Anaerobic production of surfactin by a new Bacillus subtilis isolate and the in situ emulsification and viscosity reduction effect towards enhanced oil recovery applications

Emulsification and viscosity reduction effect of biosurfactants to crude oil are significant for enhanced oil recovery. Although biosurfactants for enhanced oil recovery were extensively studied, information on the anaerobic production of biosurfactants and its in situ effect to crude oil are still limited. Bacillus subtilis AnPL-1 was isolated from oil reservoirs production water and produced 150 mg/l of biosurfactants under anaerobic conditions. Sucrose and nitrate were favorable for anaerobic production of biosurfactants by strain AnPL-1. Strain AnPL-1 anaerobically produced biosurfactants at temperatures (20 degrees C-50 degrees C), pH values (6-9) and 0-7% of NaCl. FTIR and HPLC-MS analysis showed that the anaerobically produced biosurfactants was a mixture of C-13-, C-14- and C-15-surfactin congeners. Anaerobically produced surfactin decreased water surface tension to 28.5 mN/m with a critical micelle concentration of 30 mg/l. It can also emulsify crude oil with an emulsion index (EI24) of 70.5%. Strain AnPL-1 also produced 115 mg/l biosurfactants under simulated oil reservoirs conditions (anaerobic and 10 MPa conditions). Furthermore, strain AnPL-1 anaerobically grew well in the presence of crude oil. Strain AnPL-1 reduced the crude oil viscosity by 40.6% through in situ emulsification effect of produced biosurfactants. In core flooding tests, in situ biosurfactants production by strain AnPL-1 enhanced oil recovery of 9.98%. Although B. subtilis is a facultative anaerobe, anaerobic production of biosurfactants by B. subtilis for MEOR applications has been firstly studied. Without air injection, anaerobic production of surfactin by B. subtilis AnPL-1 is promising for in situ MEOR applications.