High resolution from a new laterolog with azimuthal imaging

A new resistivity logging tool is described that improves the efficiency of drilling and logging operations by halving the length of traditional Dual Laterolog arrays to 16 ft. The reduced length and weight of the monolithic sonde lead to faster rig-up and can save several meters of rat-hole. The array, based on the configuration of a Dual Laterolog and complemented by an azimuthal electrode array in the center, was designed for high vertical resolution and optimized for invasion response and borehole effect. The tool`s operation is based on a number of independent and simultaneous measurement modes that are combined by software to yield a series of resistivity measurements with different depths of investigation and resolutions. The standard deep and shallow laterolog curves are output with improved resolution, but the flexible computed focusing also allows the substitution of different focusing conditions, which simultaneously yield deep and shallow resistivity curves with still higher resolutions of around 8 in. The passive azimuthal array at the center of the tool provides resistivity imaging of the formation in deep and shallow mode and an auxiliary ultra-shallow measurement sensitive to the radial distance from the borehole wall. An additional in-situ determination of the mud resistivity permitsmore » accurate real-time borehole corrections to be made. Examples from recent field tests show the invasion and thin-bed response of the tool together with applications of the resistivity images.« less