Component wave analysis of borehole seismoelectric wavefields in a porous formation

Abstract

In this work, the axisymmetric seismoelectric logging response excited by a point-pressure source is formulated as an integral in the frequency-wavenumber domain. To analyze the properties of each constituent wavepacket in the seismoelectric logs, the poles and the branch points of the integrands are examined by the complex analysis. The electromagnetic wavenumber in the borehole fluid proves to be a removable branch point. The argument principle is used to search for the complex poles. After the excitation intensity as well as the dispersion curves has been obtained for each component wave for a typical sandstone formation, the ratio of the electric excitation intensity to the acoustic excitation intensity is evaluated. Especially it is found that the argument of this ratio of the Stoneley wave is sensitive to the permeability. The excitation curves corresponding to the branch points show that the compressional wave has a higher seismoelectric conversion efficiency than the shear wave and the mode waves.