In the late 60s, Wold & Jenkins, a Wyoming coal exploration company, in conjunction with the US Atomic Energy Commission, proposed nuking the Tertiary Fort Union coal formation in Wyoming.
In 1967, the AEC's Plowshare program - investigating peaceful uses for nuclear explosions - turned ten years old. Plowshare investigated a wide variety of concepts, but the main inspiration for the program - and source of political backing - was nuclear excavation, the use of hydrogen bombs, as Edward Teller put it, in "geographical engineering. We will change the Earth's surface to suit us."[TB] But after ten years, despite extensive nuclear testing, the AEC seemed to be getting further and further away from actual operational employment of the technology, due to treaty limitations on atmospheric nuclear tests and growing public concern over the radiological consequences. As a result, the program began to shift towards alternative uses, what the AEC called "underground engineering": fully-contained underground applications of nuclear explosives, in cooperation with private industry (who would also shoulder much of the development costs), in which, at least in principle, no fallout would escape into the environment.
THUNDERBIRD was one of those projects. The concept was proposed in either 1966 or early 1967, by John S. Wold - who later became the first professional geologist to serve in Congress - and Thomas C. Woodward of Wold & Jenkins.[DRI][Wo] The Tertiary Fort Union coal formation consisted of five separate, overlapping deposits, each layer averaging 50 feet thick. A 50-kiloton nuclear device would be set off beneath the coal, 2,200 feet underground. The blast would create a cavity, which would then collapse, forming a 254-feet-wide, 635-feet-tall chimney of broken rock filled with superheated gases - about 2 million tons of broken rock, of which about half a million tons would be coal. Oxygen would be injected into the chimney area, which would react with the coal to produce synthesis gas, a mixture of hydrogen and carbon monoxide, which would be pumped to the surface to a processing plant to produce gasoline and other useful fuels through the Fischer-Tropsch process. Steam might also have to be added, using water from the nearby Powder River, but it was thought the water content of the rocks might be enough to make this unnecessary.
The 50 kiloton shot would be a preliminary experiment prior to a larger, one megaton shot. A megaton bomb would fragment 3.32 million tons of coal in a chimney 1,200 feet tall and 620 feet wide. A financial analysis by Professor E. J. Hoffman of the University of Wyoming suggested an average of 3.75 bombs would be needed per year, each costing $720,000. He estimated this process would produce 17,000 barrels per day of gasoline, as well as 1,600 barrels of LPG and 1,400 barrels of diesel. The process would cost in total $22.8 million per year, and yield a net profit of $2.8 million to $9.2 million per year, depending on the price of the product. The 100 square mile area THUNDERBIRD hoped to use contained more than 22 billion tons of coal, equivalent in theory to more than 60 billion barrels of oil. This was twice as much energy as contained in the entire US known oil reserves of 1968, although I suspect in practice they would not be able to get anywhere near 100% of that even if the project had gone ahead - in particular, according to their own presentation, underground gassification using more conventional approaches generally had only a 40% energy efficiency.
If coal gassification didn't work out, Wold & Jenkins suggested nuclear explosives might still be useful in conventional underground mining, or for breaking up coal-bearing rock so that fluids could be injected to dissolve the coal or float it to the surface for recovery.[WW]
Wold & Jenkins did some exploratory drilling in the area, but the project never went any further. The last hole was drilled in June of 1969. In July, an independent engineering firm submitted a negative critique of the proposal on technical and economic grounds. In August, Lawrence Radiation Laboratory - the AEC nuclear lab with primary responsibility for Plowshare - issued a concurring report, and that was the end of it. Wold & Jenkins allowed the leases for the land to lapse in the 70s.[DRI]
[DRI]: The Off-Site Plowshare and VELA UNIFORM Programs: Assessing Potential Environmental Liabilities Through an Examination of Proposed Nuclear Projects, High Explosive Experiments, and High Explosive Construction Activities. Desert Research Institute, 2011. Volume 3, pp. A-157 - A-159. DOE/NV/26383-22. http://www.osti.gov/bridge/servlets/purl/1046576/ (pdf).
[TB]: Teller, Edward, and Brown, Allen. The Legacy of Hiroshima. Doubleday, 1962.
[Wo]: Wold Company Website, History Page. Accessed August 16 2013. http://www.woldcompanies.com/History/history.html.
[WW]: Wold, John S., and Woodward, Thomas C. "Project THUNDERBIRD." Wyoming Geological Association Guidebook, 20th Field Conference, 1968, pp. 147-153.