Coal bed methane extraction

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Coal bed methane extraction (CBM extraction) is a method for extracting methane from a coal deposit. The methane is chemically bound onto the coal macerals and is released when the coal seam is depressurised. To economically retrieve reserves of methane, wells are drilled into the deposit, the seam is dewatered, then the methane is extracted from the seam, compressed and piped to market. The goal is to decrease the water pressure by pumping some of the water through the well. The decrease in pressure coaxes dissolved methane into its gaseous form, enabling it to be recovered. Disposal of the water, which may contain impurities such as salt, presents an environmental problem as does the resulting lowering of the water table. Seven percent of the natural gas (methane) currently produced in the United States comes from CBM extraction.

This process involves the drilling of tens of thousands of wells, and extensive support facilities such as roads, pipelines and compressors.

The use of this method is currently expanding with great controversy in the Powder River Basin.

The drillling and discharge water is under the framework of NPDES, the "National Pollution Discharge Elimination System", a system primarily intended for point source pollution based on refineries, brown fields, waste water treatment plants etc. and ill-suited to a problem area which is Geological, Geographic and water shed based. The discharge limits of the chemical constituents in the water are generally under the Chapter 1 drinking water standard, and in some cases Chapter 8 of the water quality regulations. In many cases, the exact same coal seams were used to supply water for both domestic and agricultural uses, hence the concern about well draw downs.

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