Method and device for estimating sonic slowness in a subterranean formation

A computing system comprising:

• one or more processors for processing data;
• and
• one or more memories operatively coupled to the one or more processors that comprise program instructions for causing said one or more processors to perform a method for estimating sonic slowness that comprises:
• obtaining a plurality of sonic waveforms received by a plurality of receivers after emission of a source sonic wave by a transmitter through the subterranean formation to obtain a plurality of recorded sonic waveforms, the plurality of receivers located at different positions in the subterranean formation;
• obtaining at least two slowness models of the subterranean formation, a slowness model being defined by at least one cell of constant slowness for at least one wave energy mode;
• computing, for each slowness model, a set of candidate travel times, each candidate travel time of a set of candidate travel times being computed for one said wave energy mode and a position of the transmitter and a position of a receiver in the plurality of receivers;
• computing a relevance indicator for each set of candidate travel times based on the recorded sonic waveforms by extracting from at least one of the recorded sonic waveforms at least two wave components corresponding respectively to at least two wave energy modes and computing the relevance indicator for the corresponding set of candidate travel times by numerically combining operator output values corresponding to the at least two wave energy modes;
• searching a match between the sets of candidate travel times and the recorded sonic waveforms by searching the relevance indicators for a relevance indicator that is optimum;
• and
• computing a sonic slowness estimate for the subterranean formation from a set of candidate travel times for which the relevance indicator is optimum.

One or more non-transitory computer-readable media comprising processor-executable instructions executable to cause a computing system to:

• obtain a plurality of sonic waveforms received by a plurality of receivers after emission of a source sonic wave by a transmitter through the subterranean formation to obtain a plurality of recorded sonic waveforms, the plurality of receivers located at different positions in the subterranean formation;
• obtain at least two slowness models of the subterranean formation, a slowness model being defined by at least one cell of constant slowness for at least one wave energy mode;
• compute, for each slowness model, a set of candidate travel times, each candidate travel time of a set of candidate travel times being computed for one said wave energy mode and a position of the transmitter and a position of a receiver in the plurality of receivers;
• compute a relevance indicator for each set of candidate travel times based on the recorded sonic waveforms by extracting from at least one of the recorded sonic waveforms at least two wave components corresponding respectively to at least two wave energy modes and computing the relevance indicator for the corresponding set of candidate travel times by numerically combining operator output values corresponding to the at least two wave energy modes;
• search a match between the sets of candidate travel times and the recorded sonic waveforms by searching the relevance indicators for a relevance indicator that is optimum;
• and
• compute a sonic slowness estimate for the subterranean formation from a set of candidate travel times for which the relevance indicator is optimum.