Acid foam fracturing

A method for fracturing subterranean formations comprising the steps of:

• a. forming a gelled acid-liquid solution by combining an acid chemically reactive with a subterranean formation with about 250 to about 15,000 ppm of a gelling agent selected from carboxymethylcellulose polymers, polyacrylamides, and polysaccharides,
• b. adding a sufficient amount of a surfactant to said gelled acid-liquid solution obtained in (a) to form a stable foam at formation injection conditions, said surfactant being compatible with the other ingredients of the gelled acid-liquid solution and capable of producing foam in an acidic environment,
• c. introducing said gelled acid-liquid solution containing surfactant and an inert gas into a subterranean formation under sufficient pressure to form a foam and cause fracturing of said subterranean formation, and
• d. allowing the acid contained in said foam to react with the subterranean formation and cause etching thereof.