Geothermal/Exploration
From Open Energy Information
Geothermal Exploration
[edit]
Geothermal Exploration searches the earth’s subsurface for geothermal resources that can be extracted for the purpose of electricity generation. A geothermal resource is as commonly a volume of hot rock and water, but in the case of EGS, is simply hot rock. Geothermal exploration programs utilize a variety of techniques to identify geothermal reservoirs as well as information that can point to areas of low density, high porosity, high permeability, and subsurface fault lines that can help define well field development.
Groups of Exploration Techniques
There are many different techniques that are utilized in geothermal exploration depending on the region’s geology, economic considerations, project maturity, and other considerations such as land access and permitting requirements. Geothermal techniques can be broken into the following categories:
- Data and Modeling Techniques
- Downhole Techniques
- Drilling Techniques
- Field Techniques
- Geochemical Techniques
- Geophysical Techniques
- Lab Analysis Techniques
- Remote Sensing Techniques
Full List of Exploration Techniques
Exploration Phases
Geothermal exploration is commonly separated into phases - a set of techniques that the developer will use to determine if a location is worth investigating further. Many geothermal developers define phases based on economic considerations and permitting requirements. Typically a developer will perform the least expensive techniques earlier on in the exploration program to reduce the risk of drilling a well with inadequate temperatures or flow. For example many developers will start with a desktop analysis, which includes a review of existing exploration techniques, a site visit, and in some cases inexpensive remote sensing techniques. If that set of techniques shows favorable conditions the developer will move on to the next phase. It is not uncommon for developers to start exploration at 5-10 locations and only drill at 1 location.
Note: The exploration phases described here should not be confused with the GEA Development Phases. The GEA Development Phases are used for reporting which stage in development a power plant is in (i.e. Procurement, Exploration, Permitting, Construction)[1].
Typical Exploration Phases[2]
- Phase 1 - Regional Reconnaissance
- for example: Geothermal Literature Review, Geothermometry, Multispectral Imaging, Data Acquisition-Manipulation
- Phase 2 - Prospect Evaluation
- for example: Hyperspectral Imaging, Compound and Elemental Analysis, Geothermometry, Field Mapping, Modeling-Computer Simulations
- Phase 3 - Project Appraisal
- for example: Geophysical Techniques, Field Mapping, Modeling-Computer Simulations
- Phase 4 - Exploratory Drilling
- for example: Thermal Gradient Holes, Core Holes, Slim Holes, Modeling-Computer Simulations
Exploration Best Practices
At a workshop in March 2013, IFC (International Finance Corporation), a member of the Word Bank Group, together with the International Geothermal Association launched “Geothermal Exploration Best Practices: A Guide to Resource Data Collection, Analysis, and Presentation for Geothermal Projects” in Istanbul, Turkey.
This Best Practice Guide for Geothermal Exploration was produced for IFC by GeothermEx, Inc. and outlines procedures and exploration techniques for geothermal projects and provides guidelines for presenting a geothermal project to funding entities and insurance companies. A focus is placed on high temperature geothermal resources for electricity generation. Project focus is also to attract potential investors by mitigating the associated risks with the help of insurance companies.
1st Edition (March 2013):
- GeothermEx (International Finance Corporation (IFC)). 2013. Geothermal Exploration Best Practices: A Guide to Resource Data Collection, Analysis and Presentation for Geothermal Projects. Bochum, Germany: International Geothermal Association.
2nd Edition (June 2014):
- Colin Harvey, Graeme Beardsmore, Inga Moeck, Horst Rüter, Stefan Bauer (International Geothermal Association). 2014. Best Practices Guide for Geothermal Exploration. 2nd Edition. Bochum, Germany: International Finance Corporation (IFC).
Exploration Cost and Time
The costs of exploration and the time required to complete an exploration program both add to the risk associated with the development of geothermal power plants. A typical geothermal exploration program for an individual location may require a financial commitment of 7 Million USD prior to drilling the first exploration hole[2]. The time required to bring a geothermal power plant online in many cases is at least 3-5 years with the majority of that time due to exploration[3]. In the case of Glass Mountain KGRA in Northern California the permitting delays were significant enough that it took over 20 years to complete an exploration program[3].
A representation of the cost and time commitments required for a typical geothermal exploration program can be viewed and modified using the Exploration Cost and Time Metric tool that was developed from a collaboration between government and industry.
