The Synthesis Of Biodegradable Surfactants For VES Fracturing Fluid And Property Evaluation

Compared to conventional water-based fracturing fluid, viscoelastic surfactant(VES) fracturing fluid has some advantages, such as simple preparation process, high efficiency, easiness to break gel and flow-back, low reservoir damage. At present, for a number of oil and gas fields, quaternary ammonium salt cationic surfactant fracturing effect is not very ideal, it's difficult to degrade under natural conditions and destroy the reservoir, which limits its further development.Ester containing sulfobetaine surfactant will be able to biodegradation, it is capable of forming a high viscosity fluid with counter-ions at a lower concentration. In the paper, four-containing ester sulfobetaine surfactants were synthesized by using long-chain fatty acids and N, N- dimethylethanolamine after esterification and quaternization reactions. The structures of products were characterized by FTIR, H-NMR spectra, the results showed that the synthetic products are consistent with the desired products. Meanwhile physical and chemical properties of synthetic surfactants were studied, four surfactants have a solubility characteristics of general surfactant, critical micelle concentration was lower than conventional long chain betaine. Using the viscosity-temperature method in different sittuations, screened stearate sulfobetaine(SESB) was filtered as a fracturing fluid master agent, and counter ion EDTA·4Na was an additive which made the viscosity increased significantly. The best formulations of the main agent and additives were identified eventually. With liquid nitrogen rapid freezing method, fracturing fluid microstructure were measured by FSEM, different degrees of worm-like three-dimensional network structure were observed, which explained the effect of different ions and different formulations of anti-system viscosity.The performance of several optimized formulations were tested by many methods, the results show that the apparent viscosity of SESB/EDTA·4Na system is higher than 30mPa·s at 80 ? and shear rate 170s-1, it has good heat and shear resistance performance and the system processes high shear stability and recovery at room temperature. According to viscoelastic test, the system mainly depends on elastic to carry sand. Static settling velocity of sand is 0.042mm/s under high temperature conditions of 95 ?. The fluid viscosity is less than 5mP·s after contacting with cyclohexane within 4h, which is consistent with SY / T 6376-2008 ?Fracturing Fluid General Technical Conditions?national standards.Using different complex formulations(KCl, MES, nano-SiO2) to modified 2.0% SESB / 0.4% EDTA·4Na system, the viscosity-temperature characteristics of complex solution study indicated that KCl and MES can not increase the viscosity at high temperatures, while 0.1% nano-SiO2 has obvious synergies effect, temperature resistance and shear resistance performance of the complex system significantly improved and the morphology tends to be regular.