The effects of bonding conditions on the propagation of acoustic wave along a cased borehole

Based on the wave equations in cylindrically layered structures and boundary conditions, we have derived the frequency equation for axisymmetric guided waves and the expression for sound fields in a cased borehole excited by a monopole and multipole source. The synthetic full waveforms excited by the monopole and dipole source are simulated using a real axis integration and FFT method. According to the axisymmetric guided wave modes, we have analyzed the synthetic full waveforms and studied the effects of the interface conditions on the sound field in cased boreholes. Numerical results indicate that it may be difficult to distinguish well-bonded, poor bonded or unbonded intermediate layer between the metal tube and formation if only using a monopole source or dipole source. To precisely estimate the case boundary conditions, a combination of monopole source logging with dipole source logging is suggested.