Barnett and Appalachian Shale Water Management and Reuse Technologies, Report No. 08122-05.FINAL

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2012

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Abstract

During the fracture process, between 1 and 5 million gallons of water and sand are expended "downhole" into each extraction well to aid in the fracture. A portion of this water is recovered during the initial extraction of the gas. With proper management, recovered flowback water can represent a significant resource. Conversely, flowback water can represent a costly disposal problem. The nature of the chemistry and dynamics of recovered flowback water is of vital interest for effective environmental stewardship of a gas field. The objectives of this report are to better understand the chemical character of flowback water, its treatability, and long-term sustainability issues associated with flowback water management.

This project approaches flowback water management at shale gas sites from several distinct levels, from broad management issues to testing potential treatment technologies, to full-scale verification of a commercially available technology. Alternative water sources and treatment options are presented to reduce impact and provide potential cost savings. The scientific, engineering, and economic data presented in this report may be used to form the basis of rational engineering and sustainability management tools. This final report summarizes these findings, with data links to more detailed topical reports and (publication-ready) papers available on the RFSEA website.

Perhaps the broadest findings of this project are presented in the final task, Task 11: Preliminary Engineering Systems Analysis of Shale Gas Water Management, in which the water collection and salt generation at a hypothetical Marcellus gas play with 16 wells per field and 300 fields (4,800 wells) are projected for a period of 45 years into the future. In the early years of the play (its youth), the active fracture of new wells provides ample opportunity for the reuse of recovered flowback water within the play. As rates of fracturing of new wells and the refracturing of existing wells decline, the play enters middle age (first crossover year) and the planned recovery volume exceeds the planned reuse volume. Segregation and pre-treatment of recovered water are at a premium. At some more future time, the rate of collection of produced water exceeds the rate of reuse (second crossover) and the play is in old age. Water treatment and waste disposal become overarching management issues. These findings put the remaining chapters into the perspective of these management needs.

Chapter 4 investigates the chemistry of 19 flowback events in the Marcellus and 5 flowback events in the Barnett. These data suggest that the organic nature of the flowback water is very similar to produced water from oil wells. Heavy metals are not an issue. The major disposal issue appears to be inorganic scale formers. The initial 30% of the recovered water is much less salty than the final 70%, suggesting that one viable option for management of these waters is simple segregation (Chapter 5). Treatment of mid-range waters (TDS 10,000-60,000 mg/l) with advanced innovative reverse osmosis membrane technology is investigated in Chapters 9-10 and with enhanced electrodialysis in Chapter 8. The treatment of heavy brine (60,000-100,000 mg/l) with distillation (mechanical vapor recompression) is verified in a report on a full-scale facility in the Barnett (Chapter 7). Alternate water sources in the Barnett are examined in Chapter 6.

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