Shallow Water Imaging Using Ocean Bottom Cable Data with Time-lag FWI in Southern Gulf of Mexico

The study area is in a shallow water region with water bottom depth ranging from approximately 10 m to 100 m. Building an accurate velocity model in the study area has been challenging due to complex geology. There are two major velocity model building tools: tomography and full waveform inversion (FWI). Geological complexity reduces ray tracing stability and degrades migrated gathers, making tomography-based model building ineffective. In contrast, FWI does not depend on ray tracing or gather quality. It updates the velocity model by minimizing the data misfit between full waveform synthetic and real data. In this case study, we use Time-lag FWI (TLFWI), a cross-correlation based FWI algorithm, as the core of velocity model building. With the velocity updated from TLFWI, some structures are still not well imaged. Due to the sparsity of the OBC data and complex geology, there are illumination problems from shallow to deep. Reverse time migration (RTM) images have suboptimal coherency in poorly illuminated areas. We derived the FWI Image from the TLFWI velocity model. The FWI Image utilizes full wave fields, including primary and multiples, which provide better illumination. FWI Image offers superior imaging for complex structures compared to RTM.