Thermal Recovery From Tar Sands
Authors: Carrigy Maurice A. 
Published: December 2007

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering.

On the basis of the progress made in developing improved technology for recovery of bitumen from tar sands, it is logical to assume that as the world'ssupply of light and heavy oil is depleted, production of' synthetic oil from the bitumen resources in tar sands will accelerate. As most of the known deposits of tar sands were discovered by accident, there is reason to believe that a worldwide exploration program based on sound geological principles will discover much more of this material, principles will discover much more of this material, The long lead times required to turn this massive resource into-acceptable alternative refinery feedstock at a reasonable price make it imperative that we vigorously pursue the development price make it imperative that we vigorously pursue the development of recovery technology at this time if we are to avoid shortages of liquid fuel early in the next century. There is no question that the light-crude-oil substitute developed from this resource will be more expensive than the conventional light and heavy crudes being used today. However. there is reason to believe that the differential in costs will narrow as the search for new sources of light oil swings to deeper targets in more remote and hostile environments, such as the continental shelves and arctic islands, and more expensive enhanced recovery techniques are used to recover the oil now left behind in deep depleted light- and heavy-oil reservoirs.

The Resource Tar sands have been defined pragmatically by petroleum engineers as oil too viscous to flow into a well in sufficient quantities to be produced economically. This definition, if universally applied, causes problems because oils of different gravities are included. depending on their depth of burial and the reservoir temperature. Others have defined tar sands as reservoirs containing bitumen-i.e., oils heavier than water or with gravity of less than 10API. A compromise definition proposed by UNITAR states that tarsands contain crude bitumen with a gravity of less than 10API at 60F or have a viscosity greater than 10,000 mpas at original reservoir temperature. Nodefinition of tar sands enunciated to date is universally acceptable to geologists, petroleum engineers, and refiners. If one were to classify a reservoir as a tar and only if it contains a semiliquid hydrocarbon that is heavier than water (less than 10API gravity), has a viscosity of more than10,000 cp at reservoir temperature, and cannot he produced in significant quantities through a well by primary production, some large deposits widely accepted as tar sands, such as the Orinoco belt reservoirs in Venezuela, the Cold Lake deposit in Alberta, and the Asphalt Ridge deposit in Utah, would be excluded for failing to meet one or more of the three criteria. For the purposes of this paper have selected for discussion reservoirs that contain low-gravity oil ( = 10API or less) and need a large thermal input to reduce the oil viscosity to a level that will allow it to be produced through a well at economic rates. Defining crude bitumen as oil with gravity less than 10API at60F puts these ultraheavy oils in a group consistent with their commercial value, regardless of their depth of burial, once they have been produced. It also is a good indication of the amount of "upgrading" necessary to make the minto refinery feed stocks.

JPT

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