Salt Exit Velocity Retrieval Using Full-waveform Inversion

Accurate retrieval of salt exit velocity has been a important part in drilling hazard prediction, and is essential to achieve a clear subsalt image. Subsalt velocity retrieval is in many cases a difficult task to perform as the subsalt signal is often very weak. The common industrial practice to derive the subsalt velocity is to superpose a regional velocity gradient below the salt.However, using regional velocity gradient trend to estimate subsalt velocity ignores the relation between effective stress and velocities, which is extra important in determining the salt exit velocity. Full-waveform inversion(FWI) emerges as a advanced model building tool in recent years; however,the capability of FWI is limited due to lack of low-frequency and large-offset dataset, which are essential to the success of FWI retrieval. In this work, we successfully use time-domain full waveform inversion together with large offset dataset to retrieve the salt exit velocity, which improve the subsalt image and benefit the pore pressure prediction.