Determining the Impedance of Material Behind a Casing in a Borehole

Abstract

A method for estimating an impedance of a material behind a casing wall in a borehole, the method comprises exciting (602) the casing wall with an acoustic pulse, and measuring (603) an experimental acoustic waveform (W) reflected from the casing wall. The method further comprises initializing (600) an impedance parameter (Zin), computing (601) an inverse casing response (Rcas−1) as function of the impedance parameter, and deconvoluting (604) the experimental acoustic waveform with the inverse casing response to obtain a transducer (T). An iterative loop (605, 606, 607) is performed, comprising the computing of an inverse casing response and the deconvoluting of the experimental acoustic waveform by varying (607) the impedance parameter until the transducer response becomes compact (605, 606) in the time domain. The estimated impedance (Zcem) is obtained (606) from the impedance parameter when the transducer response is compact.

Dependencies are inferred from the claim text.