Dipole source mismatch and its effects on sonic logging

Wavefields excited by a dipole source with amplitude mismatch are investigated through a 3D finite difference method. It is revealed that the directional patterns of a dipole source mainly depend on the source frequency and the amplitude ratio of the two monopoles combining the transmitter. A mismatched dipole will not generate the non-dipole components in the borehole as long as the dipole receivers are ideally matched. When both the transmitter and receivers are mismatched, the Stoneley mode with strong amplitudes appears in the in-line and cross-line components of the cross-dipole sonic logging data. It would probably lead to incorrect evaluations of shear velocity and azimuthal anisotropy of the formation.