Theoretical and numerical simulation of LWD acoustic cement logging

The demand for cementing quality evaluation of high-angle and horizontal wells have promoted the development of cementing quality inspection technology based on Logging-While-Drilling (LWD) acoustic tools. Based on the propagation theory of elastic waves, we established a cased LWD model of radially layered media. The acoustic responses of various cementing situations in the LWD environment, mainly the waveforms, are numerically simulated. The results show that the collar waves still exist even after acoustic isolation, which is greatly different from the wireline response. Especially when cement is bonded well, the amplitude of collar waves can compare to or even be larger than that of casing waves. The collar waves and the casing waves overlap in the time domain, leading to that conventional cementing quality evaluation methods of wireline logging (CBL/VDL) is unsuitable for the LWD environment. We also investigated the relationship between casing wave amplitude (or attenuation) and cement bond index in the LWD condition. The calculation method of the LWD hybrid bond index using both amplitude and attenuation was formed, providing theoretical guidance for the cementing quality evaluation based on acoustic logging while drilling.