Abstract: Copolymers of a predominant proportion of an olefinically unsaturated sulfonic acid, an acrylamide, a vinyl phosphonic acid, and optionally other copolymerizable vinyl monomers, form aqueous acid gel compositions when added to the aqueous acid along with a gelling agent selected from titanium or zirconium compounds, and retarded gel destabilizing compounds containing fluoride, sulphate or phosphate anions, the apparent viscosity and time of stability of the acid gel composition being controlled by the addition of these essential ingredients.

Abstract: Copolymers of a predominant proportion of an alkyl allyl ammonium halide and a vinyl phosphonic acid, optionally with other copolymerizable vinylidene monomers, form aqueous acid gel compositions when added to the aqueous acid, along with a gelling agent selected from titanium or zirconium compounds, and gel destabilizing compounds containing fluoride, sulphate or phosphate anions, the apparent viscosity and time of stability of the acid gel composition being controlled by the addition of these ingredients. These acid gels are particularly effective as fracture-acidizing fluids in deep, hot oil or gas well stimulation.