| 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. |
| The most direct use of FWAL is the measurement of formation shear wave velocity. Together with P wave velocity and density, one can obtain the shear modulus and compressibility of the formation, which are very important in engineering applications. P wave to S wave velocity ratio is a good indicator for lithology, and borehole S wave velocity information is necessary for tie-in with shear wave reflection profiles, amplitude versus offset studies, and elastic wave equation migrations, among many other uses. | | The most direct use of FWAL is the measurement of formation shear wave velocity. Together with P wave velocity and density, one can obtain the shear modulus and compressibility of the formation, which are very important in engineering applications. P wave to S wave velocity ratio is a good indicator for lithology, and borehole S wave velocity information is necessary for tie-in with shear wave reflection profiles, amplitude versus offset studies, and elastic wave equation migrations, among many other uses. |
| The FWAL is also commonly used to identify and characterize fractures. Fractures are easily identified by a significant attenuation in all the wave modes—P, S, and Stoneley. An example of data across a fracture zone is shown in [[:file:full-waveform-acoustic-logging_fig2.png|Figure 2]]. Various models are available to estimate the permeability of the fracture from the Stoneley wave attenuation across a fracture<ref name=pt07r44>Paillet, F. L., 1983, Acoustic characterization of fracture permeability at Chalk River, Ontario, Canada: Canadian Geotechnical Journal, v. 20, p. 468–476., 10., 1139/t83-055</ref> <ref name=pt07r57>Tang, X. M., Cheng, C. H., 1989, A dynamic model for fluid flow in open borehole fractures: Journal of Geophysical Research, v. 94, p. 7567–7576., 10., 1029/JB094iB06p07567</ref> and reflection from a fracture.<ref name=pt07r21>Hornby, B. E., Johnson, D. L., Winkler, K. W., Plumb, R. A., 1989, Fracture evaluation using reflected Stoneley wave arrivals: Geophysics, v. 54, p. 1274–2188., 10., 1190/1., 1442587</ref> | | The FWAL is also commonly used to identify and characterize fractures. Fractures are easily identified by a significant attenuation in all the wave modes—P, S, and Stoneley. An example of data across a fracture zone is shown in [[:file:full-waveform-acoustic-logging_fig2.png|Figure 2]]. Various models are available to estimate the permeability of the fracture from the Stoneley wave attenuation across a fracture<ref name=pt07r44>Paillet, F. L., 1983, Acoustic characterization of fracture permeability at Chalk River, Ontario, Canada: Canadian Geotechnical Journal, v. 20, p. 468–476., 10., 1139/t83-055</ref> <ref name=pt07r57>Tang, X. M., Cheng, C. H., 1989, A dynamic model for fluid flow in open borehole fractures: Journal of Geophysical Research, v. 94, p. 7567–7576., 10., 1029/JB094iB06p07567</ref> and reflection from a fracture.<ref name=pt07r21>Hornby, B. E., Johnson, D. L., Winkler, K. W., Plumb, R. A., 1989, Fracture evaluation using reflected Stoneley wave arrivals: Geophysics, v. 54, p. 1274–2188., 10., 1190/1., 1442587</ref> |