Our Business - CBM.
CBM has been proven a viable energy source in North America and eastern Australia where commercial production has become an important part of their respective energy mix. Dart Energy believes CBM is positioned to provide an alternative source of cleaner energy into an increasingly energy constrained world. We believe the CBM successes in North America and Australia can be replicated in Asia and Europe and that the nature of these markets in many respects present an even more attractive commerical prospect than the US and Australia.
CBM or coal bed methane is natural gas produced from coal. The coal seam is both the source and the reservoir, which is different from conventional oil and gas.
During the coalification process, organic matter is converted into coal. Some of this organic matter is transformed into natural gas, which is then adsorbed onto the surface of the coal. The internal coal matrix has a tremendous surface area and is capable of storing methane up to seven times the amount of natural gas stored in a conventional sandstone reservoir.
CBM is produced when the pressure of the coals at depth is released. This occurs when water, which is found trapped within the coal, is removed. When the pressure reaches what is known as the desorption point, gas molecules are desorbed from the matrix. This process is called dewatering.
Coal seams often cover a large geographical area and gas accumulations are typically found throughout the coal. The challenge in developing CBM is to find ‘sweet spots’ that have the geological characteristics that allow gas to flow at commercial rates. These factors include gas content and saturation in the coal, the permeability of the coal, thickness of the coal seams and the areal extent.
How is CBM produced?
A 300 to 1,200 metre deep well is used to extract CBM from the coal bed. The top section of the well is cased with steel and cement to prevent the loss of water from any upper aquifers.
A special rotating blade is lowered to the bottom section of the well to ream out cavities in the coal seams. This production zone is then lined with alternating perforated and blank steel casing.
Water, released from the coal, is pumped from the well using a rotating screw. This lowers the water pressure in the coal seam and allows the gas to separate from the coal and flow into the well.
The gas and water rise to the surface through separate pipes. The water is transported through underground pipes to a dam for possible reuse and recycling. The gas passes through a separator near the well head to remove water traces before being piped to a processing facility to be compressed and dehydrated. The gas is then fed into commercial pipelines.