Worldwide partially hydrolyzed polyacrylamides (HPAM) are preferentially used for polymer-based enhanced oil recovery (EOR) processes, due to cost-competiveness. However in recent past several reports suggested that there are certain issues associated with treatment of produced water – post HPAM applications such as, oil-water separation due to emulsions and toxicity associated with degradation products of HPAM, such as acrylamides. Biopolymers are biodegradable and environmental friendly alternative to chemical polymers used for EOR applications. In present work we studied the biopolymer-pullulan production by fungal isolates of Aureobasidium pullulans, isolated from Oman, partial structural characterization and potential applications in Microbial Enhanced Oil Recovery (MEOR).
Different production media containing carbohydrate based carbon sources were screened for better biopolymer production. During the course of experiments we studied fungal growth profile and biopolymer production under different conditions, and rheological properties of biopolymer, chemical characterization and application of biopolymer in enhancing oil recovery using Berea sandstone cores.
The observed growth and production temperature was up to 35 °C and optimum was at 30 °C for Omani A. pullulans isolates. The better growth was observed under shaking conditions. A. pullulans strains are reported to produce a type of biopolymer – pullulan. Thus samples were analyzed from Omani isolates for biopolymer production using rheological studies for any changes in viscosities with respect to time. The cell-free broth showed increase in viscosity from 1-4 cP of the abiotic control production media (without biopolymer) to 28-59.9 cP of the cell free broth at 25 °C. The initial yield of crude extracted biopolymer was ≥12.68 g/L. The biopolymer was extracted in crude form and partially identified by Fourier transform infrared spectroscopy (FTIR), which showed similarity in chemical structure with reference standard pullulan from Sigma, USA. When this biopolymer-pullulan was used for MEOR studies using Berea core-plugs in core-flooding experiments, it recovered additional 9.4% oil over residual oil saturation (Sor).