geothermal energy

GEOTHERMAL ENERGYGEOTHERMAL ENERGY

Marianne Salomón

OutlineGeothermal EnergyNature and origin of geothermal energy

Structure of the EarthPlate TectonicsGeothermal AreasEvidence of the Earth's Heat

History of Geothermal EnergyClassification of Geothermal FluidsUtilization of Geothermal Energy

Domestic UsesDomestic UsesBalneologyMineral ExtractionElectrical Power Generation

Geothermal ResourcesGeothermal ResourcesHydrothermal ResourcesGeo-Pressurised ResourcesHot Dry Rock (HDR)MagmaMagmaGeothermal Exploration ProgrammesThermal Gradients and Heat FlowMain Characteristics of Geothermal ReservoirsPresent Status on Geothermal Energy

Renewable Energy Technology Course 2

Present Status on Geothermal EnergyExploration of Geothermal Resources

Drilling And ExtractionHigh temperature wellsR ll bitRoller-cone bitsPDCLow temperature wellsCost of drillingE t ti f fl idExtraction of fluidsWell-testingReservoir modellingDistribution of fluidsR tResource assessmentResource sustainability

Cost of Generating Power from Geothermal EnergyCapital Costs Associated with Geothermal Power GenerationOOperating and Maintenance costs

Problems Associated with Geothermal EnergyEnvironmental Aspects/IssuesMineral depositionHydrological ChangesCorrosionPollutants in geothermal steamGeothermal Waters


Carbon dioxide emissionsReinjection of thermal fluids into the reservoir after useEcological and Environmental Considerations

Geothermal Energy

Definition: geothermal energy is the g gythermal energy stored in the earth’s crust 'Geothermal energy' is oftencrust. Geothermal energy is often used nowadays, however, to indicate that part of the Earth's heat that can orthat part of the Earth s heat that can, or could, be recovered and exploited by man.

(From Mary Dickson and Mario Fanelli. Geothermal energy – Utilization and Technology. 2003)


Earth’s structure


Geothermal energy

Heat passes by p y1. Natural cooling and friction from the

corecore

2 Radioactive decay of elements such2. Radioactive decay of elements such as uranium (U235 and U238), thorium (Th232) and potassium (K40) This(Th232) and potassium (K40). This represents the major source of heat

3. Chemical reactionsRenewable Energy Technology Course 7

Geothermal gradientTemperatures within the Earth's interior increase with depthThe normal temperature gradient p gwithin the Earth's interior is about 2.5~3°C/100 meters2.5 3 C/100 meters Examples of geothermal gradient in different areasdifferent areas

10 – 20 Kkm-1 in shield crust30 60 Kk 1 i l tf30 - 60 Kkm-1 in platform areas>100 Kkm-1 in volcanic areas


Typical Geothermal Gradients


Tectonic Plates


Tectonic Plates Processes


j


Geothermal Areas


Geothermal ReservoirsGeothermal resources have four important characteristics:

A permeable aquifer that contains fluids that is accessible by drilling. An impermeable (nonporous) cap of rock that

t th l fl id f iprevents geothermal fluids from escaping. Impermeable basement rock that prevents downward loss of the fluiddownward loss of the fluid. A heat source need for exploitable geothermal resources.resources.Permeability and porosity of the reservoir rocks.


Geothermal Reservoir


High Heat Flow – Sedimentary


High Heat Flow – Volcanic


Classification of Geothermal ResourcesResources

By typeLow-enthalpyIntermediate-enthalpyHigh-enthalpyHigh-enthalpy

By sourceHot Dry RockLiquid-Dominated HydrothermalVapor-DominatedG i d fl idGeopressurized fluidsMagma


Classification of Geothermal Resources (by type)Resources (by type)

Muffler and

Hoechstein (1990)

Benderitter and Cormy

Nicholson (1993)and

Cataldi(1990) and Cormy

(1990)(1993)

High Enthalpy > 150 > 225 > 200 > 150

Medium 90 – 150 125 – 225 100 – 200 -Enthalpy

Low Enthalpy < 90 < 125 < 100 < 100


High Enthalpy Areas


Classification of Geothermal Resources (by source)Resources (by source)Liquid-dominated resources

Th th t f thThese are the most commons of the hydrothermal resources. In a liquid-dominated resource the water is thedominated resource the water is the continuous phase. It can be present as vapour but also as bubbles. Depending on th t t d th ithe temperature and pressure there is more or less vapour.

