GC: n

CT: Shale gas refers to natural gas that is trapped within shale formations. Shales are fine-grained sedimentary rocks that can be rich resources of petroleum and natural gas. Sedimentary rocks are rocks formed by the accumulation of sediments at the Earth’s surface and within bodies of water. Common sedimentary rocks include sandstone, limestone, and shale.
Over the past decade, the combination of horizontal drilling and hydraulic fracturing has allowed access to large volumes of shale gas that were previously uneconomical to produce. The production of natural gas from shale formations has rejuvenated the natural gas industry in the United States.

S: http://www.shaletec.org/whatis.htm (last access: 1 March 2015)

N: 1. shale (n): 1747, possibly a specialized use of Middle English schale “shell, husk, pod” (late 14c.), also “fish scale,” from Old English scealu (see shell (n.)) in its base sense of “thing that divides or separate,” in reference to the way the rock breaks apart in layers. Compare Middle English sheel “to shell, to take off the outer husk” (late 15c.). Geological use also possibly influenced by German Schalstein “laminated limestone,” and Schalgebirge “layer of stone in stratified rock.”
gas (n): 1650s, from Dutch gas, probably from Greek khaos “empty space”. The sound of Dutch “g” is roughly equivalent to that of Greek “kh.” First used by Flemish chemist J.B. van Helmont (1577-1644), probably influenced by Paracelsus, who used khaos in an occult sense of “proper elements of spirits” or “ultra-rarified water,” which was van Helmont’s definition of gas.
Modern scientific sense began 1779, with later specialization to “combustible mix of vapors” (1794, originally coal gas); “anesthetic” (1894, originally nitrous oxide); and “poison gas” (1900). As short for gasoline, it is American English, first recorded 1905.
2. A natural gas stored in organic rich rocks such as dark-coloured shale, interbedded with layers of shaley siltstone and sandstone.
3. Shale can be the source, reservoir and the seal for the (shale) gas. Shale gas plays are classified as a “continuous” type gas accumulations extending throughout large areas, typically with low permeability and perhaps natural fractures.

S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=shale+gas&searchmode=none; http://www.etymonline.com/index.php?allowed_in_frame=0&search=gas&searchmode=none (last access: 1 March 2015). 2 & 3. TERMIUM PLUS (last access: 1 March 2015).

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CR: fracking, natural gas, petroleum, shale oil.