A History of Geothermal Energy Research and Development in the ...

EXPLORATION
Inclusions generally contain a liquid phase and a gas phase, the latter seen as a
bubble under the microscope. The temperature of the inclusion’s formation is
considered the temperature at which heating causes the fluid to homogenize
(i.e. the bubble to disappear). By freezing the fluid in the inclusion, a measure
of freezing-point depression can be obtained and related to the salinity of the
contained fluid. Temperatures and salinities, calculated as equivalent weight
percent NaCl, can be interpreted in terms of boiling, cooling, and mixing in much
the same way as chemical analyses of well and spring waters are evaluated. 191
Researchers used fluid-inclusion data to characterize the thermal and geochemical
structures of geothermal systems. 192-193 Measurements on fluid inclusions from
more than 15 wells at Coso Hot Springs demonstrated that hydrothermal fluids
on the western side of the field moved upward and northward from an upflow
zone in the south. Present-day flow and geochemical patterns are similar to
those defined by the fluid-inclusion data; fluid-inclusion salinities indicated
the presence of low-salinity groundwater not present in the field today.
Figure 19. Examples of fluid inclusions from Karaha-Telaga Bodas, Indonesia.
(A) Homogenization temperatures and salinities of fluid-inclusion populations in a single crystal of quartz. (B)
Primary vapor-rich inclusions. (C) Secondary planes of all liquid- and all vapor-rich fluid inclusions. (D-E) A liquid-rich
fluid inclusion containing a daughter crystal of fluorite at room temperature (D) and after heating and cooling (E).
66 A History of Geothermal Energy Research and Development in the United States | Exploration