Blasting Technology for Modified In-Situ Oil Shale Retorts
Authors: Ricketts Thomas E. 
Published: December 2007

Ricketts, Thomas E., Cathedral BluffsShale Oil Co.

Occidental Oil Shale Inc. has spent nearly $200 millionsince 1972 developing and demonstrating its modifiedin-situ (MIS) oil shale process at its Logan Wash minenear De Beque, CO. During this time, eight MIS retorts were constructed and processed, five of which werefull-scale, commercial-size retorts. More than 300,000 bblof shale oil were produced, with two-thirds of this amount obtained from the final two retorts. Thus, we feel that this MIS technology is ready to be applied commercially to the thick, rich Federal Lease C-b Tract. To this end, Cathedral Bluffs Shale Oil Co. (CB), an equal partnership between Occidental and Tenneco Shale Oil Co., has spent more than $200 million to prepare the C-b tract for commercial development of shale oil. The MIS process has been found to be economically competitive with other underground types of operations designed to feed an above ground retorting process. CB will use both types of processes; the MIS technology will be combined with an above ground process for more enhanced total resource recovery and improved overall economics. Although there are inherent economic and technical risks in shale oil development, as in any pioneering venture, we feel that the long term national needs justify continued development of synthetic fuels. This commitment, along with the extremely successful results of the last two retorts, 7 and 8, at Logan Wash, prompted the decision to file an application to the U.S. Synthetic Fuels Corp. (SFC) for financial assistance in response to SFC's third solicitation for commercial development. The Retorts 7 and 8 design (which is basically our commercial design), explosive technology, and blasting results for these commercial-size retorts are presented in this paper.

Introduction

Oil shale is neither shale nor does it contain oil. It is a sedimentary formation comprising marlstone deposit with layers containing an organic polymer called kerogen which, upon heating, decomposes to produce liquid and gaseous products. This formation containing kerogen is called oil shale and the liquid hydrocarbon product is called shale oil. The most significant deposits, which can be up to 1,500 ft thick, are located within the Green River formation and underlie about 34,000 sqmiles in Colorado, Utah, and Wyoming. Within this formation there is an estimated oil in place (OIP)of about1.8 trillion bbl. A recovery of 40% would provide a total production of 720 billion bbl. When compared with the U.S. and world proven crude-oil reserves of 28 and 650billion bbl respectively, these oil shale reserves contained in a single formation could represent a significant reduction in U.S. dependence on imported oil for many years to come. A number of methods have been developed for processing oil shale that involve either first mining the kerogen-bearing shale and then processing the shale on the surface, or processing the shale in situ with modified in-situ technology. The surface processing method produces high recovery values but requires the mining of only shales with grades greater than 30 gal/ton, and the recovery is limited to extraction ratios of about 50% in mining sections, which cannot exceed about 60 ft in height. MIS technology produces lower recovery values, but the process can treat shale zones several hundred ft thick and can be used effectively in average shale grades a slow as 20 to 25 gal/ton, which results in better utilization of the total resource than the surface processing method.

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