A new logging while drilling (LWD) device acquires laterolog resistivity logs and borehole images in 6-in. holes drilled with conductive mud. On a single drill collar, the tool combines a standard laterolog azimuthal measurement with a new, high-resolution imaging capability. The tool uses monitored button electrodes and toroidal antennas to produce focused laterolog resistivity measurements with azimuthal sensitivity, made at multiple depths of investigation. A new measurement configuration within the button electrodes gives downhole mud resistivity. The toroidal antennas provide bit resistivity and azimuthally averaged focused laterolog measurements at multiple depths of investigation.

The orientation system in the tool uses the earth’s magnetic field as a reference to determine the azimuthal tool position as it rotates. Together with the multi-depth sensitivities of the measurements, this allows structural and borehole invasion profile analysis. The four laterolog images can be compressed and transmitted uphole in real-time for well placement and for wellbore-stability applications.

The high-resolution imager is an array of button electrodes on a removable sleeve. The resulting formation image combines the high resolution of wireline imager with the full borehole coverage of an LWD device. A dedicated data compression algorithm allows real-time transmission of this image with moderate resolution losses, enabling applications such as fracture detection while drilling. This paper describes the tool’s main features and performances in the initial field tests