Azimuthal Resistivity To Characterize Fractures In A Glacial Till

Abstract

Azimuthal resistivity was used to characterize fractures in a glacial till at the King site, near Birsay SK. The King site is a hydrogeological test site where the presence of fractures has been identified, but the fracture orientation was not previously known. Preliminary azimuthal resistivity surveys indicated that the site was electrically heterogeneous. There was no interpretable anisotropy in the azimuthal resistivity data. A revised methodology was developed where the effects of heterogeneity could be removed from the azimuthal resistivity data. A detailed 3D, isotropic, geoelectric model was developed for the site. This model was used to predict the azimuthal resistivity observations from an isotropic, heterogeneous earth. These predictions were removed from the observations, leaving the anisotropy. The process resulted in an interpretable anisotropy over portions of the site where the variations in resistivity varied by approximately a factor of two. However the process did not remove the heterogeneity from portions of the site with larger resistivity contrasts.