Alterations in wettability and immiscible fluid flows by bacterial biosurfactant production for microbial enhanced oil recovery: Pore-scale micromodel study

Abstract

This study investigates alterations in wettability during bacterial growth and biosurfactant production and its ensuing impacts on immiscible fluid flow at a pore scale. Here, pore-scale experiments were carried out with two types of patterned micromodels. First, the experiments with a single-channel micromodel visually captured the real-time wettability alteration from oil-wet to water-wet while cultivating the model bacteria Bacillus subtilis, in which the bacterial cells and produced biosurfactant significantly lowered the contact angles, including static, advancing, and receding angles, by ∼70–90°. In addition, the emulsification-demulsification phenomena at brine-oil interfaces and the contact angle alterations by biofilms were also observed. Second, the surfactant-flooding process was emulated in the experiments with multi-channel micromodel while examining the effect of surfactant concentration on oil sweeping efficiency. The results of the multi-channel micromodel experiment show that a biosurfactant concentration of 70 mg/L, which is twice the critical micelle concentration, resulted in a lower contact angle, reduced residual oil saturation, and more homogeneous and stable patterns of oil displacement. Particularly, a significant level of variations in the contact angles at fluid-solid interfaces was observed in the multi-channel micromodel, and the extent of variation decreased with an increase in biosurfactant concentration. The presented results provide insights into pore-scale coupled microbial-hydrological processes in porous media as well as the biosurfactant-aided flooding in microbial enhanced oil recovery (MEOR).