US patent 9,772,419 - Decomposing full-waveform sonic data into propagating waves for characterizing a wellbore and its immediate surroundings
A method for estimating parameters of a propagating wave field, such as the direction of propagation in 3D space of an acoustic wave from borehole-acoustic data. The estimation technique uses phase delays between recordings made by the individual receivers related to a plane wave travelling across the receiver array. The estimated plane waves include the wave field generated directly by the acoustic source, as well as refracted and reflected components of these fields. The technique can be used with overlapping wave fields. This will provide significant improvements in the quality of formation properties estimated from full-waveform data that are obtained either from wireline or from while-drilling sonic data. The inventive method enables characterization of abnormalities outside multiple casing strings where acoustic signals are transmitted from a source located inside said multiple casing string.