Study And Application Of Viscoelastic Surfactant Fracturing Fluids

Long chain alkyl quaternary ammonium salts cationic surfactant was screened and determined to be used as the clean-fracturing fluids. On the basis of the structure, four Gemini quarternary ammonium surfactants were synthesized, using tetramethyl hexamethylene diamine and alkyl halides or 1,4-dibromobutane and long chain alkyl dimethyl amine as the starting materials. The molecular structure of products was characterized by IR and 1HNMR.By comparing the Gemini quarternary ammonium surfactants with their corresponding "monomer" , the capacity of former for becoming micelle was much stronger. The rheological property and viscoelasticity were also investigated, and the result indicated that this kind of structure was proved to be excellent as fracturing fluid. Besides that, two formulas of fracturing fluids were screened with Gemini quarternary ammonium surfactants as main agent, and the effect of concentration, temperature, shear stress, inorganic salts, small organic molecules, as well as the pH value on the system was also investigated. In addition, the capacity of suspending proppant, filtration and gel breaking property were evaluated, and the results showed that the systems had excellent performance.The clean-fracturing fluids were applied to peripheral low permeability reservoirs in Daqing and thin and bad reservoirs of Daqing oil field. Combined with practical, the technology of"firstly the low ratio and later high ratio"and composite gel breaking technology was established. The test results of 13 wells showed that the fracturing fluid systems had obvious advantages and provided an effective technical means for low permeability reservoirs.