The paper was presented at the SPE/DOE Unconventional Gas Recovery Symposium of the Society of Petroleum Engineers held in Pittsburgh, PA, May 16-18, 1982. The material is subject to correction by the author. Permission to copy is restricted to an abstract of not more than 300 words. Write: 6200 N. Central Expwy., Dallas, TX 75206.
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 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 Michigan 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 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 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.
During the course of the Eastern Gas Shale Program (EGSP) sponsored by DOE's Morgantown Energy Technology Center (METC) more than 2400 individual core samples, as well as several hundred cuttings samples, were taken from Devonian Shale Wells drilled in the Appalachian Basin (Figure 1). These samples were submitted to a rather comprehensive suite of geochemical analyses (Figure 2). The analyses were performed 1) to identify the original hydrocarbon source potential of the dark shales, 2) to assess the source potential that has been realized, 3) to identify the nature of the product, i.e., dry gas, wet gas, oil, or any combination of these, that has product, i.e., dry gas, wet gas, oil, or any combination of these, that has been generated regionally and locally within the potential source rock, and 4) to ultimately estimate the gas in place.
This paper reviews the organic geochemical data, illustrates the interrelationships of the data and identifies the parameters which have exploration significance and which can be used for an assessment of gas in place. The identified diagnostic parameter which include organic carbon place. The identified diagnostic parameter which include organic carbon content, biofacies and thermal alteration, are mapped to pinpoint the richest sediment wedges which could serve as future exploration targets.
Of course, the fact that a rock has hydrocarbon source potential does not necessarily mean that contiguous reservoirs will contain any oil or gas, but shows that the rock does satisfy one of the three major requirements for the presence of pooled hydrocarbons.