--> Browse Basin 2014 Marine Survey—Investigating Containment for Potential Late Cretaceous CO2 Storage Plays

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Browse Basin 2014 Marine Survey—Investigating Containment for Potential Late Cretaceous CO2 Storage Plays

Abstract

Geoscience Australia conducted a marine survey in the Caswell Sub-basin of the Browse Basin, offshore Western Australia, in late 2014 to investigate containment questions relating to the potential long-term geological storage of CO2. The survey aimed to identify and characterise indicators of natural hydrocarbon or fluid seepage that may suggest the presence of deep plumbing systems which could compromise seal integrity. Prior to the survey, 2D and 3D seismic data were used to map fault networks connecting the Aptian regional seal to the sea floor and any associated amplitude anomalies. This mapping informed survey site selection aimed at testing seal integrity over Maastrichtian, Campanian, Valanginian and Barremian submarine fans in the Caswell Sub-basin, and up-dip migration and leakage of hydrocarbons, via channels and basin margin faults, such as the Heywood Fault, into shallow marine sands on the eastern shelf margin. Vessel and Autonomous Underwater Vehicle (AUV) multibeam bathymetry and sub-bottom profiler systems confirmed the presence of recently active faults in the area, some with significant seafloor surface expression (up to 40m offset). A subset of these faults was visually inspected with a Remotely Operated Vehicle (ROV) which also confirmed the presence of diverse biological communities. Indications of shallow gas were observed on sub-bottom profiles, including amplitude anomalies, cross-cutting reflectors and zones of signal starvation. Water column observations including sidescan sonar, single-beam and multibeam echosounders, underwater video and photography did not conclusively identify hydrocarbon or other fluid seepage. Strong currents encountered during parts of the survey may have interfered with the direct detection of seeps in the water column. However, headspace gas and high-molecular weight hydrocarbon analysis from shallow cores also provided no evidence for migrated thermogenic gas or oil. While no active signs of seepage were observed, the geochemical and biological sampling undertaken will aid in baseline environmental investigations for this region.