3D seismic classification of fluid escape pipes in the western Exmouth Plateau, North West Shelf of Australia

Abstract

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, NW 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 geomorphological 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 palaeo-pockmarks affecting 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 near 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 hydrocarbon 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 study.