Contribution of Make-Up Water to the Microbial Community in an Oil Field from Which Oil Is Produced by Produced Water Reinjection

Much of the world’s oil is produced by water injection. Produced water (PW) is often mixed with make-up or source water (SW) in a water plant and re-injected. The effluent from a sewage treatment plant is used as the SW in an oil field in Southern Alberta. Untreated SW (SW-U) was subjected to continuous chlorination, as well as to quarterly treatment with the biocide acrolein, then filtered (SW-F) and further treated with the oxygen scavenger ammonium bisulphite. The treated water (SW-T) was then mixed with PW in the water plant. We aimed to determine whether the mixing of SW and PW created favorable conditions for microbial growth. Numbers of viable anaerobic heterotrophs, enumerated on trytone-yeast extract plates, were 100 to 102/ml for SW-U and SW-T, but higher for SW-F (105/ml), whereas those in PW were between 105/ml and 106/ml. Mixing of the two types of waters increased the CFU/ml by maximally 1 log unit, indicating some additional growth. Analysis of the microbial community composition indicated many similarities. However, obligate anaerobes (Nitrosomonas, Nevskia) were only present in SW, whereas some strict anaerobes like the methanogens Methanosaeta and Methanolinea and the nitrate reducer Thauera predominated in PW.