Proving Up Gas Shale Potential by Redefining Exploration and Production Models
Dan B. Steward
Republic Energy, Dallas, Texas
The Barnett Shale play in North Texas ushered in a new understanding of gas shales and as a result, industry’s approach to their exploration and development. It is common knowledge that the first commercial use of shale gas in the United States occurred in 1821 from a Devonian Shale well at Fredonia, Chautauqua County, New York in the Appalachian Basin. Probably the first major gas shale field, Big Sandy in Eastern Kentucky and West Virginia, was Devonian Shale of the Appalachian Basin. This field spurred additional exploration and development throughout the basin, but nothing with the size and success of the Big Sandy was found.
Based on GRI’s Atlas of Major Appalachian Gas Plays the producing mechanism for all these fields was attributed to natural fracturing in the reservoir. They attributed the recognition of this concept to C. D. Hunter and D. M. Young in 1953. Therefore, the result was an exploration model aimed at finding areas of intense open natural fracture networks. Explorationists then looked for areas of structural complexity such as flexures, anticline closures or faulting to high grade prospects. Commonly wells were drilled and tested and if some natural flow could not be established on initial testing the area was considered non-productive. If some flow could be initiated then small stimulations might be utilized to improve production.
Mitchell initiated its Barnett Shale evaluation in 1981 using this same concept. However we quickly found that it was not open natural fractures, but the ability to induce fractures that would make the play. Initially we believed in areas where large induced fracs did not work, the shale would be non-commercial. In time we found this also to be in error. It was only through the expansion of our understanding of shales, and the integration of all the geosciences with engineering practices that the play was able to grow. Many technologies are being applied to shale plays today primarily as a result of the Barnett experience. Many new and difficult approaches are being tried in shales and some of these will prove successful. Next years’ technology will progress beyond todays’ and unconventional gas shales will become an ever increasing source of our daily needs.
AAPG Search and Discover Article #90065©2007 AAPG Southwest Section Meeting, Wichita Falls, Texas