Effect of CR³+ on the rheology of xanthan formulations in porous media: Before and after gelation

Experiments were performed to probe the rheology of chromium(III)-xanthan gels and gelants in porous media. For a large portion of the time before gelation, the presence of 90-ppm Cr³+ did not significantly affect the rheology of a 3000-ppm xanthan solution in Berea sandstone. After gelation, residual resistance factors were not much greater than those for xanthan solutions without Cr³+. Clay and carbonate minerals in Berea may have inhibited gelation by forcing the reaction to occur near neutral pH rather than at the injection pH of 3.8.