| 摘要 |
The problem of detecting sedimentary formations having an abnormally high fluid pressure that are underneath a relatively impermeable formation, (118) , having normal fluid pressures is addressed. At shallow depths, a formation with abnormally high fluid pressure has a shear velocity that is close to zero, (134), and is thus significantly different from the shear velocity of overlying sediments, (118). The high shear wave-velocity contrast is detecte d by measuring, (116), a change in the amplitude of seismic waves reflected fr om the top of the abnormally pressured formation, (130). This may be done by an amplitude versus offset (AVO) analysis of the reflected amplitudes of compressional or shear reflections. Measurements of the amplitude of reflect ed shear waves from a formation, (118), at some depth below the anomalous zone are may also be used to detect the presence of abnormally pressured interval s with low shear velocity, (138), and high shear wave attenuation.
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