Factors Affecting the Selection of Foaming Agents For Foam Stimulation

Foamed fluids have indeed become recognized as effective fluids for stimulation treatments. The unique properties of foam make it particularly suited for stimulation. The low fluid loss, low liquid content and high proppant-carrying capability of foams are among the many advantages. In addition, the lightened fluid column provides a built-in gas assist in returning the treatment fluid. Foam stimulation, however, often presents abstruse problems in fluid design and application. Successful foam stimulation treatments require careful design of foam quality, bubble texture and half-life. These design features are influenced not only by fluid volume and gas control, but also by surfactant and stabilizer selection. A variety of liquids can be foamed, such as fresh water, brines, acid, alcohol, hydrocarbons and combinations thereof. Thus, there is growing need to understand the chemical phenomena involved in producing high quality, stable foams in all these systems. This paper presents a review of the surfactant types commonly used as foaming agents. These surfactants may be classified by their ionic nature, which often influences performance. Anionics (soaps), non-ionics (alkyl polyoxyethylene), amphoterics and cationics (amine derivatives) are available for use as foaming agents. The performance of such additives in water, acid, alcohol, and hydrocarbon systems is compared. In addition, the chemical stress factors which must be considered when selecting surfactants for a foam treatment are outlined. These include formation character, interaction with other fluid additives, and surfactant wetting properties. Techniques for stability enhancement are discussed.