Antrim Shale
Encyclopedia
The Antrim Shale is a formation of Upper Devonian
age in the Michigan Basin
, in the US state of Michigan
, and extending into Ohio
and Indiana
. It is a major source
of natural gas
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
. The formation was previously known as the St. Cleric Shale in Michigan, and the Genessee Shale in Indiana.
, 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
, and is the stratigraphic equivalent of the New Albany Shale
in the Illinois Basin
. It is overlain by the Bedford Shale, and underlain in some areas by the Jordan River Formation, and elsewhere by the Thunder Bay Limestone.
, 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 140 Gcuft 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 40 acres (161,874.4 m²) to 160 acres (647,497.6 m²). 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
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.
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
age in the Michigan Basin
Michigan Basin
The Michigan Basin is a geologic basin centered on the Lower Peninsula of the US 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 the center of the peninsula.The basin is centered in...
, in the US state of Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
, and extending into Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
and Indiana
Indiana
Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...
. It is a major source
Source rock
In petroleum geology, source rock refers to rocks from which hydrocarbons have been generated or are capable of being generated. They form one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposited in a variety of environments including...
of natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
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, Michigan
-History:Antrim County was formed in 1863. In 1950 its population was 10,721. The county seat was originally located in Elk Rapids, but was moved to Bellaire in 1904 after 25 years of litigation.-Demographics:...
. The formation was previously known as the St. Cleric Shale in Michigan, and the Genessee Shale in Indiana.
Stratigraphy
The Antrim is a brown to black, pyritic, and organic-rich shaleShale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
, 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
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, and is the stratigraphic equivalent of the New Albany Shale
New Albany Shale
The New Albany Shale is an organic-rich geologic formation of Devonian and Mississippian age in the Illinois Basin of the United States. It is a major source of hydrocarbons. -Stratigraphy:...
in the Illinois Basin
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...
. 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 gasShale gas
Shale gas is natural gas produced from shale. Shale gas has become an increasingly important source of natural gas in the United States over the past decade, and interest has spread to potential gas shales in the rest of the world...
, 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 140 Gcuft 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 40 acres (161,874.4 m²) to 160 acres (647,497.6 m²). 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
Coalbed methane or Coal Bed Methane, coalbed gas or coal mine methane 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, and other countries...
wells.
Unlike most other shale gas plays, the natural gas from the Antrim appears to be biogenic gas
Methanogenesis
Methanogenesis or biomethanation is the formation of methane by microbes known as methanogens. Organisms capable of producing methane have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with...
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.