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Numerical simulation of the Alum lakes geothermal outflow

Numerical simulation of the Alum lakes geothermal outflow. J. Newson and M. J. O’Sullivan. BACKGROUND. Part of a study on simulation of geothermal surface features If water is taken by geothermal wells, is there less for the springs? What about heat? Is this important?

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Numerical simulation of the Alum lakes geothermal outflow

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  1. Numerical simulation of the Alum lakes geothermal outflow J. Newson and M. J. O’Sullivan

  2. BACKGROUND • Part of a study on simulation of geothermal surface features • If water is taken by geothermal wells, is there less for the springs? • What about heat? • Is this important? • Used data from Alum Lakes, Wairakei

  3. TAUPO VOLCANIC ZONE

  4. WAIRAKEI-TAUHARA

  5. ALUM LAKES

  6. CONCEPTUAL MODEL

  7. Pirorirori (Alum Lake) • Ceased flowing in late 1990’s • Photo taken Nov 2004

  8. AVAILABLE DATA • Mass flow (including streamflow) • Temperature • Chemistry • Water level (recent)

  9. 3 SPRINGS WITH DATA Pirorirori

  10. RESERVOIR SIMULATION • Simulator that represents heat and mass flow in porous and fractured media (rocks) • Two phase (steam, water, water vapour, and air) TOUGH2

  11. RESERVOIR SIMULATION: GRID Design a 2-D or 3-D block structure that will represent the system:

  12. VERTICAL SECTION Alum Lakes 0 mrsl Te Mihi Western Borefield Eastern Borefield

  13. DETAIL, 2-D GRID

  14. RESERVOIR SIMULATION: PARAMETERS Give each block properties such as permeability, porosity, thermal conductivity… SURFACE FOLLOWS TOPOGRAPHY Pirorirori Butterfly Spring Lower Devil’s Eyeglass

  15. RESERVOIR SIMULATION: B.C.’s 10% AV. ANN. RAINFALL Assign boundary conditions: SIDE BOUNDARIES CLOSED HOT WATER HEAT

  16. RUNNING A RESERVOIR SIMULATION • Simulator calculates the temperature and pressure at the centre of each block • T & P differences lead to flows between blocks • Control the flows by changing the permeability and porosity in each block

  17. RESERVOIR SIMULATION TELLS US: • If the hypothesis is possible • Possible permeability, porosity distribution • Information about the subsurface flow paths • Information on the future behaviour of the system

  18. NATURAL STATE MODEL • Reservoir temperature vs depth for Wairakei before production (1953) • the mass flow data for Alum Lakes

  19. NATURAL STATE MODEL Alum Lakes: mass flow data (kg/s) Eastern Borefield

  20. PRODUCTION PERIOD MODEL • Use the natural state model as a starting point for production simulation • Check the response of the Alum Lakes in the model, compare with known fiels data (mass flow over time) • Production enthalpy, and reservoir pressure for the Wairakei borefields

  21. Eastern Borefield PRODUCTION HISTORY Western Borefield Enthalpy time history Reservoir pressure time history

  22. ALUM LAKES MASS OUTFLOW

  23. NATURAL STATE LIQUID FLOWS PIRORIRORI BUTTERFLY SPRING LOWER DEVIL’S EYEGLASS

  24. NATURAL STATE GAS FLOWS PIRORIRORI BUTTERFLY SPRING LOWER DEVIL’S EYEGLASS

  25. 1975 LIQUID FLOWS PIRORIRORI BUTTERFLY SPRING LOWER DEVIL’S EYEGLASS

  26. 1975 GAS FLOWS PIRORIRORI BUTTERFLY SPRING LOWER DEVIL’S EYEGLASS

  27. 2003 LIQUID FLOWS PIRORIRORI BUTTERFLY SPRING LOWER DEVIL’S EYEGLASS

  28. FINAL PERMEABILITY STRUCTURE

  29. NEW CONCEPTUAL MODELNATURAL STATE

  30. CONCEPTUAL MODEL2003

  31. SUMMARY • Behaviour of Alum Lakes Flows linked to reservoir changes • Low permability zones control the shallow subsurface flow • Groundwater now flows down into the reservoir • Groundwater diverted from Alum Lakes springs, and from flowing further eastward

  32. FUTURE WORK • Model chloride component • Model the water level change

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