17.08.2015   IAEA RADIATION TECHNOLOGY SERIES No

LAHENDONG GEOTHERMAL FIELD (INDONESIA)

I.4.1. Tritium tracer test in Lahendong geothermal field

The Lahendong geothermal field is located in North Sulawesi province at an elevation of 800-1100 m above mean sea level and is producing about 20 MW(e) of electricity annually.

Tritium tracer with an activity of 629 GBq (17 Ci) was injected into LHD-7 injection well in July 2006. Monitoring of tritium tracer has been done in several production wells surrounding LHD-7. The tracer monitoring in production wells LHD-8, LHD-11, LHD-12 and LHD-15 was done periodically every two weeks during the first three months after injection, and then periodically every month.

Tritium in water samples was analysed using a Packard-TR 1900 liquid scintillation counter. The direct counting method was used and samples were distilled before counting. A 10 mL sample of distilled water and 11 mL of Instagel cocktail (Ultima Gold) were added to the counting vial and homogenized by shaking. The counting time for each sample was 20 min and the counting rate was converted to tritium units.

I.4.2. Results and discussion

Table 15 shows the result of tritium tracer in Lahendong geothermal field, whereas Fig. 65 shows the plot of time versus tracer concentration curve.

TABLE 15. MONITORING RESULTS OF TRITIUM TRACER IN LAHENDONG GEOTHERMAL FIELD

Production wells

Tritium concentration (tritium units)

LHD-8

LHD-11

LHD-12

LHD-15

LHD-10

Background

0.53

0.24

0.25

0.43

0.12

Time (d)

3

0.74

0.38

0.31

0.72

21

1.05

1.18

0.95

1.15

33

1.59

1.33

1.21

1.21

47

1.6

1.04

1.98

3.59

61

1.05

4.2

6.57

4.18

65

3.61

3.23

3.03

5.05

81

0.84

0.85

1.72

1.24

95

0.47

1.7

1.42

1.21

121

0.84

0.93

1.19

1.7

148

1.33

2.34

1.9

1.9

226

1.57

5.51

1.47

252

5.06

4.11

5.51

309

4.5

7.39

4.76

342

12.57

20.29

24.14

370

112.47

112.5

112.17

405

125.19

174.4

227.78

433

75.84

69.19

69.88

472

73.65

38.58

18.22

508

39.59

30.73

40.62

625

25.08

11.04

16.7

image124

Figure 65 shows that tritium concentration in monitored production wells fluctuated around background value until 300 d after injection. Tracer breakthrough occurred in 309 d after tracer injection. The tracer concentration peak of the response curves of three wells (LHD-10, LHD-12 and LHD-15) was recorded around 400 d after injection with a maximum tritium concentration of 228 tritium units.