Uncertainties in the Analysis of Avoa for Determination of Fracture Orientation

摘要

Amplitude variation with offset and azimuth (AVOA) of a P-wave reflection indicates azimuthal anisotropy in at least one of the layers surrounding the reflector. A likely cause of such anisotropy is a set of aligned vertical cracks or fractures. We present a case study of AVOA analysis of a single reflection in a portion of a 3-D multi-azimuthal seismic marine dataset. We consider two approaches to estimating the orientation of a hypothetical fracture set and attempt to assess the uncertainties in the relevant parameters. This allows us to identify which amplitude variations are significant. Some local trends can be seen, but there does not appear to be any globally-preferred orientation. Unfortunately the results of our analysis cannot be confirmed due to the absence of other data (e. g. from wells).