Coal bed methane extraction

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Coal bed methane extraction (CBM extraction) is a method for extracting methane from a coal deposit.

1 Basic Principles
2 Areas with Coal Bed Methane Extraction
3 Water Issues
- 3.1 Surface Discharge
- 3.2 Aquifer Depletion
4 External links

[edit] Basic Principles

The methane is adsorbed into the solid coal matrix (coal macerals) and is released when the coal seam is depressurised. To economically retrieve reserves of methane, wells are drilled into the coal seam, 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 water from the well. The decrease in pressure allows methane to desorb from the coal and flow as a gas up the well to the surface.

[edit] Areas with Coal Bed Methane Extraction

This process has resulted in the drilling of tens of thousands of gas wells, and extensive support facilities such as roads, pipelines and compressors.

The use of this method is currently expanding in the Powder River Basin of northeast Wyoming and southeast Montana.

Seven percent of the natural gas (methane) currently produced in the United States comes from CBM extraction.

[edit] Water Issues

Extraction and discharge of water from the coal seam may pose environmental problems.

[edit] Surface Discharge

Surface discharge of the water, which may contain undesirable concentrations of dissolved solids.

Surface discharge of produced water is under the framework of the NPDES (National Pollution Discharge Elimination System), a system originally intended for point source pollution based on refineries, waste water treatment plants, etc. rather than for coal bed methane operations. 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.

[edit] Aquifer Depletion

Lowering of the water table in the coal seam may also be a problem. In some cases, CBM extraction may adversely affect water wells that supply water for domestic and agricultural uses from the same coal seams.