1.4 Plate tectonics and geothermal resources

Plate tectonics shape Earth's geothermal resources. Understanding how plates move and interact reveals where heat concentrates underground. This knowledge is crucial for finding and tapping into geothermal energy sources.

Geothermal potential varies based on tectonic settings. Plate boundaries often have high heat flow, while stable regions have lower-temperature resources. Analyzing tectonic factors helps engineers locate and assess geothermal systems for energy production.

Fundamentals of plate tectonics

• Plate tectonics forms the foundation for understanding geothermal systems and their distribution across the Earth's surface
• Geothermal Systems Engineering relies heavily on plate tectonic principles to locate and assess potential geothermal resources
• Understanding plate movements and interactions provides crucial insights into heat flow patterns and geological structures relevant to geothermal energy extraction

Earth's lithosphere structure

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• Lithosphere consists of the crust and uppermost mantle, ranging from 50-250 km thick
• Divided into rigid tectonic plates floating on the partially molten asthenosphere
• Oceanic lithosphere thinner (5-10 km) and denser than continental lithosphere (30-50 km)
• Lithospheric plates move relative to each other, driven by convection currents in the mantle

Types of plate boundaries

• Divergent boundaries where plates move apart, forming new crust (mid-ocean ridges)
• Convergent boundaries where plates collide, leading to subduction or mountain building
• Transform boundaries where plates slide past each other horizontally
• Plate boundary interactions create zones of intense tectonic activity and heat flow

Plate movement mechanisms

• Mantle convection currents drive plate motion through drag on the lithosphere's base
• Ridge push forces new oceanic crust to spread outward from mid-ocean ridges
• Slab pull exerts downward force on subducting plates due to their increased density
• Gravitational sliding causes plates to move down slopes in the asthenosphere

Geothermal resources and tectonics

• Tectonic processes play a crucial role in the formation and distribution of geothermal resources worldwide
• Plate boundaries and associated geological features often correlate with areas of high geothermal potential
• Understanding the relationship between tectonics and geothermal systems aids in resource identification and assessment

High-enthalpy vs low-enthalpy systems

• High-enthalpy systems characterized by temperatures >200°C, often found near plate boundaries
  • Utilized for electricity generation through steam turbines
  • Typically associated with volcanic or magmatic activity
• Low-enthalpy systems have temperatures <150°C, more common in stable continental regions
  • Suitable for direct use applications (space heating, agriculture)
  • Often result from deep circulation of groundwater or radioactive decay heat

Tectonic settings for geothermal

• Divergent boundaries produce high heat flow and magmatism (Iceland, East African Rift)
• Convergent boundaries create volcanic arcs with geothermal potential (Ring of Fire)
• Transform boundaries can generate fractured zones conducive to fluid circulation
• Intraplate hotspots form localized geothermal resources (Yellowstone, Hawaii)

Plate boundary geothermal potential

• Divergent boundaries offer consistent heat sources and permeable fractured crust
• Subduction zones provide magmatic heat and create pathways for fluid circulation
• Transform boundaries create extensive fracture networks enhancing permeability
• Plate boundary regions often exhibit higher heat flow and geothermal gradients

Heat transfer in tectonic zones

• Tectonic processes significantly influence heat transfer mechanisms in the Earth's crust
• Understanding heat transfer in tectonic zones aids in geothermal resource characterization
• Heat flow patterns in different tectonic settings guide exploration and development strategies

Conduction vs convection

• Conduction transfers heat through direct contact between particles
  • Dominant in stable continental crust with low permeability
  • Follows Fourier's Law: $q = -k \frac{dT}{dx}$
• Convection involves heat transfer through fluid movement
  • Prevalent in fractured or porous rock with circulating fluids
  • Enhances heat transfer efficiency in geothermal systems

Magmatic heat sources

• Intrusive magma bodies provide localized high-temperature heat sources
• Partial melting in subduction zones generates magma and associated heat
• Mantle plumes create hotspots with sustained magmatic activity
• Magma chambers act as long-term heat reservoirs for geothermal systems

