Delve deep: Seismic revolution in acquisition and model building for exploration

Abstract

Sparse-node acquisition is the latest approach to improve the earth model through the inclusion of ultra-long offsets and low-frequency generating sources. The new designs of node data collections with simultaneous shooting can be deployed on a regional basis, covering thousands of square miles in a cost-effective manner. In complex geologic settings such as salt environments, salt interpretation has a direct impact on subsalt imaging. However, salt interpretation can be quite time intensive and challenging. Full-waveform inversion (FWI), as a data-driven optimization algorithm with full-wavefield modeling, has become an essential tool for earth model building. However, its use in salt tectonic contexts, especially with streamer data collection, is limited because the frequencies acquired are not sufficiently low and the offsets are not sufficiently long. The recent advancement of the objective function enables the application of an FWI workflow, coupled with sparse-node acquisition in the deepwater settings of the Gulf of Mexico, to refine the salt geometry, correct the background velocity error in subsalt, and uncover a basin's structural framework. The increased frequency content of the FWI-updated fields enables us to extract the FWI-derived reflectivity (FDR), which is an image created by the FWI nonlinear iterative process with the full wavefield. Additionally, the classic extraction of amplitude-versus-angle/amplitude-variation-with-offset parameters employs the elastic Zoeppritz formulation to obtain rock-physics volumes and explain the amplitude on the prestack image gathers, which are typically generated by Kirchhoff or reverse time migration (RTM) depth migration. The next step is to substitute these migrations with FWI and output not only the poststack FDR but use it in a prestack mode to aid amplitude analysis at an early stage of model building.