Due to their thermal stability, organically cross-linked gels have been used to control water production in high temperature applications. Most of these gels consist of a polyacrylamide-based polymer and an organic cross-linker. Polyethyleneimine (PEI) has been used as an organic cross-linker for polyacrylamide-based copolymers.

Recent work indicated that PEI can form ringing gels with polyacrylamide homopolymers (PAM). However, no study reported on the kinetics of PAM/PEI gels. The gelling system examined in the present study is based on a PAM cross-linked with PEI. This paper will show for the first time the possibility of cross-linking polyacrylamide with PEI at high temperatures and pressures.

Therefore, the gelation time of the PAM cross-linked with PEI at high temperatures up to 285°F (140°C) and pressures up to 435 psi (30 bars) was measured. The effects of polymer concentration, cross-linker concentration, temperature, salinity and the initial degree of hydrolysis of the polymer on the gelation time were examined in detail. All measurements were conducted in the steady shear mode at low shear rates using an Anton-Paar high temperature/high pressure viscometer. C13 Nuclear Magnetic Spectroscopy (C13 NMR) was extensively used to relate gelation time to changes in the structure of the polymer and hence, explain the variation in the gelation time in terms of the system chemistry.

Thermally stable gels were obtained by cross-linking PEI and PAM at high temperatures (120°C) for at least 2 weeks. The activation energy of this system at high temperatures in distilled water was found to be 71.3 kJ/mol. The addition of sodium ions increased the activation energy to 88 kJ/mol.

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