The pressure in these resources is fairly low typically 0.5-1 MPa and the temperature istypically 0.5 1 MPa and the temperature is around 180 °C.


Classification of Geothermal Resources (by source)Resources (by source)Vapour-dominated systems

liquid water and vapour normally co-exist in the yreservoir, with vapour as the continuous, pressure-, pcontrolling phase.

Geothermal systems of this type, the best-known of which are Larderello in Italy and Th G i C lif i h tThe Geysers in California, are somewhat rare, and are high-temperature systems. They normally produce dry to superheated


They normally produce dry-to- superheated steam.

Classification of Geothermal Resources (by source)Resources (by source)Geopressurized fluids

G i d th l t h t tGeopressurised geothermal systems are hot waterreservoir (aquifer) mixed with dissolved gases likemethane that can reach 200C and are under hugegpressures (50-100 MPa). The depth ranges from 3–6 km, and are normally located in sedimentaryformationsformations.

The resource can be exploited for their thermalThe resource can be exploited for their thermalenergy, calorific energy of gases and hydraulicenergy due to high pressure. The price of electricity

t d b i d fl id i tgenerated by geopressurised fluids is notcompetitive when compared with conventionalresources.


resources.

Classification of Geothermal Resources (by source)Resources (by source)Hot Dry Rock (HDR)

P j t i t d f th fi t ti t LProjects were experimented for the first time at Los Alamos, New Mexico, USA, in 1970, both the fluid and the reservoir are artificial. High-pressure water is pumped through a specially drilled well into a deep body of hot, compact rock,

i it h d li f t i Th tcausing its hydraulic fracturing. The water permeates these artificial fractures, extracting heat from the surrounding rock, which acts as a natural o e su ou d g oc , c ac s as a a u areservoir. This 'reservoir' is later penetrated by a second well, which is used to extract the heated waterwater. The system therefore consists of (i) the borehole used for hydraulic fracturing, through which cold


used for hydraulic fracturing, through which cold water is injected into (ii) the artificial reservoir, and (iii) the borehole used to extract the hot water.

Schematic of a commercial-scale Hot Dry RockHot Dry Rock

Developments in France, Australia, Japan, the U.S. and Switzerland. The biggest HDR project is currently installed in Australia.


Classification of Geothermal Resources (by source)Resources (by source)Magma

These resources offer extremely high-temperature geothermal opportunities, butp g pp ,existing technology does not allow recoveryof heat.

However in the future there might beHowever, in the future there might beavailable them the technology required toexploit these resources and thus mightexploit these resources, and thus mightbecome an important resource of energy


TerminologyResource Base

all of the thermal energy contained in the earth’s crust, whether its existence is known or unknown and regardless of cost considerations

Accessible Resource BaseAccessible Resource BaseAll of the thermal energy between the earth’s surface and a specific depth in the crustsurface and a specific depth in the crust beneath a specified area and referenced to a mean annual temperature


Resource Base EstimatesResource type Total Q [1021 J]

Hydrothermal 130

G i d 540Geopressurized 540

Magma 5’000g

Hot Dry Rock 105’000

Moderate to high grade (T > 40°C/km)

26’500

Low grade (T > 40°C/km) 78’500

Renewable Energy Technology Course 29*For depths of 10 km

TerminologyResource:

Thermal energy that could be extracted at cost competitive with other forms of energy at a f bl ti d bl tiforeseeable time, under reasonable assumptions of technological improvement and economic favorabilityfavorability

ReserveTh t t f th th l th t iThat part of the geothermal resource that is identified and also can be extracted at a cost competitive with other commercial energycompetitive with other commercial energy sources at present.


Depth vs. Temperature


ExplorationThe main objectives of geothermal exploration are:1 T id tif th l h1. To identify geothermal phenomena.2. To ascertain that a useful geothermal production field

exists.3. To estimate the size of the resource.4. To determine the type of geothermal field.5 To locate productive zones5. To locate productive zones.6. To determine the heat content of the fluids that will be

discharged by the wells in the geothermal field.7 To compile a body of basic data against which the results7. To compile a body of basic data against which the results

of future monitoring can be viewed.8. To determine the pre-exploitation values of

i t ll iti tenvironmentally sensitive parameters.9. To acquire knowledge of any characteristics that might

cause problems during field development.


