Wormholes from retarded acid systems

Quite often, acid will form predominantly single wormholes from limited numbers of perforations, without significant branching. That is the case with strong acids, such as HCl. Weaker acids, such as carbox)dic acids (e.g., acetic add), and retarded acid systems tend to create more branching of wormholes, which is desirable but only to a certain extent. Retarded acid systems include viscosified acids (e.g., polymer- or surfactant-gelled acid, emulsified acid, and foamed acid) or chemically retarded (surfactant-retarded) acid. The nature of wormholes created depends on injection rate, temperature, and formation reaction characteristics as well. 

Retarded acid systems can extend the length and number of wormholes. Such systems include slightly gelled acid, chemically modified acid, surfactant-retarded acid, emulsified acid, and foamed acid. However, the time it takes for acid to spend is still short in most cases. Usually, only the formation near the wellbore can be treated effectively. Thus, effective uniform matrix treatment beyond several feet from the wellbore is exceptional. 

---

See also in sourсe #XX -- [ ]

---