Self-potential methods pdf

For some field use, heavy twine or light rope may need to be twisted and knotted to long lengths of wire to add strength. Survey wire must have abrasion-resistant insulator wrapping. Pulling the wire over roadway surfaces can expose bare wire. Usually random bare wire positions will not fully ground to the soil, and the effects will be variable as differing lengths of wire are unreeled and occupy differing positions for the survey. This error will only modify the signal by a few to tens of millivolts mV.

Twisted two-conductor, gauge, multistrand not solid conductor copper wire has been found to be strong and abrasion resistant. Resistance will be constant for survey wire between stations if the wire for a reading set is not permanently stretched in length, does not develop insulator leaks, and is not repaired.

Repairs to wire should be made when needed because of bare wire or severe plastic stretching of the wire. No changes to the wire may be made during a loop or grid of readings without reoccupation of those positions. Wire accidentally severed requires a remeasurement of that complete set of circuit stations. Millivolt Meter. An inexpensive, high-input-impedance voltmeter is used to read the potential in the millivolt range.

Actual field voltage will be in error when the source potential is within an order of magnitude of the input impedance of the meter. The meter uses a bias current to measure the desired potential. Higher input impedances are desirable due to the impedance reduction of air's moisture. The resolution of the meter should be 0.

Several useful options on meters are available. Digital voltmeters are more easily read. Water-resistant or sealed meters are extremely beneficial in field use. Notch filters about 60 Hz will reduce stray alternating current AC potentials in industrial areas or near power lines. Field Deployment. Background potentials for these surveys may be at a level of a few tens of millivolts.

Source self-potentials must exceed the background to be apparent. Potentials exceeding 1. When large potentials are expected or have been found at the site with nonpolarizing electrodes, the easier to use copper-clad steel electrodes have been substituted for porous pots, but steel electrodes are not recommended. Contact potentials of the steel electrodes and reversing electrode positions are required systematically for steel electrodes.

Large errors may develop from the use of steel electrodes Corwin Measurements with the electrodes may require a system of reversing the electrode position to resolve contact potentials at the electrodes. Previously measured locations may need to be remeasured on a systematic or periodic basis. Reoccupation of stations is necessary when very accurate surveys are being conducted and for sites with temporal potential changes or spatial variations of electrode potential.

Changes temporally in the electrodes or due to the self potential of the field require the survey to be conducted in a gridded or loop array. Loops should have closure voltages of zero or only a few millivolts. High closure potential requires remeasuring several to all of the loop stations.

Station reoccupation should be in the same exact position of the earlier reading s. Unclosed lines should be avoided. Reoccupation of particular station intervals should be made when closed loops are not possible. The traveling electrode should periodically remeasure the base location to observe contact potential, dirty electrodes, or other system changes. Reversing the survey electrodes or changing the wire polarity should only change the voltage polarity. Electrodes may have contact differences due to varying soil types, chemical variations, or soil moisture.

Temporal and temperature variations are also possible, which may require the reoccupation of some of the survey positions on some arranged loop configuration.

Electrode potentials have minor shifts with temperature changes Ewing Variation in the flow of fluid due to rainfall, reservoir elevation changes, channelization of flow, or change of surface elevation where measurements are obtained are sources of variation of streaming potential.

Self potentials may have temporal or spatial changes due to thunderstorm cloud passage, dissemination of mineralization or electrolytic concentration, and in the groundwater flow conduits and location. High telluric potential variations may require the SP survey to be delayed for a day. Some simple procedures are required to perform accurate and precise SP surveys.

Good maintenance of porous pots, wires, and voltmeters must be observed through the survey. The traveling pot needs to be kept clean of soil with each position. Contact with moist soil, or more elaborate measures for good electrical contact with roadways or rock, must be assured. A water vessel may be carried to moisten the soil hole and clean the porcelain surface. Wire reels speed the pulling of cable and wire recovery for changing loops, and lessen wear on the cable.

Reversing the wire polarity for some measurements and reoccupation of adjacent stations assures the cable has not been grounded or stripped. Repair and checking of the wire must be made between loops and is easily done when rewinding the cable reel. Quality assurance in the field is conducted by reoccupation of loop closure points with the same base position. Repeated and reversed readings of particular loop-end stations and checking base locations provide statistics for the assessment of measurement quality.

Grid surveys offer some advantages in planning SP surveys. Changes in elevation changing the distance to the potential source and cognizance of cultural effects can be minimized with planning survey grids or loops. AC power lines, metal fences, and underground utilities are cultural features that affect the potential field extraneous to the normal sources of interest.

Most SP investigations use a qualitative evaluation of the profile amplitudes or grid contours to evaluate self- and streaming-potential anomalies. Flow sources produce potentials in the direction of flow. Fluid inflow produces negative relative potentials, as would greater distance from the flow tube; outflow of the fluid results in positive potentials.

Quantitative interpretations for a dam embankment with possible underseepage would be determined from the profiles across the crest. Negative anomalies may be indicative of flow from the reservoir at some depth. Seismoelectric coupling Appendix A: a simple model of the Stern layer Appendix B: the u-p formulation of poroelasticity References Index. View via Publisher. Save to Library Save.

Create Alert Alert. Share This Paper. Background Citations. Methods Citations. Topics from this paper. Potential method. Citation Type. Has PDF. Publication Type. More Filters. Fluid injection in Enhanced Geothermal Systems: a study on the detectability of self-potential effects and on their correlation with induced seismicity.

Abstract We present a numerical modeling aimed at investigating nature and role of the self-potential SP anomalies induced by water injection in boreholes at the Soultz-sous-Forets SsF hot dry … Expand.

Asian Journal of Applied Sciences. Self-potential is a geophysical method as an inexpensive, practical, and simply used measurements. View 1 excerpt, cites methods.

Pure and Applied Geophysics. The redox field generated by electrically conductive minerals is one of the main constituents of self-potentials. It can be explained by electrochemical reactions in which conductors participate. The … Expand. Determination of the permeability of seepage flow paths in dams from self-potential measurements. Abstract The flow of the pore water in porous media generates an electrical current known as the streaming current.

This current is due to the drag of the excess of charges contained in the … Expand. A review on modeling, inversion and interpretation of self-potential in mineral exploration and tracing paleo-shear zones.