Title: The Race is On!
Author: Ira Pasternack
Publication: The Outcrop, September 2011, p. 12-14
Article Type: President’s Column
One of the world’s most notable and potentially valuable races to develop new technology is going on right now in western Colorado. Even if only moderately successful, the technology has the potential to supply energy production that will rival the largest Middle Eastern oil fields. The objective of the new technology is, of course, petroleum extraction from the kerogen-rich intervals of the Green River Formation.
The Green River Formation was deposited in Eocene Lake Uinta, a large, internally drained lake that extended across the Piceance Basin in western Colorado and the Uinta Basin in eastern Utah. The Green River Formation in southwestern Wyoming was deposited in a separate but largely contemporaneous lake, Lake Gosiute.
The Green River Formation is more correctly described as a kerogen-bearing dolomitic marlstone, but it has been called an “oil shale” for so long that the inaccurate terminology has stuck. Kerogen is an insoluble complex organic compound that is a precursor to petroleum, and requires additional thermal exposure before it matures into oil and gas.
The Piceance Basin Green River Formation is the largest known oil shale deposit in the world and was recently estimated by the U.S. Geological Survey (Johnson et al., 2010) to contain 1.5 trillion (with a “t”) barrels of in-place oil, 50 percent more than the previous estimate. Nearly all of this increase was due to new areas and intervals being assessed that had insufficient data to evaluate or were considered too low grade to consider during the previous assessment. Most of the newly identified resource is of low grade and unlikely to be developed, but 1 trillion (still with a “t”) barrels remains a vast resource. It is impossible to predict how much of the resource will be commercially producible as the extraction processes are still being evaluated and are currently uneconomic.
The Johnson et al. (2010) study was based on a comprehensive assessment of Fischer assay results from 2178 core holes drilled to evaluate the Green River oil shale potential. Fischer assays are a standardized laboratory method that has been almost universally used to determine oil yields of Green River Formation oil shales. The method consists of heating a crushed and screened (2.38-mm mesh) 100-gram sample in a small aluminum retort to 500° C at a rate of 12° C per minute and then held at that temperature for 40 minutes. The volatilized components are passed through a water-cooled condenser, collected in a graduated centrifuge tube and then separated by centrifuging. Weight percentages are determined for the shale oil, water, shale residue and the lost non-condensed gas. The shale oil specific gravity is measured and used to calculate the oil yield in gallons per ton (GPT).
The Green River oil shale interval in the Piceance Basin may be subdivided into seventeen alternating “rich” and “lean” zones that were originally defined by Cashion and Donnell (1972) using logs generated from Fischer assay data. These zones are roughly time-stratigraphic units consisting of distinctive, laterally continuous sequences that can be traced throughout much of the Piceance Basin. All of the oil shale zones grade into marginal lacustrine rocks towards the basin edges making correlations difficult. Another major cause of correlation difficulties occurs near the lake depocenter, where mass-movement processes prior to lithification resulted in the formation of discontinuous breccias. The Mahogany zone has received considerable attention because it is one of the richest oil shale intervals, and because it crops out around the basin margins where it has been mined at several locations.
The Green River oil shale extraction methods currently under development can be subdivided into two main categories, surface or in situ retort processes. Surface retorting methods extract oil by heating mined oil shale in high temperature kilns and were operated in the Piceance Basin as early as 1917. The largest and most evolved surface retort plant was operated by Unocal near Parachute, Colorado and produced around 5 million barrels of oil during the 1980s. Shale Technologies, LLC currently operates a pilot surface retort near Rifle, Colorado and is capable of producing small oil volumes using minimal externally sourced energy and water in the process.
There are several Green River oil shale in situ retort pilot projects underway in western Colorado, including operations by Shell, ExxonMobil and AMSO. Shell has successfully demonstrated their In situ Conversion Process (ICP) on an experimental scale at the Mahogany Demonstration Project using electric heaters installed in closely spaced vertical wells to slowly heat the oil shale. Shell is also developing technology to isolate the oil shale extraction area by surrounding it with very closely spaced (8 feet apart) vertical wells that chill water until frozen to prevent groundwater movement and contamination (Deeg et al., 2009). ExxonMobil has developed the Electrofrac(TM) process (Symington et al., 2009) that distributes heat by hydraulic fracturing the oil shale and filling the fractures with an electrically conductive material that forms a resistive heating element. AMSO’s process (Day, 2009) involves drilling closely spaced horizontal or highly deviated wells that also use down hole electrical heaters to slowly heat the oil shale. The AMSO pilot is targeting only the lower Green River oil shale intervals that are isolated from aquifers to eliminate the risk of ground water contamination.
The Center for Oil Shale Tech-nology and Research (COSTAR), under the direction of Dr. Jeremy Boak, has coordinated annual Oil Shale Symposia at the Colorado School of Mines for the last five years and provides access to much excellent information on the extraction technology and other oil shale research on their website (http://www.costar-mines.org/).
The large size of the Green River oil shale resource will continue to draw the attention of many researchers and it is only a matter of time before commercial production is established. The race is on!
Selected References and Websites
Cashion, W.B., and Donnell, J.R., 1972, Chart showing correlation of selected key units in the organic-rich sequence of the Green River Formation, Piceance Creek Basin, Colorado, and Uinta Basin, Utah: U.S. Geological Survey Oil and Gas Investigations Chart OC–65.
USGS Piceance Basin Green River Oil-In-Place Assessment Fact Sheet. Downloaded from: http://pubs.usgs.gov/fs/2009/3012/pdf/FS09-3012.pdf
Johnson, R.C., Mercier, T.J., Brownfield, M.E., Pantea, M.P., and Self, J.G., 2010, An assessment of in-place oil shale resources in the Green River Formation, Piceance Basin, Colorado: U.S. Geological Survey Digital Data Series DDS–69–Y, chapter 1, 187 p. Downloadable from: http://pubs.usgs.gov/dds/dds-069/dds-069-y/
Shale Technologies, LLC website: http://www.shaletechnologies.com/
Deeg, W., S. Arbabi, R. Mykitta, J. Smith, and L. Crump, 2009, Construction and Testing of Shell’s Freeze Wall, Shell Exploration & Production: Presentation to the 29th Oil Shale Symposium Golden, Colorado Oct. 19-23, 2009. Downloaded from: http://www.costar-mines.org/oss/29/presentations/PRES_03-3_Deeg-Wolfgang.pdf
Shell Mahogany Demonstration Project website: http://www.shell.us/home/content/usa/aboutshell/projects_locations/mahogany/technology/ [link no longer active]
Symington, W. A., J. S. Burns, A. M. El-Rabaa, G.A. Otten, N. Pokutylowicz, P. M. Spiecker, R. W. Williamson, and J. D. Yeakel, 2009, Field testing of Electrofrac (TM) Process Elements at ExxonMobil’s Colony Mine: Paper prepared for presentation at the 29th Oil Shale Symposium, held at the Colorado School of Mines in Golden, Colorado, October 19-23, 2009. Downloaded from: http://www.costar-mines.org/oss/29/papers/Paper_03-4_Symington-Bill.pdf
Day, R.L., 2009, AMSO’s Colorado Oil Shale RD&D Lease Tract: Progress and Plans, Presentation to the 29th Oil Shale Symposium, Golden, Colorado, October 20, 2009. Downloaded from: http://www.costar-mines.org/oss/29/presentations/PRES_05-2_Day_Roger_AMSO.pdf
American Shale Oil (AMSO) website: http://www.amso.net/