Evaluation of a More Environmentally Sensitive Approach to Microbiological Control Programs for Hydraulic Fracturing Operations in the Marcellus Shale Using a Nitrate-Reducing Bacteria and Nitrate-Based Treatment System

Abstract

Control of micro-organisms during the completion of hydraulically fractured wells is a significant component in the successful development of a production system. Detrimental bacteria, such as sulfatereducing bacteria (SRB), introduced into the reservoir during the completion process, can facilitate biogenic sulfide production, resulting in souring of the production fluids and gas, iron sulfide formation, and SRB associated microbiologically influenced corrosion (MIC). Biocides are routinely dosed at low levels into the fracturing fluids to control microbe populations and thus the subsequent adverse effects associated with bacterial activity. Biocides, by their very nature and intended purpose, are not well tolerated by certain aquatic organisms. In an effort to improve the ecological profile of the microbiological control program in fracturing operations, a treatment system using nitrate and nonhazardous live nitrate-reducing bacteria (NRB) for the control of SRB was developed.Nitrate-based mitigation of SRB has been used as an alternative to biocide injection in the oil and gas industry for decades. Successful SRB control using nitrate-based treatment applications has been observed in several waterflooding programs throughout the world. Nitrates stimulate the metabolic activity of NRB. NRB can mitigate SRB activity by means of three primary mechanisms: competition for available carbon sources, direct metabolic inhibition through the generation of nitrite, and certain species of NRB, which directly oxidize biogenic sulfide. This case study is an evaluation of the application of live NRB, selected for their tolerance of the temperature and salinity of the Marcellus shale, and sodium nitrate nutrient solution, as an alternative treatment to the application of biocides for hydraulically fractured wells. Both live NRB and nitrate solution were added into the fracturing fluids during the fracturing operation.Multiple wells were treated in the Marcellus shale using the tested NRB and nitrate treatment system, and these wells were monitored for periods ranging from three to 18 months depending on the date of completion. Treatment efficacy was evaluated by comparing data from the NRB and nitrate-treated wells to data collected from wells completed in the same manner and, in some cases, on the same well pad with a biocide that historically exhibited good microbial control. The results from the wells treated with NRB and nitrate demonstrated that the treatment was similarly effective compared to successful biocide applications for the control of SRB activity.

Assessment of the Decomposition Kinetics of Sulfur-Containing Biocides to Hydrogen Sulfide at Simulated Downhole Conditions

“…During the fracturing of a well, large volumes of water are used from multiple sources (river, lakes, municipal water supplied, or fresh water wells) which can contain some bacteria . To avoid microbial contamination and reservoir souring from both native and non-native bacteria, biocides are added during drilling (as part of the drilling mud), during fracturing (as a chemical additive in the fracturing fluid), and for long-term bacterial control in the formation and gathering system. , Ideally, a biocide or a combination of biocides should sterilize the reservoir during a hydraulic fracturing procedure, as reservoir souring in the fractures is known to be very difficult to treat. In reality, complete sterilization is not achievable, and long-term treatment is often required as part of a microbial control strategy.…”