corrosive species and scaling in wells at olkaria ... - Orkustofnun
corrosive species and scaling in wells at olkaria ... - Orkustofnun corrosive species and scaling in wells at olkaria ... - Orkustofnun
e applied because the steam samples were collected at wellhead separator pressures and the water at the weir box. Case 2: Webre separator on a two-phase pipeline discharging into an atmospheric silencer. The total steam fraction relative to the total discharge is given by the following equation: X a2 = X w + X w−a 5.2.4 Here, X a2 represents the total steam fraction of the well discharge at atmospheric pressure, X w is the steam fraction in the Webre separator and X w-a represents the steam fraction that forms by depressurisation boiling from vapour pressure P w to atmospheric pressure. A portion of the steam is not sampled when using the Webre separator and this fraction is given by X w−a t h = − h L a l, a t h − − h L w 1, w = a w X − X 5.2.5 and L w represent the enthalpies of the steam saturated water at the vapour pressure in the Webre separator and its latent heat of vaporization, respectively. h l, w For correction of gas composition of steam sampled by use of a Webre separator and depressurisation boiling from vapour pressure P w to atmospheric pressure, the following equation was used: X m * X w t w g = m al g 5.2.6 where m w g represents the concentrations of gas in a steam sample collected from the Webre separator. This correction is applicable to steam samples collected from exploration wells, and for steam samples collected before 2001 from wells in the Olkaria North East Field, Olkaria Domes and Olkaria West Fields. The composition of Olkaria well fluids is shown in Table1a of Appendix A and calculated gas concentrations in steam are shown in Table 2a for production wells in Olkaria East and Table 2b of Appendix A for exploration wells in Olkaria North East, Olkaria West and Olkaria Domes. 5.3 Calculation of aquifer water compositions and speciation distribution Component concentrations and aqueous species distribution in the water was calculated with the aid of the WATCH chemical speciation program (Arnόrsson et al., 1982; Bjarnason, 1994), version 2.1A, on the assumption that excess discharge enthalpy was due to phase segregation only and that no equilibrium steam is present in the aquifer. It was further assumed that any phase segregation that has taken place occurs between 180°C and the initial aquifer temperature. For wells in the Olkaria East sector which have a steam separator at the wellhead the calculation involves three steps: Firstly the composition and speciation, including the pH, of the water in the wellhead separator was calculated from the analytical data on the water samples from the weirbox on the assumption that the secondary steam discharged from the atmospheric silencer was free of gas. Secondly, water composition and pH so obtained were used, together with steam analysis data and measured discharge enthalpy, to calculate liquid water and steam composition at 180°C (10 bars abs. vapour pressure). Thirdly, the calculated liquid water and steam composition at 180°C was used to calculate the composition and speciation distribution in the aquifer water taking the fluid enthalpy to be that of steam saturated water at the aquifer temperature, but this temperature was taken to be the average of the tNa/K and tqtz geothermometer temperatures, the latter being consistent with the phase segregation model. 18
The procedure for calculating aquifer water compositions for wells in other sectors than Olkaria East is somewhat different because the two phases of the discharges travel together to the atmospheric silencer. Firstly, the steam composition at atmospheric pressure was calculated from the analytical data in Table 1a of Appendix A taking the steam fraction, which forms by depressurisation boiling between the gas sampling pressure and atmospheric pressure. Steam and water composition was calculated at 180°C using the discharge enthalpy values, the water composition in Table 1a of Appendix A and calculated gas concentrations in the steam phase at atmospheric pressure. The third step is the same as that for Olkaria East wells. The selection of the intermediate step at 180˚C is based on the following considerations: the enthalpy of saturated steam reaches maximum at around 235°C and in the range 180-270°C (10-55 bars-abs. vapour pressure) it has a value close to this maximum but at lower and higher temperatures it drops significantly. As a consequence of this, the steam to water ratio (enthalpy) of a fluid has little effect upon depressurisation of the liquid water in the interval 10-55 bars-abs. Below 10 bars abs. steam formation by depressurisation boiling is enhanced by decreasing steam enthalpy. The opposite is the case above 55 bars-abs. Most of the Olkaria wells have temperatures less than 270°C. The calculation procedure just described to retrieve the component concentrations in the initial aquifer water closely matches the phase segregation model. 19
- Page 1 and 2: GEOTHERMAL TRAINING PROGRAMME Repor
- Page 3 and 4: INTRODUCTION The Geothermal Trainin
- Page 5 and 6: ABSTRACT The Olkaria geothermal sys
- Page 7 and 8: Page 9. CONCLUSIONS ...............
