Shale gas Totally Explained

Everything about Shale Gas totally explained

ť Shale gas may also refer to gas generated from oil shale

Shale gas is natural gas produced from shale. Because shales ordinarily have insufficient permeability to allow significant fluid flow to a well bore, most shales are not sources of natural gas. Shale gas is one of a number of “unconventional” sources of natural gas; other unconventional sources of natural gas include coalbed methane, tight sandstones, and methane hydrates. Shale has low matrix permeability, so gas production in commercial quantities requires fractures to provide permeability. Shale gas has been produced for years from shales with natural fractures; the shale gas boom in recent years has been due to modern technology in creating extensive artificial fractures around well bores. Horizontal drilling is often used with shale gas wells.
Shales that host economic quantities of gas have a number of properties in common. They are rich in organic material, and are mature petroleum source rocks in the thermogenic gas window. They are sufficiently brittle and rigid enough to maintain open fractures. In some areas, shale intervals with high natural gamma radiation are the most productive.
Some of the gas produced is held in natural fractures, some in pore spaces, and some is adsorbed onto the organic material. The gas in the fractures is produced immediately; the gas adsorbed onto organic material is released as the formation pressure declines.

Environment

The extensive use of ground water and the potential for contamination of the groundwater and/or runoff due to the use of chemical solutions is an environmental concern. Chemicals are added to the water to facilitate the underground fracturing process that releases natural gas. The resulting volume of contaminated water is generally kept in aboveground ponds to await removal by tanker or injected back into the earth.
There have been incidents of dangerous concentrations of naturally occurring radioactive material, or NORM, aboveground at shale gas well sites.

Economics

Although shale gas has been produced for more than 100 years in the Appalachian Basin and the Illinois Basin, the wells were often economically marginal. Higher natural gas prices in recent years and advances in hydraulic fracturing and horizontal completions have made shale gas wells more profitable. In 1996, shale gas wells in the United States produced 0.3 TCF (trillion cubic feet), 1.6% of US gas production; by 2006, production had more than tripled to 1.1 TCF, 5.9% of US gas production. By 2005 there were 14,990 shale gas wells in the US. Shale gas tends to cost more to produce than gas from conventional wells, because of the expense of massive hydraulic fracturing treatments required to produce shale gas, and of horizontional drilling.
The prices required to make drilling and producing shale gas economic are different for each shale area. One study concluded that a wellhead gas price above $4.25 per thousand cubic feet (MCF) was required to make wells completed in the Fayettville Shale in Arkansas economic, while wells to the Woodford Shale in Oklahoma required a price above $6.50. Another study concluded that the Fayettville shale required a NYMEX gas price above $5.95 per million British thermal units (MMBTU), and the Woodford shale a price above $7.24; the same study arrived at break-even NYMEX prices of between $5.40 to $7.39 for the Barnett, and $6.31 for Appalachian gas shale. (Note that although the conclusions appear to be different, one is in terms of wellhead price per MCF, and the other study is in terms of NYMEX price per MMBTU).
To date, almost all successful shale gas wells have been in rocks of Paleozoic age, but shales of other ages are being evaluated, particularly in Cretaceous shales in Rocky Mountain basins.(External Link

) North America has been the leader in developing and producing shale gas because of high gas prices in that market. The great economic success of the Barnett Shale play in Texas in particular has spurred the search for other sources of shale gas across the United States.

United States

Barnett Shale, Texas

The Barnett Shale of the Fort Worth Basin is the most active shale gas play in the United States. The first Barnett Shale well was completed in 1981 in Wise County. Drilling expanded greatly in the past several years due to higher natural gas prices and use of horizontal wells to increase production. In contrast to older shale gas plays, such as the Antrim Shale, the New Albany Shale, and the Ohio Shale, the Barnett Shale completions are much deeper (up to 8,000 feet). The thickness of the Barnett varies from 100 to, but most economic wells are where the shale is between 300 and thick. The success of the Barnett has spurred exploration of other deep shales.

