We have used a sintered glass bead core to simulate the spaces and surfaces of reservoir rock in studies of the bacterial plugging phenomenon that affects waterflood oil recovery operations. The passage of pure or mixed natural populations of bacteria through this solid matrix was initially seen to promote the formation of adherent bacterial microcolonies on available surfaces. Bacteria within these microcolonies produced huge amounts of exopolysaccharides and coalesced to form a confluent plugging bioffim that eventually caused a >99% decrease in core permeability. Aerobic bacteria developed a plugging biofilm on the inlet face of the core, facultative anaerobes plugged throughout the core, and dead bacteria did not effectively plug the narrow (33-,um) spaces of this solid matrix because they neither adhered extensively to surfaces nor produced the extensive exopolysaccharides characteristic of living cells. The presence of particles in the water used in these experiments rapidly decreased the core permeability because they became trapped in the developing biofilm and accelerated the plugging of pore spaces. Once established, cells within the bacterial biofilm could be killed by treatment with a biocide (isothiazalone), but their essentially inert carbohydrate biofilm matrix persisted and continued to plug the pore spaces, whereas treatment with 5% sodium hypochlorite killed the bacteria, dissolved the exopolysaccharide biofilm matrix, and restored permeability to these plugged glass bead cores. * Corresponding author. were both replicable and approximately equal to those of an "open" sandstone. Thus, especially in our early studies in which pure cultures of aquatic bacteria were used, any changes in permeability that occurred in the model cores could be attributed fully to microbiological factors.

Attached populations of corrosion enhancing sulfate-reducing bacteria (SRB) and organic acid-producing bacteria (APB) were measured on steel plugs at an oil field water injection plant near Wainwright, Alberta. The sample plugs were colonized to ca. 106 SRB/cm2. Counts for APB ranged from 102 to 10/cm2. Scanning electron microscopic examination of the sample plugs revealed an uneven distribution of surface corrosion deposits. A thin iron sulfide layer covered most of the exposed areas. Thicker sulfur-enriched deposits occurred randomly. The bulk of the thicker deposits were smooth, whereas peripheral regions exhibited a porous texture. The elemental composition of the different regions was the same; however, bacterial cells were concentrated in the porous areas and were not found in the thinner deposits. In transmission electron microscopic thin sections cut perpendicularly through corrosion deposits, bacterial cells were found mineralized in successive stages by iron sulfides. The corrosion deposit matrix also generated strong Cl peaks in energy dispersive X-ray spectra. This entrainment of bacterial cells within a corrosion deposit matrix is consistent with the concept of bacterial enhancement of corrosion by removal of reducing power from iron sulfides galvanically coupled to the steel surface. Key words: microbial corrosion, iron sulfide, cathodic hydrogen, electron microscopy.

This study was carried out in an oilfield waterflood operation in which produced brine is reinjected to displace oil from the reservoir. Significant corrosion problems are associated with bacterial colonization of the water handling system. Previous work has focused on optimizing biocide treatments, but there are limits to what is economically achievable by this approach. This report describes results of an audit of chemical, biological and corrosion parameters measured across the Wainwright waterflood operation over a 30-month period. The intent of the audit was to provide a basis for understanding and improving monitoring and control practices in such operations. Corrosion-monitoring methods generally failed to correlate in a simple way with corrosion failures. Failure frequency correlated with several water chemistry parameters. Common treatment chemicals showed evidence of promoting bacterial growth. Sulfate-reducing bacterial numbers were found to be a function of position in the system, population composition and water chemistry. Based on the insights obtained, a series of runs was carried out in a special test facility to assess the effects of trace nitrate, oxygen scavenger, and nutrient addition on the sessile bacterial populations present in an operating unit. Results are briefly described.