Deposits of unconventional fuels—both crude oil and natural gas—occur in geological environments with very low energy. The exploitation of these low-energy deposits/reservoirs will require...
Nuking the Tar Sands
Can nuclear heat allow for low-cost commercial reclamation?
bitumen deposits as “continuous,” not having migrated from their source rock into a conventional reservoir. Industry refers to the extraction of kerogen and its upgraded products as manufactured oil.
The migrated and concentrated nature of the degraded bitumen in oil sands, and the non-migrated and disseminated nature of pyrobitumens in oil shales, largely account for the differences in economic exploitation and in the application of nuclear power as a thermal energy source for mobilization of bitumen, especially for in-situ extraction.
The more favorable (higher) the porosity and permeability of the host sandstone reservoir that originally received the liquid hydrocarbons, the lower the extraction temperature and greater recovery efficiency of in-place bitumens. If the source rock is composed of oil shales, higher extraction temperatures are needed. Typically, 15 percent to 20 percent of the oil-in-place can be recovered from host sandstones, depending on the level of bitumen degradation and of residual reservoir energy. Only 5 percent to 10 percent of the oil-in-place currently can be recovered from kerogen shales. The injection of thermal energy from hydrocarbon combustion for steam generation can increase in-situ recovery by up to 40 percent (rarely 70 percent) in bitumen sandstones and up to 20 percent in bitumen shales.
Some 80 percent of North America’s technologically recoverable bitumen is extractable by in-situ methods. Nuclear power for direct heat without steam potentially could economically displace use of hydrocarbon fuels as an energy source. However, nuclear power as a thermal heat source must accommodate the following geologic parameters of the deposit:
Depth of burial (geothermal and rock/fluid pressure gradients);
• “Reservoir” heterogeneity including geochemical distribution (thermal maturity, total organic content) and petrophysics (mineralogy and rock fabric);
• Deposit geometry (shape of core and periphery of bitumen distribution);
• Size of the extraction pool and extraction rate; and
• Maximum transportation distance between injection well and reactor (approximately 4,000 feet).
The lease-block configuration also is important. Avoiding fragmentation of surface rights can minimize the purchase of surplus electricity.
Nuclear thermal discharge can heat the host sandstone and shale directly, eliminating the need for steam and electricity for wellbore heaters from fossil fuels, and reducing the energy requirement for retorting by as much as 50 percent. It also uses less water and produces less greenhouse gases, essentially avoiding CO 2 emissions from the production of electricity. Direct heating of bitumen-bearing rocks also can produce more bitumen than traditional surbsurface recovery because in-situ volumes will not be required to heat the host rock.
Nuclear heat can be operated for decades to transfer heat to an intermediate heat-transfer fluid within insulated loops that are limited to short distances. The likely maximum reactor-to-wellhead distance is approximately 4,000 feet, due to heat degradation. This factor is very similar to transfer of thermal energy in geothermal brines to binary heat recovery systems for power generation. Nuclear heat transfer technology can recover 100,000 bbl/d of bitumen in the Piceance basin from 30 acres/year, and would require a 600-MW reactor. 1
Production of Canada’s oil sand is projected at 3 million barrels and will require