GEOTHERMAL POWER

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GEOTHERMAL POWER Ken Williamson General
Manager, Geothermal Technology
Services, Unocal Corporation WORKSHOP ON
SUSTAINABLE ENERGY SYSTEMS November 29 - December
1, 2000 Georgia Tech, Atlanta, GA
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Heat in the Earth (Rybach et al., 2000)

• Stored in the earth 1031 J
• Beneath continents (lt1km) 4.1026J
• Current Annual Usage 4.1020J

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Geothermal Power Worldwide

• 8 GWe in 21 nations
• 50 TWh generated in 1999
• In the last 5 years
• Worldwide increased by 17
• U.S. decreased 20

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Geothermal Power in U.S.0.38 of Countrys
Generation

• California 2,294 MW
• Nevada 196 MW
• Hawaii 25 MW
• Utah 31 MW
• TOTAL 2,400 MW

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HIGH ENTHALPY FIELDS PROSPECTS
Pacific Ring of Fire
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Exploration Oil seep analogy
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Geothermal Fields Developed by Unocal
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Geothermal BasicsExtracting the Heat Commercially

• Water transports heat to surface
• Naturally fractured rock permits circulation
• Drill to reach at least 200 C
• Future technology may use man-made fractures

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GEOTHERMAL RESOURCE TYPES

• Liquid-dominated
• Vapor-dominated

• Low Enthalpy
• Hot Dry Rock

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Example Vapor-Dominated High Enthalpy Resource
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Unocal at The Geysers 1967 -1999
380 wells drilled2.5 trillion lbs steam
produced124 billion kWh generated186 million
bbl oil equiv.
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Example Liquid-Dominated High Enthalpy Resource
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Unocal 330 MW in Java, Indonesia Liquid-dominated
225 - 310º C 1 - 3 km deep
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CROSS-SECTION THROUGH AWIBENGKOK FIELD
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(No Transcript)
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During Project Life Produce gt10 12 lbs
steam Inject 16 billion bbl brine
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Turbine and Generator
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Proposed Research Timeline2000 - 2030

• Optimize exploited geothermal systems
  reduce development cost of high enthalpy
  systems
• Locally enhance permeability in the tight margins
  of existing systems (EGS)
• Explore for and develop hidden high enthalpy
  systems, with no surface features
• Develop impermeable systems with artificial
  fracturing (HDR)
• -----gt Time

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Optimize exploited geothermal systems
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Life Cycle of a Geothermal Field (Lovekin, 1998)
develop
maintain
decline
sustain
MW
Time ----gt
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Opportunity

• Only a fraction (20) of available heat is
  currently extracted from a high enthalpy
  reservoir
• Smart injection management could greatly increase
  efficiency and longevity
• The Salak natural laboratory presents a unique
  opportunity to examine fractured-system behavior

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Challenge

• Reservoirs have km-scale fracturing
• hard to map permeability at km-scale
• heat transfer properties poorly known
• current models inadequate
• Injected liquids are channeled along fractures
  and heat sweep is inefficient

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Research Characterize permeability and heat
transfer in fractured systems
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Image Log Salak Well FMI
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Salak Tracer pathways
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Tracer Returns at Salak
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Proposed Research Designer tracer cocktails

• average path temperature
• maximum path temperature
• surface contact area along flow path

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SALAK NUMERICAL MODEL FEATURES
NORTHERN OUTFLOW
SHALLOW EASTERN RESERVOIR
WESTERN OUTFLOW
DEEP WESTERN RESERVOIR
SOUTHERN OUTFLOW
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Technical ChallengeCombine sparse, complex
data to predict heat sweep in naturally fractured
systems
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Reduce development cost of high enthalpy systems
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Reducing development costs

• Drilling Technology
• Energy Conversion Technology

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Challenges

• Need active continuous drilling programs to
  create improvements in drilling
• Geothermal industry too small to attract research
  in service companies
• Geothermal turbines are not designed and built in
  the U.S.

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Opportunities

• Sandia and developers collaborate in drilling
  technology
• Remarkable drilling improvements have occurred -
  more are possible

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Drilling Cost Reduction at Salak
DAYS PER WELLAWIBENGKOK EXPANSION
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Geothermal

• The Benefits

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Power Plant CO2 Emissions
Fossil fuel data from Goddard and Goddard
(1990) Unocal data includes The Geysers
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Capacity Factors
Percentage
Wind Solar Conv. Average Biomass/ Fossil Geotherm
al Hydro MSW
Source DOE/Energy Information Agency data for
1996
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U.S. Government Royalties
Millions
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Conclusions

• Ultimate geothermal resource is huge
• Present research focus should be
• extend life of existing fields,
• reduce cost of developing new high enthalpy
  projects
• Artificially stimulated systems (HDR/EGS) hold
  greatest opportunity in the long term
• HDR/EGS research should focus on technology which
  can be tested in existing fields

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The End