The Characterization of Sulfate-Reducing Bacteria in Heavy Oil Waterflood Operations

Abstract

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.

Monitoring Microbial Fouling and Corrosion Problems in Industrial Systems

“…Failures also correlated with the concentration of sulphate present consistent with sulphate reducing bacteria promoting corrosion (Jack et al, 1994). Microbial numbers (SRB or APB) correlated negatively with hardness but were favoured as pH increased from 6.5 to 7.0 and by residuals from treatment chemicals used to inhibit corrosion, scavenge oxygen and control scaling (Jack et al, 1994). These chemicals likely promoted the microbial population that biocide additions to the same system were trying to control by providing extraordinary sources of nitrogen, sulphur and phosphorus for bacterial growth (Sunde et al, 1990).…”

“…The corrosion rate correlated not with the absolute number of SRB but with the increase in SRB seen through the flow system. This increase in SRB also correlated with the number of APB present suggesting that the mixed microbial community was important to the development of high SRB counts (and corrosion failures) in the downstream parts of these systems (Jack et al, 1994).…”

“…Suspended solids or hydrocarbons correlated with increased failures in the upstream part of the system presumably by promoting surface fouling and increased deposits. Failures also correlated with the concentration of sulphate present consistent with sulphate reducing bacteria promoting corrosion (Jack et al, 1994). Microbial numbers (SRB or APB) correlated negatively with hardness but were favoured as pH increased from 6.5 to 7.0 and by residuals from treatment chemicals used to inhibit corrosion, scavenge oxygen and control scaling (Jack et al, 1994).…”

“…Comparison of readings taken in the same system over a short exposure period varied considerably; a correlation was only evident when data averaged over many readings were compared. Soluble iron or manganese, pitting index or corrosion rates did not correlate with failure cost or frequency (Jack et al, 1994). This raises concern about predictions of risk based on these measurements.…”

Omics-based approaches and their use in the assessment of microbial-influenced corrosion of metals

“…Thus, there can be a competition between sulphate-reducing bacteria (SRB) and iron-reducing bacteria (IRB) so that IRB may decrease SRB activity (Potekhina et al, 1999). In contrast, acid-producing bacteria, as well as being corrosive in themselves, may provide nutrients and environmental conditions conducive for SRB growth (Jack, Rogoz, Bramhill, & Roberge, 1994).…”