Laboratory evaluation on a kind of potential retarded mud acid charactered with hydrolyzed ester

To resolve the problem of the high reaction rate and the short operating distance of mud acid, a kind of retarded acidizing fluid, which is a kind of acid self-generated by ester and villiaumite, is studied in the article. Acidity characteristic curve of self-generated HF demonstrates that, the potential retarded acid based on hydrolytic ester presents better buffering effect. Dissolution experiment at different ratios of ester and villiaumite concludes that the best ratio of ester and villiaumite is 2∶1, and 3% self-generated HF acid with 10% hydrochloric acid is devised under the 2∶1 ratio of ester and villiaumite through many experiments. The dissolution rate of the acid system increases from 20% at 70℃ to 33% at 100℃ with NO.5 core, and its initial reaction rate is half of conventional mud acid with NO. 7 core at 80℃. It presents better temperature control capability and better dissolution inhibition capacity. It presents more than 33% dissolution rate to three kinds of mud fluid and presents more than 20% dissolution rate to clay minerals, and presents stronger dissolution capability to slurry and clay mineral. The permeability of Core II that is acidized by potential acid is 4.01 times as large as before, which is 2 times effect of mud acid, and the potential acid presents better deep penetration capacity.