--> Comparison of The Appalachian Basin Devonian Shale and the Fort Worth Basin Mississippian Shale: Why the Barnett Success Predated the Marcellus

Southwest Section AAPG Annual Convention

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Comparison of The Appalachian Basin Devonian Shale and the Fort Worth Basin Mississippian Shale: Why the Barnett Success Predated the Marcellus


The Department of Energy (DOE) and the Gas Research Institute (GRI) began the Eastern Gas Shale Project (EGSP) in 1976 as a result of dwindling supplies of conventional gas in the 1970's. This project included the Appalachian, Michigan and Illinois Basins, generating studies and reports in all three provinces. However, for a number of reasons, the Appalachian Basin was the centerpiece of the project. To begin, there was established gas production from Devonian shales in this basin. Upper Devonian shales had been productive in several locations: at Fredonia, New York as early as 1821 and at the Big Sandy Field of eastern Kentucky and western West Virginia beginning in 1920. In addition, small volumes of gas production had been initiated in southeast Ohio and western Pennsylvania since the mid 1800's at relatively shallow depths. Clearly, the best place to begin understanding and studying shales was where they had already produced. Secondly, this existing production and ongoing drilling activity could be used in the analysis and to provide necessary core and wellbore data and test sites for stimulation. In addition, as a result of this study, the 1980 Energy Act exempted Devonian shales from federal price controls and provided Section 29 tax incentives to unconventional gas. Devonian shales received the greatest of these government incentives. Lastly, Hunter and Young's 1950s exploration model for shales specified the need for open natural fractures for commercial production. This model seemed to be supported by basin production history and surface exposures. The project lasted for 17 years, until 1992, during which time it incorporated efforts from government, private industry and academia. The study generated an exciting introduction into the shale effort and provided an excellent technical knowledge base on shale characteristics and testing procedures. However, there were no major breakthroughs in the Appalachian Basin for the significant commerciality of shale gas.

In 1981 Mitchell Energy drilled their first test of the Mississippian Barnett Shale in the Fort Worth Basin. While this initial test proved non-commercial, it prompted George Mitchell and his technical staff to develop a better understanding of shales. During the early years of the evaluation, the company focused heavily on the well reports and accumulated knowledge from the EGSP. This provided much of the foundation for the company's initial efforts. However, there appeared to be an immediate disconnect between the Devonian experience and what Mitchell was encountering in the Barnett. The purpose of this presentation is to explain these differences and why the Barnett had to be a successful project prior to unlocking the Marcellus Shale.