The Fayetteville Shale Play: A Geologic Overview

(This abstract originally was prepared for publication at the Mid-Continent Section Meeting of the American Association of Petroleum Geologists to be held at Wichita, Kansas, Sept. 9-11, 2007. Slight editorial changes have been made to the original text. Permission for reproduction is granted by the AAPG.)

The Mississippian Fayetteville Shale, present in the subsurface across a large portion of northern Arkansas, is the focus of an intensive shale-gas exploration and development campaign by several energy companies.

About 2.5 million acres of subsurface minerals were leased during a 2 1/2-year period. This shale-gas play is in transition, moving from leasing and testing to a focus now on well-completion techniques and the production of natural gas.

A multibillion-dollar investment by energy companies has resulted in a sharp increase in Fayetteville well production and has helped Arkansas to offset declining production from conventional gas wells. An estimated 500 wells are scheduled to be drilled in the Fayetteville Shale during 2007 and a new natural gas transmission line is planned to facilitate development of the resource.

A joint research project studied the geochemical and thermal maturity characteristics of the Fayetteville Shale Formation. The project was conducted by the Arkansas Geological Survey of Little Rock, Chesapeake Energy of Oklahoma City and EOG Resources of Houston and Oklahoma City. Well cuttings were collected at the Norman F. Williams Well Log Library in Little Rock, and Humble Geochemical Services of Humble, Texas, analyzed the samples.

The study indicates that the Fayetteville Shale is thermally mature and is restricted to dry gas resources. A highly organic-rich facies within the Fayetteville Shale is the stratigraphic interval that currently produces natural gas from wells in north-central Arkansas and is characterized by very high radioactivity and resistivity log signatures, which differentiate it easily from the overlying upper Fayetteville Shale and from the underlying Batesville Sandstone, Moorefield Shale and Boone Formations.

Continuing research by the Arkansas Geological Survey is focused on reservoir characterization, analysis of produced gases and outcrop to basin modeling of the Fayetteville Shale Formation.

(Ed Ratchford is senior petroleum geologist for the Arkansas Geological Survey.)