corrosive species and scaling in wells at olkaria ... - Orkustofnun

variation in chloride concentration, pH
and temperature. The chloride
concentration in the aquifer waters at
Olkaria varies between ~ 40 ppm and ~
2000 ppm in the aquifer and the aquifer
pH from ~ 6 to 8. Aquifer temperatures
vary between ~ 200° and 300°C. The
wide range in the concentrations of
chloride, pH and temperatures at
Olkaria contribute to the wide range of
HCl aq concentrations. At Nesjavellir,
HCl in the aquifer fluids is very low due
to the very low chloride in the aquifer
water, ~ 150 ppm and a pH of the
aquifer fluids of ~ 8. Aquifer
temperatures at Nesjavellir range
between ~ 270° and 300°C for the wells
studied.
LogHCl aqueous (ppm)
1
0.1
0.01
0.001
0.0001
1E-005
Olkaria East
Olkaria West
Olkaria North East
Olkaria Domes
Reykjanes
Svartsengi
Nesjavellir
The high HCl concentrations in the
aquifer water in Reykjanes and
Svartsengi are very high compared to
those of Olkaria and Nesjavellir. The
high HCl concentration in the aquifer
water at Reykjanes and Svartsengi is a result of
high chloride concentrations and low pH in the
aquifer waters of these two fields. The chloride
concentrations in the waters of these two fields
are ~ 20,000 ppm and ~ 13,000 respectively and
the pH of the aquifer water in the range of ~ 5.1
to ~5.6. Temperatures in Reykjanes range
between 250° and 320°C. At Svartsengi the
temperatures are almost homogenous, being in
the narrow range of 235° and 240°C.
180 200 220 240 260 280 300
Temperatures °C
FIGURE 20: Aquifer water HCl concentrations vs.
aquifer temperature (°C) of selected wells
in the study areas
100
10
1
0.1
OW-901 Olkaria Domes
OW-301 Olkaria West
OW-306 Olkaria West
OW-20 Olkaria East
OW-30 Olkaria East
OW-714 Olkaria North East
OW-34 Olkaria East
OW-709 Olkaria North East
SV-05 Svartsengi
SV-11 Svartsengi
RN-10 Reykjanes
RN-11 Reykjanes
NJ-14 Nesjavellir
NJ-22 Nesjavellir
Upon boiling the dissolved HCl is partly
transferred to the steam that forms. The quantity
transferred is affected by several parameters.
The most important ones include changes in pH,
which occur during boiling, and the temperature
of the fluid mixture. Figure 21 shows how HCl
concentrations in steam decrease during one step
adiabatic boiling for all the wells considered in
the present study.
LogHCl in vapour (ppm)
0.01
0.001
0.0001
1E-005
1E-006
1E-007
1E-008
1E-009
Early steam is somewhat enriched in HCl
relative to the source aquifer water. Upon
continued boiling the cause of the decrease is
largely due to an increase in pH upon boiling
and by changes in the value taken by the HCl
distribution coefficient. Because it is
80 120 160 200 240 280 320
Temperature °C
FIGURE 21: HCl in vapour formed by several
steps of single-step adiabatic boiling of
selected wells in the study areas
temperature dependent the distribution coefficient, is affected by the decrease in temperature when the
fluids cool by adiabatic steam loss. Changes in the Cl content of the water, which are caused by steam
formation, have small effect. The HCl concentrations in steam are ~ 10 3 -10 5 times more for Reykjanes
1E-010
25