- Data and Modeling Techniques
- Downhole Techniques
- Drilling Techniques
- Field Techniques
- Geochemical Techniques
- Geophysical Techniques
- Lab Analysis Techniques
- Remote Sensing Techniques
Looking for exploration techniques that might provide Structural Information? Thermal Information? This query has been included to allow you to use the black arrows in the table header cells to sort the table data.
| Technique | Exploration Group | Exploration Sub Group | Lithology Info Provided | Structure/Stratigraphic Info Provided | Hydrologic Info Provided | Thermal Info Provided |
|---|---|---|---|---|---|---|
| 2-M Probe Survey | Field Techniques | Data Collection and Mapping | Identify and delineate shallow thermal anomalies | |||
| Acoustic Logs | Downhole Techniques | Well Log Techniques | determine porosity of layers | map discontinuities to determine their orientation. | ||
| Active Seismic Methods | Geophysical Techniques | Seismic Techniques | ||||
| Active Seismic Techniques | Geophysical Techniques | Seismic Techniques | Rock unit density influences elastic wave velocities. | Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc. | Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation. | High temperatures and pressure impact the compressional and shear wave velocities. |
| Active Sensors | Remote Sensing Techniques | Active Sensors | Detect fault and ground movement, delineate faults, create high-resolution DEMS, quantify fault kinemaics, develop lineament maps, Geophysical Monitoring | Can give indications about subsurface geothermal fluid flow | ||
| Aerial Photography | Remote Sensing Techniques | Passive Sensors | map structures/faults | map surface water features | if photos taken in winter snow cover, can map thermal anomalies | |
| Aeromagnetic Survey | Geophysical Techniques | Magnetic Techniques | map structure, basin fill thickness, and magnetic mineral concentrations in ore bodies | |||
| Airborne Electromagnetic Survey | Geophysical Techniques | Electrical Techniques | provide data on rock type and mineral content | can be used to detect changes in density of fluids and indicate if there is salt water intrusion | ||
| Airborne Gravity Survey | Geophysical Techniques | Gravity Techniques | Distribution of density in the subsurface enables inference of rock type. | Delineation of steeply dipping formations, geological discontinuities and faults, intrusions and the deposition of silicates due to hydrothermal activity. | Density of sedimentary rocks are strongly influenced by fluid contained within pore space. Dry bulk density refers to the rock with no moisture, while the wet bulk density accounts for water saturation; fluid content may alter density by up to 30%.(Sharma, 1997) | Determination of potential heat source of the system related to the low density signature of molten intrusions. (Bruhn, 2010) |
| Analytical Modeling | Data and Modeling Techniques | Modeling Techniques | ||||
| Audio-Magnetotellurics | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Borehole Seismic Techniques | Downhole Techniques | Borehole Seismic Techniques | Rock unit density influences elastic wave velocities | Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc | Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation | High temperatures and pressure impact the compressional and shear wave velocities |
| Caliper Log | Downhole Techniques | Well Log Techniques | ||||
| Cation Geothermometers | Geochemical Techniques | Geochemical Data Analysis | Used to estimate reservoir temperatures. | |||
| Cement Bond Log | Downhole Techniques | Well Log Techniques | ||||
| Chemical Logging | Downhole Techniques | Well Log Techniques | Presence and geochemical composition of fluid producing zones | Calcium-alkalinity ratios versus depth assist in defining warm and hot water aquifers | ||
| Compound and Elemental Analysis | Lab Analysis Techniques | Fluid Lab Analysis | Results can aid in the determination of fluid source regions and circulation pathways. | Certain elements exhibit high spatial correlation with high-temperature geothermal systems. | ||
| Conceptual Model | Data and Modeling Techniques | Modeling Techniques | Rock types, rock chemistry, stratigraphic layer organization | Location and shape of permeable and non-permeable structures, faults, fracture patterns | Hydrothermal fluid flow characteristics, up-flow patterns | Temperature and pressure extrapolation throughout reservoir, heat source characteristics |
| Controlled Source Audio MT | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Controlled Source Frequency-Domain Magnetics | Geophysical Techniques | Magnetic Techniques | Locate geothermal groundwater and flow patterns. | |||
| Core Analysis | Lab Analysis Techniques | Rock Lab Analysis | Core analysis is done to define lithology. | Core analysis can locate faults or fracture networks. Oriented core can give additional important information on anisotropy. | Thermal conductivity can be measured from core samples. | |
| Core Holes | Drilling Techniques | Exploration Drilling | Core holes are drilled to identify lithology and mineralization | Retrieved samples can be used to identify fracture networks or faults | Thermal conductivity measurements can be done on retrieved samples. | |
| Cross-Dipole Acoustic Log | Downhole Techniques | Well Log Techniques | Rock stress and fracture analysis | Use for fracture identification in open and cased holes. Also used for evaluating hydro fracturing/well stimulation effectiveness. | ||
| Cuttings Analysis | Lab Analysis Techniques | Rock Lab Analysis | Cuttings are used to define lithology | |||
