Logging-while-drilling (LWD) sonic data collected during Ocean Drilling Program Leg 196 in low-velocity turbidites and hemipelagic sediments were analyzed to extract P-wave velocity using high-resolution dispersion analysis and appropriate tool and borehole modeling. The sonic waveform data show an overall increase in velocity with decreasing frequency. Numerical modeling indicates that velocity computations should be made in the frequency band of highest waveform energy. Estimates of velocity using this approach compare well with core data and wireline sonic logs at the reference site (Site 1173), whereas conventional semblance analysis and dispersion corrections using a look-up table tend to underestimate the velocity by as much as 10%. Synthetic seismograms computed using this approach from the LWD sonic data correlate well to seismic reflection profiles at Site 1173. At Site 808, correlation of synthetic seismograms from our LWD data analysis suggests that transverse velocity anisotropy is present in the prism sediments. High-resolution dispersion analysis is recommended for velocity analysis from LWD sonic data in similar low-velocity marine sediments.
1Goldberg, D., Cheng, A., Gulick, S.P.S., Blanch, J., and Byun, J., 2005. Velocity analysis of LWD sonic data in turbidites and hemipelagic sediments offshore Japan, ODP Sites 1173 and 808. In Mikada, H., Moore, G.F., Taira, A., Becker, K., Moore, J.C., and Klaus, A. (Eds.), Proc. ODP, Sci. Results, 190/196 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/190196SR/352/352.htm>. [Cited YYYY-MM-DD]
2Borehole Research Group, Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades NY 10964, USA. goldberg@ldeo.columbia.edu
3SensorWise, Inc., 2908 Rodgerdale Road, Houston TX 77042-4119, USA.
4Institute for Geophysics, Jackson School of Geosciences, University of Texas, 4412 Spicewood Springs Road, Building 600, Austin TX 78759, USA.
5Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, E34-366, 77 Massachusetts Avenue, Cambridge MA 02139-4307, USA.
Initial receipt: 3 November 2003
Acceptance: 19 October 2004
Web publication:
7 January 2005
Ms 196SR-352