Crustal heat flow patterns

• Varies significantly across tectonic settings and geological provinces
• Higher heat flow observed near plate boundaries and active tectonic zones
• Continental shields exhibit lower heat flow due to thicker, stable lithosphere
• Local variations influenced by radiogenic heat production and thermal conductivity

Geothermal resource identification

• Tectonic analysis forms a crucial component of geothermal resource exploration
• Integrating tectonic indicators with geophysical and remote sensing data enhances resource identification
• Understanding tectonic controls on geothermal systems guides exploration strategies and reduces risk

Tectonic indicators of geothermal

• Active faults and fracture zones indicate potential fluid pathways
• Recent volcanism suggests presence of magmatic heat sources
• Elevated heat flow anomalies correlate with tectonic activity
• Crustal thinning in extensional settings enhances geothermal potential
• Presence of hydrothermal alteration minerals (quartz, calcite, clay minerals)

Geophysical exploration methods

• Magnetotelluric surveys map subsurface electrical conductivity variations
• Seismic tomography reveals crustal structure and potential heat sources
• Gravity surveys detect density contrasts associated with geothermal reservoirs
• Heat flow measurements provide direct evidence of geothermal potential
• Microseismic monitoring identifies active fault zones and fluid circulation

Remote sensing techniques

• Thermal infrared imaging detects surface temperature anomalies
• Satellite-based interferometry measures ground deformation related to geothermal activity
• Hyperspectral imaging identifies hydrothermal alteration minerals
• LiDAR surveys map surface expressions of faults and fractures
• Landsat imagery analysis reveals large-scale tectonic features and thermal anomalies

Plate tectonics and reservoir properties

• Tectonic processes significantly influence the development and characteristics of geothermal reservoirs
• Understanding the relationship between tectonics and reservoir properties aids in resource assessment and development planning
• Plate tectonic settings determine the nature and extent of fracture networks crucial for geothermal fluid circulation

Permeability in tectonic settings

• Extensional tectonic regimes create high permeability through normal faulting
• Compressional settings may reduce permeability but create overpressured reservoirs
• Strike-slip faults generate complex fracture networks enhancing fluid flow
• Tectonic stresses influence fracture orientation and connectivity
• Hydrothermal alteration can either increase or decrease permeability over time

Fracture networks and faults

• Tectonic stresses create primary fracture sets controlling fluid flow
• Fault zones act as conduits or barriers to fluid movement depending on their properties
• Fracture density and orientation determine reservoir productivity
• Active faults may continuously regenerate permeability through seismic activity
• Fracture aperture and connectivity influence overall reservoir transmissivity

Fluid circulation patterns

• Convection cells develop in fractured reservoirs driven by temperature gradients
• Fault-controlled fluid flow channels heat from deep sources to shallower levels
• Tectonic uplift and subsidence affect hydraulic gradients and fluid movement
• Magmatic intrusions create localized circulation systems around heat sources
• Regional stress fields influence preferential fluid flow directions in fractured media

Geothermal potential assessment

• Tectonic analysis forms a crucial component in evaluating geothermal resource potential
• Integration of tectonic data with heat flow measurements provides a comprehensive assessment approach
• Understanding the relationship between tectonics and geothermal gradients guides exploration and development strategies

Tectonic-based resource estimation

• Plate boundary proximity correlates with higher geothermal potential
• Crustal thickness variations influence heat flow and resource distribution
• Tectonic stress regimes affect reservoir permeability and fluid circulation
• Magmatic activity in different tectonic settings indicates heat source presence
• Structural features (faults, fractures) control reservoir properties and productivity

Heat flow mapping techniques

• Borehole temperature logging provides direct heat flow measurements
• Surface heat flow surveys using shallow temperature probes
• Satellite-based thermal infrared imaging for regional heat flow patterns
• Integration of geophysical data (gravity, magnetics) to infer crustal heat sources
• Numerical modeling of heat transfer processes in different tectonic settings

