Bioreactor for Accurately Assessing Biocide Effectiveness in Controlling Biogenic Souring in Mature Oil Wells

Summary Biocide injections are used for controlling biological souring in mature oil wells, but unpredictable results of such practices are also frequently reported. To address this problem, this research aimed to quantify the effect of four new biocides, and one commonly used biocide, within a dynamic system (packed-bed bioreactor) without using batch testing. The bioreactor was operated for 591 days, and the results showed that sulfate-reducing-bacteria (SRB) activity could recover within a period that varied from 15 to 60 days. Neem-oil (NO) (1.5% vol/vol) and 3,5-dimethyl-1,3,5-thiadiazinane-2-thione (Dazomet, DZ) (0.5% vol/vol) were the most efficient in controlling SRB activity. The tests showed that the mechanistic interaction controlling souring is not only associated with the compounds’ toxicity. Immiscible biocides not only killed cells, but they also can control SRB-recovery rates after the injection of biocides.