Abstract
Fresh river water is used to flush production lines to control halite deposits in unconventional carbon steel wells near, North Dakota, USA. Raw river water is stored in 400 (bbl) fiberglass tanks and is treated with oxygen scavenger before injection. Quarterly testing showed high levels of bacteria. The remote location, cold seasonal temperatures, tank design, USA EPA regulations and restricted access limit treatment options to biocide application in solid form added to tank tops. To cover all reasonable product candidates, range of both liquid and solid biocides were tested on site to determine an effective formula and dose. Selection was based on multiple factors including, effect on bacteria, compatibility with water, worker safety, product label restrictions and cost. Based on the results, calcium hypochlorite was selected for tank treatments. Hypochlorite is corrosive, however testing showed acceptable corrosion rates (<3mp/y) against carbon steel at target treatment rates for extended periods of time. Tanks were dosed not to exceed 3 ppm free available chlorine residual. Bacteria monitoring showed that bacteria levels in the tank were reduced by as much as 5 log to non-detectable levels post quarterly treatments with calcium hypochlorite.
