Prestack depth migration of primary and surface-related multiple reflections: Part II - Identification and removal of residual multiples

摘要

Depth imaging using primary and multiple reflections (DIPMR), as described in Part I of this study, allows subsurface information carried by multiple reflections to be utilized. In the presence of strong lateral heterogeneity, however, the migration results may be distorted by artifacts originating from reflections associated with layers above the imaging plane that are commonly referred to as crosstalk. We present an image enhancement procedure that allows such artifacts to be effectively suppressed by predicting the initial crosstalk in a second migration phase. This second migration uses reflections imaged at shallower depth levels and requires knowledge of the total and primary downgoing wavefield at the receiver level. The predicted crosstalk image itself may assist the interpretational effort by indicating areas where artifacts may result in incorrect identification of geologic structures or may cause local distortions of amplitude information. Furthermore, a clean depth image can be obtained by adaptively subtracting the predicted crosstalk-related noise from the original image. The proposed method is an extension of the DIPMR procedure outlined in Part I of this study. However, it is also applicable to seismic data imaged by using conventional migration techniques that are based exclusively on primary reflections. In the latter case, the enhancement procedure allows the effects of imperfect multiple removal during preprocessing to be revealed in the migrated sections. When applied to synthetic data simulated for a complex salt model, the proposed enhancement procedure proved to be valid and effective.