Knowledge of pressure compartments is essential for identifying potential r
isks in advance of drilling and in understanding the mechanism of hydrocarb
on trapping and migration. These compartments are bounded by pressure seals
which, under certain conditions, can be detected and characterized with se
ismic reflection data. Use of prestack seismic data requires the analysis o
f reflections generated at the pressure seals, such as the top of a reservo
ir, rather than the properties of the rock volume. In this sense, amplitude
variations with offset (AVO) techniques can be a good tool to obtain infor
mation from such pressure seals or pressure transition zones. In this work,
I investigate the AVO response of compartment seals by analyzing the plane
-wave reflection coefficients as a function of pore pressure (above and bel
ow the seal), incidence angle, and seal thickness. For the case investigate
d in this work (Berea sandstone with high gas saturation), the AVO effects
are important at low effective pressures, that is, when the pore pressure a
pproaches the confining pressure. In shale-free transition zones, the anoma
ly is, in general, negative, whereas in shale/sandstone sequences, the anom
aly can be positive or negative depending on seal thickness and formation p
ressure, In terms of the four-category classification for AVO crossplotting
, the rr anomalies are mainly class IV and class I.