DC Resistivity Survey (Wenner Array)

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Exploration Technique: DC Resistivity Survey (Wenner Array)

Exploration Technique Information
Exploration Group: Geophysical Techniques
Exploration Sub Group: Electrical Techniques
Parent Exploration Technique: Vertical Electrical Sounding Configurations
Information Provided by Technique
Lithology: Rock composition, mineral and clay content
Stratigraphic/Structural: 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
DC Resistivity Survey (Wenner Array):
The Wenner array is a type of electrode configuration for a DC resistivity survey and is defined by its electrode array geometry.
Other definitions:Wikipedia Reegle

Use in Geothermal Exploration

Field Procedures
The Wenner array consists of four collinear, equally spaced electrodes. The outer two electrodes are typically the current (source) electrodes and the inner two electrodes are the potential (receiver) electrodes. The array spacing expands about the array midpoint while maintaining an equivalent spacing between each electrode. [1]

The advantages of the Wenner array are that the apparent resistivity is easily calculated in the field and the instrument sensitivity is not as crucial as with other array geometries. Relatively small current magnitudes are needed to produce measurable potential differences.[2] The disadvantages are that for each sounding, all of the electrodes have to be moved to a new position. In order to image deep into the earth, it is necessary to use longer current cables; handling the cables and electrodes between each measurement can be cumbersome, especially in difficult terrain. The Wenner array is also very sensitive to near surface inhomogeneities which may skew deeper electrical responses. [3]

Wenner electrode array geometry and apparent resistivity[4]

Physical Properties

Potential Pitfalls
See Direct-Current Resistivity Survey

• The Wenner array is a labor-intensive survey because of the cable lengths required and the movement of the electrodes during the survey.

• Substantial lengths of cable energized with current at high voltage present a safety hazard.

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