Strategies for Assessment of Geothermal ResourcesGeothermal Resources

SURVEYSOn national, local and site-scale,Key parameters: temperature, permeability, volume, existing infrastructure

Inventory hot springs, temperature in drill holes

Satellite imagery and aerial photographySatellite imagery and aerial photography

Geological and hydrological StratigraphyGeological and hydrological Stratigraphy, Lithology porosity

permeabilityS


Structure modelling 33

Strategies for Assessment of Geothermal ResourcesGeothermal Resources

Geochemical chemistry of natural waterGeochemical chemistry of natural water

Geophysical subsurface structure Gravity (porosity)S i i ( )Seismics (structure)Magnetic (structure, temperature)Electric (porosity)Electromagnetic (porosity)modelingmodeling

Exploratory wells confirmation of modelsMeasurements electric resistivity

other physical propertieschemistry of ground water


chemistry of ground water flow testsfracturing tests 34

Exploration programmeIt consist of 3 steps:

reconnaissance, pre-feasibility and f ibilitfeasibility

Th i bj ti i t li i t lThe main objective is to eliminate less interesting areas and concentrate I the most promising onespromising ones.The size and budget of the entire programme should be proportional to itsprogramme should be proportional to its objectives, to the importance of the resources we expect to find, and to the


resources we expect to find, and to the planned forms of utilization.

Utilization of Geothermal EnergyEnergy

DIRECT USE C li 0 20 °CDIRECT USE Cooling 0 – 20 °CHeating Low temperature 25-35 °C

High temperature 70 –110 °Cg pHot water production

COMBINED USE Cooling – heating (seasonal storage systems)Heating – electricity

INDIRECT USE Electricity low temperature 70-100 °CINDIRECT USE Electricity low temperature 70 100 CHigh temperature 100 – 200 °C


Energy Use


Geothermal Utilization in the World for Electricity Generation and Direct Heat UsesElectricity Generation and Direct Heat Uses


Geothermal Power Generation


Installed Geothermal Energy in Europe (1999)Europe (1999)

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Potential Power Production

biogas

biofuel

biomass

wind

geothermal

biogasminmax

hydro

solar

0 100 200 300 400 500 600 700 800

[TWh/a]


Potential Final Energy

biofuel

biomass

i d

geothermal

biogas present useminmax

hydro

solar

wind max

0 50 100 150 200 250 300

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[TWh/a]


AdvantagesIts reserves are enormous- virtually i fi it hi t i l linfinite on historical scale.It is less polluting than combustible f l lfuels or nuclear energy. It is an indigenous resource that can b d l d d k tbe developed and make a country less reliant politically and economically and can alleviate theeconomically and can alleviate the national balance of payments. As a rule of thumb; one kilowatt ofrule of thumb; one kilowatt of geothermal base load can substitute about 2 tons of oil annually.


about 2 tons of oil annually.

Advantages

It is highly versatileg yUnlike hydropower it is not subject t th i ti f th thto the variations of the weather.It is not labour intensive Once theIt is not labour intensive. Once the exploitation of geothermal energy is

t bli h d it i th lestablished; it is thus less vulnerable to disputes such as say p ystrikes in coal mining.


Disadvantage

There are no many places on the earth y phighly suitable for exploit. Most suited areas are on edges of the tectonicareas are on edges of the tectonic plates, namely areas of high volcanic and tectonic activityand tectonic activity. expensive explorationbrines are corrosive and poisonouscomplicated reservoir managementcomplicated reservoir managementsensitive to underground disturbances


g

SustainabilityThe earth radiogenic heat productionand average heat flow

are insufficient to sustain geothermal energy retrieval over very long time periods.

Geothermal energy uses the stored heat in the uppermost crustal regions (to ca 5 km depth), accumulated over a very long period of heat diffusion and warming.

Geothermal energy retrieval results in long term slow cooling of the heat exchange region at reservoir depth.

Depending on flow rate and re injection temperature a two hole exchangeDepending on flow rate and re-injection temperature, a two hole exchange system with ca 1.5 km spacing is calculated to last ca 20 years.

After that period adjacent volumes can be explored. In the exhausted volume gradually ambient temperatures will be re establishedgradually ambient temperatures will be re-established.

Heat exchange volumes may gradually degrade by poor reservoir management, precipitation of minerals in the flow paths, compaction of

h t d lRenewable Energy Technology Course 48

exhausted volumes, …

SustainabilityThere are some important exceptions to the stated situations:

In volcanic and sub-volcanic regions (occurrence of recent intrusive rocks at depth) extremely high heat flows can provide sustainability over very long time periodsy y g p

If heating requirements can be balanced with cooling requirements over the seasonal cycle q y

Increased sustainability can be achieved by low temperature drop, low temperature heating systems or energy cycles, and g y gy yproper reservoir management.

