P-wave anisotropy from azimuthal AVO and velocity estimates using 3D seismic data from Saudi Arabia

A horizontal well is most productive in tight reservoirs when it intersects a large number of vertical fractures, yet strata near the borehole remain mechanically stable. Azimuthal velocity analysis and P-wave amplitude versus offset (AVO) using 3D wide-azimuth prestack surface seismic data provide a remote yet defailed way to map a fracture pattern away from well control. We estimate fracture direction and relative fracture intensity from Such data at two gas fields in Saudi Arabia. Our results show it small azimuthal variation in P-wave velocity (maximum 5%) and a larger variation in azimuthal AVO at the reservoir (larger than 100%). Computed fracture attributes for field I show a consistent east-west fracture direction. However, in field 2, fracture azimuth is variable but generally east-west and north-south, with the strongly anisotropic north-south orientation correlating with faults and areas of large structural curvature in the reservoir. In both fields, azimuthal AVO analysis shows a more consistent estimate of fracture orientation than velocity analysis. These estimates have been instrumental in planning prolific and safe horizontal wells