Single-Well and Cross-Well Resistivity

GEOTHERMAL ENERGY

Exploration Technique: Single-Well and Cross-Well Resistivity

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• Activities (15)
• Areas (14)
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Exploration Technique Information
Exploration Group:	Downhole Techniques
Exploration Sub Group:	Well Log Techniques
Parent Exploration Technique:	Well Log Techniques
Information Provided by Technique
Lithology:	Identify different lithological layers, rock composition, mineral, and clay content
Stratigraphic/Structural:	-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
Hydrological:	Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water
Thermal:	Resistivity influenced by temperature
Cost Information
Median Estimate (USD):	5,000.00 500,000 centUSD 5 kUSD 0.005 MUSD 5.0e-6 TUSD / well

Single-Well and Cross-Well Resistivity:

Electrical methods in which resistivity data are collected via downhole electrodes.

Other definitions:Wikipedia Reegle

 

Introduction

• "Downhole resistivity methods come in numerous forms and there are many different variations, configurations, and instruments used for downhole resistivity surveys. Many different companies perform single-well and cross-well resistivity surveys and countless different names have been coined for the surveys; some examples are: Formation Micro-Imager (FMI) Logs, Electric-micro Imager (EMI) Logs, Micro Resistivity, Resistivity Log, Resistivity Tomography, Fullbore Formation MircroImaging, and Formation Micro-Conductivity Imaging. '"`UNIQ--ref-00000000-QINU`"''"`UNIQ--ref-00000001-QINU`"' '"`UNIQ--ref-00000002-QINU`"' There is also a configuration called Single-point Resistance in which one electrode is placed down a well and one is on the surface.'"`UNIQ--ref-00000003-QINU`"'" cannot be used as a page name in this wiki.
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Downhole resistivity methods come in numerous forms and there are many different variations, configurations, and instruments used for downhole resistivity surveys. Many different companies perform single-well and cross-well resistivity surveys and countless different names have been coined for the surveys; some examples are: Formation Micro-Imager (FMI) Logs, Electric-micro Imager (EMI) Logs, Micro Resistivity, Resistivity Log, Resistivity Tomography, Fullbore Formation MircroImaging, and Formation Micro-Conductivity Imaging. There is also a configuration called Single-point Resistance in which one electrode is placed down a well and one is on the surface.

 

Use in Geothermal Exploration

• "Similarly to Single-Well And Cross-Well Seismic methods the downhole resistivity methods can be conducted in many different configurations. Single well resistivity methods require the transmitter and receivers to be lowered down the well on one line, so vertical cross section images of the formations immediately around the borehole can be collected. The horizontal range is dependent on the electrode spacing. With larger electrode spacing range increases, but resolution is sacrificed. The technique complements core sample data and is useful for describing intervals of a well that were not cored.'"`UNIQ--ref-00000004-QINU`"' Cross-well methods require two or more wells and are highly useful for creating cross sectional images of resistivity structures between the two wells. With cross-well methods faults, fracture patterns, and zones of permeability between the wells can be mapped.'"`UNIQ--ref-00000005-QINU`"' Single-well and cross-well resistivity is useful in geothermal exploration because down hole structural features can be revealed in high detail. This information can be very useful for siting future production wells and selecting depths for collecting core samples. Downhole resistivity measurements are useful for mapping resistivity structures, dip, porosity, rock texture, stress patterns, faults, and fractures, thus helping to create a more complete geologic model of the geothermal area and pinpointing future drilling targets.'"`UNIQ--ref-00000006-QINU`"''"`UNIQ--ref-00000007-QINU`"'" cannot be used as a page name in this wiki.
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Similarly to Single-Well And Cross-Well Seismic methods the downhole resistivity methods can be conducted in many different configurations. Single well resistivity methods require the transmitter and receivers to be lowered down the well on one line, so vertical cross section images of the formations immediately around the borehole can be collected. The horizontal range is dependent on the electrode spacing. With larger electrode spacing range increases, but resolution is sacrificed. The technique complements core sample data and is useful for describing intervals of a well that were not cored. Cross-well methods require two or more wells and are highly useful for creating cross sectional images of resistivity structures between the two wells. With cross-well methods faults, fracture patterns, and zones of permeability between the wells can be mapped.

Single-well and cross-well resistivity is useful in geothermal exploration because down hole structural features can be revealed in high detail. This information can be very useful for siting future production wells and selecting depths for collecting core samples. Downhole resistivity measurements are useful for mapping resistivity structures, dip, porosity, rock texture, stress patterns, faults, and fractures, thus helping to create a more complete geologic model of the geothermal area and pinpointing future drilling targets.

 

Related Techniques

"<br>

• Well Log Techniques
  • Acoustic Logs
    • Cement Bond Log
    • Cross-Dipole Acoustic Log
  • Caliper Log
  • Chemical Logging
  • Density Log
  • Gamma Log
  • Image Logs
  • Mud Logging
  • Neutron Log
  • Pressure Temperature Log
  • Single-Well and Cross-Well Resistivity
  • [[Spontaneous Potential Well Log|Spontaneous Potential Well Log" cannot be used as a page name in this wiki.

Well Log Techniques

• Acoustic Logs
  • Cement Bond Log
  • Cross-Dipole Acoustic Log
• Caliper Log
• Chemical Logging
• Density Log
• Gamma Log
• Image Logs
• Mud Logging
• Neutron Log
• Pressure Temperature Log
• Single-Well and Cross-Well Resistivity
• Spontaneous Potential Well Log

 

Field Procedures

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An FMI logging tool, this downhole tool provides high resolution borehole resistivity image data. Each arm is meant to keep in contact with the wall of the well so there is a good contact for electrons to flow into the formation. The arms are also meant to keep the tool in the centralized in the well.

