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FUELS FROM OIL SHALE 185

to create void space. Recent technology advances are expected to improve the viability of
oil shale technology, leading to commercialization.
Of importance in the in situ processing option is the characteristic that oil shale is rela-
tively hard impermeable rocks through which fluids will not flow. Also of interest is the specific
gravity of the oil shale since much of the inorganic material must be disposed. The specific
gravity of the Green River kerogen is approximately 1.05 and the mineral fraction has an
approximate value of 2.7 (Baughman, 1978).
In situ processes can be technically feasible where permeability of the rock exists or can be
created through fracturing. The target deposit is fractured, air is injected, the deposit is ignited
to heat the formation, and resulting shale oil is moved through the natural or man-made frac-
tures to production wells that transport it to the surface (Fig. 6.2). However, difficulties in
controlling the flame front and the flow of pyrolized oil can limit the ultimate oil recovery,
leaving portions of the deposit unheated and portions of the pyrolized oil unrecovered.

Drilling and site Heating and Oil to
preparation production refinery

Postproduction
clean-up

FIGURE 6.2 Process steps in thermal in situ conversion.
(Source: Bartis, J. T., T. LaTourrette, and L. Dixon: “Oil Shale
Development in the United States: Prospects and Policy Issues,” Prepared
for the National Energy Technology of the United States Department of
Energy, Rand Corporation, Santa Monica, Calif., 2005.)

Thus, in situ processes avoid the need to mine the shale but require that heat be supplied
underground and that product be recovered from a relatively nonporous bed. As such, the
in situ processes tend to operate slowly, behavior that the Shell in situ process (Fig. 6.3)
exploits by heating the resource to around 650ºF (343ºC) over a period of 3 to 4 years.

Overburden

Heater Producer Heater

FIGURE 6.3 Schematic of the Shell in situ conversion process.
(Source: Shell Exploration and Development Company, Houston, Texas.)