Natural Gas From Eastern U.S. Shales

Abstract

Abstract A project has been initiated by the Energy Research and Development Administration (ERDA) to characterize gas-bearing shale formations and develop improved gas-extraction technology for these low-permeability "tight" reservoirs. The Eastern Devonian Shales are very prominent in this assessement, since they underlie a large section of the eastern and central portions of the United States. There is considerable portions of the United States. There is considerable uncertainty in the magnitude of the hydrrocarbon resource base since estimates range as high as 460,000 TCF (gas equivalents) in the Appalachian Basin alone; however, a recent estimate places the gas in place at 2,400 TCF. If only 10 percent of this latter figure were recovered, this would be enough natural gas to supply the eastern United States for 30 years at the current rate of consumption. Obviously, the potential payoff from the Eastern Shale is much greater if payoff from the Eastern Shale is much greater if technology can be developed to increase the rate and amount of natural gas recovery. The primary reason why the natural gas has not been more fully exploited is that the wells that have been completed normally have low productivities, i.e., they produce at an average rate of 50,000 scf per day. By using advanced fracturing and stimulation methods, this rate may be increased two to four times. Fracturing results have been mixed since many new techniques have been tried. Massive Hydraulic Fracturing (MHF), foam, gas, dendritic, and high yield explosives have already been tested with varying degrees of success or failure. In comparing data for conventional shot wells and induced hydraulic fracturing, it became evident that hydraulically fractured wells would produce considerably more gas and return higher profits. This was consistently true, even though the completion costs using hydraulic fracturing were 50 percent higher. Introduction The natural gas shortages and curtailments experienced during the winter of 1976–77, coupled with the continually increasing U.S. energy demand, have highlighted the need to develop additional supplies of gas. Natural gas supplied 27 percent of the total energy used in 1976 and will continue to be a major source of energy. The U. S. Bureau of Mines, now the Energy Research and Development Administration, in 1968, began a project to evaluate unconventional natural gas reservoirs which could be future sources of supply. Following this examination, the Eastern Devonian Shales were selected as a gas resource in which a large natural gas potential existed and one in which new extraction R and D technologies would have to be developed. The Eastern Gas Shales Project was formally initiated in 1976 by ERDA at its Morgantown Energy Research Center. The ultimate objective is to increase production of natural gas from the Eastern Shale Basins through advanced exploration and extraction techniques. The Project is specifically directed toward:*Determining the magnitude of potential gas reserves,*Thoroughly characterizing the shale,*Improving current state-of-the-art stimulation technology, and*Providing an R and D technology base for low permeability "tight" natural gas reservoirs. FIELD DESCRIPTION The Eastern Gas Shales constitute a vast, essentially unexploited resource of gas. The extent of the Mississippian and Devonian Shales is shown in Figure 1. This area represents a potential producing area of approximately 250,000 square miles of which 160,000 square miles is located within the Appalachian Basin. Devonian Shales are typically brown to gray to black rocks composed of tightly compacted quartz and clay particles contained in organic matter (1 to 15 percent).