Model Based Inversion of Acoustic Impedance of Annulus Behind Casing

摘要

Techniques involve obtaining acoustic data from an acoustic logging tool, where the acoustic data includes waves reflected from the casing, the annular fill material, the formation, and/or interfaces between any of the casing, the annular fill material, and the formation. A crude casing thickness, tool position (e.g., eccentering), mud sound velocity may be estimated using the acoustic data. A specular reflection signal may also be estimated based on the acoustic data. A modeled waveform may be generated using the estimated specular reflection signal and one or more model parameters, such as an estimated crude casing thickness, an estimated tool position, an estimated sound velocity of mud between the acoustic logging tool and the casing, an estimated impedance of the annular fill material, and an estimated impedance of the mud. The modeled waveform may be calibrated in some embodiments. Furthermore, a casing thickness may be estimated by matching the modeled waveform with the corresponding measured acoustic data. The techniques may output one or more of a thickness of the casing, an apparent impedance of the annular fill material, and the impedance of mud.

主权项

1. A method of determining properties of a wellbore in a formation, the wellbore comprising a casing and an annular fill material between the casing and the formation, the method comprising:
obtaining from an acoustic logging tool, acoustic data comprising acoustic waves reflected from the casing, the annular fill material, the formation, one or more interfaces between any of the casing, the annular fill material, and the formation, or combinations thereof;
estimating a specular reflection signal based on the acoustic data; generating a modeled waveform using the estimated specular reflection signal and one or more model parameters comprising an estimated crude casing thickness, an estimated tool position, an estimated sound velocity of mud between the acoustic logging tool and the casing, an estimated impedance of the annular fill material, and an estimated impedance of the mud; matching the modeled waveform with the acoustic data; and determining one or more of a thickness of the casing, an apparent impedance of the annular fill material, and the impedance of mud, based on the match of the modeled waveform with the acoustic data.