Corrosion-Inhibitor Design for Compatibility with Acid-Gelling Polymers

Abstract

Abstract Polymers used for delayed acid gelling are designed to crosslink with metal crosslinkers once the acid is spent to a certain pH so that the resultant solution-viscosity increase will cause acid diversion. However, some organic molecules have the ability to react with the functional groups of the polymers and cause crosslinking before a pH rise. Consequently, the higher viscosities resulting from early crosslinking can affect the pumpability of the acid blend and can also lessen the ability of the polymer to clean up from the formation following diversion. Aldehydes, used as active components in many acid corrosion inhibitors, have the potential side effect of prematurely crosslinking polyacrylamide-based acid-gelling agents because of the reaction of the aldehyde with the polymer amide groups. Furthermore, other unsuspected inhibitor active ingredients might also convert to aldehydes in an acidic environment and cause crosslinking problems. The chemistry of the reaction of different aldehydes with polyacrylamide-based gelling agents is presented through use of analytical techniques, along with viscometer studies that simulate downhole conditions. These investigations consider how the molecular structure of the aldehyde affects crosslinking with temperature and acid strength. Based on information learned from the study of aldehyde interactions with the polymer-gelling agent, an acid corrosion inhibitor can be designed that does not cause any interference when used in conjunction with acid-gelling polymers. Development of such a corrosion inhibitor is presented.