Determination of Salt Exit Velocity and Its Application in Subsalt Exploration

In recent years, our ability to image the subsalt structure has improved significantly with the availability of wide azimuth data, reverse time migration (RTM) and routine use of anisotropic imaging and tomography. In subsalt exploration, derivation of subsalt velocity, especially velocity directly below the base of salt, i.e., salt exit velocity, remains challenging due to complex salt overburden. Anomalous high BOS amplitudes can often be found, which indicate the relatively strong impedance contrast in the salt-subsalt boundary. Reflectivity inversion for dirty salt is extended to derive salt exit velocity and is further combined with high resolution tomography with high-fidelity RTM 3D angle gathers to invert the sub-salt velocity model for better pressure prediction and imaging in subsalt exploration. We demonstrate the methodology with a synthetic and real WAZ data example.