Historically, conventional natural gas deposits have been the most practical and easiest deposits to mine. However, as technology and geological knowledge advance, unconventional natural gas deposits are beginning to make up an increasingly large percent of the supply picture.
There is no set definition of what constitutes ‘unconventional’ gas, and is subject to change because new technological advances or processes can mean specific gases can become ‘conventional’. In the broadest sense, unconventional natural gas is gas that is more difficult or less economical to extract, usually because the technology to reach it has not been developed fully, or is too expensive to deploy.
Generally, theses gases are seen as being:
Deep natural gas
- natural gas that exists in deposits very far underground, beyond 'conventional' drilling depths.
Tight natural gas
- Also called Tight Gas. This is gas that is stuck in a very tight formation underground, trapped in unusually impermeable, hard rock, or in a sandstone or limestone formation that is unusually impermeable and non-porous (tight sand). Several techniques exist that allow the gas to be extracted, including fracturing and acidising. We expect there will be fraccing operations of Tight Gas in Victoria this year.
– which has been trapped in shale deposits. Shale is a very fine-grained sedimentary rock, which is easily breakable into thin, parallel layers. It is a very soft rock, but it does not disintegrate when it becomes wet.
Coalbed Methane (or Coal Seam Gas)
- many coal seams also contain natural gas, either within the seam itself or the surrounding rock. Victoria mostly has brown coal deposits, which is generally not likely to contain CSG, however it is believed that the Black Coal resource in Victoria may have CSG.
Adapted from http://www.naturalgas.org/overview/unconvent_ng_resource.asp
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