Propagation features about the characteristic wave of acoustic full waveform in cased boreholes

Abstract

Cementing quality directly influences exploitation of oil or gas layers in oil or water boreholes. Characteristic wave (or pseudo-Rayleigh wave) in acoustic full waveform can evaluate the cementing quality of the secondary interface in cased boreholes. Before evaluating the cementing quality of secondary interface, we must analyze bath propagation velocity and amplitude of the characteristic wave. To achieve this, we simulate the acoustic full waveform and 2-D spectrum (frequency-wavenumber spectrum) for various cementing quality of the secondary interface based on the real axis integration method, and analyze relation between bath velocity and amplitude of the characteristic wave and thickness of the water layer on the secondary interface. The simulating results for the waveform and 2-D spectrum of characteristic wave indicate that the velocity of characteristic wave is influenced by the velocity of bath the casing and cement annulus together and is small than that of cased wave. The velocity is increasing and up to the velocity of cased wave with the thickness of water layer. In efficient range of the thickness of water layer, the amplitude of characteristic wave is increasing with the thickness of water layer. Moreover, we validate the simulation results by comparing with experiment data in calibration pits. It is shown that the difference of amplitude or velocity for the characteristic wave can indicate the cementing quality of the secondary interface. These results are of great importance to build the standards of extracting the characteristic wave and criteria of evaluating the cementing quality of the secondary interface.