Environmental Engineering Reference
In-Depth Information
CO
2
, N
2
, CH
4
and Ar were usually detected in fluid inclusions from eleven geothermal
fields, but H
2
S was detected in fluid inclusions from the Kirishima geothermal field (Sasada
et al., 1992).
The gas analytical chart of individual liquid-rich inclusion trapped a liquid
heterogeneously in anhydrite from the Matsukawa field is shown in figure 8b. The peak ratios
of CO
2
/H
2
O (e.g. L1, L2 and L3 in figure 8B) decrease with decrepitation temperature. These
anhydrites may have trapped liquids that have undergone different degrees of boiling and
vapor-loss. In this case, later trapped liquids are likely to have lower gas contents because of
CO
2
-rich vapor-loss during boiling of CO
2
-rich fluid.
Bulk Gas Analytical Data
Degassing trend on a plot of log X
CO2
versus temperature of liquid is illustrated in figure
9. The decrease in CO
2
content by vapor-loss was calculated for a single step separation
process with adiabatic cooling by assuming the hypothetical initial liquid composition of 1.5
mol % CO
2
at 350 ºC (open star). Equations for the vapor-liquid fractionation are taken from
Giggenbach (1980). As boiling proceeds, CO
2
content decreases in the residual liquid phase
because CO
2
preferably fractionate to vapor phase. If a fluid had boiled and all inclusions
Figure 9. Schematic model to show general trends produced as a result of two processes operating on an
initial reservoir liquid in terms of temperature and CO
2
content The decrease in CO
2
content by vapor-
loss was calculated for a single-step separation process with adiabatic cooling by assuming the
hypothetical initial reservoir liquid composition of 1.5 mol% CO
2
at 350 ºC (open star). Equations for
the vapor-liquid fractionation are taken from Giggenbach (1980). The schematic dilution curve (1) and
curve (2) are the mixing lines between the air-saturated groundwater at 20 ºC and the hypothetical
initial reservoir liquid, and between the groundwater and the reservoir liquid differentiated at 300 ºC by
vapor-loss, respectively.
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