Attributes Assisted Seismic Interpretation in Pre-Stack Time Versus Depth Migration Data

Abstract

Pre-stack time migration (PSTM) has pitfalls in processing seismic data which causes artificial features on seismic images and might mislead the structural interpretation. First, fault shadows give rise to a second (artificial) discontinuity coherence images computed from PSTM data. Second, velocity pull-up and push-down caused by the lateral changes in the overburden such as carbonate buildups and incised valleys will give rise to erroneous curvature anomalies in PSTM data. Besides, PSTM data may be poorly focused in complex structures. Fault terminations of reflectors may be misaligned, giving rise to “wormy” coherence anomalies. Channels and other stratigraphic features may be diffused, making them hard to interpret. To remove the above pitfalls caused by PSTM, pre-stack depth migration (PSDM), which assumes that seismic waves are propagated in straight rays, is necessary in the presence of strong lateral velocity variation to avoid these artifacts. The more accurate velocity model established by PSDM better images complex structures. The seismic data from the Bohai Bay Basin in China are separately processed by PSTM as well as PSDM, combining with seismic attributes, to compare the seismic imaging quality. Several sub-fault splays artifacts in coherence generate the fault-shadow zones under dipping main faults in PSTM data, but disappear in PSDM data. The curvature anomalies related to the lateral variations may be misinterpreted as real structures in PSTM data, which are removed in precise velocity PSDM data. Therefore, In the presence of strong lateral variations in velocity, PSDM is better for interpreting complex structures comparing PSTM which fails to properly image the subsurface.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015