Synthesis of Organic Geochemical Data From the Eastern Gas Shales

Abstract

ABSTRACT Over 2400 core and cuttings samples of Upper Devonian shales from wells in the Appalachian, Illinois, and Michigan Basins have been characterized by organic geochemical methods to provide a basis for accelerating the exploitation of this unconventional, gas-rich resource. This work, sponsored by the United State's Department of Energy's Morgantown Energy Technology Center, was part of a program initiated to provide industry with criteria for locating the best areas for future drilling and for the development of stimulation methods that will make recovery of the resource economically attractive. The geochemical assessment shows that the shale, in much of the Appalachian, Illinois, and Michican Basins is source rock that is capable of generating enormous quantities of gas. In some areas the shales are also capable of generating large quantities of oil as well. The limiting factors preventing these sources from realizing most of their potential are their very low permeabilities and the paucity of potential reservoir rocks. Low permeability has prevented migration of most of the free hydrocarbons from their site of origin in the shale matrix into nearby reservoirs. This retention of generated hydrocarbons has retarded the further generation of hydrocarbons within the shale, particularly the liquid (oil) ones, over much of the basin. Where there is fracturing, the shales themselves provide both source rock and the reservoir, and allow generation to proceed. In some cases, contiguous or interbedded siltstones provide small reservoirs, and the fractures provide migration channels through which the hydrocarbons move for relatively short distances. This geochemical data synthesis gives direction to future selection of sites for stimulation research projects in the Appalachian Basin by pinpointing those areas where the greatest volumes of gas are contained in the shale matrix. Another accomplishment of the geochemical data synthesis is a new estimate of the total resource of the Appalachian Basin. The new estimate of 2,500 TCF is 25 percent greater than the highest previous estimates. This gives greater incentive to government and industry to continue the search for improved stimulation methods, as well as for improved methods for locating the sites where those improved stimulation methods can be most effectively applied.