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Coal Seam Gas
Coal Seam GasWhat is coal seam gas?

Methane (CH4) is formed as part of the burial of peat to form coal. Biogenic (bacterial activity) methane forms at shallower depths and thermogenic (burial heat) methane at greater depths. The methane remains attached (adsorbed) to the coal. The methane is held in the coal by burial pressure and water. Because of natural fractures called cleats, coal has a large internal surface area. Coal is, therefore, capable of holding larger volumes of gas than conventional sandstone reservoirs. The amount of gas present in a coal seam depends on the depth of the seam, the thickness and the extent to which the fracture system is interconnected.

How is coal seam gas produced?

Coal Seam GasWhen water is released from coal, the pressure is reduced, and gas flows through the cleats. When a well is first drilled into a coal seam, gas does not normally flow to the surface. Water is pumped from the well (dewatering) with gas flowing subsequently. As water production declines, gas production increases. To assist the flow of gas through the coal to the producing well, the coal can be mechanically fractured (referred to as ‘fracturing’ or ‘fraccing’). At the surface, the methane, other gases and water are separated. The gas from several wells is collected and passed to a central compressor station, where it is added to a pipeline network for delivery to users.
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