Chemical Forms and Reactions of Barium in Mixtures of Produced Water with Seawater

Abstract

High concentrations of Ba in produced water have been linked to adverse biological impacts during toxicity testing. This observation, along with interest in modelling chemical processes during produced water discharges to the ocean, led to the present study. Essentially all the Ba in produced water collected for this study was dissolved and passed through 0.4-μm pore size filters and 1-KDa ultrafilters. Using 1:99 and 1:199 mixtures of produced water with seawater, initial amounts of dissolved Ba of 180–600 μg/L did not change over 72 h and were oversaturated with respect to BaSO4 by factors of ~5–16. For 1:9 mixtures of produced water with seawater, precipitation was observed to either start immediately or be delayed for as long as 12 h; however, the dissolved Ba that remained after 24–72 h in these mixtures ranged from 340–1,200 μg/L, or ~10 to >30 times above apparent saturation. Field sampling of a discharge in the Gulf of Mexico showed that >98% of the Ba added to seawater via produced water was still dissolved 5 min after discharge at a distance of 20 m from the source and at >1,600-fold dilution. Overall, the results show the importance of considering both dilution and precipitation when interpreting the behavior or impact of Ba based on laboratory and field studies.