Jökull - 01.12.1977, Page 57

m moles
Fig. 4. Changes in the hydrogen content of the discharges of wells 4 to 8 during the period
1970—1976. The hydrogen concentrations have been calculated from the reported enthalpy of
the well discharges, which corresponds to the quartz equilibrium temperature at the initiation of
the discharge period.
Mynd 4. Breytingar cí vetnisinnihaldi í borholum 4 til 8 á timabilinu 1970—1976. Styrkur vetnis
hefur veriö reiknaður út frá ofanskráðu entalpiugildi. Svarar þetta gildi til kisilhitans við upphaf
nýtingartímans.
sulphide, and carbon dioxide, the remainder
being mostly nitrogen and methane (Table 2).
The analytical results for the major gas con-
stituents are rather erratic, which makes it diffi-
cult to observe any trends in the gas content
of individual well discharges with time. Yet it is
certain that the gas content of the total dis-
charge of wells 6, 7, and 8 has declined with
time during the period 1970—1976. For well 7
this decline is estimated to be 10%, but 45%
for wells 6 and 8. During the same period no
changes could be observed for wells 4 and 5.
Well 9 is not included here. Insufficient data
are available from this well in this respect. As
the gas content of wells 6, 7, and 8 has declined,
an apparent lowering of the CO2/H2S and
H2/H2S ratios has occurred, but changes in the
same ratios cannot be detected for wells 4 and
5- The erratic results for carbon dioxide and
hydrogen sulphide make this statement some-
what uncertain. The analytical results for liydro-
gen are presented in Fig. 4. They give an im-
pression of the erratic nature of the data. The
results for hydrogen sulphide and carbon di-
oxide are more erratic.
The gas content of individual well discharges
varies much more than the observed time varia-
tions just discussed (Fig 5A). The liottest aqui-
fer, which feeds well 7, contains the highest gas
concentrations, whereas the coldest aquifer,
which feeds well 5, is lowest in gas. Degassing
by flashing of the reservoir water does not ex-
plain the relation of the ratios of CO2/H2S and
H0/H2S to the total gas content. There is no
relationship between the total gas content and
the CO2/H2S ratio although progressive de-
crease with falling temperature is observed for
the H2/H2S ratio (Fig. 5B).
Flashing, which leads to increased pH of the
water causes precipitation of calcite (Arnórsson,
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