Petroleum prospectivity and CO2 storage assessment in the offshore Browse Basin, North West Shelf, WA/AC

Under the National CO2 Infrastructure Plan (NCIP) and the National Low Emissions Coal Initiative (NLECI), Geoscience Australia undertook multi-purpose basin analysis to address dual priorities to assess long-term CO2 storage potential while simultaneously provides new insights into hydrocarbon prospectivity. The Browse Basin assessment is part of this five year program and provides better understanding of basin-scale storage potential and new insights into hydrocarbon prospectivity to manage the potential resource conflicts.

The Browse Basin is a northeast-trending Paleozoic to Cenozoic depocentre situated offshore on Australia's North West Shelf and is being actively explored for hydrocarbons. It hosts large undeveloped gas and condensate accumulations, and is soon to become Australia's next major conventional liquefied natural gas (LNG) province. The basin was identified as potentially suitable for offshore geological storage of CO2 due to its favourable geological setting on a passive margin, and its proximity to offshore gas resources that can contain high amounts of naturally occurring CO2.

The multi-purpose basin approach in the Browse Basin included the acquisition and integration of pre-competitive data derived from an airborne magnetic survey, two marine surveys, and the geochemical analysis of oils, gases and rocks, provided by industry through the Offshore Petroleum Titles Administrator (NOPTA)-managed repository. All of this precompetitive data had applications towards, and addressed questions relevant, to the assessment of both CO2 storage potential and hydrocarbon prospectivity.

The concurrent basin analysis research provided a new understanding of the basin's Cretaceous succession based on an integrated sequence stratigraphic analysis of 60 wells and an extensive set of industry and government 2D and 3D seismic reflection data. The basin's tectonostratigraphic framework was updated, and the integration of revised biostratigraphic data enabled an improved understanding of variations in depositional facies and the spatial distribution of reservoir, seal, and source rock (condensed) sections. The outputs include models and maps of environments of deposition, petroleum systems and play fairways.

Consequently, prospective CO2 storage sites throughout the succession were identified in areas that were least likely to conflict with hydrocarbon exploration. Results from this pre-competitive project will improve future storage site selection in suitable reservoirs for the commercial deployment of CCS technology, and will promote new hydrocarbon exploration opportunities.