A new approach in reverse time migration for properly imaging complex geological media

Abstract

Reverse time migration (RTM) artifacts usually start to appear in large reflection angles which include a wide-angle range. On the other hand, the only proposed starting reflection angle for RTM artifacts is 60 degrees which is not based on a proven investigation and it seems to be just a suggestion based on trial and error. As an important issue, we determine a predominant starting reflection angle (PSRA) for RTM artifacts which enables us to suppress artifacts properly. Therefore, first we try to open and discuss some issues from a new fundamentally perspective about the number of cross-correlations (NOCC) and its relationship with RTM amplitude and artifacts at reflection and nonreflection points. Second, the cross-correlation and its related NOCC at each subsurface position form a new approach to determine PSRA for RTM artifacts. Using NOCC values, the reflection angle of 55 degrees was determined as PSAR at which the RTM artifacts often start to appear. Finally, a new imaging condition based on the down- and upgoing wave fields and a new weighting function were proposed to suppress RTM artifacts. The new imaging condition can maintain the desired information and suppress artifacts properly for the angle domain of 55° to 90°. A key point in the suppressing process is the direct relationship between reflection angle and artifact production where each reflection angle in the domain of 55° to 90° can produce a different amount of artifacts. Therefore, the proposed imaging condition is able to designate a suitable weight for each reflection angle to properly maintain the desired amplitude and suppress artifacts.