Improving seismic resolution of prestack time-migrated data

Abstract

Seismic resolution significantly affects the quality of seismic interpretation. Processing parameters that effect resolution such as picking velocities in the presence of interbed multiples benefit from an understanding of the underlying geology. Three-dimensional migration is almost always performed by an external service company or internal specialty processing group, with the “final” product being migrated gathers and the final migration-stack section. In the Chicontepec Basin, Mexico, we have evaluated improvements in data quality made after 3D prestack time migration. By first mapping shallow volcanics that generated strong interbed multiples, we performed a new velocity analysis to better image the weaker, underlying primaries of interest. We remove the local migration stretch through an inverse NMO correction, followed by a nonstretch NMO correction and prestack structure-oriented filtering. Such compensation for migration stretch improves the vertical resolution and preserves far-offset data valuable to subsequent prestack inversion that would otherwise need to be muted. Because S-impedance inversion depends heavily on the farther offsets, the resulting S-impedance images have resolution that is in general equivalent to and, in the target area of rapid S-impedance seen in the well logs, exceed that of the P-impedance images. Attributes such as coherence and curvature show improved fault resolution, whereas noisy areas look more chaotic because of the increased frequency content.