As mature fields produce larger quantities of water, operators and service companies find themselves challenged with disposing flowback and produced water to reduce costs, handling the logistics of getting enough water to hydraulically fracture the well, as well as complying with stricter governmental regulations. As produced water is recycled and used in fracturing applications, each cycle of re-used water returns with a more complex chemical make up than before. Therefore, the usable lifetime of the recycled water is shortened or requires expensive cleaning or dilution with fresh water to make it a viable solvent base for fracturing fluids. This paper describes the process to properly design fracturing fluids using flowback and produced water. The importance of flowback water analysis is highlighted for optimizing fluid performance downhole. Recent developments in proper selection of fluid additives and viscosifiers for slickwater and crosslinked fluids are discussed. We will describe in detail how the salinity, biological activity, and scaling tendency of these waters can impact fluid performance. Other factors, including organics and suspended solids will be included in the discussion. Laboratory examples will be shown to demonstrate the importance of following a systematic approach. Ultimately, this paper focuses on how to optimize well performance using recycled waters in stimulation applications. Introduction The exploration and production (E&P) industry in the United States generates approximately 210 bbls/day in produced water (Arnold et al., 2004). Other reports suggest that for every barrel of oil produced in the United States, 10 barrels (bbl) of produced water is generated (Khatib and Verbeek, 2002). Even though some of this material can be managed at the well site, many operators in the United States seek offsite management options for their waste. Offsite disposal companies must comply with state and federal laws including the Resource Conservation and Recovery Act (RCRA), the Environmental Protection Agency (EPA), the Clean Water Act (CWA), and the Safe Drinking Water Act. For instance, to discharge into surface water in Pennsylvania and Wyoming, the company must do so under a National Pollutant Discharge Elimination System (NPDES) permit or into a publicly owned treatment work (POTW). Typical costs associated with disposal range from $0.30 to $10/bbl for injection or cavern disposal to $15 to $22/bbl for solidification and burial in a landfill (Puder, 2007). Operators in the United States have reported that disposal and treatment costs for their produced water exceeded $400 MM/yr (Khatib and Verbeek, 2002). Finding alternative uses for flowback water in the E&P industry is both an economic as well as an environmental issue. In an effort to circumvent some of the extra costs, operators have reported the use of recycled produced waters in reservoir management processes (Khatib and Verbeek, 2002). Water treatment options have been discussed that include desalination, reverse osmosis, and 'floc 'n drop' methods but trucking costs associated with moving water to treatment facilities often make this an expensive option for operators (Kaufman et al., 2008, Horn, 2009). Literature has also been documented on the use of untreated recycled waters in high rate, low permeability shale reservoirs (Arthur et al., 2009). Water volumes for a typical slickwater hydraulic fracture treatment can average 715 m3 (6,000 bbl) per stage with 6 to 10 stages per horizontal well. Large treatment volumes for these applications offer a unique opportunity for cost savings if flowback water can be used in place of other fresh water sources. This approach saves on logistical problems as the water source is near the next treatment site.
Effective microbiological control is an important aspect of a successfully executed fracturing job. Control of bacterial growth is often accomplished through the use of biocides such as glutaraldehyde, particularly in the multi-stage, high-volume fracturing of unconventional shale gas reservoirs. Biocidal additives, which are toxic by necessity, can persist in flowback water, so their use in shale fracturing has come under increasing scrutiny since high biocide concentrations in flowback water increase fluid cost and limit the options for disposal. The case for designing a bactericide program to match, and not exceed, the required amount of bacterial control is clear, but rarely is the bacterial load determined during and after the job to verify this balance. Herein, we report a case study undertaken to evaluate the bacterial load of field mix water and flowback water during and after a large hydraulic fracturing job in the Marcellus Shale. A novel oxidative biocide product was used during the fracturing job that has both an effective fast kill and a low toxicity profile (e.g. HMIS rating of 1,0,0). Because of its rapid biodegradability, there was concern that the effective kill of this biocide would not persist beyond a few days. Industry standard techniques (NACE Std. TMO194-94) for quantifying bacteria were applied to water samples taken during the job and over several weeks of production. The biocide was also evaluated for compatibility with common fracturing additives and for its corrosivity to surface equipment and tubular goods. This study determines that the new biocide does not persist in flowback water beyond a few days. However, analysis of flowback water samples reveals that the bacteria count stays low (less than 10 cells/mL) for up to 81 days after application of this biocide in a slickwater fluid. Additionally, genetic fingerprinting using Denaturing Gradient Gel Electrophoresis Analysis (DGGE) was applied to the bacteria in the initial field mix water to allow comparison to any bacteria detected in the flowback samples. This paper will describe the details of this case study. Since the completion of this case study, we have successfully deployed this technology on treatments in the Barnett, Haynesville, Marcellus, and Granite Wash shale regions. This paper reveals details of a field test and of the efficacy of this biocide as tested in flowback waters from the Piceance and Marcellus Shale basin. The results of the bacteria enumerated from each job site sample are presented. Finally, dosage requirements for biocidal efficacy were optimized for slickwater hydraulic fracturing applications are described.
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