True Amplitude Azimuth-Sectored Angle Gathers
PGS True Amplitude Azimuth-sectored Angle Gathers (TA3GS) are routinely used for velocity model building of multi-azimuth and full-azimuth surveys using angle-based tomography and Angle Domain Common Image Gathers (ADCIG) generated by various migration algorithms.
When imaging beneath complex geology, it is common that the events of interest are only illuminated by a limited range of reflection angles and for a narrow azimuth corridor. Therefore, the clearest image of the subsurface can be obtained by selective stacking of specific angle and azimuth contributions that best illuminate the target while discarding the noisy components associated with imaging artifacts.
The PGS depth imaging workflow enables the production of true amplitude azimuth-sectored angle gathers that can be used for post migration processing of the partial images to enhance the signal-to-noise ratio and minimize the artifacts in the final stack. In addition to image enhancement, the angle gathers are reliably employed for Amplitude versus Angle (AVA) analysis and final velocity model refinement.
While PGS TA3GS is independent of the migration algorithm, using PGS RTM migration benefits from a novel Inverse Scattering Imaging Condition (ISIC) that reduces the back-scattering noise traditionally observed on RTM images form cross-correlation imaging conditions. TA3GS has been upgraded to account for attenuation effects and various types of anisotropy in the earth. Currently, all migration algorithms for which TA3GS output is available, are designed to employ velocity models up to Orthorhombic anisotropy and are fully Q-compliant.
True Amplitude Azimuth-sectored Angle Gathers
Two different common azimuth stack images illustrating the advantage of selective azimuth stacking. The circle shows increased resolution in one azimuth sector (left) illuminating a salt flank. The image on the right, from a different azimuth sector, highlights the subsalt reflectivity (arrow).
RTM angle gathers with a traditional cross correlation imaging condition (left) and the PGS Inverse Scattering Imaging Condition (right). Note the backscattering noise dominating the image on the left. ISIC successfully eliminates this noise (right).