| DC Resistivity Survey (Dipole-Dipole Array) | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| DC Resistivity Survey (Mise-A-La-Masse) | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| DC Resistivity Survey (Pole-Dipole Array) | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| DC Resistivity Survey (Schlumberger Array) | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| DC Resistivity Survey (Wenner Array) | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Data Acquisition-Manipulation | Data and Modeling Techniques | Data Techniques | ||||
| Data Collection and Mapping | Field Techniques | Data Collection and Mapping | Locates active faults in the area of interest. Map fault and fracture patterns, kinematic information | Can reveal whether faults are circulating hydrothermal fluids. Map surface manifestations of geothermal systems. | Identify and delineate shallow thermal anomalies. Map surface temperature. | |
| Data Techniques | Data and Modeling Techniques | Data Techniques | ||||
| Data and Modeling Techniques | Data and Modeling Techniques | Rock types, rock chemistry, stratigraphic layer organization | Stress fields and magnitudes, location and shape of permeable and non-permeable structures, faults, and fracture patterns | Visualization and prediction of the flow patterns and characteristics of geothermal fluids, hydrothermal fluid flow characteristics, up-flow patterns | Thermal conduction and convection patterns in the subsurface, temperature and pressure extrapolation throughout reservoir, heat source characteristics | |
| Density Log | Downhole Techniques | Well Log Techniques | provides data on the bulk density of the rock surrounding the well | Stratigraphic correlation between well bores. | Porosity of the formations loggesd can be calculated for the Density log andprovide an indication potential aquifers. | |
| Development Drilling | Drilling Techniques | Development Drilling | Identify lithology and mineralization, provide core samples and rock cuttings | Retrieved samples can be used to identify stratigraphy and structural features such as fracture networks or faults | -Water samples can be used for geochemical analysis -Fluid pressures can be used to estimate flow rates | -Temperatures can be measured within the hole -Thermal conductivity measurements can be done on retrieved samples. |
| Direct-Current Resistivity Survey | Geophysical Techniques | Electrical Techniques | Rock type, mineral and clay content may be inferred. | Determination of fracture zones, faults, depth to groundwater aquifers. | Resistivity influenced by porosity, permeability, fluid saturation, fluid type and phase state of the pore water. | |
| Downhole Fluid Sampling | Downhole Techniques | Well Testing Techniques | Water composition and source of fluids. Gas composition and source of fluids. | Water temperature. Distinguish magmatic/mantle heat inputs. Can be used to estimate reservoir fluid temperatures. | ||
| Downhole Techniques | Downhole Techniques | Determination of lithology, grain size | Thickness and geometry of rock strata, fracture identification | Porosity, permeability, water saturation | Formation temperature with depth | |
| Drilling Methods | ||||||
| Drilling Techniques | Drilling Techniques | Identify lithology and mineralization, provide core samples and rock cuttings | Retrieved samples can be used to identify stratigraphy and structural features such as fracture networks or faults | -Water samples can be used for geochemical analysis -Fluid pressures can be used to estimate flow rates | -Temperatures can be measured within the hole -Thermal conductivity measurements can be done on retrieved samples. | |
| Earth Tidal Analysis | Downhole Techniques | Well Testing Techniques | Enables estimation of in-situ reservoir elastic parameters. | Enables estimation of in-situ reservoir hydraulic parameters. | ||
| Electrical Profiling Configurations | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Electrical Techniques | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Electromagnetic Profiling Techniques | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Electromagnetic Sounding Techniques | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Electromagnetic Techniques | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Exploration Drilling | Drilling Techniques | Exploration Drilling | Identify lithology and mineralization, provide core samples and rock cuttings | Retrieved samples can be used to identify stratigraphy and structural features such as fracture networks or faults | -Water samples can be used for geochemical analysis -Fluid pressures can be used to estimate flow rates | -Temperatures can be measured within the hole -Thermal conductivity measurements can be done on retrieved samples. |
| Exploratory Boreholes | Drilling Techniques | Exploration Drilling | Can provide core or cuttings | Identify stratigraphy and structural features within a borehole | -Water samples can be used for geochemical analysis<br:/>-Fluid pressures can be used to estimate flow rates | -Temperatures can be measured within the hole<br:/>-Information about the heat source |
| Exploratory Well | Drilling Techniques | Exploration Drilling | Can provide core or cuttings | Identify stratigraphy and structural features within a well | -Water samples can be used for geochemical analysis<br:/>-Fluid pressures can be used to estimate flow rates | -Temperatures can be measured within the hole<br:/>-Information about the heat source |
