Depth velocity model building beyond reflection tomography, a case study, Offshore Vietnam

Abstract

In the Southeast Asia offshore exploration, shallow reefs and channels, widely spread volcanic rocks and basement fracture system are some of the major challenges in seismic imaging. However, conventional reflection tomography has hard time to provide accurate and high resolution model to solve these challenges and other model building techniques are needed to introduce those velocity anomalies. First, reflection tomography has limited resolution at shallow (50-400m) because of limited number of offsets. So geo-mechanical modeling is used to put fast and slow velocity of reefs and channels. Second, the intrusive and extrusive volcanic rocks are too thin (around 50m-100m) to be resolved by tomography. Reflectivity inversion is used to derive the high resolution velocity of the volcanic rocks. Third, TTI/HTI anisotropy is used to simulate the situation, that image velocity is always much slower than well sonic velocity inside basement, and improve the image. Overall, geo-mechanical modeling, reflectivity inversion and TTI/HTI modeling in basement, together with the conventional reflection tomography, generate high resolution velocity model for PSDM thus provide much needed imaging uplift.