Reduction of porous media permeability from in situ bacterial growth and polysaccharide production.

Abstract

In situ core-plugging experiments and transport experiments, using the model bacteria Leuconostoc m., have been conducted. Results demonstrated that cellular polysaccharide production increases cell retention in porous media and causes an overall decrease in media permeability. Further, a parallel-core-plugging experiment was conducted and showed the feasibility of this system to divert injection fluid from high-permeability zones into low-permeability zones within porous media as is needed for profile modification. To implement this type of application, however, controlled placement of cells and rates of polymer production are needed. Therefore, kinetic studies were performed. A kinetic model, i.e. the modeling of the production of cells and polysaccharides, was subsequently developed for Leuconostoc m. bacteria. This model is based on data generated from batch growth experiments and allows for the prediction of saccharide utilization, cell generation, and dextran production. These predictions can be used to develop injection strategies for field implementation. Additional core plugging experiments have also been performed to determine the effects of the nutrient injection rate and nutrient concentration on the rate of porous-media plugging. As shown experimentally and as predicted by a model for in situ growth, an increase in nutrient concentration and/or its injection rate will result in a faster rate of porous-media plugging. Through continuum model simulations, it has been shown that increasing the depth of cell placement (inoculum) into the porous media reduces the rate of core plugging once nutrients are injected. Controlling the location of the inoculating cells is thus another key factor in using bacteria for profile modification. Questions that still need addressing are: understand the actual plugging mechanism microscopically, determine plug stability, further improve the growth model for different environmental conditions, determine cell profile directly during cell inoculation phase, and determine parameter that influence cell growth lag times.