The organic-rich Devonian shales underlying the Appalachian, Illinois and Michigan basins are potentially the most productive underdeveloped source of natural gas in the northeast United States. Though considerable quantities of natural gas are produced from these unconventional shale "reservoirs", standard well log evaluation techniques developed for sandstones and limestones are not suitable for the Devonian shales.
This work represents an attempt to quantify well log evaluation techniques in these shale reservoirs. The response equations for the Density and Neutron logs are used to establish the density and neutron log porosities appropriate for shale matrix. The Simandaux equation has been modified and adapted for the shale reservoir. With these modifications, the total porosity (intrinsic plus fractured), hydrocarbon density and the water saturation can be computed in these Devonian shales. Results have been consistent in four air drilled wells located in Ohio and West Virginia. Intervals in the shales which are characterized by development of porosity and where a gas saturation has been computed correspond invariably to "hot" zones on the Gamma-ray log. The organic content of these zones is also high when analyzed by the method proposed by Schmoker1 . A pattern of high organic content corresponding to the development of porosity and the presence of increasing amounts of gas is discernable. Production tests indicate that large quantities of gas have been produced from intervals identified as porous and gas bearing according to the proposed technique.
Computed logs and listings of results from several wells are presented. Although this technique has been developed for the Devonian shales of the northeast United States, it could extend to other fractured shale reservoirs.