Biocide efficacy studies targeting extended contact times, 7 days, and elevated temperatures, 80 o C, led to the discovery of a synergistic combination of Dimethyl Oxazolidine (DMO) and glutaraldehyde. When applied together in specific ratios, most notably a 1:4 ratio of glutaraldehyde to DMO, these two chemistries exhibited superior performance after extended exposure relative to traditional biocide treatments utilizing chemicals such as THPS, glutaraldehyde, and glutaraldehyde/alkyl dimethy benzyl ammonium chloride (ADBAC) blends. The combination of glutaraldehyde and DMO applied in a 1:4 ratio was able to achieve equal performance with lower combined actives. The result of this synergy has a twofold impact on the environmental footprint: it requires less overall biocide for the same level of control, and DMO has a more favorable eco-toxicity profile compared to conventional organic biocides. Field trials on eleven wells and 4 separate well pads in the Marcellus Shale area were treated with the Glutaraldehyde and DMO combination and evaluated using various microbial detection techniques. The benchmark for performance was set by the prior standard chemical treatment in the same shale formation area which utilized the biocide combination, 42.5% active glutaraldehyde and 7.5% active ADBAC blend. Seven wells on three separate well pads treated with Glut/ADBAC were used for comparison to the test wells. The wells treated with the Glut/ADBAC were all dosed at a rate of 300 ppm active ingredient (600ppm product), and the wells used to test the glutaraldehyde/DMO combination treatment were dosed at 200 ppm active (285ppm product). The results of the field trials showed equal or slightly better performance with the combination treatment while utilizing 33% less active chemical, and yielding a reduction of 50% less biocide product applied.
This paper was prepared for presentation at the 1999 SPE International Symposium on Oilfield Chemistry held in Houston, Texas, 16-19 February 1999.
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.
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