Environmental sustainability requires closed systems for the heat exchange (re-injection of extracted ground water).

The best energy is the energy not used


Environmental ImpactsThe most important issues regarding geothermal energy are:

Land Used Disposal of Drilling FluidsNoiseGround subsidenceNon-Condensable Gas Emissions and Air PollutionInduced SeismicityEffluent Disposal and Water Pollution


p

Environmental issuesKey issues: Air pollution, water pollution, noise

Dissolved in natural water CO2 , H2S (oxidises to SO2 and finally H2SO4), N2, Rn (from uranium containing rocks, radioactive decay products emit -radiation) NH B Hgradioactive decay products emit -radiation), NH3, B, Hg, HgS,3H (age indicator)

C t i d i t CO2 H S HCl HF NH CH HContained in steam CO2, H2S, HCl, HF, NH3, CH4, H2.

From added energygyWhen produced by combustion (of oil, gas, biomass…)

CH4HH2CO2NOx causes ozone formation in lower

t hRenewable Energy Technology Course 51

atmosphere

Environmental issuesGround water pollutionFrom system leakage NH3 (in case of low temperature energy y g 3 ( p gycycles)

From brinesWh di h d i t t l tWhen discharged into natural waters

Cl- , F- , Br-, I-SO4

2-

HCO -HCO3Ca2+ Mn2+ , Fe2+,Na+, K+ , Li+ , Rb+ , Cs+,SiO NH As B noble gasesSiO2, NH3, As, B, noble gases

Re-injection should always be practicedLand subsidenceLand subsidence

from withdrawal of fluidsInduced seismicity

Low level earthquakes from withdrawal and re-injection of fluids

Renewable Energy Technology Course 52NOISE

during drilling operations and pump testing

Comparison of CO2 Emissions from Electricity Productionfrom Electricity Production


Local Emissions from District Heating SystemHeating System

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Fuel Oil Plants

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Investment Cost of Typical PhasesPhases

M€


Risk Management


Field Cost Typical Breakdown


Plant Cost Typical Breakdown (55 MW)MW)


Drilling Cost in Europe versus Well DepthWell Depth


EU incentivesTo stimulate the creation of European consortia and joint venturesTo favour National Geothermal Associations, and the European Branch of IGATo support the newly created EGEC (European Geothermal Energy Council)(European Geothermal Energy Council)The maintenance and improvement of the EU’s existing research and financingEU s existing research and financing programmes,


EU incentivesTo promote the environmental benefits of geothermal energy through favourable financing condition such as:

tax exemptions or reductions for RE products;tax incentives to be addressed to geothermal projects financingfinancial incentives for end-users to buy

i d iequipment and servicesloans and special interest rates devoted to i t t i RE i linvestments in RE resources in general.


EU incentivesGeothermal energy should be included in

ifi "t t j t " d d t tispecific "target projects" and demonstration projects such as the European Green Cities. Examples of special target projects couldExamples of special target projects could be:

partial or total replacement of fossil fuels bypartial or total replacement of fossil fuels by geothermal energy for the generation of electricity in the Azores, the Greek islands, as

ll It l ’ ll i l d d th C iwell as Italy’s small islands and the Canaries technical and financial support for demonstration projects in the use of medium temperatureprojects in the use of medium temperature geothermal water for electricity production using binary fluids.


EU incentivesTo establish an insurance system for EU countries in order to cover the geological risk which is anin order to cover the geological risk which is an effective measure to stimulate and re-launch the geothermal European market and improve the exploitation of this renewable resourceexploitation of this renewable resource. Implement proper actions devoted to the systematic integration of geothermal energy into existing and ne EU and national RE de elopmentnew EU and national RE development programmes. This action should move in two directions:

integration of geothermal energy in national and regional New and Renewable Energy development programmes integration of geothermal energy use in the development of

di t i t h ti t d th h bilit ti fnew district heating systems and the rehabilitation of existing networks within EU countries and especially in countries which could become associated in the near future.


future.

EU incentives

Promote directives in order to acknowledge RE investments with an extra price or a contribution for theextra price or a contribution for the KWhe/KWht produced → tax (green tax) charged on the KWhe/KWhttax) charged on the KWhe/KWht produced through conventional sources.


geothermal energy

Documents

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geothermal systems

geothermal energydefinition

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g gy thermal energy