TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractDifferent acid systems have been used to stimulate production and injection wells for more than a century. Several chemicals are added to the acid to enhance the efficiency of the acidizing treatments, including various types of surfactants.Surfactants play a key role in many well treatments because of their unique properties. Surfactants are used to reduce surface tension, change wettability, mobilize residual oil, and disperse corrosion inhibitors. They are also used as anti-sludge agents, emulsifiers in acid-oil emulsions, and demulsifiers. This wide spectrum of applications is due to the ability of surfactants to adsorb on various surfaces and associate in the bulk of solutions and form micellar structures. The properties of surfactants depend on the size of the head, tail length, and configuration of the tail, surface charges, ionic strength and temperature.Recent advances in surfactant technology have introduced a new class of surfactants with special characteristics useful in oilfield applications. This new class of surfactant has the ability to form viscoelastic systems, which can be used to increase viscosity of the treating fluids, without causing formation damage. These surfactants have been used in Saudi Arabian fields to enhance diversion during matrix acid stimulation, reduce leak-off during acid fracturing and to minimize losses (well control) during workover. The system proved successful to provide fracture extensions in acid fracturing applications of low temperature seawater injectors and high temperature gas wells. These surfactant systems are non-damaging and do not require sized solids to control losses, which eliminates the need for remedial acid treatments.

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