ANALYSIS OF GEOTHERMAL CASING THINNING RATE OF LEYTE GEOTHERMAL PRODUCTION FIELD
Corrosion is one of the technological problems that geothermal management faces in the operation of geothermal wells. The primary cause of corrosion in geothermal wells is exposure to geothermal brine where conductive and convective heat transfer happens from the reservoir to the surface. The geothermal well supplies the motive two-phase steam fluid from the reservoir to the surface fluid collection facility, and then to the separator where steam is separate from brine. The casing of the well is the first equipment that encounters the field’s geothermal fluid. The flow of geothermal brine from the reservoir causes the casing to deteriorate by way of corrosion. The impact of turbulence, corrosion and erosion significantly reduce the integrity of the casing. Thus, monitoring these facilities is vitally important to minimize the risks to geothermal operations. Caliper measurements are taken to monitor the thickness of the casing for safety and environmental concerns. The effective management of a geothermal well necessitates a very thorough knowledge of the extent to which the aforementioned factors contribute to casing degradation. In this paper, the contribution of factors affecting the thinning rate of a geothermal casing, such as temperature, flow velocity, pH, well geometry and corrosion species, was studied. The effects of several corrosive species on casings were also studied. The corrosive species and the factors affecting the thinning rate of the production wells of the Leyte geothermal production field were analysed with multiple linear regression models in order to determine the dependency of the thinning rate on these parameters. Fluid discharge measurements and sampled chemistry concentrations at the surface were simulated at downhole conditions using software HOLA and WATCH. The results were analysed statistically using ANOVA, a P value test, and multiple regression coefficients. Adjusted R2 of the regression analysis and mean absolute percentage error (MAPE) aided in selecting a good regression model. The study showed that fluid discharge characteristics such as temperature, velocity, pH, steam fraction and geometry of the well contribute about 56.71% to the thinning rate of the casing. The predicted thinning rate model also shows similar trending of the average thinning rate compared to the measured thinning rate for the first and second surveys of repeatedly measured wells.
Corrosion is one of the technological problems that geothermal management faces
in the operation of geothermal wells. The primary cause of corrosion in geothermal
wells is exposure to geothermal brine where conductive and convective heat transfer
happens from the reservoir to the surface. The geothermal well supplies the motive
two-phase steam fluid from the reservoir to the surface fluid collection facility, and
then to the separator where steam is separate from brine. The casing of the well is
the first equipment that encounters the field’s geothermal fluid. The flow of
geothermal brine from the reservoir causes the casing to deteriorate by way of
corrosion. The impact of turbulence, corrosion and erosion significantly reduce the
integrity of the casing. Thus, monitoring these facilities is vitally important to
minimize the risks to geothermal operations. Caliper measurements are taken to
monitor the thickness of the casing for safety and environmental concerns. The
effective management of a geothermal well necessitates a very thorough knowledge
of the extent to which the aforementioned factors contribute to casing degradation.
In this paper, the contribution of factors affecting the thinning rate of a geothermal
casing, such as temperature, flow velocity, pH, well geometry and corrosion species,
was studied. The effects of several corrosive species on casings were also studied.
The corrosive species and the factors affecting the thinning rate of the production
wells of the Leyte geothermal production field were analysed with multiple linear
regression models in order to determine the dependency of the thinning rate on these
parameters. Fluid discharge measurements and sampled chemistry concentrations at
the surface were simulated at downhole conditions using software HOLA and
WATCH. The results were analysed statistically using ANOVA, a P value test, and
multiple regression coefficients. Adjusted R2 of the regression analysis and mean
absolute percentage error (MAPE) aided in selecting a good regression model. The
study showed that fluid discharge characteristics such as temperature, velocity, pH,
steam fraction and geometry of the well contribute about 56.71% to the thinning rate
of the casing. The predicted thinning rate model also shows similar trending of the
average thinning rate compared to the measured thinning rate for the first and second
surveys of repeatedly measured wells.
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Ponce 746 Report 30
Well
name
TABLE 4: Sampled gas chemistry of two-phase wells in Leyte geothermal production field
Sampling
date
WHP
Sampling
pressure
Surface concentration (mmol / 100 mol)
H CO2 H2S NH3 He H2 Ar N2 CH4 Na
Well 1 6-May-12 1.01 0.991 1742 610 37.7 0 1.4 0.05 4.5 3.03 25.1
Well 2 20-Aug-12 1.01 0.01 2399 892 38 1.62 0 1.81 0.03 4.08 3.11 54.1
Well 3 29-May-10 1.08 1.06 2265 374 45 1.31 0 0.62 0.02 1.54 0.58 15.1
Well 4 7-Jun-09 1.03 0.95 1822 984 59 41.2 0 2.23 0.54 49.3 3.53 5.32
Well 5 19-Jan-11 1.03 0.87 1558 513 22.4 1.56 0 0.36 0.08 4.44 0.83 40.2
Well 6 23-Aug-10 1.27 1.24 1232 780 25 3.08 0 0.55 0.21 12.2 6.09 708
Well 7 14-Sep-12 1.16 1.082 1078 399 13.2 1.41 0 0.09 0.34 20.7 1.16 290
Well 8 20-Aug-10 1.25 1.16 1441 843 21 1.12 0 0.69 0.06 4.82 1.5 59.5
Well 9 30-Aug-10 1.21 1.06 1222 556 13.2 1.31 0 0.18 0.04 2.8 1.63 143
Well 10 19-Nov-08 1.403 1.393 1088 536 11.6 1.15 0 0.54 0.4 26.8 6.43 1.06
Well 11 23-Jun-12 1.41 1.41 1539 503 23.9 1.38 0 2.14 0.04 3.39 2.09 171
Well 12 10-Feb-11 1.37 1.29 1264 148 15.1 1.56 0 0.12 0.01 0.61 0.05 150
Well 13 29-Oct-11 1.4 1.395 2476 460 38.6 2.05 0 0.42 0.18 13.5 0.28 54.9
Well 14 26-Apr-12 1.19 1.052 1212 183 21.2 1.68 0 0.77 0.17 14.5 0.71 8.28
Well 15 13-Jun-11 1.66 1.4 1409 358 16.8 0.18 0 0.5 0.01 0.99 0.19 35.8
Well 16 25-Jul-12 1.5 1.4 2463 706 26.3 0.86 0 3.06 0.18 17.2 1.14 40
Well 17 11-Jan-12 1.73 1.4 1351 895 20.4 2.46 0 0.16 0 0.32 0.52 45.9
Well 18 26-Aug-10 1.55 1.4 2536 750 23.6 2.92 0 2.63 0.3 24 4.69 13.9
Well 19 23-Jul-12 1.32 1.4 2370 306 35.6 0.53 0 3.66 0.04 2.42 1.06 67.7
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