The Study On Viscoelastic Surfactant Self-diverting Acid And Applied Technology

The preparation and comprehensive performance evaluation of VDA-SL viscoelatic surfactant and its compatible inhibitor were studied in this paper. The results shows that the viscosities at 30℃of the viscoelastic surfactant self-diverting acid were 65mPa?s, 337mPa·s and 3mPa·s in 25%, 15% and 1% hydrochloric acid, respectively. And the viscosity at 120℃ of the viscoelastic surfactant self-diverting acid was 69 mPa·s and it could still be 58 mPa·s after 100mins’ shear, which shows that the self prepared viscoelastic surfactant self-diverting acid has good properties of temperature and shear resistance. The research also shows that the corrosion rate was only 1.91 g·(m2·h)-1 when the compatible inhibitor was added to the acid system, which shows that the viscoelastic surfactant self-diverting acid has good property of corrosion inhibition as well. The micro-structure of VDA-SL viscoelatic surfactant solution was analyzed by polarizing microscope. The results show that the solution of VDA-SL viscoelatic surfactant was multilamellar vesicles micellar structure, and its good viscoelasticity was gotten by the deformation of the vesicles. It is showed that viscoelatic surfactants with different structures have different effects on their viscoelasticities. The effects of acids’ PH, shear rate, the content of SL surfactant, temperature, inorganic salt alcohol molecules and additives on rheological properties of the acid system were also studied in this paper.The advantages of VDA-SL viscoelatic surfactant self-diverting acid are summarized by laboratory evaluation and field test. Firstly, VDA-SL viscoelatic surfactant self-diverting acid has well enough viscoelasticity, which can realize effective temporary plugging to the formation with high porosity and high permeability in acidizing process and make the fluid shunt and shift. Secondly, VDA-SL viscoelatic surfactant self-diverting acid has the effect of viscous acid, which can control acid-rock reaction, increase injection distance of acid solution, improve reasonable distribution of acid solution in the reservoir space and finally raise the effect of acidizing process. Thirdly, VDA-SL viscoelatic surfactant self-diverting acid has the characters of situ self diverting acid system whose fresh acid stage has the properties of low viscosity and good rheology, which can be pumped to formation easily. With acid-rock reaction, the viscosity of self-diverting acid change atomatically. The quicker the reaction rate is, the higher the viscosity is. And the acid with high viscosity can realize effective temporary plugging and reconstruction formation evenly.Fourthly, as a new type self-diverting acid, crosslinking agent and gel breaker are not added. Viscosity of the self-diverting acid change automatically with acidity, and the hydrocarbon can act as gel breaker in the formation. Fifthly, VDA-SL viscoelatic surfactant self-diverting acid can decrease fluid loss effectively, which overcomes the shortcoming bought by other kinds of acid that can put damage on the formation. Sixthly, the field process of acid fracturing is simple, which can pump in many times to realize delayed acidizing. Also, the preparation of diverting acid solution is simple, which can be made in the right site. Sevenly, VDA-SL viscoelatic surfactant self-diverting acid has low surface tension, and is easy to flowback.