In-situ crosslinked gelled hydrochloric (HCl) acid systems have been extensively used in matrix acidizing and acid fracturing treatments to help achieve acid diversion. These systems also help control fluid leakoff and help retard the acid reaction to allow deeper acid penetration. Presently, in-situ crosslinked gelled acid systems are generally comprised of acrylamide-based polymers, an iron crosslinker, and a breaker chemical, in addition to other additives, with HCl acid. Many iron-based crosslinker systemscan form iron depositions, precipitation/sludge, and/or scale formation during or after the acidizing treatment when the acid spends, which can causeformation damage. In addition, thismight also lead to increased operating costsbecause of the need for sludge- and/or scale-removal treatments.

To overcome these issues, a new non-iron-based composition was developed for in-situ gelled acid systems that can work in 5 to 20% HCl acid at temperatures up to 300°F. The new composition performs identicallyto that of iron-crosslinker systems but can avoid problems associated with scale formation and precipitation. The new non-iron-based composition crosslinks the polymer in the pH range of 1.5 to 3, which helps withdiverting the next acid stage into tight or damaged zones. The gelation or crosslinking can be observed as acid reacts with a carbonate formation and the pH rises above 1.5. Further, as acid continues to spend on the formation and when the pH becomes greater than 3, the gel shows a reduction in crosslinked viscosity. This newly developed system does not require any reducing agent or breaker aid because the crosslinked gel shows a complete break with acid spending. The crosslinked-gel stability of this systemfor temperatures up to 300°F is evaluated and discussed in this paper. The effect of corrosion inhibitors, along with other additives, on this new crosslinked system is also described.

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