Least-Squares Dip Angle 4D Migration for OBN and Towed Streamer Imaging

The migrated dip-angle domain provides a powerful opportunity to distinguish 4D noise from signal based on similarity filtering applied to data decomposed by position, frequency, and geological dip. However, 4D signal protection is problematic when the signal itself forms from differences between baseline and monitor. A set of dip-angle similarity filtering methods applied to towed streamer and OBN data from South Arne field show that 4D signal preservation is possible even with strong timeshift signals between baseline and monitor. Signal protection can be achieved with wrap-around timewarping applied within the filtering methods. A better approach detects lack of coherent signal rather than similarity of coherent signal when present. Using this method it is possible to attenuate significant levels of migration noise without appreciably altering the 4D signal. Dip-angle filtering with workflows that preserve surface offset also allow the similarity filtering to be combined with least-squares Kirchhoff migration using single-iteration migration deconvolution. Results show noise attenuation via similarity filtering complementing the illumination compensation achieved by the least-squares method.