Magnitude of polymer and tracer dispersion coefficients

From the effluent concentration profile in a polymer or tracer flood, the total core Peclet number is calculated by fitting the analytic form of the convection-dispersion equation as described above. The most direct experimental comparison between the dispersion appropriate for polymer and for an inert tracer should be done in experiments in which both species are present in the injected pulse of labelled polymer solution. This helps to reduce greatly errors that may arise when separate tracer and polymer experiments are carried out. For example, in the study by Sorbie et al (1987d), the dispersion properties of two different xanthans were examined in consolidated outcrop sandstone cores. In all floods, the inert tracer, Cl, was used, thus allowing the dispersion coefficient of the xanthan and tracer to be measured in the same flood. An example of this is shown for a low-concentration (low- 

Effluent profiles for a 1-pv slug of 50 ppm xanthan in brine labelled with Cl 1-m sandstone core (Sorbie et ai, 1987d). 

Similar experiments to those using polymer have been conducted using viscous solutions made up of carbon-14-labelled glycerol, with Cl again being used as tracer. In these, it has been found (Sorbie et al, 1987d) that the glycerol and chloride dispersion coefficients are identical within experimental error. Thus, it has been identified that the difference in dispersion coefficient arises from the macromolecular nature of the polymer for the xanthan biopolymer. Similar experimental results on polymer/tracer dispersion behaviour have also been found by Kolodziej (1988). 

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