Page 431 - Acquisition and Processing of Marine Seismic Data

422 9. VELOCITY ANALYSIS

affecting the velocity, different velocity types lithology by seismic velocities only. For instance,
widely used in seismic data processing, and measured P wave velocities of sandstones range
common methods used to obtain velocity infor- from 1.8 to 4.8 km/s (Sheriff and Geldart, 1995)
mation from seismic data are explained. The depending on several factors, including
acquisition and processing parameters affecting • Lithology
the quality and accuracy of velocity analysis are
• Saturation and fluid type
also discussed.
• Porosity
Seismic wave velocities change over a wide
• Cementation, grain size and pore shape
range in nature, even for the same rock type
• Age of the rock
(Fig. 9.1A), since several factors control the
• Pressure/compaction or depth
velocity of a specified medium. This phenome-
• Density of the medium
non generally prevents defining the subsurface
• Temperature

FIG. 9.1 (A) P wave velocity range of some specific rock types, and (B) effect of different factors on P wave velocity. Com-
piled from Telford, W.M., Geldart, L.P., Sheriff, R.E., 1990. Applied Geophysics. Cambridge University Press; Jones, E.J.W., 1999. Marine
Geophysics. John Wiley.