Microbial improved oil recovery—bacterial induced wettability and interfacial tension effects on oil production

Microbial Improved Oil Recovery (MIOR) utilizes the effect of oil degrading bacteria that grow on the oil–water interface. It has been demonstrated that the presence of growing bacteria in an oil and water saturated sandstone core can result in significant increased oil recovery upon water flooding [Torsvik, T., Gilje, E. and Sunde, E., Aerobic Microbial Enhanced Oil Recovery, Paper presented at the 5th International Conference on Microbial Enhanced Oil Recovery, Dallas TX, USA, Sep. 11, 1995]. Several mechanisms are proposed to explain this observed effect, among which are reduction in the oil–water interfacial tension (IFT) and changes in the wettability of the system. The experimental results from the present study indicate that bacterial growth can both reduce IFT and change the wettability towards less water-wet conditions. A subsequent simulation study shows that a change in wettability towards a less water-wet behavior can reproduce the increased oil recovery observed during the core flood reported by Torsvik et al. Furthermore, the simulations also indicate that a gradual and strong reduction in IFT can reproduce the same experimental data. Both the effect of changed wettability and reduction in IFT was included in the simulation model as changes to the relative permeability curves, constructed from general theory on IFT reduction and wettability alteration.