| FLIR | Remote Sensing Techniques | Passive Sensors | Map surface temperatures | |||
| Fault Mapping | Field Techniques | Data Collection and Mapping | Locates active faults in the area of interest | Can reveal whether faults are circulating hydrothermal fluids | ||
| Field Mapping | Field Techniques | Data Collection and Mapping | Map surface geology and hydrothermal alteration. | Map fault and fracture patterns, kinematic information. | Map surface manifestations of geothermal systems. | Map surface temperature. |
| Field Sampling | Field Techniques | Field Sampling | Rock samples are used to define lithology. Field and lab analyses can be used to measure the chemical and isotopic constituents of rock samples. | Can reveal relatively high permeability zones. Provides information about the time and environment which formed a particular geologic unit. Microscopic rock textures can be used to estimate the history of stress and strain, and/or faulting. | Water composition and source of fluids. Isotope geochemistry can reveal fluid circulation of a geothermal system. | Water temperature. Used to locate active hydrothermal systems. Thermal conductivity of a rock sample can provide information to calculate heat flow. Hydrothermal alteration of a rock sample can indicate certain temperature or fluid compositions. |
| Field Techniques | Field Techniques | Locates active faults in the area of interest. Map fault and fracture patterns, kinematic information. Can reveal relatively high permeability zones. Provides information about the time and environment which formed a particular geologic unit. Microscopic rock textures can be used to estimate the history of stress and strain, and/or faulting. | Can reveal whether faults are circulating hydrothermal fluids. Map surface manifestations of geothermal systems. Water composition and source of fluids. Isotope geochemistry can reveal fluid circulation of a geothermal system. | Identify and delineate shallow thermal anomalies. Map surface temperature. Water temperature. Used to locate active hydrothermal systems. Thermal conductivity of a rock sample can provide information to calculate heat flow. Hydrothermal alteration of a rock sample can indicate certain temperature or fluid compositions. | ||
| Flow Test | Downhole Techniques | Well Testing Techniques | Flow tests provide information on permeability, recharge rates, reservoir pressures, fluid chemistry, and scaling. | Flow tests can measure temperature variations with time to estimate characteristics about the heat source. | ||
| Fluid Inclusion Analysis | Lab Analysis Techniques | Fluid Lab Analysis | Fluid composition at a point in time and space | The minimum temperature of fluid inclusion formation | ||
| Fluid Lab Analysis | Lab Analysis Techniques | Fluid Lab Analysis | Results can aid in the determination of fluid source regions and circulation pathways, and assist in determining the degree of mixing between different hydrothermal fluids. | Certain elements exhibit high spatial correlation with high-temperature geothermal systems; Isotopic ratios can be used to characterize and locate subsurface thermal anomalies. | ||
| Formation Testing Techniques | Downhole Techniques | Formation Testing Techniques | ||||
| Frequency-Domain Electromagnetic Survey | Geophysical Techniques | Electrical Techniques | Detection of high-conductivity bodies in the subsurface. | Detection of the presence of a thermal anomaly through its resistivity signature. | ||
| Gamma Log | Downhole Techniques | Well Log Techniques | provides information on changes in rock type near the wellbore from changes in measured gamma radiation | using multiple gamma logs over an area, the depth to the sandstone and shale layers can be correlated over larger areas | ||
| Gas Flux Sampling | Field Techniques | Field Sampling | High flux can be indicative of conduits for fluid flow. | Anomalous flux is associated with active hydrothermal activity. | ||
| Gas Geothermometry | Geochemical Techniques | Geochemical Data Analysis | ||||
| Gas Sampling | Field Techniques | Field Sampling | High flux can be indicative of conduits for fluid flow. | Gas composition and source of fluids. | Anomalous flux is associated with active hydrothermal activity. Distinguish magmatic/mantle heat inputs. Can be used to estimate reservoir fluid temperatures. | |
| GeoTeam | ||||||
| Geochemical Data Analysis | Geochemical Techniques | Geochemical Data Analysis | ||||
| Geochemical Techniques | Geochemical Techniques | |||||
| Geodetic Survey | Remote Sensing Techniques | Passive Sensors | Map regional strain rates | |||
| Geographic Information System | Data and Modeling Techniques | Data Techniques | Any mapable information | Any mapable information | Any mapable information | Any mapable information |
| Geophysical Methods | Geophysical Techniques | Geophysical Techniques | ||||
| Geophysical Techniques | Geophysical Techniques | may be inferred | may be inferred | may be inferred | may be inferred | |
| Geothermal Literature Review | Data and Modeling Techniques | Data Techniques | ||||
| Geothermometry | Geochemical Techniques | Geochemical Data Analysis | used to estimate reservoir temperatures | |||
| Gravity Methods | Geophysical Techniques | Gravity Techniques | ||||
