Microbial Biomass for Improving Sweep Efficiency in Fractured Carbonate Reservoir Using Date Molasses as Renewable Feed Substrate

Selective plugging by microbial biomass is one of the proposed mechanisms for improving reservoir sweep efficiency in highly fractured reservoirs. In this study, the potential of Bacillus licheniformis strains isolated from oil contaminated soil from the Sultanate of Oman was tested for their ability to grow in induced fractures in carbonate rocks and to divert subsequent injection water to the unswept matrix zones. Three B. licheniformis strains were tested: B17, B29 and W16. Their ability to grow in minimal media with Omani date molasses as the sole carbon source was investigated. Two different concentrations of date molasses (3% & 8% w/v) were tested. It was found that the higher concentration of molasses gave higher growth rate for all strains. The combination of B. licheniformis strain W16 in a minimal medium containing 3% molasses was the optimum condition for maximum cell growth within 18 hours of incubation. Standard Indiana limestone core plugs were used for coreflooding experiments where a fracture was induced by slicing the cores vertically into two sections using a thin blade. The bacterial cells were injected into the cores and the ability of the microbes to grow and plug the fracture was examined. Coreflooding experiments showed promising results where enhancement of oil recovery was observed after bacterial injection. A total of 28.57% of the residual oil was produced after 18 hours of incubation. The results showed the high potential of using date molasses as the carbon source for microbial biomass production for selective plugging in fractured reservoirs.