Mechanistic Understanding of Microbial Plugging for Improved Sweep Efficiency

Microbial plugging has been proposed as an effective low cost method of improving sweep efficiency by reducing permeability of water-swept regions of a reservoir. To optimize the field implementation of this method, better mechanistic and volumetric understanding of biofilm growth within a porous medium is needed. In particular, the engineering design hinges upon a quantitative relationship between amount of nutrient consumption, amount of growth, and degree of permeability reduction. As a first step toward such a relationship, a Pseudomonas aeruginosa culture was inoculated into columns of glass beads and Berea sandstone cores. A mineral medium with acetate as carbon and energy source was injected continuously. Growth substrate utilization and permeability changes were used to track aerobic microbial growth, and in-situ staining of biomass provided visual evidence of colonization and growth. Imaged growth was grain coating, with extra-cellular materials filling pore throats and bodies significantly reducing the effective porosity of the beads. Permeability was reduced noticeably in each experiment with an average permeability reduction of 54%. The experiments demonstrated that microbial growth is effective for reducing permeability in porous media. Tracer tests were used to characterize the flow behavior of bead packs before and after biofilm growth. In a heterogeneous bead pack containing a layer of coarse beads and