AVA and AVAZ of 3D pre-stack seismic data in Altamont-Bluebell field

Khaled Al Dulaijan and Gary F. Margrave


In this paper, the Altamont-Bluebell 3D pre-stack seismic data is analyzed using AVA to identify sweet spots and using AVAZ to identify azimuthal seismic anisotropy zones and correlate them to sweet spots. In AVA analysis, the reflection coefficient is a function of incident angle and the three elastic parameters or P-wave velocity, S-wave velocity, and density. Therefore, those parameters are inverted for. In AVAZ analysis, four additional quantities (the symmetry angle and the three TI symmetry parameters) need to be obtained by inversion of the azimuth/angle-dependent reflection coefficient. Since the reflection coefficient in the AVAZ case is a higher-order function of seven parameters, we may require include information from larger incident angles as compared to AVA analysis. This will be discussed here. The geology of the field, and seismic data acquisition were described earlier in Al Dulaijan (2017). Our focus will be on the main two targets. The first target is the most prolific oil interval within the overpressured Wasatch. This interval is about 500’ thick, and called Wasatch 180. Most horizontal wells are drilled within this target. The second target is the shallower and thicker gas reservoir within the Upper Green River (UGR) formation.

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