Preparation Of Viscosifying Agent For Acidizing And Its Evaluation

Viscous acid used in acid fracturing is the main acidizing fluid system for carbonate rock reservoir. The key constituent of viscous acid is viscosifying agent. At present, the viscosifying agent used widely is synthetic polymer. A cationic viscosifying agent, the compolyor of Dimethyl Diallyl Ammonium Chloride (DMDAAC) and Acrylamide (AM), and an anionic viscosifying agent, the compolyor of 2-acrylamido-2-methylpr-opanesulfonate (AMPS) and Acrylamide (AM), were prepared by solution polymerization. The factors affecting copolymerization were studied, and the reacting condition was optimized. The results showed that the molecular weights of anionic viscosifying agent WD-1 and cationic viscosifying agent WD-2 were high. At the condition of room temperature, the viscosity of the WD-1 acid was 46.3mPa·s. The heat resistance after thermal treatment at 90℃was 85.5%. The shear stability was 90% after shearing two hours at the condition of room temperature and 170s-1. At the same condition, the viscosity of the WD-2 acid got 63.18mPa·s. The heat resistance got 80% and shear stability got 93.6%.A new viscosifying agent which has good viscosifying when being injected and low viscosity when being flowbacked is studied.That viscosifying agent was prepared by AM, DMDAAC and a chain extender. Its viscosifying ability was better than DSGA at the beginning. But with the acid temperature ascending and the contact time prolonging, the viscosity of that acid descended. This properly is good for the flowbacking of spent acid.