| As an important method in transformation of oil and gas reservoirs, hydraulic fracturing is an effective measure of oil-gas well augmented production and water well increasing injection. The quality of fracturing fluid properties is directly related to the success or failure of the construction operations. Currently, to conventional hydraulic polymer-based fracturing fluid, the liquid flowback rate is very low because of the uncomplete gel breaking, polymer residues would clog the pore space of proppant-pack layer, and reduce the permeability of fractures, lead to a loss in fracturing effectiveness and even invalid. However, because the new surfactant fracturing fluid has the advantages of the unique rheological properties, not requiring gel breaker, gel broken spontaneously in the formation environment and lower formation damage, domestic and foreign scientific and technical personnel in oil and gas field pay widespread attention to it.The application of dual quaternary ammonium salts surfactant in the fracturing fluids as the research main line of this paper, two works were mainly carried out, the first part is about the synthesis of high yield, high purity dual quaternary ammonium surfactant and the choice of formula to the fracturing fluid, the second part is about the appraisal of some performance to the formula of elected fracturing fluid. Research progress as follows:1. Three high yield 2-hydroxy propylidene connected dual quarternary ammonium (DQ)surfactants were synthesized, using three straight-chain primary amines, formic acid, formaldehyde, epichlorohydrin, and concentrated hydrochloric acid as the starting materials, they are 12-3-12,16-3-16 and 18-3-18, respectively. In the mixed indicator solution, the contents of quaternary ammonium cations of there targets were determined, the corresponding purities were gotten.2. Taking 12-3-12 as an example, through single factor experiment and orthogonal test, investigated the effect of the target rate on solvent, molar ratio, reaction temperature and reaction time, the optimal reaction conditions were got:water as solvent, mole ratio of raw materials was 2:1:1.5, the reaction temperature was 60℃, reaction time was 3.5h, the yield of target could reach 96.27%, and the molecular structure of products were characterizde by IR and 1H NMR.3. Targets have good surface activity. The cmc of 12-3-12,16-3-16 and 18-3-18 are 5.0×10-4mol/L,3.1×10-5mol/L and 9.1×10-6mol/L, respectively. Comparing with common quaternary ammonium surfactant, they are 1/32 by DTAC,1/29 by CTAC and 1/31 by OTAC;γcmc are 24.8mN/m,29.5mN/m and 32.1mN/m, respectively. Comparing with DTAC, CTAC and OTAC, they are respectively lower 12.1mN/m,10.6mN/m and 10.7mN/m.4. Investigated the effect of main agent, activating agent and temperature on the viscosity of DQ solution. Through this,16-3-16 and 18-3-18 were selected as the main agents of fracturing fluids, and the corresponding formulas of fracturing fluids were gotten.5. The rheological parameters of the 16-3-16 and 18-3-18 fracturing fluids were measured.The results show that:two systems are pseudoplastic fluids, fracturing fluids have larger consistency coefficient K and smaller mobility index n; K would decline with the increasing of temperature, and the K of 18-3-18 system is greater than 16-3-16. Two systems also have good shear thinning, recovery properties and time stability.6. The temperature resistance of the 16-3-16 and 18-3-18 fracturing fluid were measured, and investigated the effect of viscosity of two fracturing fluids on pH value and salinity. The results show that:two systems have very good low temperature resistance and high temperature resistance,18-3-18 system also have very good temperature stability; increasing the concentration of surfactants can increase the maximum use temperature of fracturing fluid; whether in high or low temperatures, the viscosity of two systems have not essentially changed with pH value, having good compatibility with formation water.7. Through small frequency oscillatory shear experiments, Storage modulus G’, loss modulus G" and complex modulus G* of the 16-3-16 and 18-3-18 fracturing fluid were measured, two systems have obvious viscoelastic.8. The suspended sand properties of the 16-3-16 and 18-3-18 fracturing fluids were measured. The viscosity of DQ surfactant fracturing fluids is lower than the polymer solution, but the static settling velocity of proppant in 16-3-16 and 18-3-18 fracturing fluids is lower than the polymer solution.So, the suspension mechanism of these fracturing fluids is different.9. The broken plastic properties of the 16-3-16 and 18-3-18 fracturing fluid were measured. Two systems would be broken spontaneously after meeting oil and water, the viscosity of the breaking glue liquid are less than 3mPa-s and 2mPa-s, respectively; the surface tension and oil-water interfacial tension of the breaking glue liquid are very low, and no residue. |
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