Method for identifying arrival times of waveforms on acoustic borehole well logs

Claim 1

A method for identifying the arrival times of waveforms on an acoustic borehole well log obtained by running a borehole logging tool having at least one acoustic transmitter and at least one acoustic receiver through a borehole and activating said transmitter at a plurality of spaced-apart depth points within the borehole so that an acoustic trace is obtained of the transmission of acoustic energy from the transmitter to the receiver through the earth formations surrounding the borehole at each of said plurality of depth points, comprising the steps of: (a) selecting a plurality of at least three successive depth point acoustic traces from a single transmitter-receiver pair, (b) measuring the arrival time of the acoustic wave on the center trace of said plurality of traces from visual observation, (c) placing a first window about the arrival time of the acoustic signal along the trace of the center trace of said selected plurality of successive traces, (d) positioning said first window across each of the remaining plurality of successive traces with a linear moveout function between the traces, (e) performing a first n-fold correlation on those portions of said plurality of successive traces which lie within said first window positions across said traces, (f) incrementally pivoting said first window about its fixed position on said center trace thereby repositioning said first window in accordance with the linear moveout function across each of the remaining plurality of successive traces, (g) performing additional n-fold correlations on the portions of said plurality of successive traces which lie within each of the incrementally pivoted first window positions, (h) identifying a trend for the arrival times of the acoustic wave across said plurality of successive traces based on the n-fold correlation yielding the best signal coherence among the incremental first window positions across said plurality of successive traces, (i) employing said trend to position a second window across said center trace and the next successive trace in depth within the borehole, (j) performing a two-fold correlation on those portions of said center trace and said next successive depth trace which lie within said second window, (k) identifying the arrival time of the acoustic wave on said next successive depth trace with respect to the measured arrival time of the acoustic wave on the center trace based on the correlation yielding the best signal coherence between said center trace and said next successive depth trace within said second window, and (l) repeating steps (c) through (k) for each sequential grouping of said plurality of successive traces along said borehole.

Claim 2

A method for identifying the arrival times of waveforms on an acoustic borehole well log obtained by running a borehole logging tool having at least one acoustic transmitter and at least one acoustic receiver through a borehole and activating said transmitter at a plurality of spaced-apart depth points within the borehole so that an acoustic trace is obtained of the transmission of acoustic energy from the transmitter to the receiver through the earth formations surrounding the borehole at each of said plurality of depth points, comprising the steps of: (a) selecting a plurality of at least three successive depth point acoustic traces from a single transmitter-receiver pair, (b) measuring the arrival time of the acoustic wave on the center trace of said plurality of traces from visual observation, (c) placing a first window about the arrival time of the acoustic signal along the trace of the center trace of said selected plurality of successive traces, (d) positioning said first window across each of the remaining plurality of successive traces with a linear moveout function between the traces, (e) performing a first n-fold correlation on those portions of said plurality of successive traces which lie within said first window positions across said traces, (f) incrementally pivoting said first window about its fixed position on said center trace thereby repositioning said first window in accordance with the linear moveout function across each of the remaining plurality of successive traces, (g) performing additional n-fold correlations on the portions of said plurality of successive traces which lie within each of the incrementally pivoted first window positions, (h) identifying a trend for the arrival times of the acoustic wave across said plurality of successive traces based on the n-fold correlation yielding the best signal coherence among the incremental first window positions across said plurality of successive traces, (i) employing said trend to position a second window across said center trace and the next successive trace in depth within the borehole, (j) performing a two-fold correlation on those portions of said center trace and said next successive depth trace which lie within said second window, (k) identifying the arrival time of the acoustic wave on said next successive depth trace with respect to the measured arrival time of the acoustic wave on the center trace based on the correlation yielding the best signal coherence between said center trace and said next successive depth trace within said second window, and (l) repeating steps (c) through (k) for each sequential grouping of said plurality of successive traces along said borehole.