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Organically crosslinked gels have been used to control water production in high-temperature reservoirs. Most of these gels consist of a polyacrylamide-based polymer and an organic crosslinker. Polyethyleneimine (PEI) has been used as an organic crosslinker for polyacrylamide tertiary butyl acrylate (PAtBA) copolymer. Literature reported that PEI can also form ringing gels with polyacrylamide (PAM) copolymers in addition to simple PAM homopolymers.We report a comparative study of two water-control gel systems (i.e., PAtBA copolymer and PAM crosslinked with PEI). Several techniques were used in the present study, including gas chromatography (GC), carbon 13 nuclear-magnetic-resonance (C13 NMR) spectroscopy, and steady-shear viscometry. The gases produced during the reaction, structural changes, and gelationtime data were all integrated to provide further insights into differences between the two gelling systems.The evolution of isobutene gas was identified at temperatures as low as 60 C during the formation of PAtBA/PEI gels. In addition, GC studies revealed the release of carbon dioxide (CO 2 ) as a product of thermal decomposition of the tBA groups on PAtBA during PAtBA/PEI gelation.Lower initial pH values were found to delay the gelation time of the two systems. Salts were found to increase the gelation time. This paper summarizes these results and investigates the main reaction mechanisms involved. It also discusses how these new findings will affect the application of these gels in the field.

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