Sustainability 2011 , 3 2316
The wording of Mr. Maddox’s response to the energy balance question suggests that the answer
refers to direct energy consumption. The values cited line up with the downhole heating energy
demands in the RAND study, which are “one-sixth the energy value of the extracted product,” or a 6:1
EROI if natural gas provides the heat. With 50% efficient generation, the EROI would be 3:1 for
electric heating in situ production. Other indirect energy costs and indirect energy costs are excluded.
3.6. Cleveland (2005) [16]
Cleveland (2005) [16] offers an extensive discussion of EROI methodology. The values reported
for the EROI for oil shale are above and below the break-even point, with the median estimate around
5:1 or less. These findings are based on Cleveland et al. (1984) [15], which assessed the EROI of a
range of energy resources based on the then-current literature. The studies referenced by Cleveland
et al. (1984) [17] via Lind and Mitsch (1981) [18] date from the mid-1970s. They show EROI ranging
from 0.7:1 to 13.3:1. This wide range is partly due to very limited experience with actual projects, and
partly due to the less-developed state of EROI analysis at the time. The range cited by
Cleveland (2005) [16], based as it is on these earlier studies, is not representative of the current state of
technology and resource assessment.
3.7. Burnham et al. (2010) [19]
American Shale Oil LLC (AMSO) has proposed a new method of producing oil shale from the
source rock. This method relies on heating an illitic shale layer under pressure to fracture it, increase
permeability, and perform in situ retorting, while a nahcolitic shale oil layer above serves to insulate
the producing layer from groundwater. The process is still under development and has not yet been
field-tested. AMSO projects water consumption of less than one barrel per barrel of oil produced, CO 2
emissions from downhole heating of 50 kg per barrel of oil (roughly 10% of the CO 2 from burning that
oil), and an EROI of possibly 5:1 (considering all energy uses) to 8:1 (considering direct energy only).
3.8. Bunger and Russell (2010) [20]
Bunger and Russell (2010) [20] analyze the thermal efficiency of shale oil production, modeling a
surface retort. The study notes the increasing energy cost of petroleum recovery, and states that shale
oil production will soon be “thermodynamically competitive” with petroleum. Bunger and Russell use
an “efficiency of conversion” approach, where the energy required for each step gives an efficiency
value for that point in the process. For example, mining and ore preparation require approximately 4%
of the energy content in the shale (96% efficiency), while upgrading requires about 2.5% of the energy
in the feedstock (97.5% efficiency). The analysis also notes that the internal energy consumed has no
other economic use. The overall energy efficiency is seen to be 81%, corresponding to an EROI of
5.3:1. That is, if Ef/E 0 = 0.81, then Ef/(E 0 − Ef) = 5.3, The analysis does not included embodied energy
in materials or other indirect energy. Direct energy is considered, as is the energy required for
electricity generation (40% generation efficiency is assumed).