Zhiguang Xue

Increasing resolution of reverse-time migration using time-shift gathers

Reverse-time migration (RTM) has become an industry standard imaging method for complex geological areas. We present an approach for increasing its imaging resolution by employing time-shift gathers. The method consists of two steps: 1) migrating seismic data with the extended imaging condition to get time-shift gathers; 2) accumulating the information from time-shift gathers after they are transformed to zero-lag time-shift by a post-stack depth migration on a finer grid. The final image is generated on a grid which is denser than that of the original image thus increasing its resolution. The proposed method is based on the observation that non-zero-lag time-shift images recorded by the regular computing grid contain the information of zero-lag time-shift image of a denser grid, and such information can be continued to zero-lag time-shift and refocused at the correct locations on the denser grid. The extra computational cost of the proposed method amounts to the computational cost of zero-offset migration, and is almost negligible compared to the cost of prestack shot-record RTM. Numerical tests on synthetic models demonstrate that the method can effectively improve RTM resolution. It can also be regarded as an approach to improve the effciency of RTM by performing wavefield extrapolation on a coarse grid and generating the final image on the desired fine grid. This article is protected by copyright. All rights reserved