Expense of bactericide treatment in injection water can be a major item in the operation of a waterflood or disposal system. Each operator of such a system desires to know whether such expense is necessary and which bactericidal chemical is most economical for his system. The diagnosis to be described makes use of modifications in recognized analytical methods for on-the-spot determinations of total sulfide and of populations of "sulfate-reducing bacteria". Activity of the bacteria is judged on the basis of increases in sulfide concentrations and/or in increases in bacterial populations as the water progresses through the system under study.
The methods used in this diagnosis are of sufficient sensitivity that indications of bacterial activity should be apparent if down-hold bacterial sulfide formation is a significant factor in any water injection system. If the diagnosis fails to show a definite bacterial problem, more careful study of other factors is indicated.
Descriptions will be made to cover typical evidence for:
Uncomplicated appearance of bacterial sulfide in injection water accompanied by increasing numbers of sulfate-reducing bacteria or accompanied by high bacterial populations.
Localized pockets of bacterial sulfide formation. Water passing such pockets would pick up sulfide and bacteria either continuously or in "slugs".
Cases where one or more supply waters contain dissolved sulfide with or without significant numbers of sulfate-reducing bacteria. Little or no additional sulfide is formed by the bacteria but the soluble sulfide reacts with iron salts, metallic iron etc., to produce "black water". Treatment with chemicals having properties other than or in addition to bactericidal activity is required.
Complications associated with imperfect mixing of widely differing supply waters.
Concentrations of sulfide and bacteria passing sample points fluctuate, hence diagnosis is possible only by alterations in the operation of the system.