The Transport of Bacteria in Porous Media and Its Significance in Microbial Enhanced Oil Recovery

Abstract

Members SPE-AIMEAbstract. MEOR is a tertiary recovery process which has only recently been accepted as a technically feasible alternative to other EOR processes in certain shallow, highly permeable reservoirs. The transport of injected bacteria in the porous media is among the problems which need to be resolved before a MEOR problems which need to be resolved before a MEOR process can be successfully applied in a candidate process can be successfully applied in a candidate reservoir. In order to contact trapped oil with active metabolites generated in situ, potential strains of bacteria must be transported deep into the reservoir. The problem of transport of bacteria is linked closely with the success or failure of an MEOR process. process. This paper presents a bench-scale investigation of bacterial transport in sandpack columns and sandstone cores and its relationship with oil recovery efficiency. Various oil recovery processes utilizing Bacillus subtilis (a biosurfactant producer) have been attempted:Continuous flooding with bacterial culture,inoculation of bacteria followed by injection of nutrient,inoculation followed by repeated cycles of static incubation, pressure release and nutrient (or water) drive.Experiments revealed that the above processes recovered 30%−40% of the heavy oil (Ranger Zone, Long Beach, CA) in the sandpack column remaining after secondary water-flooding. It was found that bacteria are able to migrate 1 ft/day through the sandpack column saturated with nutrient broth.The transport of bacteria (or spores) in process (c), which is tentatively thought to be the most feasible among the three processes, is achieved through injection with nutrient followed by a period of static incubation during which cells multiply and migrate. Separate experiments simulating the two stages of bacterial transport revealed that bacterial spores of B. subtilis and C. acetobutylicum are most easily pushed through the sandstone core while B. subtilis cells migrate through the core faster than Pseudomonas putida during static incubation. This suggests that the procedure developed in this work provides a criterion of selecting bacterial cells with favorable transport properties in porous media.Introduction. Although its development has not yet resulted in economically feasible processes and some of its technical difficulties remained to be resolved, the utilization of microorganisms to recover residual oil from low-producing fields has been successfully demonstrated. Except for the proposed use of microbial cells and extracellular slimes to selectively plug the high permeable zones, microbial enhanced oil recovery (MEOR) methods mainly utilize the metabolites (biosurfactant, biopolymer, organic acid, and biogas) generated in-situ or ex-situ by bacteria to improve the oil-phase mobility. A well-known example of ex-situ MEOR process is to inject Xanthan gum separated from the growth culture of Xanthomonas to thicken the waterflood.This paper mainly deals with the factors influencing the efficiencies of oil recovery by in-situ microbial processes. Since in-situ MEOR is mainly targeted toward the residual oil left after the primary production or the secondary waterflooding, primary production or the secondary waterflooding, like most tertiary recovery processes, its success depends, among other factors, strongly on the penetration and the stability of recovering agents. In penetration and the stability of recovering agents. In other words, in order to contact trapped oil with bacteria that have favorable oil displacement properties, the microbes must be transported from properties, the microbes must be transported from wellbore to locations deep within the reservoir. Early research indicated that the penetration of the selected bacterial species is rather poor (6–8) as the suspension is continuously injected into a clean porous rock. However, recent studies showed that porous rock. However, recent studies showed that the presence of oil in the sandstone core can facilitate bacterial penetration (6). Bacterial spores Of Bacillus subtilis and Clostridium acetobutylicum were found to penetrate more easily than vegetative cells. Certain chemicals added to the suspending medium can also improve the penetration of bacteria. penetration of bacteria. Most of the work mentioned above defined bacterial