Single-Well and Cross-Well Resistivity

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Exploration Technique: Single-Well and Cross-Well Resistivity

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): 5,000.00500,000 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

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. [1][2] [3] There is also a configuration called Single-point Resistance in which one electrode is placed down a well and one is on the surface.[4]
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.[3] 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.[5]

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.[1][2]

Field Procedures
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. [1]

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.[5]

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

Data Access and Acquisition
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. [6]

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
-Difficult to interpret in very high resistivity zones and/or well mud saturated with salt water. -Most instruments cannot withstand wells exceeding 175°C[1] unless specially designed electronics or shielding is integrated into the equipment, which can drastically increase the price.

  1. 1.0 1.1 1.2 1.3 Hemisphere Technologies. Micro-Conductivity Imager Logging Tool [Internet]. 2011. [cited 2013/10/09]. Available from:
  2. 2.0 2.1 Shakeel Ahmed. Formation Micro-Imager Logs (FMI) [Internet]. 2013. [cited 2013/10/09]. Available from:
  3. 3.0 3.1 Schlumberger. FMI Fullbore Formation Microimager [Internet]. 2013. [cited 2013/10/09]. Available from:
  4. Carole D. Johnson. Borehole Geophysical Methods [Internet]. Storrs, Connecticut. USGS. [cited 2013/10/22]. Available from:
  5. 5.0 5.1 Crosswell Electromagnetic Resistivity Imaging: Illuminating the Reservior [Internet]. 2006. Middle East Asia Reservior Reviiew. [cited 2013/10/22]. Available from:
  6. Schlumberger (Schlumberger). 2002. FMI Borehole Geology, Geomechanics and 3D Reservoir Modeling. N/A: N/A.

Page Area Activity Start Date Activity End Date Reference Material
Electric Micro Imager Log At Coso Geothermal Area (2003) Coso Geothermal Area 2003 2003

FMI Log At Glass Buttes Area (DOE GTP) Glass Buttes Area

FMI Log At Maui Area (DOE GTP) Maui Area

FMI Log At New River Area (DOE GTP) New River Area

FMI Log At Wister Area (DOE GTP) Wister Area

Resistivity Log At Alum Area (Moos & Ronne, 2010) Alum Geothermal Area

Resistivity Log At Fish Lake Valley Area (DOE GTP) Fish Lake Valley Area

Resistivity Log At Fort Bliss Area (Combs, Et Al., 1999) Fort Bliss Area

Resistivity Log At Fort Bliss Area (DOE GTP) Fort Bliss Area

Resistivity Log At Long Valley Caldera Geothermal Area (Nordquist, 1987) Long Valley Caldera Geothermal Area 1986

Resistivity Log At The Needles Area (DOE GTP) The Needles Area

Resistivity Log At Valles Caldera - Redondo Geothermal Area (Rowley, Et Al., 1987) Valles Caldera - Redondo Geothermal Area 1984 1984

Resistivity Log At Valles Caldera - Sulphur Springs Geothermal Area (Wilt & Haar, 1986) Valles Caldera - Sulphur Springs Geothermal Area 1986

Resistivity Tomography At Crump's Hot Springs Area (DOE GTP) Crump's Hot Springs Geothermal Area

Resistivity Tomography At Silver Peak Area (DOE GTP) Silver Peak Area

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