| Gravity Techniques | Geophysical Techniques | Gravity Techniques | Distribution of density in the subsurface enables inference of rock type. | Delineation of steeply dipping formations, geological discontinuities and faults, intrusions and the deposition of silicates due to hydrothermal activity. | Density of sedimentary rocks are strongly influenced by fluid contained within pore space. Dry bulk density refers to the rock with no moisture, while the wet bulk density accounts for water saturation; fluid content may alter density by up to 30%.(Sharma, 1997) | Determination of potential heat source of the system related to the low density signature of molten intrusions. (Bruhn, 2010) |
| Ground Electromagnetic Techniques | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Ground Gravity Survey | Geophysical Techniques | Gravity Techniques | Distribution of density in the subsurface enables inference of rock type. | Delineation of steeply dipping formations, geological discontinuities and faults, intrusions and large-scale deposition of silicates due to hydrothermal activity. | Density of sedimentary rocks are strongly influenced by fluid contained within pore space. Dry bulk density refers to the rock with no moisture, while the wet bulk density accounts for water saturation; fluid content may alter density by up to 30%.(Sharma, 1997) | Determination of potential heat source of the system related to the low density signature of molten intrusions. (Bruhn, 2010) |
| Ground Magnetics | Geophysical Techniques | Magnetic Techniques | Presence of magnetic minerals such as magnetite. | Mapping of basement structures, horst blocks, fault systems, fracture zones, dykes and intrusions. | The circulation of hydrothermal fluid may impact the magnetic susceptibility of rocks. | |
| Groundwater Sampling | Field Techniques | Field Sampling | Water composition and source of fluids. Determination of mixing ratios between different fluid end-members. Determination of fluid recharge rates and residence times. | Water temperature. | ||
| Hand-held X-Ray Fluorescence (XRF) | Field Techniques | Data Collection and Mapping | Bulk and trace element analysis of rocks, minerals, and sediments. | |||
| Hydroprobe | Drilling Techniques | Exploration Drilling | Collection of ground water samples for geochemistry and geothermometry | Temperature measurements down to 50 m | ||
| Hyperspectral Imaging | Remote Sensing Techniques | Passive Sensors | mineral maps can be used to show the presence of hydrothermal minerals and mineral assemblages | aerial photographs can show structures | delineate locations of surface water features | vegetation maps can show plants stressed due to nearby thermal activity |
| Image Logs | Downhole Techniques | Well Log Techniques | Identify different lithological layers, rock composition, grain size, mineral, and clay content | -Fault and fracture identification
-Rock texture, porosity, and stress analysis -determine dip, thickness, and geometry of rock strata in vicinity of borehole -Detection of permeable pathways, fracture zones, faults | Locate zones of aquifer inflow/outflow | |
| InSAR | Remote Sensing Techniques | Active Sensors | Geophysical Monitoring | Can give indications about subsurface geothermal fluid flow | ||
| Injectivity Test | Downhole Techniques | Well Testing Techniques | Permeability of the well | |||
| Isotope Geothermometry | Geochemical Techniques | Geochemical Data Analysis | ||||
| Isotopic Analysis- Fluid | Lab Analysis Techniques | Fluid Lab Analysis | Water rock interaction | Origin of hydrothermal fluids; Mixing of hydrothermal fluids | Isotopic ratios can be used to characterize and locate subsurface thermal anomalies. | |
| Isotopic Analysis- Rock | Lab Analysis Techniques | Rock Lab Analysis | Water rock interaction | |||
| Lab Analysis Techniques | Lab Analysis Techniques | Water rock interaction; Rapid and unambiguous identification of unknown minerals; Bulk and trace element analysis of rocks, minerals, and sediments; Obtain detailed information about rock composition and morphology; Determine detailed information about rock composition and morphology; Cuttings are used to define lithology; Core analysis is done to define lithology | Anomalously high concentrations can indicate high permeability or conduit for fluid flow; Identify historic structure and deformation of land; Core analysis can locate faults or fracture networks. Oriented core can give additional important information on anisotropy | Reconstructing the fluid circulation of a hydrothermal system; Field wide soil sampling can generate a geometrical approximation of fluid circulation; Determine origin of hydrothermal fluids; Calculate mixing ratios of hydrothermal fluids; Determine fluid composition at a point in time and space | High mercury vapor concentration in soils can be indicative of active hydrothermal activity; Isotopic ratios can be used to characterize and locate subsurface thermal anomalies; Constrain the minimum temperature of fluid inclusion formation; certain elements exhibit high spatial correlation with high-temperature geothermal systems; Thermal conductivity can be measured from core samples | |
| LiDAR | Remote Sensing Techniques | Active Sensors | delineate faults, create high-resolution DEMS, quantify fault kinemaics, develop lineament maps | |||
| Liquid Geothermometry | Geochemical Techniques | Geochemical Data Analysis | ||||
| Long-Wave Infrared | Remote Sensing Techniques | Passive Sensors | Map characteristic minerals associated with hot springs/mineral deposits | Map surface temperatures | ||
| Macrophotography | Field Techniques | Data Collection and Mapping | Identify and document surface geology and mineralogy | |||
| Magnetic Techniques | Geophysical Techniques | Magnetic Techniques | Presence of magnetic minerals such as magnetite. | Mapping of basement structures, horst blocks, fault systems, fracture zones, dykes and intrusions. | The circulation of hydrothermal fluid may impact the magnetic susceptibility of rocks. | |
