Top: Water Outfall
Bottom: Water Resevoirs

Toolbox to Evaluate Treatment Technologies
for Coalbed Natural Gas Co-Produced Water

June 11, 2007 - To produce coalbed natural gas in the Wyoming Powder River Basin requires the removal of water in the coal seam. This reduces the pressure sufficiently to allow the natural gas to desorb from the coal and be recovered. The co-produced water is a by-product that must be managed. Investigators for a project to evaluate treatment technologies for coalbed natural gas co-produced water include David M. Bagley and Drew W. Johnson of the Department of Civil and Architectural Engineering and student researcher Eric Sajtar, M.S. candidate in environmental engineering. The project is funded by the Department of Energy National Energy Technology Laboratory and is under the direction of principal investigator, Harold Bergman of the Department of Zoology and Physiology and director of the Ruckelshaus Institute and Haub School of Environmental and Natural Resources.

Much of the water produced so far has been high quality and suitable for direct discharge and use for irrigation. This is a major benefit for the Powder River area which is naturally arid. As additional coal seams are developed, however, the quality of the water can deteriorate. Depending on the concentrations of key constituents, the water can be discharged after minimal treatment (Top) into storage ponds (Bottom). An increasing quantity of water, however, contains too much sodium, in particular, to be safely stored or otherwise used. Sodium concentrations can range up to 800 mg/L with total dissolved solids ranging from 270-2,010 mg/L, and sodium adsorption ratios ranging from 5.7-33. These waters require treatment before they can be discharged or otherwise beneficially used.

The primary treatment challenge is to cost-effectively remove sodium. Current technologies being used to treat Powder River basin coalbed natural gas co-produced waters include ion exchange (Higgins loop or fixed bed processes) and reverse osmosis. Other technologies in various stages of development include: controlled-contact ion exchange, electrodialysis, electrodialysis reversal, high efficiency electro-pressure membranes, electrodeionization, capacitive deionization, advanced zeolites, constructed wetlands, and rapid spray evaporation. Most of these technologies produce a concentrated brine stream. Brine management options include: deep well injection, evaporation ponds, evaporation crystallization, and drying.

The purpose of this project is to develop a spreadsheet-based toolbox for comparing water treatment and brine management technologies for Powder River Basin coalbed natural gas co-produced waters. The toolbox will compare technologies with respect to both technical performance and cost, using specific water characteristics and discharge criteria as input, and will facilitate the rapid identification of suitable technologies while providing a preliminary estimate of the cost A preliminary version of the toolbox has been developed for ion exchange, reverse osmosis, electrodialysis reversal, and high efficiency electro-pressure membranes. Our initial predictions indicate that the amortized costs to remove 530 mg/L of sodium from a barrel (42 gallons) of water range from $0.12-$0.24 per barrel, depending on the technology being used. We are continuing to validate and upgrade the toolbox and ultimately hope to have it available on-line.