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Potential Breakthrough Could Protect Groundwater from CBM Production

Researchers have discovered a way to distinguish between groundwater and the water co-produced with coalbed methane (CBM) gas, which may allow natural gas producers to tap more resources with less impact to the environment.

The Department of Energy (DOE) Oil and Natural Gas Program announced the findings Thursday based on a project managed by the National Energy Technology Laboratory for the DOE Office of Fossil Energy. Researchers at the University of Wyoming successfully used the isotopic carbon-13 to carbon-12 ratio for water that is co-produced with CBM, which culminated in a patent application, DOE noted.

"The co-mingling of groundwater and coalbed natural gas co-produced water has placed environmental limits on recovering natural gas and limited the nation's ability to make full use of its domestic energy resources," said DOE's Victor K. Der, acting assistant secretary for fossil energy. "The University of Wyoming's success provides a technical opportunity to drill new wells in Wyoming and Montana, while monitoring the quantity and quality of water at the well sites and protecting freshwater resources."

Dealing with co-produced water has been one of the most difficult issues for researchers involved in finding the best, most environmentally sound methods for recovering natural gas in Wyoming's Powder River Basin, DOE noted. The issue is significant for domestic energy and environmental health because "the number of coalbed methane wells in the basin increased from 18,077 total wells in December 2004 to 27,280 in November 2008 -- an increase of 50%," said the agency.

Preserving water resources has long been an objective of drillers, but in recent months environmental protests and regulators have voiced their concerns for water resources in some of the large and emerging domestic gas plays, including in the Marcellus Shale (see related story), and other parts of the country (see NGI, March 16; Feb. 23; Nov. 24, 2008).

To produce gas from CBM wells, operators first pump out some of the water that is naturally contained in the gas-bearing coal seams. Because of the large water volumes, researchers have worked to reduce the environmental impacts and ensure that there are beneficial uses for the water.

In the DOE-sponsored tests, the University of Wyoming researchers used stable isotopic "tracers," along with available water quality data, to look at three separate issues in the Powder River Basin. Researchers monitored the infiltration and dispersion of CBM co-produced water into shallower subsurface areas, and then they determined the locations where coal seams were isolated from adjacent aquifers and co-produced water was limited to coal. The information then was evaluated to determine the isotopic analyses of carbon, oxygen and hydrogen in the co-produced waters.

The findings indicated that a concentration of dissolved inorganic carbon and the isotopic carbon-13 to carbon-12 ratio are effective tracers to distinguish groundwater from co-produced water.

"This discovery holds promise that different concentrations of dissolved inorganic carbon and isotopic ratios can be used to monitor the infiltration of co-produced water into streams and groundwater over a long period of time," said DOE. "The method can also be used to reduce the amount of co-produced water."

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