Products of Slope Failure Processes as Potential Petroleum System Elements – Seismic Examples From Offshore Northwest Shelf of Australia
Modern seismic techniques are employed to investigate prime examples of slope collapse systems so to infer evolutionary paths and to explore the potential of their products as petroleum system elements. The failures presented in this work are located in the deepwater of North West Shelf of Australia and affected Jurassic rift strata as well as near seabed, Late Oligocene to Recent, post-rift sediments. The seabed collapse systems originated at water depths of ~1000 m and extend downdip to depths well in excess of 1500 m. These exhibit a width in the range of 1-5 km and extend downdip for ~15 km with estimated volumes of sediments in excess of 10 km3. A number of these failures are characterised by disrupted, slump-like facies which progressively pass downslope into packages of high amplitude, continuous reflections. This facies transition is further investigated with attribute extractions showing a downslope rheological transformation from slump to mass-flow as evidenced by hundreds of meter wide canyons that link the updip failures to well developed, downdip fan systems several kilometres across. In the rift section, slope failures affected domino extensional fault systems in the form of well imaged footwall degradation complexes. These complexes exhibit overlapping, scoop-shaped scars up to 10 km in length that deteriorated the exposed footwall breakaways. Debris from footwall collapse was resedimented in the hanging wall basins, forming talus wedges up to 300 m thick that taper away from adjacent fault planes for distances of several kilometres. These deposits are characterised by sheeted to contorted seismic facies, indicating a variety of mass-wasting processes accompanying footwall collapse. The generation of debrites and turbidites reservoirs as observed in composite ‘slump to mass-flow’ failures, and also the capacity to redistribute and accumulate rift reservoirs into hanging-wall basins as seen in fault degradation complexes, clearly indicate that slope failures have the potential of contributing to a diversity of play types in rifted passive margins.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017