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The AAPG/Datapages Combined Publications Database
Hundreds of trillions of cubic feet of natural gas are contained in the Upper Devonian black shales of the Eastern Interior basins. These organically rich (up to 15 wt. %) shales have porosities and permeabilities substantially lower than conventional clastic reservoirs. To exploit this "unconventional" resource, the results of a detailed physiochemical characterization of this shale are being used to obtain the following project goals: assess basin natural gas potential, select basin regions with relatively high potential, and design and/or improve exploration and production techniques. To date, over 500 core and drill cuttings samples are being evaluated. Appalachian, Illinois, and Michigan basin Devonian shales were obtained from eight, six, and one well, respectively, in each basin.
Evaluations of the shale by physical properties, biostratigraphy, and chemical characteristics have shown that the most significant amounts of natural gas have been associated with sediments rich in thermally mature organic matter. This organic matter is characterized as having been deposited in a restricted marine environment where restricted is used in a faunal context--precisely, an unusual environment in which a very restricted faunal assemblage was formed, deposited, and preserved within the sediment. The analyses lead to a determination of whether the organic matter is of the type suitable for optimum gas production.
The lateral and vertical continuity of the hydrocarbon resource is being investigated. The results of this investigation will have a significant impact on assessing the true potential of the Eastern Interior basin as well as aiding basin exploration.
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