Joint ray+Born least-squares migration and Simulated Annealing optimization for high-resolution target-oriented quantitative seismic imaging

A seismic processing workflow based on iterative ray+Born migration/inversion and targetoriented post-processing of the migrated image is developed for fine-scale quantitative characterization of reflectors. The first step of the workflow involves linear iterations of the ray+Born migration/inversion. The output of the first step is a true-amplitude migrated image parameterized by velocity perturbations. In a second step, post-processing of the migrated image is performed through a random search with a very fast simulated annealing algorithm (VFSA). The forward problem of the global optimization is a simple convolutional model that linearly relates a vertical profile of the band-limited migrated image after depth-to-time conversion to a one-dimensional velocity model composed of a stack of homogeneous layers of arbitrary velocity and thickness. The aim of the post-processing is to eliminate the limited-bandwidth effects of the source from the migrated image, for resolution 1 improvement and enhanced geological interpretation of selected targets. Global optimization approach allows for uncertainty analysis required by the intrinsic non uniqueness of the velocity models output by the post-processing. The relevance of the convolutional model when applied to the output of the ray+Born migrated inversion is first illustrated with a one-layer model. Then, the accuracy and the robustness of the workflow to image geologically complicated models is illustrated with an application to the synthetic Marmousi model. Some practical issues, such as the source wavelet estimate and the scaling of the migrated image required by the VFSA optimization, are discussed with an application to a 2D real seismic multichannel reflection data set collected in the Gulf of Guayaquil (Ecuador). The post-processing is applied to derive the fine-scale velocity structure of a dcollement zone on top of the subduction channel. The post-processing allows for mapping structural variations along different segments of the dcollement, which can be associated with changes in fluid content and porosity.