oa Issues in Implementing the Kirchhoff Integral for 3D Pre-Stack Depth Migration

The Kirchhoff approach to depth migration requires computation of travel times. We use dynamic ray tracing to shoot a bundle of rays upward from each subsurface point to be imaged. The number of rays varies between a few to several thousand rays per bundle and is dependent on the local complexity of the velocity-depth model. For instance, in sedimentary sections. 1500 rays may be sufficient to accurately determine travel times. However, in the presence of salt structures, up to 7000 rays may be required. For large-scale problems associated with complex structures, implementation of 3-D prestack depth migration requires efficient construction oftravel time tables and their use in Kirchhoff summation.