How Hot Is Too Hot for Bacteria? a Technical Study Assessing Bacterial Establishment in Downhole Drilling, Fracturing and Stimulation Operations

Abstract Bacterial contamination from drilling and fracturing can lead to serious problems in unconventional oil and gas shale plays. Large water volumes for these processes are transported from aquifers, municipal waters, rivers, lakes, ponds or oilfield flowback water to the wellsite and stored in frac tanks or earthen impoundments. Typically, these waters are contaminated with bacteria. Furthermore, fracturing fluids contain gelling agents or polyacrylamide-based friction reducers which are readily available bacterial food sources. If these fluids are insufficiently treated, establishment of sulfate-reducing bacteria (SRB) and acid-producing bacteria (APB) can lead to operational issues including: 1) biogenic sulfide production and formation souring, 2) plugging from iron sulfide scale production, 3) microbially influenced corrosion (MIC), and 4) premature degradation of fracturing fluids. As operators have moved into hotter, deeper unconventional shale plays, the following question has been posed: “How hot is too hot for bacteria?” Downhole reservoir temperatures can approach 260 to 360°F (127 to 182°C), temperatures previously thought to be inhibitory to bacteria. Are introduced bacterial species capable of becoming established in these hot reservoirs following the drilling and fracturing processes? Does the nutrient influx from drilling and fracturing processes stimulate viable, indigenous bacteria? These are some of the key questions addressed in this study.