Fracture anisotropy characterization in crystalline bedrock using field-scale azimuthal self potential gradient

The self-potential (SP) method for mineral exploration is seldom used on land, primarily because of electrode noise problems and nonunique interpretations. Marine measurements of the horizontal gradient of the SP field, on the other hand, are relatively simple to make with an array of electrodes towed behind a ship. With low ship speeds of 5 to 10 km/hour, dense spatial sampling (∼1 m) can be obtained with resolution of better than 1 μV/m. In this paper we report on gradient SP data recorded on the continental shelf of South Australia by a horizontal array of towed electrodes approximately 20 m above the seafloor. Ocean waves and swells with periods of 5 to 15 s yielded large amplitude signals ±20 μV/m, but subseafloor mineralization produced SP gradient anomalies of ±50 μV/m and widths of 2 km or more in a number of parallel traverses. Integrating the observed SP gradients along each line delineated SP anomalies of amplitude up to −100 mV. Self-potential and magnetic anomaly data show limited spatial correlation and have different wavelengths, suggesting that SP sources are probably nonferrous minerals, such as graphite, and are deeper than the magnetic sources. The source of the SP signal is probably reduction-oxidation (redox) potential ([Formula: see text]) variations across a conducting body below the seafloor. We approximate the source as being two dimensional and find the most probable locations of line sources by an image reconstruction method. Numerical finite-element modeling of more realistic source regions suggests shallow, easterly dipping (∼15°) conductors of 1 Ω.m in the uppermost 2 km.

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Hydraulic anisotropy characterization of pneumatic-fractured sediments using azimuthal self potential gradient

Journal of Contaminant Hydrology ◽

10.1016/j.jconhyd.2008.09.023 ◽

2009 ◽

Vol 103 (3-4) ◽

pp. 134-144 ◽

Cited By ~ 3

Author(s):

DeBonne N. Wishart ◽

Lee D. Slater ◽

Deborah L. Schnell ◽

Gregory C. Herman

Keyword(s):

Potential Gradient ◽

Hydraulic Anisotropy ◽

Self Potential

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Mapping Contaminant Plume at a Landfill in a Crystalline Basement Terrain in Ouagadougou, Burkina Faso, Using Self-Potential Geophysical Technique

Water ◽

10.3390/w13091212 ◽

2021 ◽

Vol 13 (9) ◽

pp. 1212

Author(s):

Abdoul Azize Barry ◽

Suzanne Yameogo ◽

Meryem Ayach ◽

Meryem Jabrane ◽

Abdessamad Tiouiouine ◽

...

Keyword(s):

Burkina Faso ◽

Urban Area ◽

Household Waste ◽

Spontaneous Potential ◽

North East ◽

The North ◽

Crystalline Bedrock ◽

Water Tables ◽

Borehole Water ◽

Self Potential

The delineation of pollution plumes generated by household waste landfills is not easy, particularly in the case of discontinuous or intricately extending water tables, such as those developed in a fractured crystalline bedrock context. In Ouagadougou (Burkina Faso), there are many uncontrolled landfills throughout the urban area. The water table, generally located between 3 and 10 m deep, is likely to be contaminated by the leachate from these landfills. More than 1000 measurements of spontaneous potential (self-potential), referenced by GPS, have been carried out on a landfill and its immediate surroundings to the south of the urban area. The geostatistical processing by analysis of variograms and correlograms highlights an adapted prospecting technique and reliable cartography. The response seems to be mainly due to the electrochemical component with hot spots within the landfill and a plume heading towards the North-East. The distribution of the spontaneous potential seems to be controlled, not by the topography of the site, but by the fracturing of the mother rock of dominant direction 15° N, and by the mother rock/saprolite contact. Thus, the plume does not flow to the market gardening just below the landfill but rather to a residential area where monitoring of the quality of the borehole water is required.

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Study of Fluid Flow Movement by Using Self Potential Data

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/873/1/012082 ◽

2021 ◽

Vol 873 (1) ◽

pp. 012082

Author(s):

Neng E. Jubaedah ◽

Wahyudi W. Parnadi

Keyword(s):

Fluid Flow ◽

Electrokinetic Potential ◽

Vertical Direction ◽

Potential Gradient ◽

Fluid Flows ◽

Pilot Project ◽

Test Site ◽

Water Flow Velocity ◽

Study Results ◽

Self Potential

Abstract The Self-Potential (SP) method is passive method in geophysics which works based on the natural presence of an electric field on the surface due to anomalies below the surface. SP value on surface can be generated by fluid flow through rock pores or fractures. We study fluid flow movement in subsurface using the velocity value of fluid flow derived from SP values measured on surface. For that purpose, we carried out mathematical modelling, connecting the Helmholtz-Smoluchovsky’s electrokinetic potential gradient equation with Darcy’s law. The velocity of fluid flow depends on the intrinsic permeability of rocks, electrokinetic potential gradient and electrohydrolic conductivity constant. We tested derived velocity of fluid flow on the SP data from a pilot project test site. Study results show that fluid flow in vertical direction can be identified from SP data at locations where there are significant changes of positive and negative SP values. Fluid flows from a high SP value to a low SP value and this flow is opposite the positive SP gradient. The SP value at study site lie in the range -80mV to -160mV, whereas the value of the water flow velocity lie in the range 0.08 cm/s - 0.21 cm/s.

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