Changes

With some FWAL tools, the slowness (inverse velocity or time needed to travel a fixed distance) is obtained the same way as in conventional sonic tools by picking the P wave arrival using a threshold detection algorithm and measuring the moveout between two receivers.<ref name=pt07r63>Willis, M. E., Toksöz, M. N., 1983, Automatic P and S velocity determination from full waveform acoustic logs: Geophysics, v. 48. p. 1631–1644., 10., 1190/1., 1441444</ref> Because of the lower frequency content, this method is not as accurate as that used with conventional sonic tools. The newer generation of FWAL tools take advantage of the larger number of receivers. Several different array processing techniques are used, the most common being semblance stacking along different slownesses.<ref name=pt07r29>Kimball, C. V., Marzetta, T. L., 1984, Semblance processing of borehole acoustic array data: Geophysics, v. 49, p. 274–281., 10., 1190/1., 1441659</ref>; <ref name=pt07r22>Hsu, K., Baggeroer, A. B., 1986, Application of the maximum likelihood method (MLM) for sonic velocity logging: Geophysics, v. 51, p. 780–787., 10., 1190/1., 1442130</ref><ref name=pt07r33>Lang, W. W., Kurkjian, A. L., McClellan, J. H., Morris, C. F., Parks, T. W., 1987, Estimating slowness dispersion from arrays of sonic logging waveforms: Geophysics, v. 52, p. 530–544., 10., 1190/1., 1442322</ref> This method can also be used to obtain the slownesses of the later arrivals, namely, the S wave and the Stoneley wave.

With some FWAL tools, the slowness (inverse velocity or time needed to travel a fixed distance) is obtained the same way as in conventional sonic tools by picking the P wave arrival using a threshold detection algorithm and measuring the moveout between two receivers.<ref name=pt07r63>Willis, M. E., Toksöz, M. N., 1983, Automatic P and S velocity determination from full waveform acoustic logs: Geophysics, v. 48. p. 1631–1644., 10., 1190/1., 1441444</ref> Because of the lower frequency content, this method is not as accurate as that used with conventional sonic tools. The newer generation of FWAL tools take advantage of the larger number of receivers. Several different array processing techniques are used, the most common being semblance stacking along different slownesses.<ref name=pt07r29>Kimball, C. V., Marzetta, T. L., 1984, Semblance processing of borehole acoustic array data: Geophysics, v. 49, p. 274–281., 10., 1190/1., 1441659</ref>; <ref name=pt07r22>Hsu, K., Baggeroer, A. B., 1986, Application of the maximum likelihood method (MLM) for sonic velocity logging: Geophysics, v. 51, p. 780–787., 10., 1190/1., 1442130</ref><ref name=pt07r33>Lang, W. W., Kurkjian, A. L., McClellan, J. H., Morris, C. F., Parks, T. W., 1987, Estimating slowness dispersion from arrays of sonic logging waveforms: Geophysics, v. 52, p. 530–544., 10., 1190/1., 1442322</ref> This method can also be used to obtain the slownesses of the later arrivals, namely, the S wave and the Stoneley wave.

In a “soft” formation where the S wave velocity is lower than the acoustic velocity of the borehole fluid, no refracted S wave can be detected. The S wave slowness can be estimated indirectly using the Stoneley wave slowness.<ref name=pt07r56>Stevens, J. L., Day, S. M., 1986, Shear velocity logging in slow formations using the Stoneley wave: Geophysics, v. 51, p. 137–147., 10., 1190/1., 1442027</ref>, but a number of factors including permeability can affect the Stoneley wave slowness<ref name=pt07r62>Williams, D. M., Zemanek, J., Angona, F. A., Dennis, C. L., Caldwell, R. L., 1984, The long space acoustic logging tool: Transactions of the Society of Professional Well Log Analysts 25th Annual Logging Symposium, Paper T.</ref><ref name=pt07r3>Burns, D. R., Cheng, C. H., Schmitt, D. P., Toksöz, M. N., 1988, [[Permeability]] estimation from full waveform acoustic logging data: The Log Analyst, v. 29, p. 112–122.</ref> The only reliable method is to use the direct shear wave logging tool.<ref name=pt07r62 /><ref name=pt07r3 />

In a “soft” formation where the S wave velocity is lower than the acoustic velocity of the borehole fluid, no refracted S wave can be detected. The S wave slowness can be estimated indirectly using the Stoneley wave slowness,<ref name=pt07r56>Stevens, J. L., Day, S. M., 1986, Shear velocity logging in slow formations using the Stoneley wave: Geophysics, v. 51, p. 137–147., 10., 1190/1., 1442027</ref> but a number of factors including permeability can affect the Stoneley wave slowness.<ref name=pt07r62>Williams, D. M., Zemanek, J., Angona, F. A., Dennis, C. L., Caldwell, R. L., 1984, The long space acoustic logging tool: Transactions of the Society of Professional Well Log Analysts 25th Annual Logging Symposium, Paper T.</ref> <ref name=pt07r3>Burns, D. R., Cheng, C. H., Schmitt, D. P., Toksöz, M. N., 1988, [[Permeability]] estimation from full waveform acoustic logging data: The Log Analyst, v. 29, p. 112–122.</ref> The only reliable method is to use the direct shear wave logging tool.<ref name=pt07r62 /> <ref name=pt07r3 />

==Applications==

==Applications==