Apparatus and method for reducing borehole eccentricity effects

摘要

A well logging tool (10) apparatus for conducting measurements in a borehole traversing a subsurface formation includes an elongated conductive mandrel (51) having a longitudinal axis, an antenna array positioned about the mandrel and including a transmitter (15) for transmitting electromagnetic energy into the formation, and a sleeve (11) positioned about the antenna array. The sleeve has an outer surface positioned for exposure to the borehole environment and an inner surface positioned radially inward of the outer surface. The apparatus further includes a first set of electrodes (12) and a second set of electrodes (12). Each electrode has an outer end and an inner end positioned radially inward of the outer end, and is supported on the sleeve. Further, the first and second sets of electrodes are spaced longitudinally apart such that the transmitter (15) is positioned longitudinally therebetween. Electrodes of the first and second sets are conductively interconnected with the mandrel such that when the well logging apparatus is operated in a borehole environment having borehole currents therein, one or more current path loops are provided for shorting borehole currents through the sleeve to the mandrel. The apparatus reduces borehole eccentricity or standoff effects for tools with transverse or TMD antennas.