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FUELS FROM OIL SHALE 181

yields from eastern shale could someday approach yields from western shale, with process-
ing technology advances (Johnson et al., 2004).
However, in spite of all of the numbers and projections, it is difficult to gather produc-
tion data (given either in shale oil or oil shale in weight or in volume) and few graphs are
issued. There are large discrepancies between percentages in reserve and in production
because of the assumptions of estimates of the total resource and recoverable reserves.
Thus, use of the data requires serious review.

6.4 LIQUID FUELS

In the United States, there are two principal oil shale types, the shale from the Green River
Formation in Colorado, Utah, and Wyoming, and the Devonian-Mississippian black shale
of the East and Midwest (Table 6.3) (Baughman, 1978). The Green River shale is consid-
erably richer, occur in thicker seams, and has received the most attention for synthetic fuel
manufacture and is, unless otherwise stated, the shale referenced in the following text.

TABLE 6.3 Composition (Percent By Weight) of the Organic Matter in Mahogany
Zone and New Albany shale

Component Green River Mahogany zone New Albany
Carbon 80.5 82.0
Hydrogen 10.3 7.4
Nitrogen 2.4 2.3
Sulfur 1.0 2.0
Oxygen 5.8 6.3
Total 100.0 100.0
H/C atom ratio 1.54 1.08
Source: Baughman, G. L.: Synthetic Fuels Data Handbook, 2d ed., Cameron Engineers,
Inc., Denver, Colo., 1978.
The common property of these two shale deposits is the presence of the kerogen. The
chemical composition of the kerogen has been the subject of many studies (Scouten, 1990)
but whether or not the findings are indicative of the true nature of the kerogen is extremely
speculative. It is, however, a reasonable premise that kerogen from different shale samples
varies in character, similar to petroleum from different reservoirs varying in quality and
composition.

6.4.1 Thermal Decomposition of Oil Shale
The active devolatilization of oil shale begins at about 350 to 400°C, with the peak rate of
oil evolution at about 425°C, and with devolatilization essentially complete in the range of
470 to 500°C (Hubbard and Robinson, 1950; Shih and Sohn, 1980). At temperatures near
500°C, the mineral matter, consisting mainly of calcium/magnesium and calcium carbon-
ates, begins to decompose yielding carbon dioxide as the principal product. The properties
of crude shale oil are dependent on the retorting temperature, but more importantly on the
temperature-time history because of the secondary reactions accompanying the evolution
of the liquid and gaseous products. The produced shale oil is dark brown, odoriferous,
and tending to waxy oil.