Evaluation of Fracture Imaging Using Azimuthal Prestack Depth Migration

A major uncertainty in fracture analysis based on the azimuthally variant seismic velocities is the interference from structural effects. Structural dip induces azimuthal variation in velocity, which can mask the influence on traveltimes caused by the presence of fractures. In situations where the subsurface geology is complex, Prestack Depth Migration (PreSDM) should be used to correct for the dip prior to the azimuthal velocity analysis. PreSDM is sensitive to velocity variation, thereby making it a good tool for detection of subtle velocity changes. This paper focuses on a fracture detection methodology using a 3D azimuthal depth imaging workflow. The workflow presented here utilizes scanning of azimuthally dependent residual moveout volumes for three-dimensional (3D) mapping of zones with a higher probability of fractures. This analysis can also be used to help determine the fracture style (single or multiple set of fractures). The workflow was successfully applied to wide azimuth, high-fold land seismic data acquired over a fractured formation in the northern part of Saudi Arabia