Rheological and transport effects in the flow of low-concentration xanthan solution through porous media

This paper describes certain aspects of the rheology and transport of xanthan biopolymer solution through porous media. Results are related to the depleted layer effect, where macromolecules are excluded from the pore wall due to steric hindrance. The experiments include measurement of both the in situ polymer rheology and the advancement of the polymer molecules relative to the tracer in propagation through nonadsorbing ballotini glass bead packed columns. A series of low-concentration microgel-free xanthan solutions was used in the experiments and accurate results have been obtained. These results show a clear apparent slip effect on the in situ rheology of the xanthan which is consistent with the observed exclusion factors in the transport behavior. The apparent depleted layer thickness was estimated from the rheological data which were analyzed using a simple mathematical expression (the two-fluid model) as well as a recently published analytical model (the linear layer model). The results show that the depleted layer thickness decreases quite markedly with increasing polymer concentration over the low-concentration range used in this work (30-160 ppm). In addition to the apparent slip effect on the in situ rheology of the xanthan, which is most evident at low flow rates, it is found that the porous medium power law index is higher than the bulk value (i.e., the slope of the ?_app vs y ? is lower) for all polymer concentration values, which is in accord with previous theoretical predictions. © 1991.