Improved Microbial Control Programs for Hydraulic Fracturing Fluids used during Unconventional Shale-Gas Exploration and Production
- Michael V. Enzien (Dow Chemical Co.) | Bei Yin (Dow Chemical Co.) | Donald Love (Dow Chemical Co.) | Michael Harless (Multi-Chem Production Chemicals) | Edward Corrin (Multi-Chem Production Chemicals)
- Document ID
- Society of Petroleum Engineers
- SPE International Symposium on Oilfield Chemistry, 11-13 April, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 3 Production and Well Operations, 5.8.2 Shale Gas, 4.1.2 Separation and Treating, 1.6 Drilling Operations, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.6.9 Coring, Fishing, 4.2 Pipelines, Flowlines and Risers, 4.6 Natural Gas, 2 Well Completion, 4.2.3 Materials and Corrosion, 4.1.5 Processing Equipment, 4.3.4 Scale, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation
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Biocide efficacy studies targeting extended contact times, 7 days, and elevated temperatures, 80o 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.
Biocides are routinely used as chemical additives for hydraulic fracturing operations in order to prevent biogenic H2S formation, microbiologically influenced corrosion, and plugging of the natural gas reservoirs due to microbial growth. While hydraulic fracturing technologies have been around for many decades, recent advances in drilling and well completion technologies have allowed the economic exploration of many large unconventional natural gas resources in North America. Large amounts of water are used in these hydraulic fracturing operations and depending upon location, the source and quality of water can vary dramatically. Fracturing water is treated for microbial control for two important reasons: 1) prevent injection of unwanted microorganisms into reservoirs, and 2) inhibition or kill of endemic microorganisms within the fractured formation. It is therefore important to have a biocide program that can not only rapidly disinfect injection water but also is persistent in down-hole environmental conditions.
With the completion and production of new unconventional natural gas reservoirs falling into environmentally sensitive areas, the development of new more environmentally friendly approaches to conventional biocide treatments have been pursued. These new treatments not only need to have a more favorable eco-toxicity profile compared to conventional biocide treatments, but they also need to effectively protect the wells and reservoirs. Dow and Multi-Chem jointly performed laboratory research under shale gas reservoir conditions focused on identifying synergistic biocide combinations in order to meet the more stringent conditions necessary of these reservoirs while maintaining an environmentally acceptable solution.
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