Bacterial Survival in Fractured Shale-Gas Wells of the Horn River Basin

Abstract

Summary Traditional ideology on the upper temperature limits of life suggest that extreme temperatures such as those observed in the Horn River Basin shale-gas formation (i.e., up to 175°C) should alleviate microbiologically influenced corrosion and souring concerns associated with hydraulic-fracturing procedures. The present case history investigates the accuracy of this theory. Horn River basin wells currently in the flowback or production stage and the source water used to fracture these wells were studied for the presence and identity of viable bacteria. The effectiveness of two biocides (one glutaraldehyde-based and the other cocodiamine-based) in eradicating these bacteria in both the field and the laboratory was also studied. The results show that source ponds are highly contaminated with bacteria. Furthermore, the high-temperature, high-pressure downhole conditions in this region are not sufficient for eradicating bacteria introduced during the fracturing process. These bacteria survive and establish viable, proliferating communities. Biocide, applied continuously "on the fly" during fracturing, was effective at mitigating the downhole bacteria concern. Laboratory studies further showed that more-established bacterial communities were much more resistant to biocidal treatment. Therefore, early mitigation strategies will likely be key in the prevention of microbiologically induced corrosion and souring.