DC Resistivity Survey (Schlumberger Array)

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Exploration Technique: DC Resistivity Survey (Schlumberger 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 (Schlumberger Array):
The Schlumberger 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 Schlumberger array consists of four collinear electrodes. The outer two electrodes are current (source) electrodes and the inner two electrodes are the potential (receiver) electrodes. The potential electrodes are installed at the center of the electrode array with a small separation, typically less than one fifth of the spacing between the current electrodes. The current electrodes are increased to a greater separation during the survey while the potential electrodes remain in the same position until the observed voltage becomes too small to measure. Typically, expanding the current electrodes occurs roughly six times per decade. [1][2]

The advantages of the Schlumberger array are that fewer electrodes need to be moved for each sounding and the cable length for the potential electrodes is shorter. Schlumberger soundings generally have better resolution, greater probing depth, and less time-consuming field deployment than the Wenner array.[3] The disadvantages are that long current electrode cables are required, the recording instrument needs to be very sensitive, and the array may be difficult or confusing to coordinate amongst the field crew. [4]

Schlumberger array and apparent resistivity[5]

Physical Properties

Potential Pitfalls
See Direct-Current Resistivity Survey

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

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

Page Area Activity Start Date Activity End Date Reference Material
DC Resistivity Survey (Schlumberger Array) At Coso Geothermal Area (1977) Coso Geothermal Area 1977 1977

DC Resistivity Survey (Schlumberger Array) At Raft River Geothermal Area (1974-1975) Raft River Geothermal Area 1974 1975

DC Resistivity Survey (Schlumberger Array) At Roosevelt Hot Springs Geothermal Area (Ward, Et Al., 1978) Roosevelt Hot Springs Geothermal Area 1978 1978

DC Resistivity Survey (Schlumberger Array) At Waunita Hot Springs Geothermal Area (Heinrichs Geoexploration Company, 1981) Waunita Hot Springs Geothermal Area 1981 1981

Schlumberger Resistivity Soundings At Chena Geothermal Area (Wescott & Turner, 1982) Chena Geothermal Area 1979 1980

Schlumberger Resistivity Soundings At Kilauea East Rift Geothermal Area (Kauahikaua & Klein, 1978) Kilauea East Rift Geothermal Area 1973 1976

Schlumberger Resistivity Soundings At North Brawley Geothermal Area (Meidav & Furgerson, 1972) North Brawley Geothermal Area 1968 1970

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