Fracture characterization from seismic attributes and anisotropy through core and image log integration in a giant offshore oilfield

The aim of this study is to understand the distribution of fractures in a carbonate reservoir zones in a giant offshore oilfield in Abu Dhabi. We integrated faults and lineaments interpreted from 3D OBC seismic attributes (pre-stack and post-stack data) with fractures observed in cored (Well “A”) and in Ultra High Resolution Image - UHRI (Well “B”) wells drilled in the area. We found that the maximum curvature attribute is the most suitable attribute in predicting the presence of faults and fractures in this case. The orientation of the extracted fractures is consistent with fracture orientations observed in the core and image log interpretation. The maximum curvature attribute highlights anomalies in NE-SW and NNE-SSW directions which are nearly perpendicular to the dominant fault directions. These anomalies may represent concentration of fractures in the area. It is noted that the dominant fault orientation interpreted from 3D seismic in the study area is NW-SE. The strike of the fracture orientation from the cored well is NE-SW at shallow reservoir level whereas it is in NNW-NNE and NNE-SSW directions at deeper reservoir levels. The fracture strike direction from the cored well data correlates well with the direction of dominant maximum curvature-ant tracking co-rendered attribute anomalies at these reservoir levels. Similarly the strike of the fracture orientation from the high resolution image log is NE-SW and correlates very well with the dominant direction of anomalies interpreted from maximum curvature and anisotropy attributes. The orientation of the extracted faults and fracture lineaments from maximum curvature and azimuthal anisotropy (AVOaz) at different reservoir zones are displayed in stereonet and rose diagrams and compared with the rose diagrams computed from fracture orientation observed in the cored well and in image log at different reservoir levels and a good correlation is observed between them.