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Extraction and Analysis of Complex Geobodies in Faulted Deposits Using Relative Geological Time Model Attributes and Spectral Decomposition: Exmouth Sub-Basin, Australia

Abstract

Over the recent years, comprehensive approaches have been more commonly used for seismic interpretation in order to better understand the geology across seismic volumes. This paper shows the use of a Relative Geological Time Model (RGT Model) on dataset from Northwestern Australian margin (Exmouth sub-basin), that allows the extraction of an unlimited number of horizons. Thanks to that sub-seismic stratal slicing and the analysis of both spectral and complex attributes, fine geological features were identified and characterized. A first assessment of the geological objects was made through mapping of seismic amplitude attributes on all the horizons of the stratal slicing. A “Short Time Fourier Transform” spectral decomposition of the seismic volume was then performed to highlight them. For each object, 3 frequencies characteristic of its spectral signature were selected (low, mid and high) to produce a 3-channel (Red, Green, Blue) color-blended stratal slicing volume. The numerous RGB maps allowed the detection and modeling of sedimentary complexed objects within different stratigraphic levels (Jurassic, Cretaceous and Eocene). Among them, Jurassic turbiditic channels were detected with their spectral signature (20Hz, 35Hz, 47Hz) and extracted as 3D objects. Attributes based on seismic multi-traces analysis, like variance and fault probability, are conventionally used to structurally interpret faulted deposits, but with limited results for seismic data of low quality. However, attributes derived from the RGT Model provide a high resolution evaluation of fracturing. For example, RGT Model deepest descent gradient computes the maximal dip variations and detects the fault break points on each surface. It highlights the hierarchy between major and secondary fault networks within the rift depocenter and their incidence on the Jurassic channels at a regional scale. Furthermore, the fault throw attribute derived from the RGT model and mapped on fault planes has provided a preliminary quantification of faults impact across the bodies at a reservoir scale. Thanks to a comprehensive approach enabling RGT model attributes and sub-seismic spectral analysis, both sedimentary and structural events have been correlated with a high confidence. Characterization of prospects from regional to reservoir scales within the Exmouth sub-basin was then performed. More advanced results are expected thanks to a watertight modeling which would allow a fault juxtaposition analysis.