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DOE Touts New Process to Treat Water Produced with CBM

New technology has been commercialized that could help solve the biggest problem that coalbed methane (CBM) producers face in the Powder River Basin and elsewhere -- what to do with all that salty water that's co-produced with the gas.

Environmental and conservation concerns about water disposal, chemistry and usage have become one of the major roadblocks to greater CBM production in the Powder River but a new water treatment process developed by Helena, MT-based Drake Engineering holds the promise of providing a partial solution, the Department of Energy's Office of Fossil Energy said.

CBM is the hottest natural gas play in the United States with economically recoverable reserves estimated at 100 Tcf -- it's also the fastest-growing new source of water. At least 15,000 CBM wells have been drilled just in the Powder River Basin of Wyoming and Montana, site of the most intense CBM drilling activity. But along with each of those wells has come a significant amount of water.

As coal is formed underground, methane is trapped within the coal. Coalbeds also are natural aquifers, and the water in coalbeds sustains pressure that keeps the methane adsorbed to the coal. In order to produce CBM, it is necessary to pump this water to the surface to lower the pressure in the coalbed reservoirs, thus stimulating the release of methane.

Some wells initially produce five to 10 barrels of water per minute. And the water produced has a slightly higher salinity and a different chemical composition than stream water or drinking water. Because of its chemical composition, it also has a tendency to attract other chemicals when its disposed on the surface of the land and allowed to run off into streams.

"About nine tenths of this water you can drink and 100% of it you could use for stock water," said John Ford, project manager at the DOE's National Energy Technology Lab in Tulsa. "The only thing about it is whenever it hits the ground up there, then it will pick chemicals up, and whenever it finally gets in the streams those chemicals that it had picked up on that old ground that have been out there for eons will get associated with that water since there is so much of it."

The water produced with CBM has an unusual calcium-magnesium-sodium balance that can basically lock up the soil when spilled out on the land so that so that the nutrients in the soil become unavailable to the plants, said Ford. If allowed to flow directly into streams, it also can change stream chemistry. "Whether that's good or bad is kind of a function of who is making the call," said Ford. "In some places it may actually cause plant problems or water problems because of the fish [population]. In other places it may not."

Concerns over CBM produced water present unique challenges. Some landowners and environmental groups worry that it could be a particular concern for crop irrigation. And if the public and regulators perceive a significant threat to groundwater quality from CBM produced water, operators could be forced to choose between expensively treating water from these typically low-volume gas wells and shutting them in, costing the nation an important source of gas supply and the West critically needed water.

But if rendered suitable, CBM produced water could help Western states solve their perennial problem of water shortages. The fluid-bed resin exchange treatment system that Drake Engineering has produced will remove some of the chemicals in the water and make it more acceptable for stream discharge, said Ford. It also may improve the likelihood that the water could be discharged out directly onto the land.

"There are at least one or two companies that are making an effort to try to start using [this water treatment process] and I think it is one piece of an answer," he said. "It's a travesty what has happened so far [in the Powder River]. Instead of trying to study this and trying to understand it [some bad decisions have been made], and of course the environmental groups just keep suing everybody and locking everything up and tying everything up so you can't get anything done."

Drake's water treatment process is an outgrowth of a project in which researchers at Montana State University are evaluating phytoremediation of CBM produced water. This entails selecting wetlands plant species identified for their natural filtering capabilities and using them in artificial or modified natural wetlands. The plants naturally reduce the levels and negative effects of salts in CBM produced water so that it can be discharged safely to surface land or waters.

Drake since has patented and begun commercializing its own process by field-testing it in Powder River. Equipment leasing contracts are being issued.

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