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A method for oil recovery enhancement by stimulating the growth of indigenous microbial populations in sandstones by nutrient injection was investigated. Incremental oil recovery from the cores ranged from 10–38% of the original oil in place. Volumetric and microscopic sweep efficiency was improved by the microbial selective plugging process. Biogenic gas production accompanied the oil produced from the cores. The combination of stratification correction, gas production, and pressure increase assisted in recovery of previously trapped oil.

The ability of bacteria to divert fluid flow from a high permeability sandstone layer to a low permeability sandstone layer by selective plugging 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 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, occurred in the high permeability layer, due to preferential microbial growth. Establishment of a preferential microbial growth. Establishment 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 produced from the high permeability layer once permeability reduction occurred. permeability reduction occurred. 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. Introduction Crossflow between layers within a petroleum reservoir has been identified as one of the leading causes of reduced volumetric sweep efficiencies achieved by waterflooding processes. Crossflow occurs when layers of varying permeability are in capillary contact within a permeability are in capillary contact within a reservoir, which may allow flow to occur between these layers. When water is injected into a reservoir, flow will be preferentially conducted by the high permeability layers, and flow in lower permeability layers will be diverted into high permeability layers will be diverted into high permeability layers when possible. This reduces permeability layers when possible. This reduces the amount of the reservoir contacted by the waterflood, and thus reduces volumetric sweep efficiency and oil recovery. Selective plugging has been proposed to correct sweep efficiency variation problems within reservoirs. Selective plugging agents include clays, paraffins, polymers, gels, resins, and cements. These agents are not effective in practice for a number of reasons: these agents practice for a number of reasons: these agents only plug near the wellbore, may not plug selectively, or may wash out of the formation. Bacterial selective plugging has been proposed to correct microscopic and volumetric proposed to correct microscopic and volumetric sweep efficiency variations in sandstone cores and formations by selective microbial growth in high permeability zones. Fluid flow was permeability zones. Fluid flow was diverted from high permeability cores to low permeability cores in parallel core systems permeability cores in parallel core systems without crossflow. Microbial selective plugging was shown to increase residual oil plugging was shown to increase residual oil recovery after waterflood and was stable even after killing the bacterial cells.