3D Seismic classification of Fluid Escape Pipes in the western Exmouth Plateau, North West Shelf of Australia (A)

Fluid escape pipes are vertical pathways of focused flow venting from a variety of deep overpressure sources. These geological features are typical of many sedimentary basins, including proven petroliferous provinces worldwide, such as the North Sea and the Exmouth Plateau in the Northern Carnarvon Basin, Northwest Australia. High quality three-dimensional (3D) seismic reflection data from the western Exmouth Plateau revealed the occurrence of exceptionally well-imaged fluid escape pipes affecting the Jurassic strata and the Triassic Mungaroo Formation, a key reservoir unit in the basin. A total of 171 fluid escape pipes, including blowout, seepage and hydrothermal pipes, were mapped, and their geomorphic characteristics were analysed. In the study area, these features form prominent vertical columns up to 4.5 km long disrupting continuous reflections of the Triassic to Jurassic section. Numerous fluid escape pipes terminate with paleo-pockmarks affecting at the Upper Jurassic syn-extension strata, providing evidence for pipe genesis during the early stages of the Late Jurassic rifting in the Exmouth Plateau . Fluid escape pipes were found rooting from different stratigraphic levels, suggesting multiple fluid sources within the Triassic sediments. Several fluid flow structures nucleated along or nearby rift-related fault planes within the Mungaroo Formation providing further evidence of rifting as a main triggering factor of important fluid flow in the basin.In the study area, the presence of fluid escape pipes represents a significant risk for the preservation of potential hydrocarbons accumulations as when these features form, vertical fluid venting breaches through stratigraphy compromising the integrity of seal units. This seems supported by the lack of significant discoveries within the area covered by seismic survey analysed in this research.

EVOLUTION AND MORPHOLOGY OF RAFTED BLOCKS IN AN ANCIENT DEEPWATER MASS TRANSPORT COMPLEX (EXMOUTH PLATEAU, OFFSHORE NW AUSTRALIA)

Submarine mass wasting plays a fundamental role in transporting substantial volumes of sediments basinward including gigantic slide blocks. However, the understanding of processes involved in block generation and their associated deformation until flow arrest remains limited, especially in data-starved deep-water settings. Here a 2D and 3D seismic reflection data from the Exmouth Plateau, offshore NW Australia is used to investigate the architecture of large blocks preserved within an ancient mass transport complex (MTC) and their interaction with the basal shear surface (BSS). The evolution of the investigated MTC (MTC-BDF) is related to instability along the flanks of an underlying bifurcative Miocene canyon. MTC-BDF spans ∼75 km by ∼35 km containing at least 32 well-imaged blocks (within the 3D seismic coverage) encapsulated in a well-deformed debrite background. These carbonate blocks interpreted as rafted blocks have lengths ranging from 0.48 km to 3.40 km with thicknesses reaching up to 165 m. Interestingly, the blocks are more abundant in a region characterized by moderate-high amplitude debrites. Erosional morphologies encompassing a unique groove and other circular to irregular-shaped depressions mapped along the BSS provide evidence for the erosive nature of the flow. The origin of the groove is related transported blocks gouging the BSS. Importantly, intra block deformations recorded within these blocks as fault and fold systems suggest a complex flow regime within MTC-BDF, with the deformations arising either during block translation or also possibly upon the arrest of the failed mass in interaction with bathymetric elements. Our findings suggest inherent deformations within these blocks may serve as high-permeability conduits with implications for deep-water drilling operations within this segment of the Exmouth Plateau and elsewhere in other hydrocarbon-rich deep-water settings.