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

3541
1099
792
3533
2924
2925
2825
1641
1443
1443
723
723
467
1.6
3429
2924
2854
Well NJ-14 Coupon # 10
1630
1404
1031
0.55
1099
452
0.5
3542
465
0.45
1.2
Counts
Counts
0.4
Coupon # 16 after heat exchangers
2842
1630
793
0.8
3541
2923
2854
1033
442
0.35
1630
1410
0.3
A
Well NJ -22 Coupon # 25
B
0.4
0.25
4000 3000 2000 1000 0
Wavelength cm -1
4500 4000 3500 3000 2500 2000 1500 1000 500 0
Wavelength cm -1
1099
3
1
1107
2.5
465
3533
0.8
2
Counts
1.5
1641
792
465
Counts
0.6
Re-injection well coupon # 20
467
2925
2825
2924
2852
1
3541
2924
2852
1641
Retention Tank Coupon # 5
0.4
Reinjection well coupon # 19
1641
0.5
Retention Tank Coupon # 17
C
Retention Tank Coupon # 18
D
0
0.2
4500 4000 3500 3000 2500 2000 1500 1000 500 0
Wavelength cm -1
4500 4000 3500 3000 2500 2000 1500 1000 500
Wavelength cm -1
FIGURE 34: IR spectra of scales deposited on coupons at, a) The wellheads of NJ-14 and NJ-22,
b) After the heat exchangers, c) At the entry to the retention tank, d) At the re-injection well
No clear diffraction peaks could be observed in the scale of the coupons from the wellheads of NJ-14
and NJ-22 except for a small peak at ~ 7 ˚ 2θ for the sample from NJ-22 which indicates some clay
and a peak at ~ 29.5˚ 2θ in the sample from NJ-14 which could be due to chalcopyrite.
The X-ray diffraction patterns for the scales forming from separated water after the heat exchangers
and before the retention tank are very similar. This is shown in Figure 33. The scale formed on the
coupon at the injection well was too small for X-Ray examination. The most prominent feature in the
scales is a broad peak at ~ 23˚ 2θ which is characteristic of amorphous or opaline silica. Small peaks
at ~ 7 ˚ 2θ and ~ 12.5 ˚ 2θ were identified in two samples before the retention tank. These reflect the
presence of clay minerals. Minor peaks at ~ 29.5˚ 2θ, ~31.5˚ 2θ and ~ 45.5˚ 2θ were also observed.
These reflect the presence of chalcopyrite, halite (NaCl) and sylvite (KCl). In these samples the
presence of chalcopyrite considered could indicate some minor crystalline phases in the scale. Halite
(NaCl) and sylvite (KCl) will have formed by evaporation of geothermal water on the coupons when
dried and do not represent a part of the scale. They are easy to detect in the X-ray diffraction because
of their cubic structure.
36