Storage of oil field-produced waters alters their chemical and microbiological characteristics

Abstract

Many oil fields are in remote locations, and the time required for shipment of produced water samples for microbiological examination may be lengthy. No studies have reported on how storage of oil field waters can change their characteristics. Produced water samples from three Alberta oil fields were collected in sterile, industry-approved 4-l epoxy-lined steel cans, sealed with minimal headspace and stored under anoxic conditions for 14 days at either 4 degrees C or room temperature (ca. 21 degrees C). Storage resulted in significant changes in water chemistry, microbial number estimates and/or community response to amendment with nitrate. During room-temperature storage, activity and growth of sulfate-reducing bacteria (and, to a lesser extent, fermenters and methanogens) in the samples led to significant changes in sulfide, acetate and propionate concentrations as well as a significant increase in most probable number estimates, particularly of sulfate-reducing bacteria. Sulfide production during room-temperature storage was likely to be responsible for the altered response to nitrate amendment observed in microcosms containing sulfidogenic samples. Refrigerated storage suppressed sulfate reduction and growth of sulfate-reducing bacteria. However, declines in sulfide concentrations were observed in two of the three samples stored at 4 degrees C, suggesting abiotic losses of sulfide. In one of the samples stored at room temperature, nitrate amendment led to ammonification. These results demonstrate that storage of oil field water samples for 14 days, such as might occur because of lengthy transport times or delays before analysis in the laboratory, can affect microbial numbers and activity as well as water sample chemistry.