Divalent Ion-Resistant Polymer Gels for High-Temperature Applications: Syneresis Inhibiting Additives

Abstract

ABSTRACT This paper introduces a new strategy for improving the high temperature stability of acrylamide polymer solutions and gels in aqueous solutions containing the divalent cations Ca2+ and Mg2+. Specifically, certain low molecular weight compounds capable of complexing with the divalent cations are shown to reduce significantly their negative impact on the solubility of acrylamide polymers and on the stability of crosslinked acrylamide polymer gels with regard to syneresis. Where the inhibitor-divalent ion complexes formed are soluble, it should be possible to propagate their polymer or gelant solutions through matrix rock; where insoluble divalent ion-inhibitor complexes are formed, these inhibitors may still be compatible with gel placement in fractured reservoirs or in the immediate vicinity of the wellbore. The results obtained offer the possibility to extend the upper temperature limit for the use of polyacrylamides and acrylamide copolymers in brines in both polymer flooding and polymer gel treatments. Related studies show that pH is a key factor influencing the solubility of acrylamide polymers in the presence of divalent cations. This fundamental variable has been overlooked in earlier studies correlating PAAm solubility with the degree of polymer hydrolysis, divalent cation concentration, and temperature.