What is the Antrim Shale?  The Antrim shale lies in the Michigan Basin with principal development in Ostego and Montmorency Counties, Michigan and to a lesser extent in Kalkaska, Crawford and Oscoda Counties, Michigan. While the bulk of the play lies in Michigan, the Antrim Shale covers roughly 39,000 square miles and extends into ares of Ohio and Indiana, as well as Michigan.  The Antrim shale is a brownish-black shale that overlies the Traverse Formation.  The shale mainly produces methane (CH4) with minor amounts of CO2. Most drills in the Antrim shale require stimulation by hydraulic fracturing to attain commercial production rates, however; natural fractures are still and important control on Antrim shale gas production. The U.S. Geological Survey's National Assessment of U.S. Oil and Gas estimates that approximately 7 trillion cubic feet of gas (2005) are recoverable in addition to discovered quantities from the Antrim shale. 

History - Antrim shale gas production began back in the 1940s in northern Michigan where 8 gas wells were drilled in Otsego County, Michigan.  However; it wasn't until the 1980s that the Antrim shale gained its popularity for being a key drilling objective.  New technologies during the late 1970's into the 1980's made it possible for the Antrim shale to economically produce gas.  To date, over 9,000 gas wells have been drilled throughout the Antrim shale play with depths of the wells ranging mainly from 150 feet to 1500 feet, however; a few wells have been drilled as deep as 2,200 feet. Wells drilled into the Antrim shale have proven to be relatively inexpensive, with an average cost of approximately $350,000 in late 2008.