Mechanisms of Oil Displacement by Microorganisms

Abstract

ABSTRACT Mechanisms of oil displacement at the oil-brine-sand interfaces by bacteria were investigated by microscopic observations and capillary pressure changes using unconsolidated, thin, reservoir flow cells. Three genera of bacteria, Bacillus, Pseudomonas. and Clostridium. were injected into water-wet and oil-wet cells of unconsolidated sand, saturated with brine and crude oil. The flow cells were placed under a microscope for visual and photographic observations. The flow cells were connected to a manometer to examine the complete capillary pressure hysteresis loop before and after introduction of bacteria. The thin reservoir flow cells were first saturated with brine, and then displaced to irreducible water saturation with crude oil. Oil and brine displacements were then made to determine the complete capillary pressure relationship. Next, the bacteria and nutrients were introduced and incubated in the flow cell for 24-48 hours. Microscopic observations were recorded photographically. After incubation, oil and brine displacements were again made to determine the capillary pressure hysteresis loop. During incubation, some emulsification of the oil at the oil-brine-sand interfaces were observed. Biogenic gas production caused pressure increases in the flow cells. Final measurements of the capillary pressure hysteresis loop showed decreases in residual oil saturation of 9-24% and changes in wettability to more water-wet systems. This work shows the potential of microbial enhanced oil recovery, and investigates some of the mechanisms of oil displacement by three genera of bacteria. These considerations are important with regard to the technical feasibility of microbial enhancement of oil recovery.