A coordination chemical approach for delaying the gelation of Cr+3/polymer compositions has been explored. By screening organic ligands for their gelation delaying power with hydrated Cr+3/polymer and Cr(OAc)3/polymer solutions several powerful retarding ligands have been identified. Use of the pre-formed Cr+3 complexes of these ligands together with additional, uncomplexed ligand in the gelant solution provides outstanding control over the gelation time over the temperature range 60°-135°C. With these compositions gelation times spanning the range from several hours to one month or more have been obtained at temperatures up to 120°C; such gelation delays should be suitable for a number of near-well and in-depth gel treatments. In virtue of the low toxicity of Cr+3 and its complexes, the potential environmental impact of the new gelation compositions is notably reduced relative to those employing Cr+6 or formaldehyde. A number of variables have been evaluated for their influence on the gelation delay, and preliminary experimental results on the propagation of Cr+3 in porous media at high temperature are reported. Our current mechanistic understanding of the gelation delay chemistry is also described.

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