| Magnetotelluric Techniques | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Magnetotellurics | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Mercury Vapor | Lab Analysis Techniques | Fluid Lab Analysis | Anomalously high concentrations can indicate high permeability or conduit for fluid flow | Field wide soil sampling can generate a geometrical approximation of fluid circulation | High concentration in soils can be indicative of active hydrothermal activity | |
| Micro-Earthquake | Geophysical Techniques | Seismic Techniques | Fault zones, permeable pathways | Fluid type- liquid or steam | ||
| Microgravity-Hybrid Microgravity | Geophysical Techniques | Gravity Techniques | Ground subsidence can be mapped using microgravity | Monitoring net mass changes of a geothermal reservoir due to production and reinjection processes | Changes in liquid density due to temperature changes in the reservoir | |
| Microhole Array | Drilling Techniques | Exploration Drilling | May be possible to assess fluid flow using small-diameter downhole tools designed for slim holes. | May be possible to collect limited temperature data using small-diameter downhole tools designed for slim holes. | ||
| Modeling Techniques | Data and Modeling Techniques | Modeling Techniques | Rock types, rock chemistry, stratigraphic layer organization | Stress fields and magnitudes, location and shape of permeable and non-permeable structures, faults, fracture patterns | Visualization and prediction of the flow patterns and characteristics of geothermal fluids, hydrothermal fluid flow characteristics, up-flow patterns | Thermal conduction and convection patterns in the subsurface, temperature and pressure extrapolation throughout reservoir, heat source characteristics |
| Modeling-Computer Simulations | Data and Modeling Techniques | Modeling Techniques | Stress fields and magnitudes | Visualization and prediction of the flow patterns and characteristics of geothermal fluids | Thermal conduction and convection patterns in the subsurface | |
| Mud Logging | Downhole Techniques | Well Log Techniques | Lithological layers are identified from drill cuttings | Porosity of rocks | Fluid content of the borehole while drilling can be determined | |
| Multicomponent Geothermometers | Geochemical Techniques | Geochemical Data Analysis | ||||
| Multispectral Imaging | Remote Sensing Techniques | Passive Sensors | relative mineral maps | aerial photographs can show structures | delineate locations of surface water features | vegetation maps can show plants stressed due to nearby thermal activity |
| Near Infrared Surveys | Remote Sensing Techniques | Passive Sensors | ||||
| Neutron Log | Downhole Techniques | Well Log Techniques | if used in conjunction with other logs, this technique can provide information on the rock type and the porosity | Corelation of rock units | Estimate of formation porosity | |
| Numerical Modeling | Data and Modeling Techniques | Modeling Techniques | Stress fields and magnitudes | Visualization and prediction of the flow patterns and characteristics of geothermal fluids | Thermal conduction and convection patterns in the subsurface | |
| Oblique Aerial & Ground Visible Band & Thermographic Imaging | Remote Sensing Techniques | Passive Sensors | ||||
| Observation Wells | Drilling Techniques | Development Drilling | Total dissolved solids, fluid pressure, flow rates, and flow direction | Monitors temperature of circulating fluids | ||
| Over Core Stress | Lab Analysis Techniques | Rock Lab Analysis | ||||
| PSInSAR | Remote Sensing Techniques | Active Sensors | Detect fault and ground movement | Can give indications about subsurface geothermal fluid flow | ||
| Paleomagnetic Measurements | Lab Analysis Techniques | Rock Lab Analysis | Can determine detailed information about rock composition and morphology | Historic structure and deformation of land | ||
| Passive Seismic Techniques | Geophysical Techniques | Seismic Techniques | Rock unit density influences elastic wave velocities. | Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc. | Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation. | High temperatures and pressure impact the compressional and shear wave velocities. |
| Passive Sensors | Remote Sensing Techniques | Passive Sensors | Mineral maps can be used to show the presence of hydrothermal minerals and mineral assemblages | Map structures/faults and regional strain rates | Map surface water features | Map surface temperatures |
| Petrography Analysis | Lab Analysis Techniques | Rock Lab Analysis | Provides detailed information about rock composition and morphology | |||
| Portable X-Ray Diffraction (XRD) | Field Techniques | Data Collection and Mapping | ||||
| Portfolio Risk Modeling | Data and Modeling Techniques | Modeling Techniques | ||||
| Pressure Temperature Log | Downhole Techniques | Well Log Techniques | Perturbations in temperature or pressure can be indicative of faults or other structural features | fluid cirulation, over-pressured zones, and under-pressured zones. | Temperature profile with depth | |
| Production Wells | Drilling Techniques | Development Drilling | Drill cuttings are analyzed to determine lithology and mineralogy | Fractures, faults, and geologic formations that the well passes through are identified and mapped. | Identify aquifers, reservoir boundaries, flow rates, fluid pressure, and chemistry | Direct temperature measurements from within the reservoir |
