Technology
Devonian shale deposit resources assessed Hydrocarbons of differing origin found in three major basins; recoverable minerals and "tight" shale formations may hinder recovery of gas One of the major untapped energy resources in the U.S. is the extensive eastern Devonian shale deposit. A resource assessment of the three major basins in the deposit has been made, and is continuing, by Monsanto Research Corp., Miamisburg, Ohio, under contract to the Department of Energy. Results of the assessment to date were summarized in Detroit last week for the summer national meeting of the American Institute of Chemical Engineers by Monsanto's R. E. Zielinski. The three basins in the deposit are the Michigan Basin, which generally conforms to the present geographical limits of the lower peninsula; the Illinois Basin, which includes the lower two thirds of Illinois and some of the surrounding states; and the Appalachian Basin, which is the largest of the three and runs generally from the junction of Kentucky, Tennessee, and Virginia, northeastward into central New York. All of the Devonian shale basins contain organic sediments of marine origins, but the sources for
Devonian shale resources lie in three basins
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C&ENAug. 24, 1981
each are different. Consequently, major differences in the type of hydrocarbons from basin-to-basin are manifested in core samplings. Some of the organic shale deposits originated from the normal variety of marine plants, some originated from debris of shoreline plants, and some are due to a very prolific green algae known as Tasmanites. Where Tasmanites are present, the organic carbon content is unusually high, being as much as 10% of the shale content. Tasmanite deposits also contain the largest quantities of hydrocarbon gas, which makes them of particular interest to the exploration team. The Appalachian Basin appears to have been formed primarily from Tasmanites. Thirty-nine exploratory wells have been drilled in the three basins in the Monsanto program. On the basis of core examinations, the Illinois Basin is conservatively estimated to contain more than 85 trillion cu ft of gas, the Michigan Basin about 76 trillion cu ft, and the Appalachian Basin more than 778 trillion cu ft. The study notes that estimates of gas in place do not accurately reflect the recoverable resource for a number of reasons. The most important is probably that the Devonian shales are very "tight" formations, and it is exceedingly difficult to remove gas from a natural fracture zone. The prospects for additional stimulation of shale deposits via artificial fracturing remain promising. However, the amount of test drilling is still too small to provide more than good guesses about the artificial stimulation potential of the deposits. Another problem is the presence of other potentially recoverable minerals. These range from shale oil to uranium ores. Even in the very early stages of exploration of the Devonian shales in the East, it has become apparent that much of the economic attractiveness lies in optimizing total resource recovery. Some of the problems of resource extraction in the Antrim shale of the Michigan Basin were outlined by M. L. VanDerPloeg of Dow Chemical, which also is conducting exploratory studies for DOE. The Dow project involves in-situ combustion in an explosively fractured deposit in
Sanilac County, Mich. Here the shale occurs between 1200 and 1400 feet below ground level. Thirty-four wells were drilled. Seven were used for extraction trials and three were involved in explosively fractured deposits. The in-situ burn was started by a methane burner lowered into the deposit. In general the in-situ trials exhibited a steadily decreasing product gas flow. This was attributed partly to the natural low permeability of the shale and to the swelling properties of • retorted shale; as a burn proceeds, swelling gradually decreases the permeability of the formation. Two methods of compensating were only partially successful. One was increasing the back pressure in production wells and the other was reducing flow in the injection well. Neither method could keep a burn going indefinitely. The gas from the trials was of low quality, having a heating value of 25 to 30 Btu per standard cu ft, far from enough to excite commercial interest. Methods of improving the heating value were not implemented because of the problems with permeability. Thus, unless some means of generating more void space in the deposits can be found, it is not possible to sustain in-situ combustion in the Antrim shale. The Chattanooga shale in the Appalachian Basin has been known for many years and was even studied in the 1940's as a source of uranium. Lying at depths of up to 700 feet, the Chattanooga shale has been estimated to contain an average of 55 ppm of uranium values in addition to considerable kerogen-derived oil. In a study carried out by a team from Tennessee Technological University, Cookeville, the major inorganic values included silica, magnesia, potash, and alumina, in addition to the organic values. Most of the organic values reside in the kerogen (insoluble in common organic solvents) and as bitumen (soluble). Shale oil yields, by modified Fischer Assay, vary 8.4 to 13.8 gal per ton. The studies of the eastern Devonian shales may not proceed under the sharply pruned federal budget of the Reagan Administration. Only a modest beginning has been made, but one conclusion emerges from the
