Overburden distortions - implications for seismic AVO analysis and time-lapse seismic

摘要

A 3D finite difference (FD) modelling study is used to investigate the effects of various overburden distortions on seismic data. Two types of distortions are considered: shallow diffractions randomly distributed within a 400 m thick layer and shallow lenses. We find that the presence of overburden diffractors leads to considerable local amplitude variation with offset. However, smoothing of the AVO curves reduces the risk of misinterpretation of AVO data. For shallow lenses in the overburden, we find strong impact on the AVO behaviour at top reservoir level, and that these effects ( in contrast to random overburden diffractors) are not reduced by simple smoothing of the AVO data. This study suggests that prior to AVO analysis, it is important to map and identify possible overburden distortions, since various types of overburden effects distort the AVO behaviour in different ways.