Azimuthal Geoelectric Measurements Determination of Multiple Directions of Multiple Subsurface Fissure Directions: Analogue Modelling Experiments

Abstract

To characterize fractured rocks which is principal in hydrological studies, requires knowledge of the orientation of fractures and for this aim there is not too many geophysical tools. For the geophysical determination of the prevailing orientations, so-called azimuthal geoelectric measurements seemed to be a feasible method until their disadvantages (in many cases wrong fracture orientations) were revealed.

 In this paper, we improve azimuthal measurements based on analogue modelling by using the Wenner array, which is widely used in azimuthal measurements. The authors investigate how many azimuthal measurements are needed to determine the prevailing rupture directions (at different measurement points, instead of the previously proposed single measurement for the whole area). Over the range of model parameters we use to characterise the three-dimensional fracture system, the theory of anisotropy paradox can be applied (which is not always the case).

As the model measurements suggest, our improved method for determining the fracture directions is itself slightly more expensive, but cheaper than the water-bearing test. If additional electrode arrays are included or azimuthal measurements are combined with geoelectric profile measurements, a more reliable solution can be expected at a somewhat lower cost.