Effects of source mismatch on multipole Logging

Abstract

The effects of mismatched multipole sources were investigated. Multipole sources considered here are those that they are constructed of monopoles with appropriate sign combination. To simulate mismatched dipole and quadrupole sources, we made the amplitude of one of monopoles smaller than those of the other monopoles. The dipole and quadrupole component were obtained with four monopole receiver array system by subtracting or adding appropriate responses. Mismatched dipole source excites nondipole modes in addition to the flexural mode. The strongest of these is the Stoneley mode, whose amplitude increases with increasing mismatch. Similarly, mismatched quadrupole sources produce nonquadrupole modes such as the Stoneley mode in addition to the screw mode. The amplitude of the Stoneley mode increases with mismatch. However, we can obtain the flexural mode by A-C and the screw mode by A-B+C-D processing, respectively. The Stoneley mode, which has the same amplitude at the same radial position from the borehole axis, is cancelled out by A-C and A-B+C-D processing as long as the tool is placed at the center of the borehole.