The Antrim Shale is a formation of Upper

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...

age in the

Michigan Basin The Michigan Basin is a geologic basin centered on the Lower Peninsula of the U.S. state of Michigan. The feature is represented by a nearly circular pattern of geologic sedimentary strata in the area with a nearly uniform structural dip toward ...

, in the US state of

Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and the ...

, and extending into

Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The s ...

Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th st ...

and

Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michi ...

. It is a major

source Source may refer to: Research * Historical document * Historical source * Source (intelligence) or sub source, typically a confidential provider of non open-source intelligence * Source (journalism), a person, publication, publishing institute ...

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon di ...

in the northern part of the basin. The Antrim Shale was defined by A. C. Lane in 1901, and named for type-section exposures in

Antrim County, Michigan Antrim County ( ) is a county located in the U.S. state of Michigan. As of the 2020 Census, the population was 23,431. The county seat is Bellaire. The name is taken from County Antrim in Northern Ireland. YMCA Camp Hayo-Went-Ha, the oldest ...

. The formation was previously known as the St. Cleric Shale in Michigan, and the Genesee Shale in Indiana.

Stratigraphy

The Antrim is a brown to black, pyritic, highly laminated and organic-rich

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments ( silt-sized particles) of other minerals, especial ...

, from 60 to 220 feet thick. Total organic content varies from 1% to 20%. In some places the unit includes a gray calcareous shale or limestone, and in places a fine-grained sandstone at the base. The formation is called the Kettle Point Formation in

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...

, and is the stratigraphic equivalent of the New Albany Shale in the

Illinois Basin The Illinois Basin is a Paleozoic depositional and structural basin in the United States, centered in and underlying most of the state of Illinois, and extending into southwestern Indiana and western Kentucky. The basin is elongate, extending app ...

. It is overlain by the Bedford Shale, and underlain in some areas by the Jordan River Formation, and elsewhere by the Thunder Bay Limestone.

Natural gas

The Antrim Shale, is a major source of

shale gas Shale gas is an unconventional natural gas that is found trapped within shale formations. Since the 1990s a combination of horizontal drilling and hydraulic fracturing has made large volumes of shale gas more economical to produce, and some a ...

, and produces natural gas along a swath across the northern part of the state. Most natural gas production is in Antrim, Crawford, Montmorency, Oscoda and Otsego counties. Although the Antrim Shale has produced gas since the 1940s, the play was not 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 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 600–2,200 feet. Original gas content ranges from 40 to 100 standard cubic feet per ton. Wells are developed on units of from to . Horizontal drilling is not widely used. Antrim Shale wells often have to pump much initial water before gas production becomes significant, a behavior also seen in many

coalbed methane Coalbed methane (CBM or coal-bed methane), coalbed gas, coal seam gas (CSG), or coal-mine methane (CMM) is a form of natural gas extracted from coal beds. In recent decades it has become an important source of energy in United States, Canada, Au ...

wells. Unlike most other shale gas plays, the natural gas from the Antrim appears to be biogenic gas generated by the action of bacteria on the organic-rich rock. Also unlike most other shale plays, the Antrim Shale is thermally immature in the gas-productive trend. In 2007, the Antrim gas field produced 136 billion cubic feet of gas, making it the 13th-largest source of natural gas in the United States.US Energy Information Administration, ''Top 100 oil and gas fields''
, PDF file, retrieved 18 February 2009.

References

* Robert T. Ryder
Fracture Patterns and Their Origin in the Upper Devonian Antrim Shale Gas Reservoir of the Michigan Basin: A Review
US Geological Survey, Open-File Report 96–23, 1996, accessed 3 November 2009.

Stratigraphy

Natural gas

References

See also