Environmental Engineering Reference
In-Depth Information
from the study of rock strata, especially the distribution, deposition and age of
sedimentary rocks, and various technological advances were also being looked
at. The Appalachian basin, from New York State through Ohio to Kentucky
and Illinois, was the main historic area for shale gas production, but there had
been other basins where the gas was produced, such as the Williston Basin.
This is a large intracratonic sedimentary basin in eastern Montana, western
North Dakota, South Dakota and southern Saskatchewan where the Bakken
Shale had produced gas since 1953. Stimulated by the Department of Energy
and the Gas Research Institute, shale gas areas were found in the Cretaceous
Lewis Shale of the San Juan Basin, the Mississippian Barnett Shale of the Fort
Worth Basin and the Devonian Antrim Shale of the Michigan Basin.
5
Geo-
chemical studies revealed that the gas was not produced by microorganisms
that generate heat within organic waste (thermogenic) but was produced by
bacterial anaerobic respiration (methanogenesis). The bacteria had entered
the fractured shale from ground water percolating down from the glacial drift
cover.
6
This second process for gas generation opened up new areas for ex-
ploration: areas where the source rock was previously deemed immature or
over-mature for thermogenic gas generation.
The shale gas renaissance was also brought about by improved methods of
well drilling and advances in completion technologies. The ability to drill
multiple wells off a single pad was both financially and environmentally
rewarding.
7
The ability to drill wells horizontally as well as vertically, toge-
ther with the ability to steer the drill along ''sweet spots'', enabled permeable
gas-changed zones to be tapped into. This was coupled with more dramatic
hydraulic fracturing techniques. Seismic techniques, which could use the
fracturing process as an energy source, enabled gas-charged ''sweet spots'' to
be mapped in three dimensions.
1
In the US the development of shale gas expanded dramatically from the mid
1990s, with the number of gas rigs in operation increasing from around 250 in
1993 to over 1500 by 2007.
8
This has seen production of shale gas in the US
increase from 1293 billion cubic feet in 2007 to 7994 billion cubic feet in
2011.
9
This has resulted in the US natural gas wellhead price falling from
$8.01 per thousand cubic feet in January 2006 to $2.89 per thousand cubic feet
in January 2012.
9
These are similar prices to those seen in the US in the early
1980s. However, the reduction in the price of natural gas seen in the US is
unlikely to be repeated to the same extent in Europe. This is due to the limited
export market that the US has for gas at the present time as it has no export
terminals for shipping the gas globally as liquefied natural gas (LNG). The
largest exporter of LNG worldwide, Qatar, has six operational export terminals,
whilst Australia, which is rapidly increasing its export of LNG, has three op-
erational export terminals with another seventeen projects either under con-
struction or being planned. Worldwide there are thirty-two operational export
terminals with another sixty-nine under construction or in planning.
10
In the UK, shale gas as a potential industry did not develop at all until the
British Geological Survey (BGS) noted the potential for its production in
1995.
11
Shale gas was not mentioned in reviews of future UK petroleum
