Page 146 - Geothermal Energy Renewable Energy and The Environment

132 Geothermal Energy: Renewable Energy and the Environment

Table 7.2
results of the Geothermal resource assessment for the Undiscovered
and enhanced Geothermal systems (eGs; discussed in chapter 14)
sites in the western states, based on the monte carlo methods Used by
william et al. (2008b)
Undiscovered eGs
state 95% mean 5% 95% mean 5%
Alaska 537 1788 4256 NA NA NA
Arizona 238 1043 2751 33,000 54,700 82,200
California 3256 11,340 25,439 32,300 48,100 67,600
Colorado 252 1105 2913 34,100 52,600 75,300
Hawaii 822 2435 5438 NA NA NA
Idaho 427 1872 4937 47,500 67,900 92,300
Montana 176 771 2033 9000 16,900 27,500
Nevada 996 4364 11,507 71,800 102,800 139,500
New Mexico 339 1484 3913 35,600 55,700 80,100
Oregon 432 1893 4991 43,600 62,400 84,500
Utah 334 1464 3860 32,600 47,200 64,300
Washington 68 300 790 3900 6500 9800
Wyoming 40 174 458 1700 3000 4800
Total 7.9.17. 3.0.,0.3.3. 7.3.,2.8.6. 3.4.5.,10.0. 5.17.,8.0.0. 7.2.7.,9.0.0.

Source: Williams, C. F., Reed, M. J., Mariner, R. H., DeAngelo, J., and Galanis Jr., S. p.,
Assessment of Moderate- and High-Temperature Geothermal Resources of the United
States, U.S. Geol. Survey Fact Sheet 2008–3082, 2008.
Note: Nomenclature is the same as in Table 7.1.

synopsIs
Resource assessments attempt to derive statistically meaningful estimates of the amount of energy
that could be recovered from geothermal reservoirs. The nomenclature that is used in these efforts
identifies the “reserve,” which is the energy resource that has already been identified and character-
ized and is economically viable to develop; the “resource,” which considers undiscovered resources
or known resources that are currently not economically viable but could be with modest further
development; and the resource that is simply not accessible with existing technology or technol-
ogy that may be developed in the foreseeable future. All of these together constitute the “resource
base.” For the resource itself, what must be determined in order to develop a rigorous assessment
is the volume of each reservoir of interest, its heat content, and the proportion of heat that can be
extracted from it (the recovery factor). These parameters are treated statistically, with a distribution
that is determined based on experience and history. Once established, estimates are developed using
statistical models. The most commonly used method to accomplish a rigorous resource assessment
is the Monte Carlo method.

Problems

7.1 Examine the mean values for known and undiscovered resources in Tables 7.1 and 7.2.
Notice that the ratio of known to undiscovered varies considerably between the states.
What would be an explanation for this wide variability?
7.2 Consider the same question as above for the known and EGS resources.
7.3 Identify three issues that influence whether a geothermal site would be considered a
reserve and discuss how those factors can change over time.