FLUID INCLUSION MICROTHERMOMETRY AND GAS CHEMISTRY IN GEOTHERMAL SYSTEM, JAPAN AND ITS APPLICATION FOR THE STUDY OF FLUID EVOLUTION - Energy Research Developments: Tidal Energy, Energy Efficiency and Solar Energy - page 186

geothermal fields, Japan. Semi-quantitative convenient gas analysis of liquid-rich inclusion
using a crushing experiment and microthermometry is available to estimate the CO 2 content
in inclusion fluid lower than approximately 2.0 mol%. To the contrary, the gas analytical
method using a quadrupole mass spectrometer is very useful to obtain not only semi-
quantitatively non-condensable gas content in individual inclusion, but also bulk gas
composition in transparent mineral. This method offers furthermore us significant information
about the fluid evolutions such as degassing and dilution by groundwater.
Based on the gas analysis of liquid-rich inclusions in hydrothermal quartz and anhydrite
from most 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 content in the inclusion fluid is generally higher than those
in the present reservoir fluid, mainly suggesting that early stage fluid was trapped in the fluid
before considerable boiling and vapor-loss. The decrease of CO 2 content in the reservoir fluid
occurs more or less during progressing of the exploitation of the geothermal field. The
CO 2 /CH 4 and CO 2 /N 2 ratios could be explained by degassing and/or dilution by groundwater.
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