The competition for chromium between xanthan biopolymer and the resident clays in Berea sandstone cores has been examined. Xanthan requires the Cr³+ ion to form gel while the resident clays remove the chromium from the bulk solution by a cation exchange process. These two competing factors are examined through corefloods and computer simulation to determine the amount of chormium actually available for crosslinking.

Through a series of Berea corefloods, chromium retention was examined without the presence of polymer using a 2 wt% NaCl brine as the aqueous solution. Finally, several polymer-gel floods were conducted using varying concentrations of chromium and xanthan. Chromium and polymer retention and pH as well as the pressure drop due to gel formation were analyzed.

The retention of chromium was found to be high and on the order of the cation exchange capacity of the clays in the sandstone. This causes slow transport of the Cr³+, due to its consumption by the clays, and a decreasing effectiveness of the gel indicated by a decreasing reduction in permeability with length. This study points to the need to conduct experiments with porous media containing clay and to the need for better modeling of the complex phenomena occurring under conditions of interest for field applications.