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A recent trend in developing new natural gas reserves has been the intensified efforts to exploit Devonian shale gas reservoirs in the Appalachian basin. Thus, the Department of Energy is now engaged in the support of the Eastern Gas Shale Project, which is aimed at accelerating the development of this resource.

To make an engineering and economic evaluation of Devonian shale gas-reservoir development, it is necessary to be able to predict future reservoir performance. A review of the Devonian shale modeling experience to date reveals that such a demonstration of predictive capability has not been achieved.

Most Devonian shale reservoirs are expected to consist of very tight porous shale formations which may be rather highly fractured in certain tectonic terranes. Under these conditions, the fractures may provide most of the permeability to gas flow, but contribute very little to the overall storage capacity. By comparison, the matrix of the shale may provide most of the storage capacity, but contribute very little to flow because of the low permeability. The gas-release and sorption-isotherm data from Devonian shale samples indicate that gas is present in the matrix of the shale both as a free-gas phase and as a sorbed-gas phase.

Gas transport in Devonian shale reservoirs, according to the assumption adopted here, occurs only in the permeable fractured medium, into which matrix blocks of contracting physical properties deliver their gas contents, that is, the matrix acts as a uniformly distributed gas source in a fractured medium. Furthermore, desorption from pore walls is treated in the modeling as a uniformly distributed source within the matrix blocks.

A mathematical model to simulate well and fieldwide performance of Devonian shale gas reservoirs has practical applications for gas reservoir studies such as well-test and history-matching problems.

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