Fayetteville Shale, Arkansas

The Mississippian Fayetteville Shale produces gas in the Arkansas part of the Arkoma Basin. The productive section varies in thickness from 50 to, and in depth from 1500 to . The shale gas was originally produced through vertical wells, but operators are increasingly going to horizontal wells in the Fayetteville. Producers include SEECO a subsidiary of Southwestern Energy Co. who discovered the play, Chesapeake Energy, Noble Energy Corp., XTO Energy Inc., Contango Oil & Gas Co., Edge Petroleum Corp., Triangle Petroleum Corp., and Kerogen Resources Inc.

Antrim Shale, Michigan

The Antrim Shale of Upper Devonian age produces along a belt across the northern part of the Michigan Basin. Although the Antrim Shale has produced gas since the 1940s, the play wasn't active until the late 1980s. During the 1990s, the Antrim became the most actively drilled shale gas play in the US, with thousands of wells being drilled. To date, the shale has produced more than 2.5 TCF from more than 9 thousand wells. Antrim Shale wells produced almost in 2006. The shale appears to be most economic at depths of 1,000-2,000 feet. Wells are developed on 80 acre units. Horizontal drilling isn't widely used. Unlike other shale gas plays such as the Barnett Shale, the natural gas from the Antrim appears to be biogenic gas generated by the action of bacteria on the organic-rich rock.(External Link

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Upper Devonian Shales, Appalachian Basin

The upper Devonian shales of the Appalachian Basin, which is known by different names in different areas have produced gas since the early 20th century. The main producing area straddles the state lines of Virginia, West Virginia, and Kentucky, but extends through central Ohio and along Lake Erie into the panhandle of Pennsylvania. More than 20,000 wellls produce gas from Devonian shales in the basin. The wells are commonly 3,000 to deep. The shale is most commonly produced is the Chattanooga Shale, also called the Ohio Shale. The US Geological Survey estimated a total resource of of natural gas in Devonian black shales from Kentucky to New York (External Link

) The Marcellus shale in Pennsylvania, once thought to be played out, is now estimated to hold 168-516 TCF still available with horizontal drilling.

Floyd Shale, Alabama

The Floyd Shale of Mississippian age is a current gas exploration target in the Black Warrior Basin of northern Alabama and Mississippi.(External Link

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Conesauga Shale, Alabama

Wells are currently being drilled to produce gas from the Cambrian Conesauga Shale in northern Alabama.(External Link

) Activity is in St. Clair, Etowah, and Cullman counties.

New Albany Shale, Illinois Basin

The Devonian-Mississippian New Albany Shale produces gas in the southeast Illinois Basin in Illinois, Indiana, and Kentucky. The New Albany has been a gas producer in this area for more than 100 years, but recent higher gas prices and improved well completion technology have increased drilling activity. Wells are 250 to deep.(External Link

) The gas is described as having a mixed biogenic and thermogenic origin.

Pearsall Shale, Maverick Basin

Operators have completed approximately 50 wells in the Pearsall Shale in the Maverick Basin of south Texas. The most active company in the play has been TXCO Resources, although Encana and Anadarko Petroleum have also acquired large land positions in the basin.

Caney-Woodford Shale, Oklahoma

Gas companies have been actively drilling and completing wells to the Devonian-Mississippian Woodford Shale in Oklahoma since 2004.(External Link

)

Canada

Utica Shale, Quebec

The Ordovician Utica Shale in Quebec potentially holds at production rates of 1 MMCF per day Gastem, one of the Utica shale producers, has announced plans to explore for Utica Shale gas across the border in New York state.

Muskwa Shale, British Columbia

The Devonian Muskwa Shale of the Horn River Basin in northeast British Columbia is said to contain 6 TCF of recoverable gas. Major leaseholders in the play are EOG Resources, Encana, and Apache Corp..

Further Information

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