Oil shale is petroleum source rock in which kerogen has not yet undergone conversion to oil and gas. Oil shale is processed at high temperatures (300–500°C) for relatively short periods of time (hours-months) to produce oil, gas, and spent shale. This is in contrast to the relatively mild conditions (~100°C) experienced by sedimentary formations during which petroleum is naturally generated over millions of years.
We have partially pyrolyzed replicate samples of Green River oil shale and studied the chemical and physical properties of the spent shales. Probes include wet chemistry assays, Rock Eval, infrared spectroscopy, nuclear magnetic resonance relaxation analysis, density, surface area and pore volume measurements, and scanning electron microscopy. Particular attention is paid to the organic matter: kerogen, bitumen, and coke. We find that oil shale artificially matured in a semi-open system has some properties comparable to naturally matured gas shale.
Oil shale is a natural earth material comprising inorganic mineral matter and thermally immature detrital organic matter [Tissot, 1978; Dyni, 2006; Allix, 2010]. Though recently confused with other very low permeability hydrocarbon-bearing formations (e.g. " tight oil" rocks, analogous to gas shales), oil shale has been consistently defined since the middle of the 19th century [Oxford English Dictionary (2nd ed.) X, 751–752]. Considerable amounts of oil shale are found worldwide [Dyni, 2006], with the largest concentrations in the western United States. In the Piceance Basin of western Colorado alone, within an area of about 1700 mi2 (4400 km2), there is an estimated 1.5 trillion bbl (240 billion m3) of oil equivalent in place [Johnson, 2009].
Although oil shale is a vast resource, it has been exploited at commercial scale in only a few locations, most prominently in Estonia and China [Allix, 2010]. Research and development work has mostly proceeded episodically [see e.g. Yen, 1976; Stauffer, 1981; Miknis, 1983; Chong, 1984; Snape, 1995; Ogunsola, 2010; Qian, 2010], coinciding with changes in the price and perceived scarcity of conventional crude oil.
An important formation of interest is the Garden Gulch Member of the Green River Formation of the Piceance Basin. This is an attractive interval for production due to its high concentration of organic matter and its isolation from fresh water aquifers [Reeder, 2013]. Integration of modern well logs with extensive core measurements have defined formation evaluation workflows [Skelt, 2010; Seleznev, 2011; Reeder, 2013].