A comprehensive review on acid-induced sludge formation during matrix acidizing: Nature, mechanism, and effective parameters

Acid-induced sludge formation is known as the main reason for the failure of acid stimulation operations, since its precipitation and deposition in porous media can offset the acidizing benefits by pore plugging, unfavorable wettability alteration, and viscous emulsion formation. Due to the severity of the induced formation damage by acid-sludge during acidizing treatments, the development of some approaches to control/prevent acid-sludge formation attracted more attention. As a result, several studies have been conducted to understand the acid-sludge nature and formation mechanism. However, the contradictory results reported by different authors lead to the misunderstanding of the fundamentals of acid-sludge formation. It is believed that, by putting the results of different authors together, more reliable information on the acid-sludge nature and formation mechanism as well as its dependence on different parameters can be obtained. Therefore, in this paper, a comprehensive literature review is conducted on acid-induced sludge to explain the fundamentals of acid-induced sludge formation.