Until recently, U.S. oil and gas production occurred exclusively from conventional reservoirs. Conventional reservoirs (or plays, over a large geographic area) have hydrocarbons such as petroleum and natural gas sequestered in a relatively porous rocks such as sandstone. It has long been appreciated that oil and gas are also present in less porous rocks, shale frequently being the host rock. The macro-and microscopic pictures of sandstone and shale below allude to the challenge of extracting hydrocarbons from the less porous shale.
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Shale, note fine-grained nature in above micrograph |
Sandstone, note coarser-grained nature in above micrograph |
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Natural gas resources contained in unconventional plays now comprise approximately 25% of total U.S. natural gas resources. The six principal plays contain about 600 of the 850 trillion cubic feet of unconventional gas resources in the U.S. The map and pie chart below illustrate locations and contributions, respectively, of these six plays: the Marcellus, Haynesville, Barnett, Fayetteville, Woodford, and Eagle Ford Shales. While the Barnett Play is of historical significance, given that economic unconventional gas production was first demonstrated in this play, the Marcellus Play has the greatest potential for gas production. |
