multilayer adsorption.At high concentration,S5,S7 and S10 are mainly monolayer adsorption.With a small amount of double layer adsorption,S6 and S9 are mainly multilayer adsorption.Subsequently,the particle sizes of S4 and non S4 series microemulsions are all less than 100nm,which meet the particle size standard of microemulsions.Considering the X1-X4 microemulsion,the performance of X3 is the best:the wettability of mica surface is better,the contact angle is 68°,reached the neutral and weak hydrophilicity property,the interfacial tension is the strongest,the interfacial tension is 0.204mN/m,and the increase rate of the return row is the highest of 38.36%.In W1×W6 microemulsion,the properties of four microemulsions of W2,W3,W4 and W5 are superior:the contact angles are 85.52°,81.67°,73.47° and 76°,all greater than 65°,reaching neutral and weak hydrophilicity,and the interfacial tension is 0.113mN/m,0.216mN/m,5.938mN/m and 0.564mN/m respectively,and the increase rate of back row is 21.92%,42.57%,36.25%and 32.2%,respectively.Considering comprehensively,the W3 microemulsion has the best performance,its contact angle reaches 81.67°,the interfacial tension is 0.216mN/m,and the increase rate of backflow is 42.57%.