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Nuking the Tar Sands

Can nuclear heat allow for low-cost commercial reclamation?

Fortnightly Magazine - September 2008

. There is currently no commercial production, only pilot-scale field tests in the Green River Formation in Colorado, Utah, and Wyoming.

Oil has no inherent energy to produce itself, whether in unconventional or conventional reservoirs. The natural energy in a reservoir available to move oil into a well bore is the potential energy of the reservoir pressure. This energy is stored mainly in the interstitial fluids (and to a lesser extent in the rock) compressed by gravity. This reservoir energy must be great enough to move the oil to the well by overcoming surface tension holding oil within the pore system and the viscous resistance of the oil to movement. This is accomplished by capillary pressure formed by a dynamic pressure gradient from the oil-bearing pore to the well. The differences in reservoir energy separate conventional oil deposits from unconventional deposits, as does the nature of their bitumen.

Bitumen and kerogen are naturally occurring hydrocarbons with geological differences that control their commercial exploitation, in particular the application of nuclear energy.

Bitumen is a generic term applied to natural inflammable substances composed principally of a mixture of hydrocarbons substantially free from oxygenated matter. Petroleums, asphaltites, and mineral waxes all are considered bitumens. Kerogen is a mineraloid of indefinite composition consisting of a complex mixture of macerated organic debris, which are chiefly forms of plant life that lived in the enclosed basin where it formed. An asphaltic sandstone ( e.g., Alberta tar sands) and a kerogen shale ( e.g., Colorado oil shale) are examples of bituminous rocks that yield oil on destructive distillation.

Oil Sands: Disseminated deposits of liquid bitumens can be degraded by geological processes that release dissolved gasses, by oxidation, and by bacterial digestion into high specific gravity (density measured in degrees API gravity), and into high viscosity (ability to flow measured in centipoises) liquids and semi-solid materials. The greater the loss of dissolved gas, the greater the specific gravity (the lower the API gravity), the greater the viscosity, and the lower the calorific value (measured as calories per gram) of the residual oils. The viscosity of bitumen distinguishes bitumen (tar) sands from extra heavy oil.

The tar sands of Alberta belong to this category of degraded bitumens. Such hydrocarbons migrated from their source rock and were captured in a “conventional” reservoir. These deposits are called “unconventional” because geological processes subsequently released their original reservoir energy, and they now require supplemental energy to mobilize them, such as reinjected gas, miscible fluids ( e.g., natural gas liquids) or thermal energy ( e.g., steam or direct heat) to achieve commercial rates of recovery.

Oil Shale: Surface deposits of bitumen known as kerogen shales are composed of fossilized insoluble organic material found in their original sedimentary rocks. In the chemical classification of hydrocarbon materials, kerogen is on the border between petroleum hydrocarbons and the coals. Kerogen shales do not decompose into gaseous and liquid petroleum hydrocarbons until they are heated to temperatures of 350 degrees Centigrade or more. They are a subclass of bitumens called pyrobitumens.

The United States Geological Survey (USGS) refers to these