Full Wave and Down-Going Elastic Inversion of Deepwater OBN Seismic Data: Example from Niger Delta

Summary Egina Field, which is in water depth of about 1500 m, is located offshore Niger Delta. The reservoir consists of Miocene turbiditic channel complexes. High seismic energy loss in the reservoir zone, due to shallow gas effects and mud volcanoes, necessitated the acquisition of Ocean Bottom Nodes (OBN) survey in order to improve the imaging and reservoir characterization while serving as a baseline for future 4D monitor surveys. In this paper, we discuss the FWI implementation on the OBN dataset and the added value over legacy narrow azimuth streamer seismic data. Additionally, we discuss the TTI anisotropic Kirchhoff Pre-Stack Depth Migration of the OBN Up-going and Down-going datasets. Furthermore, we detail our post stack amplitude correction implemented on the dataset prior to the inversion process. This AVO-consistent correction allows for correction of energy loss in the reservoir section due to shallow events. A model-based elastic inversion of the down-going wavefield yielded a robust and highly consistent elastic properties due in large part to the high-quality low frequency content and high signal-noise ratio. Computation of probability of success allows a more quantitative estimate of the degree of reliability of the inverted and derived properties compared to actual well log data.