| With the continuous development of low permeability reservoir fields for fracturing fluid performance requirements are also increasing. The VES developed in recent years largely solved traditional fracturing fluid gel breaking hard, high filtration residue and other defects. At present, domestic and foreign research progress of VES used in oil well reflected in the preparation of novel surfactants and its viscoelastic,injury, rheology,friction resistance, high resistance joints and other controlled experimental study, while for some low porosity and low permeability, low pressure reservoir began. But still in its infancy, most of the drugs developed by various research institutes are limited to the laboratory synthesis and the results of the development only in certain fields small-scale applications. The VES suiting for gas wells has good effects than gum fracturing fluid in terms of controling crevice,friction,low reservoir damage.VES for oil well is relatively little research and low temperature resistance.Although the VES system for simply oil application gradually extended to nature gas and coal bed methane,the new product design ideas is mainly to use single special surfactant forming rod-like micelles and thus the reticular structure.The evaluation about VES involves of viscosity change in different composition,temperature,shear rate and the fracturing fluid filtration and formation damage.At present the basic composition of VES mainly contains of viscoelastic surfactant, salt solution and stabilizer.In the research of VES, the use of surfactant chain length of more than12—18, mainly divided into anionic and cationic.Owing to the good gelation and temperature resistance,the cationic surfactant is widely used in research and applications.With deeply study,it is found that cationic surfactant has a larger adsorption to clay and sand.Due to this reason, cationic surfactant fracturing fluid causes bigger wetting injury,which would effect EOR.Although developed VES can improve the recovery ration to certain extent,the high cost and poor temperature resistance greatly limit the application promotion.Therefor it has a very important significance to develop VES with intellectual property rights and relatively low cost.Aiming at this problem, this paper develops four kinds of VES system with independent research anionic Gemini surfactant as main agentandpotassiumchloride,sodium,salicylate,dodecanol,titanium,dioxide,nanoparticles as additive. The ratio of4systems are:①5%GA-12+2.0%NaSL+4%dodecanol+0.15%TiO2;②3.5%GA-14+1.5%NaSL+3%dodecanol+0.2%TiO2;③3%GA-16+2.0%NaSL+3%dodecanol+0.15%TiO2; ④2%GA-18+1.0%NaSL+3%dodecanol+0.15%TiO2According to SY/T5107-2005" water-based fracturing fluid performance evaluation method", it start a test which contains of flow curve test,stress sweep,frequency sweep,modulus test,temperature test,gel breaking test,sand carrying test and shear resistance test.The study showed that four fracturing fluids systems belong to pseudoplastic fluid, with the rise of temperature fracturing fluid consistency coefficient K decreases, thickening performance decreased GA-16and GA-14fracturing fluids systems have higher storage modulus,excellent viscoelastic effect,GA-16system has higher temperature resistance which can be used in90℃fracturing. Four kinds of fracturing fluid systems gel breaking liquid viscosity is less than5mPa.s,it interfacial tension is low,no residue,sand carrying effect is obvious,the settling velocity of ceramsite fracturing in4fluid system is only the average1/20than in water,the shear resistance of GA-12,GA-14,GA-18fracturing fluid system is similar and lower than GA-16system.After150min shearing,four system viscosity retention rate are following:71.4%,73.8%,77.7%,73%. |
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