Study on a New Temperature-controlled Variable Viscosity Acid

A variable viscosity acid was formulated with a viscosifier BCG-5, a corrosion inhibitor HB-2 and an active agent NC-1. This acid, formulated on the theoretical basis of the Biggs’ three-stage model describing the reaction between polymer and surfactant, shows low apparent viscosity at low temperature, and shows high apparent viscosity at high temperature. Since formation temperature increases with depth, this acid, when injected into the formation, will show low viscosity in shallow depth and high viscosity in deep depth. Laboratory experiments have been conducted to compare the viscosifying capacity of different thickening agents, test the effects of the content of the active agent on the viscosifying of the acid under the control of temperature, and optimize the type and concentration of the corrosion inhibitor. It was found that the apparent viscosity of the acid was 29 mPa·s at room temperature, and gradually increased to 250 mPa·s after being heated at 90 ℃ for 20 min. At 100 ℃, the acid still had ability to change its viscosity. The corrosion rate of this acid was retarded by 90.1%. The apparent viscosity of the acid was reduced to 5 mPa·s after reaction with rocks, and the surface tension of the acid became 20 mN/m, which is helpful to increasing the flow conductivity, reducing friction and drag and performing in-depth acidizing and acid-fracturing.