- Page 9 and 10: 1. INTRODUCTION For many countries
- Page 11 and 12: deposition does not occur at depth
- Page 13 and 14: The rate of sulphide precipitation
- Page 15 and 16: the Western Sectors. The Olkaria II
- Page 17 and 18: 46.4 MWe and 125 MWt. A shallow ste
- Page 19 and 20: 3. SAMPLING AND ANALYSIS 3.1 Sample
- Page 21 and 22: 4. FLUID COMPOSITIONS The compositi
- Page 23 and 24: 5. CALCULATION OF AQUIFER FLUID COM
- Page 25: increases the difference in tNaK -
- Page 29 and 30: Concentrations of CO 2 at equilibri
- Page 31 and 32: High concentrations of HCl can be g
- Page 33 and 34: variation in chloride concentration
- Page 35 and 36: A 240°C a steam cap overlies the l
- Page 37 and 38: The solubility of CO 2 in water cha
- Page 39 and 40: where it passes through mist elimin
- Page 41 and 42: Coupon holder loosened the screws a
- Page 43 and 44: Coupon # 20 (Re-injection well): A
- Page 45 and 46: 1900 1800 C #10 Well NJ-14 1700 160
- Page 47 and 48: 0,3 13 Weeks (06-07-2005 to 14-10-2
- Page 49 and 50: 8. EVALUATION OF SCALES DEPOSITED A
- Page 51 and 52: atmospheric pressure. The results d
- Page 53 and 54: The IR spectra of scale samples #1
- Page 55 and 56: 9. CONCLUSIONS Olkaria well fluids
- Page 57 and 58: REFERENCES Allegrini, G., and Benve
- Page 59 and 60: D’Amore, F., Truesdell, A.H., and
- Page 61 and 62: Hurtado, R., Andritsos, N., Mouza,
- Page 63 and 64: Saemundsson, K., and Fridleifsson,
- Page 65: APPENDIX A: Tables with analyses, c
- Page 74: APPENDIX C: Analyses of scales and
The procedure for calcul<strong>at</strong><strong>in</strong>g aquifer w<strong>at</strong>er compositions for <strong>wells</strong> <strong>in</strong> other sectors than Olkaria East<br />
is somewh<strong>at</strong> different because the two phases of the discharges travel together to the <strong>at</strong>mospheric<br />
silencer. Firstly, the steam composition <strong>at</strong> <strong>at</strong>mospheric pressure was calcul<strong>at</strong>ed from the analytical<br />
d<strong>at</strong>a <strong>in</strong> Table 1a of Appendix A tak<strong>in</strong>g the steam fraction, which forms by depressuris<strong>at</strong>ion boil<strong>in</strong>g<br />
between the gas sampl<strong>in</strong>g pressure <strong>and</strong> <strong>at</strong>mospheric pressure. Steam <strong>and</strong> w<strong>at</strong>er composition was<br />
calcul<strong>at</strong>ed <strong>at</strong> 180°C us<strong>in</strong>g the discharge enthalpy values, the w<strong>at</strong>er composition <strong>in</strong> Table 1a of<br />
Appendix A <strong>and</strong> calcul<strong>at</strong>ed gas concentr<strong>at</strong>ions <strong>in</strong> the steam phase <strong>at</strong> <strong>at</strong>mospheric pressure. The third<br />
step is the same as th<strong>at</strong> for Olkaria East <strong>wells</strong>.<br />
The selection of the <strong>in</strong>termedi<strong>at</strong>e step <strong>at</strong> 180˚C is based on the follow<strong>in</strong>g consider<strong>at</strong>ions: the enthalpy<br />
of s<strong>at</strong>ur<strong>at</strong>ed steam reaches maximum <strong>at</strong> around 235°C <strong>and</strong> <strong>in</strong> the range 180-270°C (10-55 bars-abs.<br />
vapour pressure) it has a value close to this maximum but <strong>at</strong> lower <strong>and</strong> higher temper<strong>at</strong>ures it drops<br />
significantly. As a consequence of this, the steam to w<strong>at</strong>er r<strong>at</strong>io (enthalpy) of a fluid has little effect<br />
upon depressuris<strong>at</strong>ion of the liquid w<strong>at</strong>er <strong>in</strong> the <strong>in</strong>terval 10-55 bars-abs. Below 10 bars abs. steam<br />
form<strong>at</strong>ion by depressuris<strong>at</strong>ion boil<strong>in</strong>g is enhanced by decreas<strong>in</strong>g steam enthalpy. The opposite is the<br />
case above 55 bars-abs. Most of the Olkaria <strong>wells</strong> have temper<strong>at</strong>ures less than 270°C. The calcul<strong>at</strong>ion<br />
procedure just described to retrieve the component concentr<strong>at</strong>ions <strong>in</strong> the <strong>in</strong>itial aquifer w<strong>at</strong>er closely<br />
m<strong>at</strong>ches the phase segreg<strong>at</strong>ion model.<br />
19
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