Self Potential

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Exploration Technique: Self Potential

Exploration Technique Information
Exploration Group: Geophysical Techniques
Exploration Sub Group: Electrical Techniques
Parent Exploration Technique: Electrical Techniques
Information Provided by Technique
Lithology: SP technique originally applied to locating sulfide ore-bodies.
Stratigraphic/Structural: Detection and tracing of faults.
Hydrological: 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.
Thermal: Location of near-surface thermal anomalies: thermoelectric coupling processes due to variations in temperature in the subsurface.
Cost Information
Low-End Estimate (USD): 907.4890,748 centUSD
0.907 kUSD
9.0748e-4 MUSD
9.0748e-7 TUSD
/ mile
Median Estimate (USD): 6,473.05647,305 centUSD
6.473 kUSD
0.00647 MUSD
6.47305e-6 TUSD
/ mile
High-End Estimate (USD): 18,000.001,800,000 centUSD
18 kUSD
0.018 MUSD
1.8e-5 TUSD
/ mile
Time Required
Low-End Estimate: 15.02 days0.0411 years
360.48 hours
2.146 weeks
0.493 months
/ 10 mile
Median Estimate: 23.33 days0.0639 years
559.92 hours
3.333 weeks
0.766 months
/ 10 mile
High-End Estimate: 42.91 days0.117 years
1,029.84 hours
6.13 weeks
1.41 months
/ 10 mile
Additional Info
Cost/Time Dependency: Electrode Spacing, Size, Terrain, Weather
Dictionary.png
Self Potential:
The self-potential (SP) technique is a passive electrical geophysical method based upon the measurement of spontaneous or natural electrical potential developed in the earth due to: 1) electrochemical interactions between minerals and subsurface fluids; 2) electrokinetic processes resulting from the flow of ionic fluids; or 3) thermoelectric mechanisms from temperature gradients in the subsurface.
Other definitions:Wikipedia Reegle


 
Introduction
The self-potential (SP) survey ultimately generates a profile or map of contours of equipotential surfaces. The SP method may be applied to characterizing shallow conductive bodies or subsurface fluid flow. [1][2]
 
Use in Geothermal Exploration
The self-potential technique enables characterization of faults that may provide a conduit for the flow of geothermal fluids. This is due to a few factors: 1) thermoelectric coupling is generated when a temperature gradient exists across a rock body or geological contact (due to thermal fluid or thermal diffusion into the surrounding rock), and 2) the electrokinetic coupling which results from the flow of fluid through a porous medium (such as a thermal fluid-filled fault) causing an electric potential gradient. Steep self-potential anomaly gradients may be indicative of these structures.[3][1]


 
Field Procedures
A Self-Potential survey is a passive, non-invasive geophysical technique. The field equipment required for an SP survey is very minimal. Two non-polarizing electrodes, an insulated cable, and a high impedance voltmeter are required. The electrodes are generally buried at a depth of less than 0.5 meters. The means of access to the station (truck, hiking, etc.) is the largest impact associated with an SP survey.
 
Environmental Mitigation Measures
The small holes which are dug for the electrodes should be filled in once the measurement is complete.
 
Physical Properties
Naturally occurring electrical currents exist in the subsurface. These electrical currents are generated by various temperature, chemical and kinetic processes. It is possible to measure the voltage difference, or potential (in V or mV), resulting from these processes.
 
Data Access and Acquisition
Self-potential (SP) measurements are performed through the measurement of the voltage difference between two points on the earth's surface.


The SP field equipment consists of two non-polarizing electrodes connected by insulated cable and a high impedance voltmeter. Non-polarizing electrodes are used in order to minimize the effects of noise at the soil/electrode interface. The electrodes are porous pots containing a metallic electrode immersed in a salt solution[2] , commonly copper sulfate or lead chloride.

