Enhanced oil recovery using biotransformation technique on heavy crude oil

Abundance of heavy crude oil resources and costly enhanced oil recovery (EOR) techniques necessitate development of inexpensive heavy oil recovery methods. Microbial EOR (MEOR) techniques are environmentally friendly and need little input of energy to produce MEOR agents. One potential application of MEOR is in the biotransformation of heavy oil where bacteria break heavier fractions of heavy crude oil to lighter compounds; thus, improving oil recovery. In this study, two spore forming bacteria: Bacillus subtilis AS2 and Bacillus licheniformis AS5, which were isolated from heavy oil (13.3 °API) contaminated soil samples from a heavy oil field, Oman, were tested for their biotransformation abilities. Bacterial growth was analyzed by optical density measurements and heavy crude oil recovery was determined by core flooding experiments. At aerobic biodegradation flask experiments, M2 medium spiked with glucose had the highest bacteria growth and crude oil biodegradation in comparison with: (1) M2 medium with no added chemicals and (2) M2 medium spiked with sodium thiosulfate. At anaerobic in situ conditions Berea sandstone core flooding experiments, additional 2.9% and 3.1% of residual oil saturation was recovered by B. subtilis AS2 and B. licheniformis AS5 respectively after one week of incubation. By increasing the incubation time and inoculation percentage for isolate AS5, the oil recovery increased to 5.0%. When glucose was added to M2 medium, AS5 oil recovery increased to 16.4%.The results showed that locally isolated bacterial strains have the potential for biotransformation of heavy oil and enhanced oil recovery.