Sparse‐node acquisition for data fitting velocity model building

Abstract

The salt interpretation can be quite time‐intensive and challenging. Full‐waveform inversion, as a data‐driven optimization algorithm with full wavefield modelling, has become one of the essential tools for earth model building. However, full‐waveform inversion application in the complex salt geology, especially with streamer data collection, is limited, whereas the ocean‐bottom node with ultra‐long offsets and low frequencies unleashes the power of full‐waveform inversion. Sparse ocean‐bottom node acquisition has become a standard approach to improve the earth model building by the addition of ultra‐long offsets and possibly low frequencies. The new survey designs with ocean‐bottom node coupled with simultaneous shooting can be deployed on a regional basis covering thousands of square kilometres in a cost‐effective manner. In complex geological settings, including irregular salt geometry, salt interpretation has a direct impact on subsalt imaging. The recent development of robust objective functions allows full‐waveform inversion work with sparse ocean‐bottom node surveys in the deep‐water environment as the Gulf of Mexico to build and refine the salt geometries and correct the background velocity error in subsalt, uncovering the structural configuration of the basin that has not been seen before. Although full‐waveform inversion mostly employs the acoustic wave equation, we know that the high velocity boundaries in the earth model may require elastic wavefield propagation. Increased physics in full‐waveform inversion allows us to interrogate the power of elastic full‐waveform inversion versus acoustic full‐waveform inversion, and here, we demonstrate that elastic full‐waveform inversion has an advantage over acoustic full‐waveform inversion despite the extra cost associated with implementing the more complete physics.