Selective Plugging and Oil Displacement in Crossflow Core Systems by Microrganisms

Abstract

ABSTRACT The ability of bacteria to divert fluid flow from a high permeability sandstone layer to a low permeability sandstone layer by selective plugging and the ability of these bacteria to recover residual oil was studied. A crossflow system consisting of two layers of Berea sandstone were placed in capillary contact. Pressures were monitored in oil-brine and brine saturated systems to determine pressure gradients within the layers and estimate flow behavior. A mathematical simulation model was developed and used to analyze the results. Changes in crossflow patterns were observed in the systems. During the treatment process, up to 60% of the production from the system was from the low permeability layer. Injectivity into the low permeability layer increased by a factor of three from initial conditions, relative to constant flow into the high permeability layer The greatest decreases in permeability, and thus the largest increases in potential gradients, occured in the high permeability layer, due to preferential microbial growth. Estabilishment of a mobile gas phase by biogenic gas production also assisted flow diversion. Large amounts of gas were produced from the high permeability layer once permeability reduction occured. These results extend the previously published data obtained using parallel cores not in crossflow, and show that preferential plugging and oil release from high permeability regions do occur in crossflow systems. Oil recoveries comparable to those achieved in earlier linear core experiments were observed in the crossflow experiment. Thus, microbial metabolism apparently improves flow patterns in laboratory crossflow experiments and leads to the recovery of residual oil from waterflooding.