There are many different variations of downhole resistivity logging instruments which are designed to be integrated with standard wireline technology. The instrument is lowered down the well via wireline cable and real time resistivity images can be viewed from the logging vehicle.

Conceptual drawing of a cross well resistivity survey with a receiver array in the well on the right and the transmitter in the well on the left.

For a cross well resistivity survey two or more wells can be utilized. An array of electrical receivers is lowered down one well and a transmitter is lowered down another well. Typically the receiver array stays fixed and the transmitter moves between depth ranges while continuously broadcasting. After the profile is completed, the receiver array is moved to a new depth and the process is repeated. For thorough data collection this process is carried out until all source and receiver positions have been occupied for all zones of interest.

 

Physical Properties

See Electrical Techniques

 

Data Access and Acquisition

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Conceptual drawing of how an FMI logging tool functions. Current is sent through the well wall into the surrounding rock by the lower electrodes which are in contact with the well wall. Electrical signals are then measured through the upper electrode. The distance between electrodes will influence the distance into the formation that will be seen.

 

Best Practices

-In the oil and gas industry downhole resistivity data is often analyzed in conjunction with Acoustic Logs. -This type of logging must be done before well casing is installed or beneath the last well casing. Measurements will be unreliable through well casing.

 

Potential Pitfalls

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-Difficult to interpret in very high resistivity zones and/or well mud saturated with salt water.

-Most instruments cannot withstand wells exceeding 175°C unless specially designed electronics or shielding is integrated into the equipment, which can drastically increase the price.

 

References

Page	Area	Activity Start Date	Activity End Date	Reference Material
Electric Micro Imager Log At Coso Geothermal Area (2003)	Coso Geothermal Area	2003	2003	The Coso EGS Project, recent developments (in International collaboration for geothermal energy in the Americas)
FMI Log At Glass Buttes Area (DOE GTP)	Glass Buttes Area			GTP ARRA Spreadsheet
FMI Log At Maui Area (DOE GTP)	Maui Area			GTP ARRA Spreadsheet
FMI Log At New River Area (DOE GTP)	New River Area			GTP ARRA Spreadsheet
FMI Log At Wister Area (DOE GTP)	Wister Area			GTP ARRA Spreadsheet
Resistivity Log At Alum Area (Moos & Ronne, 2010)	Alum Geothermal Area			Selecting The Optimal Logging Suite For Geothermal Reservoir Evaluation- Results From The Alum 25-29 Well, Nevada
Resistivity Log At Fish Lake Valley Area (DOE GTP)	Fish Lake Valley Area			GTP ARRA Spreadsheet
Resistivity Log At Fort Bliss Area (Combs, Et Al., 1999)	Fort Bliss Area			Slimhole Handbook- Procedures And Recommendations For Slimhole Drilling And Testing In Geothermal Exploration
Resistivity Log At Fort Bliss Area (DOE GTP)	Fort Bliss Area			GTP ARRA Spreadsheet
Resistivity Log At Long Valley Caldera Geothermal Area (Nordquist, 1987)	Long Valley Caldera Geothermal Area		1986	Mapping the Hydrothermal System Beneath the Western Moat of Long Valley Caldera Using Magnetotelluric and Time-domain Electromagnetic Measurements The Long Valley/Mono Basin Volcanic Complex: A Preliminary Magnetotelluric and Magnetic Variation Interpretation Magnetotelluric Transect of Long Valley Caldera: Resistivity Cross Section, Structural Implications, and the Limits of a 2-D Analysis New Evidence On The Hydrothermal System In Long Valley Caldera, California, From Wells, Fluid Sampling, Electrical Geophysics, And Age Determinations Of Hot-Spring Deposits
Resistivity Log At The Needles Area (DOE GTP)	The Needles Area			GTP ARRA Spreadsheet
Resistivity Log At Valles Caldera - Redondo Geothermal Area (Rowley, Et Al., 1987)	Valles Caldera - Redondo Geothermal Area	1984	1984	Drilling Report- First CSDP (Continental Scientific Drilling Program) Thermal Regimes Core Hole Project at Valles Caldera, New Mexico (VC-1) Core Lithology, Valles Caldera No. 1, New Mexico
Resistivity Log At Valles Caldera - Sulphur Springs Geothermal Area (Wilt & Haar, 1986)	Valles Caldera - Sulphur Springs Geothermal Area		1986	A Geological And Geophysical Appraisal Of The Baca Geothermal Field, Valles Caldera, New Mexico
Resistivity Tomography At Crump's Hot Springs Area (DOE GTP)	Crump's Hot Springs Geothermal Area			GTP ARRA Spreadsheet
Resistivity Tomography At Silver Peak Area (DOE GTP)	Silver Peak Area			GTP ARRA Spreadsheet

1. Coso Geothermal Area
2. Glass Buttes Area
3. Maui Area
4. New River Area
5. Wister Area
6. Alum Geothermal Area
7. Fish Lake Valley Area
8. Fort Bliss Area
9. Long Valley Caldera Geothermal Area
10. The Needles Area
11. Valles Caldera - Redondo Geothermal Area
12. Valles Caldera - Sulphur Springs Geothermal Area
13. Crump's Hot Springs Geothermal Area
14. Silver Peak Area

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