| Radar | Remote Sensing Techniques | Active Sensors | Detect fault and ground movement | Can give indications about subsurface geothermal fluid flow | ||
| Radiometrics | Remote Sensing Techniques | Passive Sensors | Primary use is in mapping potassium alterations | |||
| Reflection Survey | Geophysical Techniques | Seismic Techniques | Rock unit density influences elastic wave velocities. | Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc. | Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation. | High temperatures and pressure impact the compressional and shear wave velocities. |
| Refraction Survey | Geophysical Techniques | Seismic Techniques | Rock unit density influences elastic wave velocities. | Can provide information on crustal thickness, depth to basement. | ||
| Remote Sensing Techniques | Remote Sensing Techniques | |||||
| Rock Density | Lab Analysis Techniques | Rock Lab Analysis | Density of different lithologic units. | |||
| Rock Lab Analysis | Lab Analysis Techniques | Rock Lab Analysis | Core analysis can locate faults or fracture networks. Oriented core can give additional important information on anisotropy. Historic structure and deformation of land. | Thermal conductivity can be measured from core samples. | ||
| Rock Sampling | Field Techniques | Field Sampling | Rock samples are used to define lithology. Field and lab analyses can be used to measure the chemical and isotopic constituents of rock samples. | Provides information about the time and environment which formed a particular geologic unit. Microscopic rock textures can be used to estimate the history of stress and strain, and/or faulting. | Isotope geochemistry can reveal fluid circulation of a geothermal system. | Thermal conductivity of a rock sample can provide information to calculate heat flow. Hydrothermal alteration of a rock sample can indicate certain temperature or fluid compositions. |
| SAR | Remote Sensing Techniques | Active Sensors | create high-resolution DEMs, detect fault and ground movement | |||
| SRT | Remote Sensing Techniques | Active Sensors | high-resolution DEMs | |||
| SWIR | Remote Sensing Techniques | Passive Sensors | map characteristic minerals associated with hot springs/mineral deposits | |||
| Seismic Techniques | Geophysical Techniques | Seismic Techniques | Rock unit density influences elastic wave velocities. | Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc. | Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation. | High temperatures and pressure impact the compressional and shear wave velocities. |
| Self Potential | Geophysical Techniques | Electrical Techniques | SP technique originally applied to locating sulfide ore-bodies. | Detection and tracing of faults. | Determination of fluid flow patterns: electrochemical coupling processes due to variations in ionic concentrations, and electrokinetic coupling processes due to fluid flow in the subsurface. | Location of near-surface thermal anomalies: thermoelectric coupling processes due to variations in temperature in the subsurface. |
| Silica Geothermometers | Geochemical Techniques | Geochemical Data Analysis | Used to estimate reservoir temperatures. | |||
| Single-Well And Cross-Well Seismic Imaging | Downhole Techniques | Borehole Seismic Techniques | Rock unit density influences elastic wave velocities. | Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc. | Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation. | High temperatures and pressure impact the compressional and shear wave velocities. |
| Single-Well and Cross-Well Resistivity | Downhole Techniques | Well Log Techniques | Identify different lithological layers, rock composition, mineral, and clay content | -Fault and fracture identification
-Rock texture, porosity, and stress analysis -determine dip and structural features in vicinity of borehole -Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Slim Holes | Drilling Techniques | Exploration Drilling | If core is collected | If core is collected | Fluid flow and water chemistry | Thermal gradient or bottom hole temperature |
| Soil Gas Sampling | Field Techniques | Field Sampling | Identify concealed faults that act as conduits for hydrothermal fluids. | Identify hydrothermal gases of magmatic origin. | Differentiate between amagmatic or magmatic sources heat. | |
| Soil Sampling | Field Techniques | Field Sampling | Can reveal relatively high permeability zones | Used to locate active hydrothermal systems | ||
| Spontaneous Potential Well Log | Downhole Techniques | Well Log Techniques | SP technique originally applied to locating sulfide ore-bodies. | -Formation bed thickness and boundaries
-Detection and tracing of faults -Permeability and porosity | Determination of fluid flow patterns: electrochemical coupling processes due to variations in ionic concentrations, and electrokinetic coupling processes due to fluid flow in the subsurface. | Location of thermal anomalies: thermoelectric coupling processes due to variations in temperature in the subsurface. |
| SqueeSAR | Remote Sensing Techniques | Active Sensors | Detect fault and ground movement | Can give indications about subsurface geothermal fluid flow | ||
| Static Temperature Survey | Downhole Techniques | Well Testing Techniques | Extrapolate the true temperature of the formation the well penetrates | |||
| Step-out Well | Drilling Techniques | Exploration Drilling | Drill cuttings are analyzed to determine lithology and mineralogy | Fractures, faults, and geologic formations that the well passes through are identified and mapped | Identify aquifers, reservoir boundaries, flow rates, fluid pressure, and chemistry | Direct temperature measurements from within the reservoir |
