Effect of the azimuthal fluid channel in a cased borehole on multipole dispersions

Summary Fluid channels generated in the annulus of incompletely cemented cased holes are problematic in developing oil, gas, or geothermal resources. The dispersion curves of borehole modes in sonic logging bring additional information on the cement bonding conditions to cement bond logs. Our research investigated the effects of the different central arc angles of a fluid channel in the annulus of a cased borehole on the dispersion curves using numerical experiments. Synthetic 3D numerical models are used to simulate wave propagation. We used a modified matrix pencil algorithm to estimate the dispersion curves both in fast and slow formations. Our results indicated that S-wave velocity measurement by flexural dispersion is stable in all cases in fast formation while only possible in the widest arc angle case in slow formation. The monopole can be utilized to detect large fluid channels. Symmetric flexural in monopole response are useful regardless of the source orientation using monopole source. We notice that the slowness of symmetric flexural is sensitive to the small angle of the fluid channel but not for the large angle case. Moreover, symmetric flexural gives a valuable response to determine fluid layer thickness that is not depending on the fluid position.