3D pole-pole responses of buried anisotropic targets and various anisotropic backgrounds in direct-current resistivity survey

Abstract

Many rocks often have the electrical anisotropy property that produces quite different responses from the electrical isotropic rocks. We applied an advanced modeling method to calculate the apparent resistivity responses over an anisotropic target in a homogenous isotropic backgound and an isotropic target embedded in different anisotropic host rocks. We demonstrated comprehensive modeling experiments to characterize the responses of surface pole-pole surveys to the buried targets in different geological backgrounds, which vary in the principal resistivities and Euler angles of the targets or the host rocks. Our modeling results show that: (1) the location of current injection controls the apparent resistivity images in value and shape; (2) almost circle-contours or more or less elongated contours appear in the apparent resistivity images for the anisotropic targets; (3) the isotropic target embedded in the anisotropic host rock generates some radial patterns from the current injection point; (4) the anisotropy strike angles can be obtained from the symmetry axis of the apparent resistivity contours;.(5) multiple locations of current injections throughout the detection region are necessary for the surface pole-pole survey to avoid misleading data interpretation.