f What does It take to Image Complex Geology?

Accurate seismic imaging is extremely difficult in foldbelts because of the presence of rugged topography, complex geology, and lateral changes in rock velocities. Since seismic is a time image of the earth, true structure identification depends on the ingenuity of the interpreter and his ability to integrate other data into the interpretation. The accuracy of seismic to image structures depends on acquisition and processing efforts. We now have pre-stack depth migration and forward modeling to help the interpreter in his quest to resolve true structure. Acquisition is the critical step, where the design for signal resolution, energy penetration, and noise reduction must be optimized. Great care must be taken throughout the processing effort, but solving static problems and accurate migration are most important. In complex areas, usually there are rapid near-surface changes that cause time pull-ups and push-downs that must be addressed in the processing effort. Because of complexity, post-stack time migration has little chance of placing diffractions and dipping events into their correct positions. With the development of pre-stack depth migration, the interpreter is able to get more accurate images of the geology. This will provide for improved success rates, and may change some of our concepts in structural deformation. Forward modeling is another process used to gauge the accuracy of interpretations in complex areas. In this process, geologic models are developed from interpretations, and synthetic seismic sections are generated from the models using finite difference modeling. The similarities of synthetic seismic sections and original seismic sections are noted, several iterations may be necessary before the two are similar. Pre-stack depth migration and forward modeling have been successfully used in Wyoming, Oklahoma, Pakistan, British Columbia, Colombia, and Ecuador.