The Haynesville Shale, is a black, organic-rich shale of Upper Jurassic age that underlies much of the Gulf Coast area of the United States. “Haynesville Shale” is a driller’s term for shale rock units within the Haynesville Formation.
The Haynesville Formation is underlain by the Smackover Formation and overlain by rocks of the Cotton Valley Group. It was deposited about 150 million years ago in a shallow offshore environment. Geologists have long known that the Haynesville Formation contained natural gas. However, because of its low permeability the Haynesville was originally considered to be a gas source rock rather than a gas reservoir.
Today, natural gas production from the Haynesville occurs from rocks about two miles beneath northwestern Louisiana, southwestern Arkansas and eastern Texas. The most productive areas have been Caddo, Bienville, Bossier, DeSoto, Red River and Webster Parishes of Louisiana plus adjacent areas in southwest Arkansas and east Texas.