A polymer flood pilot project had been performed in the Eddesse-Nord sandstone reservoir (Germany) with a depth of 350 m, a temperature of 22 °C, an average permeability of about 1/μm2, and a thickness of 5 m. The clay content in the sandstone was about 10 %.
A xanthan-solution with a concentration of 800 ppm was injected from 1985 until 1988 into 2 wells. The xanthan was provided as a 2 % fermentation broth.
In mixing of the polymer and during injection of the polymer solution no severe problems were encountered. There was no plugging tendency in the wells observed, which is attributed to a thorough laboratory quality testing.
A response in the production wells occurred earlier than predicted by reservoir simulation and the incremental oil production was somewhat higher than the predicted 6 % of the- original oil in place.
Several simulation studies have been performed using 2 different numerical simulation models. Good history matches could be obtained with respect to production performance during the water flood phase and flow of tracers in the reservoir. The different salinities of the injected and the- original reservoir water were used as tracers, as well as the polymer and the formaldehyde, which was used as biocide.
Polymer was produced in significant amounts in one well. The produced xanthan as well as the xanthan that was injected were analysed for molecular weight, chemical composition, and solution properties. The xanthan molecules were also examined by electron microscopy.
The polymer project can be regarded as successful in terms of injection and production performance. Reservoir simulation results as well as laboratory studies have shown an adsorption of xanthan of 30-40 μ g/g. The xanthan produced in one well, after it had been in the reservoir for about three years, showed no degradation, neither chemical nor bacterial.