CBM exploration involves locating highly productive areas, known...

CBM exploration involves locating highly productive areas, known as 'sweet spots' or 'fairways'. Initially, CBM was mainly sought within the Permian coal seams of the Bowen and Sydney Basins. However, since the early 2000's, CBM exploration also targeted the relatively shallow depths of the lower rank coal seams of the Jurassic age Surat and Clarence-Moreton Basins in Queensland. Although these seams have less gas content than high rank Permian age coal these lower rank coals at shallow depths (100 to 600m) are more permeable and CBM can be more easily desorbed (or extracted), resulting in higher recovery factors. Brown coal (or lignite) of Tertiary age also has become a target for CBM exploration in the Otway Basin in Victoria. Other prospective coal basins which have been targeted by CBM explorers include the Gunnedah, Gloucester, Galilee, Murray and Perth Basins. However, the Bowen Basin remains the most actively explored and developed basin in Australia for CBM. The basin's share of CBM drilling activity exceeded 80% of Australia's total in 2004.


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The principal sources of CBM are either biogenic, producing a dry gas which is generated from bacteria in organic matter, typically at depths less than 1,000 feet, or thermogenic, which is a deeper wet gas, formed when organic matter is broken down by temperature and pressure.

The three main factors which determine whether or not gas can be economically recovered from coal beds are: the gas content of the coals; the permeability or flow characteristics of the coals; and, the thickness of the coal beds. Gas content is measured in terms of standard cubic feet (scf) per ton and varies widely from 430 scf per ton in the deep (2,000 to 3,500 feet). All CBM coals must have relatively high permeability as the ability of gas to easily travel to the bore hole is essential to economic CBM production.