1887
Volume 44 Number 6
  • E-ISSN: 1365-2478

Abstract

Abstract

A case history is presented where electromagnetic (EM) methods were applied as a complement to seismic, for structural mapping in basin‐and‐range‐like geology: 366 five‐component magnetotelluric (MT) soundings were carried out together with 331 transient soundings (TDEM) along seismic lines.

Due to high structural complexity, seismic shows a number of limitations. For the same reasons, MT is highly perturbed and three specific interpretation techniques were comprehensively applied:

1. a classical correction of static effect using TDEM sounding, to determine the high‐frequency nondistorted apparent resistivities and thus the corrected tensor;

2. a so‐called regional correction based upon the same concept as the static effect, to transform distorted resistivity curves due to the horst/graben situation into plausible 1D curves, through the use of nomograms built for 2D H‐polarization situations;

3. a stripping technique which made it possible to map areas where a deep conductive Mesozoic shale was present below carbonates, at a depth of 3 km.

After the best MT interpretation was obtained along each line, it was integrated with seismic and with the results from two boreholes. A crude empirical law relating resistivity and acoustic velocity was established and the MT horizons were plotted on the two‐way traveltime seismic sections.

The final integrated cross‐sections obtained are undoubtedly of greater use to the explorationist than the initial seismic sections alone and two wells were accurately predicted.

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2006-04-28
2020-10-27
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