| Stereo Satellite Imagery | Remote Sensing Techniques | Passive Sensors | map structures/faults | map surface water features, determine the boundary conditions of hydrothermal circulation | ||
| Stress Test | Downhole Techniques | Well Testing Techniques | Fracture distribution and ambient tectonic stresses | Fluid flow direction | ||
| Surface Gas Sampling | Field Techniques | Field Sampling | Gas composition and source of fluids. | Distinguish magmatic/mantle heat inputs. Can be used to estimate reservoir fluid temperatures. | ||
| Surface Water Sampling | Field Techniques | Field Sampling | Water composition and source of fluids | Water temperature | ||
| Teleseismic-Seismic Monitoring | Geophysical Techniques | Seismic Techniques | Rock unit density influences elastic wave velocities. | Map geothermal reservoir geometry. Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc. | Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation. | High temperatures and pressure impact the compressional and shear wave velocities. |
| Telluric Survey | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Thermal Gradient Holes | Drilling Techniques | Exploration Drilling | Field wide fluid flow characteristics if an array of wells are drilled | Mapping and projecting thermal anomalies | ||
| Thermal Ion Dispersion | Geochemical Techniques | Geochemical Data Analysis | ||||
| Thermochronometry | Geochemical Techniques | Geochemical Data Analysis | Thermal history of area, rate of cooling, age that minerals reached closure temperature | |||
| Time-Domain Electromagnetics | Geophysical Techniques | Electrical Techniques | Detection of rock units or geological features with contrasting apparent resistivity. | Structural information may be inferred from TDEM data. | Hydrological information such as depth to groundwater table may be determined. | Extent of hydrothermal alteration mineralogy may be inferred. |
| Trace Element Analysis | Lab Analysis Techniques | Fluid Lab Analysis | Reconstructing the fluid circulation of a hydrothermal system | |||
| Tracer Testing | Downhole Techniques | Well Testing Techniques | Fracture zones and formation permeability | Flow rates, flow direction, hydrologic connections, storativity | ||
| Vertical Electrical Sounding Configurations | Geophysical Techniques | Electrical Techniques | Rock composition, mineral and clay content | Detection of permeable pathways, fracture zones, faults | Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water | Resistivity influenced by temperature |
| Vertical Flowmeter Test | Downhole Techniques | Well Testing Techniques | Define permeable zones within a well | |||
| Vertical Seismic Profiling | Downhole Techniques | Borehole Seismic Techniques | Rock unit density influences elastic wave velocities. | Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc. | Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation. | High temperatures and pressure impact the compressional and shear wave velocities. |
| Water Sampling | Field Techniques | Field Sampling | Water composition and source of fluids | Water temperature | ||
| Well Deepening | Drilling Techniques | Development Drilling | Drill cuttings are analyzed to determine lithology and mineralogy | Fractures, faults, and geologic formations that the well passes through are identified and mapped. | Identify aquifers, reservoir boundaries, flow rates, fluid pressure, and chemistry | Direct temperature measurements from within the reservoir |
| Well Log Techniques | Downhole Techniques | Well Log Techniques | depth and thickness of formations; lithology and porosity can be inferred | reservoir thickness, reservoir geometry, borehole geometry | permeability and fluid composition can be inferred | direct temperature measurements; thermal conductivity and heat capacity |
| Well Testing Techniques | Downhole Techniques | Well Testing Techniques | Enable estimation of in-situ reservoir elastic parameters | Fracture distribution, formation permeability, and ambient tectonic stresses | provides information on permeability, location of permeable zones recharge rates, flow rates, fluid flow direction, hydrologic connections, storativity, reservoir pressures, fluid chemistry, and scaling. | Temperature variations with time Extrapolate the true temperature of formation |
| X-Ray Diffraction (XRD) | Lab Analysis Techniques | Rock Lab Analysis | ||||
| X-Ray Fluorescence (XRF) | Lab Analysis Techniques | Rock Lab Analysis | Bulk and trace element analysis of rocks, minerals, and sediments. | |||
| Z-Axis Tipper Electromagnetics | Geophysical Techniques | Electrical Techniques |
Geothermal Regulations and Permitting for Exploration
For information about regulations and permitting related to exploration for geothermal projects, see the Regulatory and Permitting Information Desktop Toolkit.
Exploration References
<references>
- ↑ 1.0 1.1 "[http://www.geo-energy.org/reports/Factors%20Affecting%20Cost%20of%20Geothermal%20Power%20Development%20-%20August%202005.pdf Annual US Geothermal Power Production and Development Report]"
- ↑ 2.0 2.1 2.2 "Developement of Metric for Measuring the Impact of RD&D Funding on GTO's Geothermal Exploration Goals"
- ↑ 3.0 3.1 3.2 "[http://www.geo-energy.org/reports/Factors%20Affecting%20Cost%20of%20Geothermal%20Power%20Development%20-%20August%202005.pdf Factors Affecting Costs of Geothermal Power Development]"