Azimuthal Resistivity Imaging: A New-Generation Laterolog

Summary We describe a new-generation laterolog tool, the azimuthal resistivity imager (ARI). The tool makes deep azimuthal resistivity measurements around the borehole with higher vertical resolution than the Dual Laterolog (DLL). Twelve azimuthal electrodes are incorporated into the DLL electrode array to provide 12 deep, oriented resistivity measurements while retaining the standard deep and shallow laterolog measurements. To allow full correction of the azimuthal resistivities for borehole effect, a shallow auxiliary measurement is incorporated on the azimuthal array. Although the full-coverage azimuthal resistivity image has much lower spatial resolution than borehole microelectrical images, it complements these because of its lower sensitivity to shallow features. Evaluation of heterogeneous and fractured formations, and computation of fracture dip are applications of the tool's imaging capabilities and are discussed and illustrated with log examples. Other log examples cover thin-bed response and corrections for Groningen and borehole effects, including that for eccentering of the tool in the borehole.