New method in telluric prospecting for detecting deep conductors, not intersecting with wells : application in the Rouez Region (France)‎

Abstract EN

This research introduces a recent telluric logging methodology in the field of mineral prospecting for the detecting of deep conductors, not intersecting with well.

This method is characterized by its big deep penetration, compared with the conventional surface geoelectrical methods and through boreholes.

The proposed telluric method consists of measuring two telluric fields.

The first one is horizontal and obtained at the surface using a reference line (EEW & ENS).

The second one is vertical (EV) and obtained in the well between two mobile electrodes M and N.

The ratio between the horizontal and vertical telluric fields (EV/EEW & EVØENS) is of interest in this research work.

The application of this method at the Rouez Mine in France permits a location of several conductors not intersecting with the studied well No.

32.

The presence of these conductors is approved by morphological and lithological description.

The well-known macroanisotropy phenomenon is demonstrated in the studied area, where it has been found that longitudinal resistivity ρEW, obtained according to the reference line of EW direction is less than transverse resistivity ρNS, obtained according to the reference line of NS direction.

A wide telluric anomaly at the depth of 140 m has been detected, which could be related to an equivalent conductor sphere.

The horizontal distance between this conductor and well No.

32 is estimated to be 70 m.

The new telluric configuration is important in mining prospecting, since its application decreases considerably the well number needed for the detecting of spreaded conductors and gives rapidly an idea about the distribution of the conductors in the plan.

More tests at the theoretical and practical levels are still needed to make this configuration adapted and easily used in geophysical prospecting.