5D interpolation to improve AVO and AVAz: a quantitative case history

5D interpolation followed by azimuthal prestack migration results in better conditioned gathers for Amplitude Versus Offset (AVO) and Amplitude Versus Azimuth (AVAz) analysis. The data should be prestack migrated prior to AVO or AVAz analysis, but this often proves problematic for land data due to the poor sampling of the data in offset and azimuth. This sparse sampling results in incomplete constructive and destructive interference of the migration operator resulting in migration noise. By 5D interpolating the data, the wavefield is better sampled leading to better migrated gathers and AVO or AVAz results. This is demonstrated quantitatively on a 3D dataset from Western Canada. This dataset has been processed with different interpolation/migration flow combinations and then analyzed for AVO and AVAz. The AVO data has been correlated to 69 wells at the Viking level. These correlations show that by including the 5D interpolation, better AVO predictions of the Viking porosity thickness (Phi-h) are obtained. When the study was originally performed only 29 wells had been drilled. Since then, the exploration area was enlarged and an additional 19 wells were drilled for the Viking based on this new methodology resulting in an increase in the drilling success rate and the economic return. An AVAz study was subsequently performed on the Nordegg reservoir with the results being calibrated to two horizontal wells with image log data. Because of the extra dimensionality of this analysis, the data were remigrated. Both azimuthally sectored and Common Offset Vector (COV) Kirchhoff prestack time migrations were performed along with several different interpolation strategies. Each interpolated/migrated result was then analyzed for AVAz using the near offset Ruger equation, the results of which were compared to the image log data in a series of scatter plots. The correlation coefficients between the image log data and the AVAz results that were obtained using a flow which employed interpolation were superior to those obtained using a flow which did not employ interpolation.