Ch. R-4 Investigations of Microbial Mechanisms for Oil Mobilization in Porous Media

Abstract

Abstract Prior work at NIPER has identified key mechanisms that are important for improved oil mobilization by microbial formulations. Key mechanisms include wettability alteration, emulsification, oil solubilization, alteration in interfacial forces, lowering of mobility ratio, and permeability modification. Certain microbial formulations appear to shift the wettability of Berea sandstone core samples toward a more water-wet condition. The microbial cells appear to be involved in this wettability alteration since no change was observed in samples tested with filtered microbial products with cells removed. Aggregation of the bacteria at the oil-water-rock interface may produce localized high concentrations of metabolic chemical products that result in oil mobilization. Unsteady-state relative permeability tests were performed with microbial formulations in Berea sandstone cores. A decrease in relative permeability to water and an increase in relative permeability to oil was usually observed in microbial-flooded cores causing an apparent curve shift toward a more water-wet condition. Samples tested with the microbial formulation exhibited higher oil recovery before water breakthrough and lower residual oil saturations. Additive flask tests and corefloods were performed to evaluate the effects of sodium bicarbonate on microbial metabolite production and oil mobilization. These tests indicate that sodium bicarbonate does appear to alter metabolic pathways of the microbial formulation used in these studies. Cores treated with a preflush of sodium bicarbonate showed increased oil recovery efficiency.