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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWater production during oil and gas recovery is a longstanding problem that is becoming critical with maturing fields worldwide. Lifting, processing, treating and re-injection of the unwanted water add to the overall oil production costs. Also, water disposal may pose environmental problems. Recent statistical studies indicate that processing unwanted water costs the oil industry nearly 40 billion dollars per year.Polymer gels have been widely used as blocking agents for excessive water production. In this study, a copolymer of polyacrylamide tert-butyl acrylate (PAtBA) and polyacrylamide (PAM) crosslinked with polyethyleneimine (PEI) have been investigated. This PAtBA/PEI system was previously shown to be stable at temperatures up to 160 o C, typical of those encountered in deep oil and gas reservoirs. However, the crosslinking mechanisms of this system at high temperatures have not been well defined.This study examined the structural changes of PAtBA and PAM using C-13 Nuclear Magnetic Resonance (NMR) spectroscopy. Understanding these changes is a first step towards the identification of the crosslinking mechanisms of PAtBA and PAM with PEI. This will have a strong impact on the design of water shut-off treatments utilizing these systems.

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