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Generating Power Using Geothermal Resources 173

Forked or
Deviated well multiple-legged
0 m well 0 m

30''
~ 12 m
26''
22''
~ 75 m ~ 230 m
16'' 17 1/2''
~ 475 m ~ 1600 m
13 3/8'' 13 3/8''

12 1/4''

~ 2800 m
11 3/4''
~ 1400 m
8 1/2''
open hole
10 5/8''
open hole ~ 3100 m ~ 3800 m

FIGUre 9.15 Deviated and branched wells. The diameters and respective depths are approximate, and are
generalized from information presented. (From Pye, D. S. and Hamblin, G. M., Drilling Geothermal Wells
at The Geysers Field. Monograph on The Geysers Geothermal Field, Special Report No. 17, Geothermal
Resources Council, 229–35, 1992; Henneberger, R. C., Gardner, M. C., and Chase, D., Advances in Multiple-
Legged Well Completion Methodology at The Geysers Geothermal Field, California. Proceedings of the
World Geothermal Congress, vol. 2, Florence, Italy, 1995.)

The noncondensable gases can be problematic. Emission standards for H S vary from
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region to region, depending upon local restrictions established by appropriate agencies. The
Occupational Health and Safety Administration recommends that H S in the workplace not
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exceed 20 parts per million, with a maximum of 50 parts per million for 10 minutes. Typical
H S emissions from geothermal power plants are less than 1 part per billion (Energy Efficiency
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and Renewable Energy Office of the Department of Energy, http://www1.eere.energy.gov/geo-
thermal/geopower_cleanair.html). However, that is not the case at The Geysers, where the steam
can contain up to 0.15% H S by weight. As a result, an abatement program was developed to
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remove H S from the emission stream. That process oxidizes H S to elemental sulfur with an
2
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efficiency in excess of 99.9%.
Emissions of CO are also important to consider, since they have an impact on greenhouse gas
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releases to the environment. These are discussed in detail in Chapter 13 and will not be further
addressed here.
susTainabiliTy and reinjecTion
The sustainability of geothermal reservoirs for power production is an issue that deserves careful
consideration. The Geysers provide a particularly interesting example of this issue. The most basic
means for establishing sustainability of a resource is to consider the historical record of energy
production per well, or to use some proxy for that metric. With that data, one can model the long-
term behavior of the resource and establish whether it can be used in a sustainable manner. For the
context within which we are considering this question, we will define sustainability as the ability to