Biodegradation and toxicity of scleroglucan for enhanced oil recovery

Polymer flooding consists of injecting polymer-augmented water into the reservoir to control the water-oil mobility ratio, resulting in an increase in the volumetric sweep efficiency compared to water flooding. Synthetic polymers (polyacrylamides) and biopolymers (scleroglucan, xanthan gum, schizophyllan) are the two families of polymers usually evaluated for enhanced oil recovery (EOR). Scleroglucan (SCG) is resistant to electrolytes, hydrolysis, pH (3-10) and temperature (30-100°C) and has remarkable rheological properties, but it is quite susceptible to microbiological degradation. The primary objective of this study was to evaluate the biodegradation of SCG in the injection and production processes and its aquatic toxicity. The anaerobic biodegradation of the SCG solutions was determined through the viscosity changes of the solutions, while the aerobic biodegradation was calculated with the changes in the SCG concentration.  It was observed that the viscosity reduction of the SCG solution was 30% and the SCG concentration decreased from 100 ppm to 52 ppm because bacteria can metabolize the biopolymer. Daphnia Pulex, Scenedesmus Acutus and Oreochromis sp. were the organisms used in the ecotoxicological assays of the SCG solutions. The acute ecotoxicological bioassays showed that there was no evidence of acute deleterious effects of SCG on any of the three organisms. From the chronic ecotoxicological bioassays, it was concluded that there was no effect of SCG on the mortality of Daphnia Pulex, regardless of the tested SCG concentration.