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2D cross-hole inversion

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Sinkhole collapses detectionSource: Deceuster, Delgranche, Kaufmann, Faculté Polytechnique de Mons

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Sinkhole collapses detection

Source: Deceuster, Delgranche, Kaufmann, Faculté Polytechnique de Mons

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Cross-hole survey for iron prospection in Heiba (China)

Source J. Zhe, University of Adelaide

Mining application

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Mining application

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Brine tracer injection

Courtesy of Hyunday Institute of Construction Technology, Courtesy of Hyunday Institute of Construction Technology, Korea

Injection: 300 l in 2 days (brine resistivity 0.05 ohm.m)Injection: 300 l in 2 days (brine resistivity 0.05 ohm.m)

(10 days after)(10 days after)

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3D fluide migration monitoring

Source: Doug La Brecque

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3. Survey strategies and interpretation

How well-resolved are the models?

A simple test…

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DOI index approach

Homogeneous reference models:

qA = average app. resistivity * 5

qB = average app. resistivity / 5

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Using the DOI index: electrical imaging in marine environment, Denmark

Source: Marescot, L. and Loke, M.H, SAGEEP 2004, Colorado Springs

DOI Index Approach

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Using the DOI index: electrical imaging in marine environment, Denmark

DOI index approach

Source: Marescot, L. and Loke, M.H, SAGEEP 2004, Colorado Springs

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4. Summary and conclusions

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Summary example:Looking for paleo-valleys

Source: Marescot et al., 2003, Eclogae Geol. 96

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Available information

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Resistivity Mapping

Apparent

resistivity map

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P6

P5

2D resistivity tomography

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Result…

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Advantages

• Resistivity surveys are simple and robust

• Non expensive

• Allows for a rapid qualitative mapping of the underground

• Can be used for a 2D or 3D investigation of the subsurface

• Resistivity contrasts are often present in geological deposits

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Drawbacks and needs for further developments

• Sensitive to non-unicity in the modeling solutions• Quantitative aspects still need to be developed but significant progresses are

currently made (3D inversion)• Sensitivity to noise and metallic bodies such as pipes (urban area)• Usually need for a galvanic coupling• Progress needed for better defining the resistivity properties of geological

material (petrophysics)• Method mainly sensitive to the fluid in rocks. Good for hydrology but a

problem in archeology and soil investigations: the signature of a feature can dramatically change with the seasons or weather conditions!