Geothermal gradient analysis

• Calculation of temperature increase with depth: $\frac{dT}{dz} = \frac{q}{k}$
  • Where q = heat flow, k = thermal conductivity
• Higher gradients indicate greater geothermal potential
• Variations in gradient reflect changes in lithology and heat sources
• Anomalous gradients may indicate presence of convective heat transfer
• Integration of gradient data with tectonic models improves resource assessment accuracy

Tectonic hazards for geothermal

• Geothermal development in tectonically active areas faces unique challenges and risks
• Understanding and mitigating tectonic hazards essential for sustainable geothermal operations
• Integration of tectonic hazard assessment in project planning and risk management strategies

Seismic risks in geothermal areas

• Induced seismicity from fluid injection and extraction operations
• Natural earthquake hazards in tectonically active geothermal regions
• Potential for reservoir damage or well casing failures due to seismic events
• Seismic monitoring and mitigation strategies (traffic light systems)
• Design of earthquake-resistant geothermal infrastructure

Volcanic activity considerations

• Proximity to active volcanoes increases risk of eruptions and lahars
• Potential for sudden changes in reservoir conditions due to magmatic activity
• Gas emissions (H2S, CO2) and their impact on geothermal operations
• Monitoring volcanic unrest using geophysical and geochemical techniques
• Emergency response planning for volcanic hazards in geothermal fields

Ground deformation issues

• Subsidence due to fluid extraction from geothermal reservoirs
• Uplift caused by fluid injection or magma intrusion
• Differential ground movement affecting well integrity and surface infrastructure
• InSAR and GPS monitoring of ground deformation in geothermal areas
• Mitigation strategies (reinjection, controlled production rates)

Sustainable geothermal development

• Tectonic setting plays a crucial role in determining the long-term sustainability of geothermal resources
• Balancing resource exploitation with natural recharge rates ensures prolonged geothermal energy production
• Consideration of tectonic factors in development plans promotes environmentally responsible geothermal utilization

Tectonic setting sustainability factors

• Heat recharge rates influenced by tectonic heat flow and magmatism
• Crustal permeability regeneration through active tectonics
• Long-term stability of reservoir conditions in different tectonic environments
• Tectonic controls on fluid chemistry and scaling potential
• Influence of regional stress fields on reservoir management strategies

Long-term resource management

• Reservoir modeling incorporating tectonic and heat flow data
• Reinjection strategies to maintain pressure and minimize environmental impact
• Monitoring of reservoir parameters (pressure, temperature, chemistry) over time
• Adaptive management approaches based on observed tectonic and reservoir changes
• Integration of new exploration techniques to extend resource lifetimes

Environmental impact considerations

• Land subsidence and its effects on local ecosystems and infrastructure
• Induced seismicity management and public acceptance issues
• Thermal pollution of surface water bodies from geothermal effluents
• Emissions reduction potential compared to fossil fuel energy sources
• Habitat protection in tectonically active geothermal areas

Case studies: tectonics and geothermal

• Examination of real-world examples illustrates the diverse relationships between tectonics and geothermal resources
• Case studies provide valuable insights for geothermal exploration and development in various tectonic settings
• Analysis of successful and challenging projects informs best practices in Geothermal Systems Engineering

Plate boundary geothermal examples

• Iceland: Mid-Atlantic Ridge divergent boundary (Krafla, Hellisheiði power plants)
• Philippines: Subduction zone convergent boundary (Tiwi, Makban geothermal fields)
• California: Transform boundary (The Geysers, Salton Sea geothermal areas)
• New Zealand: Oblique convergent boundary (Wairakei, Ngatamariki geothermal systems)

Intraplate geothermal systems

• United States: Yellowstone hotspot (not currently exploited due to national park status)
• Turkey: Western Anatolia extensional province (Kizildere, Germencik geothermal fields)
• Australia: Cooper Basin enhanced geothermal system in stable craton
• China: Yangbajing geothermal field in Tibet, related to continental collision

Emerging tectonic-related resources

• Enhanced Geothermal Systems (EGS) in various tectonic settings
• Supercritical geothermal resources in young volcanic systems (Iceland IDDP project)
• Offshore geothermal potential along mid-ocean ridges and subduction zones
• Geothermal energy from abandoned oil and gas wells in sedimentary basins