Abstract: A method of recovering hydrocarbon from an argillaceous subterranean rock formation involving the flooding of the formation with an aqueous fluid to displace the hydrocarbon from the formation. The method involves first subjecting the formation to an acid stimulation treatment by injecting a strongly acidic solution to dissolve acid soluble pore clogging materials, although this first step can be omitted, if desired. The formation is then treated with a solution containing an acid, a surfactant and a clay stabilizing agent. The concentration of the treatment solution is initially quite high but is gradually reduced until a certain threshold concentration is reached, after which a treatment solution having this threshold concentration is continuously injected into the formation to displace the hydrocarbon.

Abstract: There is disclosed a method of treating a subterranean substantially carbonate-free sandstone formation associated with a well completed in said substantially carbonate-free sandstone formation comprising displacing into said formation through said well an effective amount of an acidic aqueous solution comprising from about 5 to about 36 weight % phosphoric acid, from about 0.6 to about 5 weight % of a highly polar surface active agent which is a citric acid-monoethanolamine elimination reaction product, and an effective amount of a ferrous metal corrosion inhibitor. For treating a subterranean limestone or dolomitic formation or a sandstone formation having a substantial carbonate content there is additionally included in the acidic aqueous solution an amount of a phosphate crystal modifying agent sufficient to control crystal growth, minimize crystal agglomeration and minimize crystal adhesion to the formation.

Abstract: There is disclosed a method of treating a subterranean substantially carbonate-free sandstone formation associated with a well completed in said substantially carbonate-free sandstone formation comprising displacing into said formation through said well an effective amount of an acidic aqueous solution comprising from about 5 to about 36 weight % phosphoric acid, from about 0.6 to about 5 weight % of a highly polar surface active agent which is a citric acid-monoethanolamine elimination reaction product, and an effective amount of a ferrous metal corrosion inhibitor. For treating a subterranean limestone or dolomitic formation or a sandstone formation having a substantial carbonate content there is additionally included in the acidic aqueous solution an amount of a phosphate crystal modifying agent sufficient to control crystal growth, minimize crystal agglomeration and minimize crystal adhesion to the formation.

Abstract: A composition for treatment of siliceous formations, comprising an aqueous solution having a phosphoric acid concentration in the range of from about 10 to about 30% by weight, to which is added at least one fluorine donor compound in an amount to provide a generated hydrofluoric acid concentration in the range of from about 1 to about 7% by weight. The composition is quite reactive towards clay and silica but, unlike conventional mud acid, displays significantly retarded reactivity towards calcium carbonate. The preferred fluorine donor is ammonium bifluoride, and an especially effective phosphoric acid solution is a Turflo.RTM. solution, components of which serve to further potentiate calcium carbonate reactivity retardation.