Fracture detection from seismic P-wave azimuthal AVO analysis – application to Valhall LOFS data

Abstract

The P-wave reflection amplitude variation as a function of offset and azimuth reveals much about the anisotropic nature of the subsurface rocks. Stress in the fractured reservoir may be closely linked to the seismic anisotropy. We propose and implement a method that systematically examines the amplitude vs. offset and azimuth (AVOAz) behavior of CMP gathers to invert for the implied fracture orientations and density, without arbitrary procedures such as azimuthal sectoring. Standard statistical methods, applied in this context, give us confidence interval and acceptance criteria for our results. We applied the technique to the Valhall Life Of Field Seismic (LOFS) dataset and produced relevant attribute maps at the reservoir level. The results indicate a strong correlation with changes in stress state associated with production-induced compaction in a fractured reservoir.