3-D Seismic Analysis of Fault-Degradation Complexes, Exmouth Plateau, NW Shelf, Australia

Abstract

Fault-degradation complexes are common and yet poorly understood features found in many hydrocarbon bearing rift basins such as, the Gulf of Thailand, Gulf of Suez and offshore Norway. The Exmouth Plateau in the NW shelf of Australia is part of a Mesozoic – Present Day passive margin that displays many spectacular fault-degradation complexes affecting the Upper Triassic-Mid Jurassic rift section. Recently released, high quality 3D seismic surveys from this area have been analysed using modern seismic techniques in order to describe and analyse these complexes. In particular volume-based seismic attributes and advanced 3D visualisation techniques have allowed unprecedented detailed imaging and interpretation of these structures. This research shows that Late Triassic to Mid Jurassic extension in the Exmouth Plateau formed a N-S to NE-SW striking domino style extensional fault system that was strongly affected by footwall degradation. On the Exmouth Plateau the uplifted footwall blocks are up to 15 km wide and 30 km long. There was very little syn-rift sedimentation such that the fault block footwalls were exposed resulting in gravitational collapse to form a series of scooped-shaped degradation complexes. These scarp collapse structures are shown in 3D visualizations and detailed seismic attribute extractions along key reflectors. These are typically a series of overlapping scoop-shaped scars, from 2 – 10 km in length along the uplifted footwall breakaways. Debris from footwall collapse complexes was resedimented in the hangingwall basins of the rift faults. These deposits are imaged in vertical seismic sections as wedge-shaped bodies, up to 300 m thick tapering away from the fault planes and characterized by sheeted to contorted seismic facies. Later reactivation of the rift faults commonly complicates these simple geometries. Three-dimensional evolutionary structural models have been developed for the fault-degradation complexes found in the Exmouth Plateau. These have been compared and contrasted with similar features on rifted margins elsewhere and scaled sandbox models. The results of this study may serve to better understand the geometries and compartmentalisation of potential reservoirs located within fault blocks of extensional systems which have been affected by fault-degradation complexes.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015