work so far—namely, that the potential resource is too large to ignore. It's possible that enough private funding can be had to continue some exploratory work. But it would seem that sooner or later the federal government will have to make the major contribution. Joseph Haggin, Chicago
Two-step COthane process uses waste carbon monoxide to make methane Vent
Disproportionation step Carbon monoxide
Preheater
Process taps energy of waste carbon monoxide A 1976 survey indicated that as much as 24 million tons per year of dilute carbon monoxide was being flared at industrial locations in the U.S., most of it from steel mills and petroleum refineries. The energy equivalent was about 570 million cu ft per day of natural gas. There was no economical way to utilize this large potential source of heat. Now a process has been tested that will convert the dilute carbon monoxide streams to methane and carbon dioxide. Called COthane, the process has been developed at Union Carbide's Tarrytown, N.Y., technical center. Carbide's Albert C. Frost described the process for the summer national meeting of the American Institute of Chemical Engineers in Detroit last week! The COthane process evolved from the observation that carbon monoxide rapidly disproportionates on a nickel catalyst to carbon dioxide and active carbon. The active carbon further reacts to form equimolar quantities of methane and carbon dioxide. According to Frost, this observation was the basis for subsequent laboratory-scale process development unit tests of the two-step process. In the first step, waste gas is pretreated and passed through a reactor containing a nickel or cobalt catalyst bed. At temperatures of 270 to 300 °C the following disproportionation occurs: 4CO ^ 2 C 0 2 + 2 C This reaction proceeds until the catalyst is loaded with the active carbon. The waste gas feed is then diverted to a second reactor that has been stripped of carbon. Low-pressure steam is then introduced into the first reactor where it reacts with the active carbon according to the reaction: 2 C + 2H 2 0 ^ CH4 + C 0 2 Eventually the carbon is consumed and the roles of the reactors are reversed. Continued alternation of the
Dowtherm condensate return Steaming step
®— 140psig pipelinequality methane
150 psig steam Preheater
r Dehydrator
Carbon dioxide removal
reactors provides continuous operation. The net reaction is: 4 CO + 2H 2 0 ^ CH 4 + 3 C 0 2 The wet carbon dioxide/methane stream is stripped of carbon dioxide and water, which are vented. The methane is fed to a local natural gas distribution system. Feed pretreatment depends on the source of the carbon monoxide. Reactive diluents, such as oxygen, react with the active carbon and are undesirable. Catalyst poisons, such as hydrogen sulfide, are also removed. A small amount of "inactive" carbon appears to be deposited during each cycle and is purged periodically. About 79% of the gross energy available in the carbon monoxide appears in the product methane. The largest single source of off-gas carbon monoxide is blast furnace exhaust, but this source is declining as antipollution measures are being implemented. However, the potential of the COthane process for upgrading exhaust from in-situ coal gasification could more than offset the decline in blast-furnace exhaust. Other major sources of carbon monoxide include basic oxygen furnaces, gray iron casting, aluminum production, and petroleum refining. Methane production costs from blast-furnace exhaust have been estimated at $5.78 per million Btu; for
Tubular reactor
\ Dowtherm condensate return
BOF off-gas, $7.11 per million Btu; and for carbon-black off-gas $8.10 per million Btu. These costs are considerably higher than the price of natural gas, which presently is running at $2.00 to $4.00 per million Btu. However, Carbide believes that the cost gap will narrow with time and that the COthane process may be a good way to minimize losses associated with exhaust gas cleanup mandated by the Environmental Protection Agency. •
Energy industry to be major hydrogen user An assessment of world hydrogen markets through the year 2025 has been completed by the International Energy Agency. Most of the consumption, it shows, will be for synfuels production and conventional chemicals production. IEA had been interested in promoting hydrogen as an energy carrier, but the economics don't favor development of this application for the period of the study, except in highly localized circumstances. Contributing to the two-year stildy are mainly countries of Western Europe, North America, and Japan. A composite report was prepared from national estimates by a group headed Aug. 24, 1981 C&EN
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