Abstract: A biocide blend can be used in an oil or gas operation. The biocide blend can include a first biocide of a formaldehyde-releasing biocide and a second biocide of a quaternary ammonium compound. The formaldehyde-releasing biocide can release formaldehyde after introduction into a wellbore. The first and second biocide can possess at least one property that is the same. The first biocide and/or the second biocide can maintain biocidal activity for extended periods of time in high salinity wellbore fluids, be thermally stable, and less expensive than other biocides.

Abstract: A biocide blend can be used in an oil or gas operation. The biocide blend can include a first biocide of a formaldehyde-releasing biocide and a second biocide of a quaternary ammonium compound. The formaldehyde-releasing biocide can release formaldehyde after introduction into a wellbore. The first and second biocide can possess at least one property that is the same. The first biocide and/or the second biocide can maintain biocidal activity for extended periods of time in high salinity wellbore fluids, be thermally stable, and less expensive than other biocides.

Abstract: Systems and methods for rapidly assessing biocide contamination and biological contamination treatments found in fluids used for subterranean well treatments and related operations are provided. In some embodiments, the methods include providing a fluid including an aqueous base fluid and one or more microorganisms; introducing a first sample of the fluid to a first culture device including an indicator reagent, wherein over a period of about 48 hours or less the indicator reagent indicates a first color change in the first sample of the fluid; and determining a first count of the microorganisms in the fluid based, at least in part, on the first color change.