Evaluation of a control-released in-situ generated acid tablet for acid fracturing

Abstract

Abstract Acid fracturing is one of the common well stimulations techniques in carbonates. There are some limitations in conventional acid systems during the application, such as fast reaction of acid-rock, high leak-off rate and strong corrosion, that s why, the retarded acid systems, like gelled acids, are developed. In this work, a control-released in-situ generated acid matrix tablet is reported as a novel retarded acid system to overcome the above limitations. In the tablets, ammonium chloride and paraformaldehyde are used as active substances to generate hydrochloric acid (HCl), with high dissolving capacity of over 85% and excellent corrosion inhibition of more than 90% at 90\u202f°C without inhibitors. A one-step and economic method is used to prepare the acid tablets by directly compacting the powder mixture of active substances. The dissolution rate of tablets is adjusted to control the release of acid, so that such form reduces the leak-off rate and slows the reaction of acid-rock. The simplicity of preparation process of the tablets along with excellent dissolution and corrosion inhibition makes the proposed acid tablets technique potential for the application in acid fracturing.