1 2D cross-hole inversion

2 Sinkhole collapses detection Source: Deceuster, Delgranche, Kaufmann, Faculté Polytechnique de Mons

3 Sinkhole collapses detection Source: Deceuster, Delgranche, Kaufmann, Faculté Polytechnique de Mons

4 Cross-hole survey for iron prospection in Heiba (China) Source J. Zhe, University of Adelaide Mining application

5

6 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) (10 days after)

7 3D fluide migration monitoring Source: Doug La Brecque

8 3. Survey strategies and interpretation How well-resolved are the models? A simple test…

9 DOI index approach Homogeneous reference models: q A = average app. resistivity * 5 q B = average app. resistivity / 5

10 Using the DOI index: electrical imaging in marine environment, Denmark Source: Marescot, L. and Loke, M.H, SAGEEP 2004, Colorado Springs DOI Index Approach

11 Using the DOI index: electrical imaging in marine environment, Denmark DOI index approach Source: Marescot, L. and Loke, M.H, SAGEEP 2004, Colorado Springs

12 4. Summary and conclusions

13 Summary example: Looking for paleo-valleys Source: Marescot et al., 2003, Eclogae Geol. 96

14 Available information

15 Resistivity Mapping Apparent resistivity map

16 P6 P5 2D resistivity tomography

17 Result…

18 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

19 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!