To begin with, while the basic definition of an oil shale suggests the fine-grained rock that is often called shale, and implies it is impregnated with oil, that might be easily recovered, Unfortunately, in most cases the rock is not a shale, and the organic material that it contains is not yet an oil that will not run out, or separate out with normal treatment. It has been described as a precursor to oil, in that, it was initially formed in the same way, but has not undergone the natural high-temperature and pressure regimes of deep burial in the earth that are needed to turn it into oil. (However, if additional kerogen were to be added to the shale it would through time more likely end up as a coal - Ref 3.). The material is known as a kerogen, and to date the most successful methods of removing it from the rock has been to heat the rock until the contents volatize, and then to condense the hydrocarbons back out (in the same fashion that one cracks the oil in a refinery - though there are some significant differences that I will get to later). However, since the initial natural process was not carried as far as with oil, then the amount of energy that is required is generally greater. The greatest deposits of interest are those found in relatively thick deposits around the point where Wyoming, Colorado, Utah, and Idaho come together.

This and the following section is taken from Ref. 4. A section through the lettered points in the above figure gives:

Note that the scale for the vertical section is in feet. The darker band shown is known as the Mahogany zone in which the Mahogany bed some 100 - 200 ft thick, is considered to be the richest layer, and is a marker for the deposit.

Shale oil has been used as a fuel source in a number of countries around the world, over the past 150 years, but only become of economic significance in the 1920's. (Ref 3). There have been over two thousand patents issued describing different ways to separate what, for convenience, I will call oil, from the shale (similarly called). (Ref 5). Only a few have, however, been demonstrated, and later in this series of posts I will explain some of the peculiar problems that arise in retorting oil shale. But, as an illustration of the type of process that could be used, I will describe the Gas Combustion Process, as developed by the US Bureau of Mines for one of its original experiments. I thought it would be useful to describe this in a little detail, since it points out some of the potential benefits that can come from retorting the material.

The retort can be simply thought of as a vertical pipe with the raw shale fed into the top. As it moves down through the retort it passes through four zones. At the top of the retort the shale is cold, and the gasses rising from the lower parts of the process, mix with this shale. This has two effects, it pre-heats the shale as it drops into the next zone, while at the same time the oil is condensed into a mist, and the product gasses are cooled. (They are both then collected as they leave the retort). As the shale continues to move down the retort it reaches, about half-way down, a series of ports that inject air mixed with a portion of the produced gas that has been collected (call this the dilution gas). These two combine to cause ignition and to raise the temperature of the shale (to between 700 and 950 degrees F) so that the hydrocarbon contents vaporize and create the oil and gas combination that rises up out of the retort. The shale residue, continues down the retort, where it is now used to pre-heat a second supply of the collected gas (known as the recycled gas) that is moving up into the retorting zone. This cools the shale as it heats the gas, and the shale residue can then be collected and moved away. By using this form of heat transfer during the process a relatively high thermal efficiency can be achieved, and the retort can produce about 90% of the original oil in the shale, as well as a secondary volume of gas, beyond that needed to energize the retort. The retort has been shown able to handle shale particles ranging in size from ¼" to 3". By design it is possible to make sure that the oil mist that is the major product does not condense onto the shale particles that are being fed into the retort. You may note that this separation process does not require any additional external fuel, nor the addition of water to the process.

Using a slightly different method Union Oil Company ran a demonstration plant that ran at rates up to 1200 tons/day, using oil shale from the Piceance Basin. The crude produced was "a waxy, intermediate gravity, high nitrogen and intermediate sulfur crude" where the wax was removed and separately cracked, and the sulfur and nitrogen levels lowered before it could be considered a "commercial shale oil" with properties similar to that of a high quality Utah crude (Ref. 6). A feed of crude shale oil at 26,900 b/d would yield 25,000 bd of commercial shale oil, and 500 t of green coke. The oil could then be cracked into 380 bd of lpg; 13,635 bd of gasoline; 1,300 bd of stove oil; 6,700 bd of diesel and 590 bd of fuel oil (ibid).

As I said at the beginning of the post, there is an awful lot of oil shale in the United States, the beds can reach up to 2,000 ft thick, and the oil content can reach 90 gallons/ton. Unfortunately these do not occur at the same time. Rather the highest grade, is found in relatively narrow layers in the Uinta Basin, although the oil-shale sequence in the area can be up to 1,200 ft. (Ref. 4). And unfortunately not all the oil in the shale is made up of the same material, or has the same sort of properties. This can lead both to difficulties in mining and in retorting.

I will discuss those, and the issue of in-situ retorting, and some of its problems in the next post. But, given what happened, it is perhaps appropriate to close this first post with a comment by Harold Carver of Union.

It should be quite obvious that if imports to the coastal states and from Canada suddenly increase disproportionately after a shale industry is started, the embryo shale industry would be placed in a severe competitive bind. Unlimited cheap foreign crude imports would make shale oil as well as a large percentage of domestic crude oil production non-competitive. What is needed is assurance that shale oil production will face a stable economic environment in which it can share in the spectrum of raw materials for our future energy needs.

Given what happened that was quite visionary.

References - since most of these papers were written before the advent of the Internet, I am going to have to give some of the references in "the old style"
Ref. 1 Cameron "Foreign oil shale industries and their influence on United States Oil Shale Development," First Symposium on Oil Shale, CSM, 1964
Ref. 2 Utter S., Oil Shale R & D - A Bureau of Mines Program, 2nd Annual UMR-MEC Conference on Energy, October 1975
Ref. 3 Oil Shale entry, Encyclopaedia Brittanica, 1978, paper edition.
Ref 4. Donnell J.R. Geology and Oil-Shale Resources of the Green River Formation, First Symposium on Oil Shale, CSM, 1964
Ref. 5 Guthrie B., Oil from Rock - The Gas-Combustion Process, First Symposium on Oil Shale, CSM, 1964
Ref. 6 Carver H. Conversion of Oil Shale to Refined Products, First Symposium on Oil Shale, CSM, 1964