Oil sands (also called tar sands) consist of bitumen (which is soluble organic matter derived from degradation of oil either as seeps that come to surface or within shallow subsurface reservoirs) and host sediment with associated minerals, excluding any related natural gas.
Today the largest single oil sand deposit in the World is the Athabasca oil sands located in northeastern Alberta, Canada. Here the shallow oil sands are recovered in open-pit mines by truck-and-shovel operations in which the World’s largest Caterpillar 797 and 797B trucks have payloads of 380 tons. The oil sand is transported to processing plants, where hot or warm water separates the bitumen from the sand, followed by dilution with lighter hydrocarbons and upgrading to synthetic crude oil (SCO).
About 20 percent of the oil sands reserves in Alberta are recoverable by surface mining where the overburden is less than 75 m. For the remaining 80 percent of the oil sands that are buried at a depth of greater than 75 m) in-situ technologies (largely thermal techniques such as Steam Assisted Gravity Drainage, or SAGD; Cyclic Steam Stimulation, or CSS; or, Hybrid Steam Assisted Gravity Drainage, or HSAGD) are used to extract the bitumen.
The most commonly used in-situ process is Steam Assisted Gravity Drainage (SAGD), in which pairs of horizontal wells are drilled near the base of the bitumen deposit. Steam is injected into q well which is placed about 5 metres above the producer well. The steam rises and heats the bitumen which loses its viscosity, and then flows down under gravity to the lower producer well, from which it is pumped to the surface. The bitumen is then either upgraded on site, or at a regional upgrading facility, or mixed with diluents and shipped to a refinery. In 2005, 200 million barrels (31.7 million m3) of synthetic crude oil was produced from the mined raw bitumen (upgraded onsite or in a regional refinery). Most of the in-situ bitumen production was marketed as non-upgraded crude bitumen.
In addition to Canada, oil sands are found in about 70 countries around the world, including the U.S.A., Venezuela, Russia, Cuba, Indonesia, Brazil, Trinidad and Tobago, Jordan, Madagascar, Colombia, Albania, Romania, Spain, Portugal, Nigeria and Argentina. Within the United States, oil sand deposits occur mainly in Utah, Alaska, Alabama, S.W. Texas, California, Kentucky, Oklahoma, and Missouri with scattered deposits in other states. A map showing occurrences in North America is shown below.
In most cases, the oil-sand deposits occur at the surface or at relatively shallow depths of burial (< 200 m), where hydrocarbon reservoirs are in contact with the atmosphere, groundwater aquifers or shallow formation waters. In North America the ages of host rocks range from Ordovician to Quaternary. Geologically, oil sand deposits can be broadly classed into two end-member categories – those very large and large deposits at the shallow up-dip edge of foreland basins; and those medium to small scale deposits that are related to loss of caprock integrity. Oil sands are commonly associated with faults and unconformities, and may also be found in association with oil seeps, springs, tufa deposits and/or mud volcanoes. A recent world-wide compilation of heavy oil and natural bitumen deposits in relation to the different types of geologic basins is given by the U.S. Geological Survey (website posting: http://pubs.usgs.gov/of/2007/1084/OF2007-1084v1.pdf).
In North America, all of the bitumen production is from Alberta. In 2007 Alberta’s crude bitumen production totaled 482.5 million barrels (76.7 million m3), with 59% (284.7 million barrels) coming from extraction by surface mining and with 41% (197.8 million barrels) coming from in-situ underground thermal operations. This production of crude bitumen is equivalent to 1.32 million barrels per day (210,000 m3/day). By 2016 it is expected that this production from Alberta will at least be double that recorded in 2005. It is expected that the contribution of bitumen to Alberta’s total crude production will increase to 86% by 2016.
Because of the expected growth in oil sands production, a large number of specialists will be needed including subsurface and mine geologists (depending upon whether it is in-situ or surface mining), geophysicists, reservoir engineers, computer modelers, environmental and reclamation specialists, policy specialists, and economists.
If you’re interested in learning more about oil sands, there’s additional information in the member’s only area of the EMD website including a compilation of references; a field guide to Alberta oil sands; a table of reserves estimates; references to pertinent and recent articles; website links; a reference to a video of oil sand extraction, production and geology; articles from the AAPG Explorer, Search and Discovery pages, and AAPG Bulletin.
For a complete version of the above, see the Committee’s Annual Report (May 2013) on the EMD Members Only page (log-in required).
If you would like to learn more about oil sands or to receive information on oil sands, or on activities of the EMD Oil Sands Committee, join the EMD. If you are already an EMD Member, see “Members Only Page” http://emd.aapg.org/members_only/oil_sands/index.cfm for updates on oil sands, for links to technical information on oil sands, and for related environmental information that may impact oil sands.
For further information on this committee’s activities, go to the Members’ Only Web page or contact:
Steven Schamel, Chair
Phone: +1 (801) 583-1146
|November 2004:||Field Trip Planned at Calgary Meeting Oil Sands Tapped as Major Resource
EMD Column by Frances J. Hein