Abstract: Contribution of Shear Waves to Stratigraphic Interpretation

G. Omnes

Theoretical and experimental studies indicate that shear waves propagating with a displacement vector parallel with the stratification, or SH-waves, have the following properties.

1. Their velocity is a function of rigidity, not of compressibility and rigidity as for P-waves. Thus, the ratio Vs/Vp can be used for mapping facies changes, particularly the proportion of sand or carbonate in shales.

2. Resolution commonly is superior because, although frequencies are somewhat lower than those of P-waves, velocities are about half of P-wave velocities and so wavelengths are shorter, allowing more detailed seismic images. Lower velocities of SH-waves facilitate the detection of small structures; sandstone/shale contacts visible on SH-waves sections frequently are undetected by P-waves; and faults with very small throws may be undetectable on P-wave sections and quite visible on the SH-wave sections when they are associated with heavier jointing and fracturing of competent formations.

3. Fluids in porous rocks do not influence directly the propagation of SH-waves. Thus, SH-waves can help to verify the nature of P-wave bright spots associated with gas-bearing reservoirs.

AAPG Search and Discovery Article #90963©1978 AAPG/SEG/SEPM Pacific Section Meeting, Sacramento, California