The survey grid and electrode spacing are specific to the particular survey design and depends on the resolution and depth of investigation desired. However, there are two electrode configurations and these are the dipole configuration (a.k.a. leapfrog or gradient configuration) and the fixed-base configuration. The dipole configuration involves recording a measurement and then moving the electrodes along a survey line, maintaining a fixed spacing. The trailing electrode becomes the leading electrode as the electrodes are leap-frogged along the line. The positive voltmeter lead is always connected to the leading electrode to maintain proper polarity. For the fixed-base configuration, one electrode remains stationary and the other electrode is moved to different measurement locations using a cable reel. The fixed-configuration electrode array may result in lower error overall, but its application in the field may be more challenging due to long wire lengths and transporting the cable reel.[2]

The electrodes are generally buried at a depth of less than 0.5 meters. It is crucial to monitor the contact resistance of the electrodes at each station as this is an indicator of the electrical contact between the soil and the electrode. A low contact resistance is desired for better electrical contact with the soil. At times, it is necessary to water the soil in the vicinity of the electrode to reduce the contact resistance, but this should be done with caution in an SP measurement as noise may be introduced to the measurement.[1]

Field notes record the voltage between the electrodes at each specified electrode spacing and station position (1mV resolution is sufficient)[2], and should also indicate the condition of the soil, if water was used to water the electrode contact surface, nearby cultural infrastructure, nearby surface bodies of water and any other condition relevant to a surface electrical measurement.


 
Potential Pitfalls
Noise may be introduced into SP measurements as a result of: drift and polarization in the electrodes; cultural noise such as interference from powerlines; cathodic protection or corrosion on buried pipelines; metallic objects in the vicinity such as well casings; and the quality of the electrical contact at the electrode/soil interface.


 
NEPA Analysis
This exploration technique may be approved on federally managed lands by conducting a categorical exclusion (CX) analysis. Off road travel can be accomplished using existing roads and ways using ATV's and off road transportation. Access can be accomplished by using horses or by foot in areas closed to off road vehicles. An EA may be required in project areas that contain resources with a potential for impacts.


Page Area Activity Start Date Activity End Date Reference Material
Self Potential At Beowawe Hot Springs Area (Garg, Et Al., 2007) Beowawe Hot Springs Area


Self Potential At Blue Mountain Geothermal Area (Fairbank Engineering Ltd, 2003) Blue Mountain Geothermal Area 1996 1998


Self Potential At Central Nevada Seismic Zone Region (Pritchett, 2004) Central Nevada Seismic Zone Geothermal Region


Self Potential At Coso Geothermal Area (2006) Coso Geothermal Area 2006 2006


Self Potential At Cove Fort Area (Combs 2006) Cove Fort Geothermal Area


Self Potential At Dixie Hot Springs Area (Combs 2006) Dixie Hot Springs Area


Self Potential At Haleakala Volcano Area (Thomas, 1986) Haleakala Volcano Area


Self Potential At Hualalai Northwest Rift Area (Thomas, 1986) Hualalai Northwest Rift Area


Self Potential At Kilauea East Rift Geothermal Area (KELLER, Et Al., 1977) Kilauea East Rift Geothermal Area 1973 1973


Self Potential At Kilauea Summit Area (Keller, Et Al., 1979) Kilauea Summit Area


Self Potential At Mauna Loa Southwest Rift Area (Thomas, 1986) Mauna Loa Southwest Rift Area


Self Potential At Mokapu Penninsula Area (Thomas, 1986) Mokapu Penninsula Area


Self Potential At Mt Princeton Hot Springs Geothermal Area (Richards, Et Al., 2010) Mt Princeton Hot Springs Geothermal Area 2008 2010


Self Potential At Mt St Helens Area (Bedrosian, Et Al., 2007) Mt St Helens Area


Self Potential At Neal Hot Springs Geothermal Area (Colwell, Et Al., 2012) Neal Hot Springs Geothermal Area 2011 2011


Self Potential At Northern Basin & Range Region (Pritchett, 2004) Northern Basin and Range Geothermal Region


Self Potential At Nw Basin & Range Region (Pritchett, 2004) Northwest Basin and Range Geothermal Region


Self Potential At Roosevelt Hot Springs Area (Combs 2006) Roosevelt Hot Springs Area


Self Potential At Roosevelt Hot Springs Geothermal Area (Ward, Et Al., 1978) Roosevelt Hot Springs Geothermal Area 1978 1978


Self Potential At Steamboat Springs Area (Combs 2006) Steamboat Springs Area


Self Potential At Twenty-Nine Palms Area (Page, Et Al., 2010) Twenty-Nine Palms Geothermal Area


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


Self Potential At Walker-Lane Transitional Zone Region (Pritchett, 2004) Walker-Lane Transition Zone Geothermal Region


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http://en.wikipedia.org/wiki/Spontaneous_potential