Environmental Engineering Reference
In-Depth Information
Chapter 7
F LUID I NCLUSION M ICROTHERMOMETRY AND G AS
C HEMISTRY IN G EOTHERMAL S YSTEM , J APAN
AND I TS A PPLICATION FOR THE S TUDY
OF F LUID EVOLUTION
Yoichi Muramatsu
Department of Liberal Arts, Faculty of Science and Technology,
Tokyo University of Science, 2641 Yamazaki,
Noda, Chiba 278-8510, Japan.
Abstract
Fluid inclusions in transparent minerals, which trapped different hydrothermal fluids at
various stages after precipitation of the minerals till now, offer us information about the
physicochemical properties of the fluid such as temperature, salinity and chemical
composition. From the point of view, fluid inclusion studies have been widely used to
estimate reservoir temperature during drilling of a well and interpret the physicochemical
evolution of reservoir fluid at geothermal field.
The minimum Th value of fluid inclusion in quartz, calcite and anhydrite from a
geothermal well can be used to estimate the reservoir temperature with real time at a
development site in most liquid-dominated and vapor- dominated geothermal fields, Japan. In
numerous methods developed for fluid inclusion analysis, semi-quantitative convenient gas
analysis of liquid-rich inclusion using a crushing experiment and microthermometry is
available to estimate CO 2 content in inclusion fluid lower than about 2.0 mol%. To the
contrary, a quadrupole mass spectrometer (QMS) is one of most useful quantitative analytical
methods to clarify gas chemistry of tiny fluid inclusion. Based on the analytical results using
the QMS on fluid inclusions in anhydrite and quartz from wells in the Japanese geothermal
fields, the main component is H 2 O with small amounts of CO 2 , N 2 and CH 4 and Ar. The CO 2
and CH 4 contents in the inclusion fluids are nearly equal to or slightly higher than those in the
present reservoir fluids. In contrast, the N 2 contents in the former are generally about one to
three orders of magnitude higher than those in the latter. The differences in the CO 2 content
and the CO 2 /CH 4 and CO 2 /N 2 ratios between the inclusion fluid and present reservoir fluid
could be explained by degassing and/or dilution. In the degassing case, early stage fluid was
trapped in the fluid inclusions before considerable boiling and vapor-loss. It appears that the
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