Full-waveform Inversion for High-resolution Velocity Model Building Offshore Trinidad

Knowing the presence and extent of shallow gas is critical to any drilling decisions, but it also is a challenge from the imaging and earth model building perspective. Here, we present two new techniques embedded within the full-waveform inversion (FWI) workflow, for data affected by shallow gas. The objective is to help the imaging and develop a model to aid interpretation and shallow characterization. Firstly we implement an adjustive misfit function for FWI on one of the first ocean-bottom field data cases, which allows us to incorporate higher-velocity contrasts as compared to the difference-based objective function, and overcome cycle-skipping to some extent. Along with the velocity model building through FWI, we also propose a workflow to incorporate a regional high-resolution near-surface model into a background FWI model using the former as a priori information. This process is an extension of adding a prior model norm term in FWI along with the data misfit term, to smoothly incorporate prior information into FWI. The objective of the workflow was to build the best possible earth model using FWI, to image the near-surface in high-resolution for shallow characterization and have an earth model that can be used as an attribute for interpretation.