Introduction To Geothermal Energy - University Of Auckland

Introduction toGeothermal EnergySummer School in Energy Economics2019Bart van Campen1

Introduction to Geothermal Energy:1.2.3.4.5.BasicsResources and locationsEnd-usesElectricity generation technologiesCosts and sustainability2

1.Geothermal BasicsGeothermal Greek wordsgeo (earth)therme (heat)Geothermal system:A system of processes involving heattransfer to the earth’s surface3

1. Geothermal:* Earth’s interior heat; @6,000 kmdeep: 5,000 C*All around the world heat flows tothe surface (av. 65mW/m2 temperature gradient of 30oC/km(depending on the thermal conductivity of the rock).*In geothermal areas(at plate boundaries etc)heat flow is much greater than65mW/m24

1. Heat Transfer:ooConducts rockHigh temp/pressure:omantle rock melts and becomemagmaoLighter/less dense than surroundingrockoMove slowly toward the earth’s crust5

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1. Heat TransferoooMagma may remain below the crustoIf it reaches the earth’s surface:Heating nearby rock and waterGeothermal water travels back upthrough faults and crackssprings/geysersoOr trapped in cracks and porous rock(geothermal reservoir)7

** Conduction: heat flows from a hot temperature rock to a cold temperature(no fluid movement) ; Heat flow conductivity x temperature gradient* Convection: in hot geothermal systems there is a large scale movement ofwater (convection), with hot water (&heat) rising. Heat flow mass flow x enthalpy ; requires pathways for water to move( PERMEABILITY)* Counter-Flow: in some geothermal systems there is a boiling zonecontaining water and steam: water trickles down and steam rises.* Heat flow steam rising – water trickling downTransfers heat (even though it may not transfer much mass) because theenthalpy of steam is higher than the enthalpy of water. Also requirespathways (permeability)8

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Geothermal Power:MidAmerican Energy Geothermal PlantVirtual Tour (4.46 mins)www.youtube.com/watch?v FKXcLa88GhQEnergy 101: Geothermal Energy (3.47 mins)www.youtube.com/watch?v mCRDf7QxjDk13

SO needed for a Geothermal System:Heat sourceWater (recharge inflowing; discharge outflowing water)Permeability structure14

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1. Russia, 2. Japan, 3. Eastern China, 4. Himalayan, 5. The Philippines, 6. Indonesia, 7. NewZealand, 8. Canada, 9. United State, 10. Mexico, 11. Central American Volcanic Belt, 12.16Andean Volcanic Belt, 13. the Caribbean, 14. Iceland,15. Northern Europe, 16. Eastern Europe,17. Italy, 18. Eastern and Southern Mediterranean, 19. East Africa Rift System

New Zealand’s firstgeothermalgenerator wascommissioned atWairakei in 195817

*Geothermal resources located in Environment Waikato boundaries18

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The idea:*Drill two wells*Use hydraulic-fracturing to create a permeablezone connecting the wells*Pump cold water down one well and producehot water from the other*Many problems: no-one has got it working well*Esp right distribution of fractures20

* A geothermal reservoir is quite different from an oil or gas reservoir, oreven a ground water reservoir.* A geothermal reservoir is usually not a clearly defined highly permeableregion confined by low permeability strata.* The quantity to be extracted, namely heat energy, is not containedentirely/mostly in the reservoir fluid (but in the rock).* The production of water and steam from a geothermal well is replaced inthe reservoir by surrounding cooler water which is heated by the reservoirrock and then becomes available for production.* This process of recharge is very important in the behaviour of geothermalreservoirs. I.e (possibly) sustainable* In convective geothermal systems the fluid is moving. In an oil reservoir thefluid is stationary. In an oil reservoir, once the oil has been extracted thereservoir is exhausted.21

3. Geothermal Uses:oooooooElectricityHot springs/bath, cooking, medicineHeat buildings (ground source heat pump)District heatingAgriculture: glass houses (plants)Aquaculture: fish/shrimp farmingIndustry: pulp&paper production,foodprocessing, pasteurize/dry milk22

LindalDiagram23

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Heat Pump system:25

Heating systemsin geothermalgreenhouses:26

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Value of Geothermal Features:Craters of the Moon (Taupo)28

4. Geothermal Electricity Generation:Production wellsNatural steamTurbine generatorCondensed in cooling towerReinjection29

4. Dry steam plant generation30

4. Flash steam plant31

4. Binary plant32

--5. Geothermal SustainabilityMany similarities to Oil&GasBut renewable/sustainable (if donewell)Source regenerates (in humantimeframes)Low CO2-content (generally)33

5. Geothermal Sustainability:a) External Impacts/effects:Pressure/Temp changes affectsgeothermal features, subsidenceb) Resource itself:-Often faster draw-down than regeneration controlled depletion (50-100 yrs)- NZ conserves other resources/fields forfuture generations34

5. Example Sustainability:Wairakei: 100-200 years to recover after 100years of extraction35

--5. Geothermal RegulationSimilar issues as Oil/Gas RegulationUnderground resource step-wiseexplorationOwnership/access to resourceEnvironmental aspectsFinancial viability (incl power prices& royalties/subsidies)36

1.2.3.4.5.6.Start-up & pre-explorationPre-feasibilityExploration & Appraisal drillingProduction drillingProduction & processingDecommissioning & rehabilitation Resource Assessment and Economic go/no-go decisions afterevery step

Source: WB Geothermal Handbook, 2012

--5. NZ Geothermal Regulation slightlydifferent:Based on water & common law: statedoesn’t own the resourceGovernment manages the resource onbehalf of ‘common good’Resource Management Act (1991)Puts Sustainable Management at theCentre:- External effects; and- Resource available for ‘future generations’41

Wai O Tapu Loop Rd (Rotorua) CThank YouQuestions?42

21 *A geothermal reservoir is quite different from an oil or gas reservoir, or even a ground water reservoir. *A geothermal reservoir is usually not a clearly defined highly permeable region confined by low permeability strata. *The quantity to be extracted, namely heat energy, is not contained entirely/mostly in the reservoir fluid (but in the rock).