Green River Oil Shale Pyrolysis: Semi-Open Conditions

Oil shale is a petroleum source rock that has not undergone the natural processes required to convert its organic matter to oil and gas. However, oil shale kerogen can be converted artificially to liquid and gaseous hydrocarbons by pyrolysis. Heating oil shale in place (in situ) has a number of operational, economic, and environmental advantages over surface retorts, particularly when the shale is too deep to mine. This work describes experiments conducted at temperatures and pressures appropriate to commercially viable in situ pyrolysis. The data are needed to construct models to plan, interpret, and optimize field experiments and commercial operations. The experiments also provide insights into the chemical compositions of the native state shale and all the products of pyrolysis-hydrocarbon and nonhydrocarbon gases, oil, bitumen, remaining pyrolyzable kerogen, residual organic matter, and inorganic matter-as functions of thermal maturation. Numerous studies of Green River oil shale pyrolysis have been published over the years. Most of these have focused on the richest interval, the Mahogany (R-7) zone and have been performed in either open (atmospheric pressure) or closed (bomb) apparatus. The new elements of this work are as follows: (1) samples were taken from the deepest of the kerogen-rich layers of the Green River Formation, the mineralogically distinct R-1 zone; (2) experiments were performed under semi-open (controlled pressure) conditions. The data generated are therefore appropriate input to models used in conjunction with in situ controlled-pressure production tests of R-1 shale. In agreement with previous work, this investigation finds that processing shale at relatively low temperatures, for longer times, and at moderately elevated pressures, reduces yields but improves product quality relative to surface retort methods. The composition of the produced oil is generally uniform over the course of artificial maturation. It has a high H/C ratio and is predominantly composed of saturates and light aromatics, which are desirable for refinery operations. The oil has little sulfur, which is mostly in thiophene-containing moieties. Extracted bitumen has a high polar content, and its H/C ratio decreases as a result of oil and gas generation during maturation. Produced gas is rich in natural gas liquids.