In situ growth of bacteria in a porous medium can alter the permeability of that media. This article reveals that the rate of permeability alteration can be controlled by the inoculation strategy, nutrient concentrations, and injection rates. Based on experimental observations a phenomenological model has been developed to describe the inoculation of the porous medium, the in situ growth of bacteria, and the permeability decline of the porous medium. This model consists of two phases that describe the bacteria in the porous medium: (1) the nongrowth phase in which cell transport and retention are occurring; and (2) the growth phase in which the retained cells grow and plug the porous media. Transition from the transport phase to the growth phase is governed by the growth lag time of the cells within the porous medium. The importance of the inoculum injection strategy and the nutrient injection strategy is illustrated by the model. © 1996 John Wiley & Sons, Inc.

Bacterial profile modification (BPM) is being developed as an oil recovery technique that uses bacteria to selectively plug oil depleted zones within a reservoir to divert displacing fluids (typically water) into oil-rich zones. Leuconostoc mesenteroides, which produces dextran when supplied with sucrose, is a bacterium that is technically feasible for use in profile modification. However, the technique requires controlled bacterial growth to produce selective plugging.A kinetic model for the production of cells and polysaccharides has been developed for L. mesenteroides bacteria. This model, based on data from batch growth experiments, predicts saccharide utilization, cell generation, and dextran production. The underlying mechanism is the extracellular breakdown of sucrose into glucose and fructose and the subsequent production of polysaccharide (dextran). The monosaccharides are then available for growth. Accompanying sucrose consumption is the utilization of yeast extract. The cell requires a complex media that is provided by yeast extract as a source of vitamins and amino acids. Varying the concentration ratio of yeast extract to sucrose in the growth media provides a means of controlling the amount of polymer produced per cell. Consequently, in situ bacteria growth can be controlled by the manipulation of nutrient media composition, thereby providing the ability to create an overall strategy for the use of L. mesenteroides bacteria for profile modification.

In-situ growth of cellular material is known to cause formation damage. Bacterial reproduction and polysaccharide production are the key factors that segregate bacterial formation damage from fines and particulate damage. Carefully controlled experiments conducted on both high-and low-permeability ceramic cores showed that bacteria can plug the pore space and damage the cores. However, further experimentation demonstrated that polysaccharide production is largely responsible for this damage. This conclusion is based on a comparison of two experimental systems: core plugging from bacterial replication and polymeric production and plugging of the porous medium caused solely by cell division with no polysaccharide production. In light of these results, the interpretation of reservoir plugging resulting from the presence of bacteria requires further scrutiny.

The precipitation of kraft lignin with poly(diallyldimethylammonium chloride), poly(DADMAC), was characterized as a function of pH. At a mass mixing ratio of poly(DADMAC) to lignin of 0.53 at pH 12.6, approximately 80% of the added lignin was removed, whereas the precipitate contained less than 35% of the added poly(DADMAC). Lignin precipitated with as much as 75% of the charges not associated with poly(DADMAC). Lower pH solutions required less poly(DADMAC) for lignin precipitation. Colloidal complex formation was measured as a function of time by dynamic light scattering, and the results could be fitted by a diffusion-controlled aggregation model.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractLaboratory core floods in highly permeable ceramic and sandstone field cores (1 -2 µm 2 ) were used to demonstrate the effectiveness of biogenic, bulk dextran gels at reducing indepth permeability. Nutrient formulation, bacteria type, bacteria growth stage, and bacteria concentration were found to influence bulk gel formation.Growth of Leuconostoc mesenteroides in a sucrose-based medium supplemented with proteins and amino acids essential for its growth resulted in production of rigid, bulk dextran gels containing over 90% water (wt/wt) that were retained on an 18-mesh sieve. Whereas, results from the growth of L. mesenteroides on a beet-molasses medium similar to that used in a previous bacterial profile modification field test produced loose, colloidal gels that easily passed through the 18-mesh sieve. Substitution of inexpensive protein hydrolysates for expensive laboratory-grade proteins resulted in formation of the best bulk gels. Also, bacteria in an early stage of growth produced better bulk gels than bacteria from a later growth stage. Corefloods indicated that conditions supporting formation of bulk dextran gels resulted in greater in-depth permeability reductions (> 90%) than conditions supporting formation of loose, colloidal gels. Batch-wise addition of nutrients (< 5 pore volumes) to ceramic cores inoculated with L. mesenteroides resulted in production of stable in-depth plugs whereas, continuous injection of nutrients was required to achieve in-depth permeability reductions in sandstone field cores flooded to residual oil saturation. These results suggested that the in-depth transport of bacterial cells in field cores was limiting to in-depth gel formation and permeability reduction.These results are significant in that they are the first to discuss the formation of bulk dextran gels produced during the in-situ growth of Leuconostoc sp., their importance in establishing in-depth permeability reduction, and factors controlling their formation.