ABSTRACT
The influence of pH, temperature, and gelation delaying ligands on the stability of Cr(III) complexes in bulk solution and on Cr(III) propagation in porous media has been investigated for acetate, glycolate, and malonate complexes of Cr(III). For a given complex, Cr(III) instability to hydrolysis and Cr(III) retention increase with increasing pH and temperature. The chemical nature of the gelation delaying ligands bound to Cr(III) and their coricentration in the solution have a profound influence on the resistance of the Cr(III) complex to hydrolysis and on Cr(III) retention. Thus, whereas the Cr(III) acetate crosslinker, by itself, propagates poorly at elevated temperature, addition of sodium glycolate to the solution markedly reduces retention. We show that Cr(III) retention in sandstone cores can be virtually eliminated at 90°C by appropriate formulation of the gel-forming solution. Other experiments establish that Cr(III) precipitation at elevated temperature is reversible in the presence of polymer and that significant accumulation of the Cr(III) precipitate can have a negative impact on injectivity.
