numerical simulation of the alum lakes geothermal outflow j. newson and m. j. o’sullivan
TRANSCRIPT
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Numerical simulation of the Alum lakes geothermal outflow
J. Newson and M. J. O’Sullivan
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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
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TAUPO VOLCANIC ZONE
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WAIRAKEI-TAUHARA
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ALUM LAKES
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CONCEPTUAL MODEL
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•Pirorirori (Alum Lake)
•Ceased flowing in late 1990’s
•Photo taken Nov 2004
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AVAILABLE DATA
• Mass flow (including streamflow)
• Temperature
• Chemistry
• Water level (recent)
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3 SPRINGS WITH DATA
Pirorirori
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RESERVOIR SIMULATION
• Simulator that represents heat and mass flow in porous and fractured media (rocks)
• Two phase (steam, water, water vapour, and air)
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RESERVOIR SIMULATION: GRID
Design a 2-D or 3-D block structure that willrepresent the system:
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VERTICAL SECTION
Alum Lakes
Eas
tern
Bo
refi
eld
Wes
tern
Bo
refi
eld
Te
Mih
i
0 mrsl
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DETAIL, 2-D GRID
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RESERVOIR SIMULATION: PARAMETERSGive each block properties such as permeability,
porosity, thermal conductivity…
SURFACE FOLLOWS TOPOGRAPHY
Pirorirori
Butterfly Spring
Lower Devil’s Eyeglass
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RESERVOIR SIMULATION: B.C.’sAssign boundary conditions:
10% AV. ANN. RAINFALL
HEATHOT WATER
SID
E B
OU
ND
AR
IES
CLO
SED
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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
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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
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NATURAL STATE MODEL
• Reservoir temperature vs depth for Wairakei before production (1953)
• the mass flow data for Alum Lakes
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NATURAL STATE MODEL
field model
Pirorirori 11.3 11.91
Butterfly Spring
7.5 7.68
Lower Devil’s Eyeglass
1.6 2.07
Alum Lakes: mass flow data (kg/s)
Eastern Borefield
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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
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PRODUCTION HISTORYEastern Borefield Western Borefield
Enthalpy time history
Reservoir pressure time history
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ALUM LAKES MASS OUTFLOW
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NATURAL STATE LIQUID FLOWS
PIRORIRORI
BUTTERFLY SPRING
LOWER DEVIL’S EYEGLASS
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NATURAL STATE GAS FLOWS
PIRORIRORI
BUTTERFLY SPRING
LOWER DEVIL’S EYEGLASS
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1975 LIQUID FLOWS
PIRORIRORI
BUTTERFLY SPRING
LOWER DEVIL’S EYEGLASS
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1975 GAS FLOWS
PIRORIRORI
BUTTERFLY SPRING
LOWER DEVIL’S EYEGLASS
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2003 LIQUID FLOWS
PIRORIRORI
BUTTERFLY SPRING
LOWER DEVIL’S EYEGLASS
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FINAL PERMEABILITY STRUCTURE
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NEW CONCEPTUAL MODELNATURAL STATE
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CONCEPTUAL MODEL2003
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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
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FUTURE WORK
• Model chloride component
• Model the water level change