The following definitions reflect those used by the
International Energy Agency (IEA); definitions used by other
organisations and publications may vary. United Arab Emirates
underground coal gasification ultra-low CO2 steelmaking
International Union of Producers and Distributors of Electrical
Energy ultra-supercritical steam cycle union territories (India)
sources of gas trapped deep underground by impermeable rocks,
such as coal, sandstone and shale. The three main types of
‘unconventional’ gas are: shale gas (found in shale deposits);
coal bed methane, or CBM (extracted from coal beds) and tight
gas (which is trapped underground in impermeable rock
formations). While different techniques are applied, depending
on the type of gas being extracted, one common method is known
as hydraulic fracturing: large volumes of water (mixed with some
sand and chemicals) are injected underground to create cracks in
the rock. This frees the trapped gas which can then flow into
the well bore created by the drill and be coll