1. INVERSE (ITOUGH2) MODELING THE PAUZHETSKY GEOTHERMAL FIELD, KAMCHATKA, RUSSIA A.V. Kiryukhin 1, N.P. Asaulova 2, S. Finsterle 3, T.V. Rychkova 1, L.A. Vorozheikina 2, and N.V.Obora 2 1 - Institute of Volcanology and Seismology FEB RAS 2 - Kamchatskburgeotermia Enterprize 3 - Lawrence Berkeley National Laboratory

2. Pauzhetsky Geothermal Field Input Data for Modeling, Grid Generation Content: Modeling Natural State Conditions Modeling of Exploitation iTOUGH2 Conclusions

3. Pauzhetsky Geothermal Field

4. The Pauzhetsky geothermal field has been developed since 1966, when a 5 MWe power plant was put into operation. Photo by V.M. Sugrobov, 1985

5. The first reservoir engineering study of this field conducted by V.M. Sugrobov (1965) revealed a liquid dominated reservoir with layer type tuffs formed at 170-190oC, with hot springs discharges at 31 kg/s.

6. The lumped parameter model by V.M. Sugrobov (1976) yielded 460 kg/s lateral high temperature outflow from the Kambalny ridge into the geothermal reservoir. Nevertheless, the initial 10 years of the exploitation at 160-190 kg/s shows gradual temperature decline and chloride dilutions of the production wells located near the natural discharge area, so new exploration wells were drilled, and exploitation gradually shifted away from the natural discharge area until 200-220oC were reached. Wells were drilled into central upflow zone located 1.5-2.0 km southeast from the old production field (V.A. Yampolsky, 1976).

7. The drop in temperatures and enthalpies continued, while total flow rate reached 220-260 kg/s between 1975 and 2005.

8. The forward TOUGH2 modeling of the field conducted by A.V. Kiryukhin and V.A. Yampolsky (2004) yielded the following estimates of the principal reservoir parameters: (1) an upflow rate of 220 kg/s with enthalpy of 830-920 kJ/kg, (2) A permeability-thickness of 70 D*m in the central part of the field, and compressibility of 5.0 10-7 Pa-1, (3) A fracture spacing of 162 m and fracture/ matrix ratio of 0.1 for double-porosity model, and (4) the existence of constant pressure boundaries. In this study, iTOUGH2 was used for parameter estimation. Nevertheless, the sustainable capacity of the Pauzhetsky field became a critical question for power plant reconstruction and new binary technology implementation, and a more detailed calibration study of the reservoir parameters was needed.

9. TOUGH2, iTOUGH2

12. Input Data for Modeling, Grid Generation

13. The current numerical model (mesh has 424 elements (294 active)) represents 3-layer system (caprock, reservoir of 500 m thickness, basement rocks with interior upflow zone) with external recharge discharge boundaries. Discharge zone Hydrothermal reservoir Caprock Basement with upflows feed zones

14. Double porosity reservoir model used: reservoir include fracture space and matrix space. Double porosity parameters: Fracture Volume assigned 0.3, Fracture Spacing FS assigned 160 m – according to wells logging data.

15. Caprock domains include natural discharge area domains (domains capr1, cap_1, ca__1) and Impermeable caprock domains (capr2).

16. Hydrothermal reservoir located at -250 masl and include domains with different permeabilities

17. Basement layer located at - 750 masl and include high temperature upflow zone and host impermeable rocks.

18. Modeling Natural State Conditions

19. For the iTOUGH2 natural state modeling, calibration data include 70 points (2 natural discharge rates, 16 reservoir pressures at -250 m.a.s.l., 52 reservoir vertically averaged temperatures). The different quality of the calibration points was expressed by specifying appropriate standard deviations.

20. Temperature matches: Actual temperatures shown as numbers (52 calibration points), modeling temperatures are shown as isotherms.

21. Pressure matches: Actual (calculated from levels and T- logs) pressures shown as numbers (16 calibration points), modeling pressures shown as isobars.

22. Pressures and Temperatures Matches in 68 calibration points

23. Upflow rate 41  5 kg/s with enthalpy 950-1050 kJ/kg Permeability-Thickness= 83 mD * 500 m [62-107] Preliminary estimates of the principal reservoir parameters are: (1) Permeability-thickness of 42 D*m in the central part of the field, and (2) an upflow rate of 40.5kg/s with enthalpy of 950-1050 kJ/kg.

24. Modeling of the Exploitation

25. Kamchatskburgeotermia Wells Flowrates and Enthalpies Measurements

26. For the iTOUGH2 exploitation modeling, calibration data include 18 transient data sets (enthalpies in 10 exploitation wells, pressures in 8 monitoring wells). We have additional data sets For model calibration (pressures In 17 monitoring wells and temperatures in 25 monitoring wells). The different quality of the calibration points was expressed by specifying appropriate standard deviations.

27. Model calibration: Exploitation wells flowing enthalpy matches

28. Model calibration: Pressure monitoring wells matches.

29. Why this model is not able to explain enthalpy drop in exploitation wells?

30. iTOUGH2 exploitation calibration modeling - 2-nd run. The different quality of the calibration points was expressed by specifying appropriate standard deviations.

31. Model calibration: Exploitation wells flowing enthalpy matches (2-nd try)

32. Model calibration: Pressure monitoring wells matches (2-nd try).

33. Modeling of the exploitation phase using iTOUGH2 is still on-going. The principal parameters estimated include: (1) reservoir compressibility 7.17e-7 Pa-1, (2) (2) fracture volume porosity 0.54 and (3) caprock permeability in downflow recharge zones 60-400 mD. C=7.17e-7 Pa-1  f =0.54 60-400 mD

34. Mass and Heat balances derived from the model:

35. iTOUGH2 estimates Monitoring System Sensitivity

36. Conclusions The sustainable capacity of the Pauzhetsky field became a critical question for power plant reconstruction and new binary technology implementation, and a more detailed calibration study of the reservoir parameters was performed based on iTOUGH2 applications to 3D reservoir model. iTOUGH2 application to existing numerical model of the field yield revision of conceptual model, re-estimations of the mass-flow balances and principal reservoir parameters: permeability-thickness, upflow rate, compressibility and double porosity parameters. Modeling of the exploitation phase using iTOUGH2 is still on-going. Gas and chemistry of fluids transient data will be also used for model calibration. The next modeling application is to optimize future exploitation (including Analysis of reinjection effect and possibilities of new binary technologies use) and to forecast exploitation reserves for the following 25 years.

37. Conclusions 2: We are ready to develop the heat and mass transfer model of Bezymyanny volcano, If someone will drill enough monitoring and production wells around and give us corresponding P-T, flowrate and enthalpy data sets to be used as input data for 3D reservoir model calibration. Appreciated to E.P. Belov, M.F. Krasnoperov (Kamchatskburgeotermia Board) and V.D. Evseenko, A.A. Zakharov (Geological Department) for support of this study. Acknowledgements: