Composition containing a polyvinylpyrrolidone and method for stimulating well production

The production of hydrocarbons from a subterranean hydrocarbon-bearing formation containing acid-soluble components, such as one containing clays or siliceous minerals as exemplified by sandstone, shale, etc. is stimulated by injecting into the formation a composition comprising an aqueous solution of a mineral acid and a fluorine-containing acid or salt and having dissolved therein a vinylpyrrolidone polymer and, if desired, a small amount of a water-soluble acrylic acid-type polymer. The in-depth increase in the permeability and porosity of the formation achieved utilizing the method of invention results in a substantial improvement in hydrocarbon recovery.