Evaluation of Bacillus Licheniformis strains and their dominant type of oil recovery mechanisms under hydrocarbon-rich conditions

Abstract

Selection of potential bacteria and identification of their type of oil recovery mechanisms are keys to in-situ Microbial Enhanced Oil Recovery (MEOR) process. However, bacterial survivability, adaptability and functionality under oil reservoir environment has never been evaluated as a complete set for this process. As a consequence, mechanism of the potential bacteria to assist oil recovery became unpredictable and their performance are inconsistent under oil reservoir condition. Therefore, this study aimed to evaluate selected bacteria as MEOR agents based on their survivability, adaptability and functionality in hydrocarbon-rich conditions. The study was executed in the hydrocarbon-rich conditions to emulate the hydrocarbon contents of oil reservoir. Conducted analyses in batch experiments involved: 1) analysis of bacterial growth; 2) bacterial cell physiology and behaviour characterization; 3) in-situ monitoring of biofilm/ biofloc/ biosurfactant formation and 4) substrate utilization. The substrates were selected from different types of polycyclic aromatic hydrocarbons (PAHs: naphthalene and pyrene) with different concentrations (0.1 and 10 g/L). In addition, flow experiments utilising paraffin oil in porous media (micromodel and glass-bead packed column) were conducted with the purpose of validating the function of potential bacteria as MEOR agent in bacterial flooding test. Results from the experiments were statistically examined with single factorial, general and two-level (2k) factorial design. Three strains of Bacillus licheniformis coded M1, Ta62bi and P6 were selected as potential MEOR agents. Results from batch experiments showed that strains M1 and Ta62bi acted as plugging agent whereas strain P6 functioned as emulsification-like agent in pyrene-rich medium. However, the flow experiments revealed only strains M1 and P6 consistently showed features similar to findings from batch experiments. The plugging effects of strain Ta62bi was most probably due to production of gas and not formation of biofilm. Nevertheless, these strains exhibited average oil recovery efficiency (%) of 31.2 ± 7.0 (Ta62bi), 34.8 ± 3.4 (M1) and 36.0 ± 5.7 (P6) from the remaining oil in column study. In conclusion, these selected bacteria were able to recover residual oil, but through different types of oil recovery mechanisms. Findings from this study have contributed to better understanding of bacterial application and to improving the evaluation strategy of potential bacteria selection for in-situ MEOR process.