A new series of prepackaged acid systems have been developed for stimulation of sandstone formations. The original system, containing phosphoric acid and other additives (labelled P.P.A.S.* throughout this article) was specifically formulated to overcome several limitations of existing acid systems. The scope of applications for P.P.A.S. has since been expanded by combining HCl (Hydrochloric acid) or HF (Hydrofluoric acid) with the P.P.A.S. to form hybrid systems that have unique properties. These new systems have been successfully used for stimulating sandstone formations that have been difficult to treat with existing acid systems. The problems associated with currently used acids and their limitations are compared to the P.P.A.S to illustrate the advantages of these new systems.

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