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

Abstract

ABSTRACT 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 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. 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 bio-surfactant producer) have been attempted: (a) Continuous flooding with bacterial culture, (b) inoculation of bacteria followed by injection of nutrient, (c) 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 mutiply 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.