A regional assessment of CO2 storage potential in the Browse Basin: Results of a study undertaken as part of the National CO2 Infrastructure Plan

Brief description

Geoscience Australia undertook a regional assessment of the geological CO2 storage potential of the Browse Basin, offshore northwest Australia, between 2013 and 2015 as part of the Australian Government's National CO2 Infrastructure Plan (NCIP). The NCIP program aimed to accelerate identification and development of suitable areas within Australia for long-term CO2 storage proximal to major emission sources. The Browse Basin was selected with two other offshore sedimentary basins and several onshore basins for pre-competitive data acquisition and geological studies under the NCIP funding. The basin is a proven hydrocarbon province that hosts significant reserves of gas and condensate, with the majority of accumulations being characterised by high concentrations of CO2. This study implemented an integrated approach in assessing CO2 storage potential in the context of remaining hydrocarbon prospectivity, in light of the numerous existing hydrocarbon discoveries and a high probability of undiscovered accumulations within the basin. Potential CO2 storage plays were assessed for the likelihood of conflict with exploration for, and access to, existing and remaining hydrocarbon resources in within the basin. As the bulk of discovered, commercial hydrocarbon accumulations are hosted within the Jurassic and the lowermost Cretaceous successions, the study focused on the Cretaceous succession where there is a reduced risk of conflict between CO2 storage and hydrocarbon exploration (Jurassic and Lower Cretaceous units). The data used for this study include information from over 60 wells, regional 2D and 3D seismic reflection surveys, potential field data, as well as existing and newly acquired pre-competitive geochemical, aeromagnetic and marine environmental data. A key part of this work was an update to regional-scale structure of the basin, including deep faults associated with PermianCretaceous rifting events, and inversion and recent faulting associated with the Cenozoic collision between Australia and Asia. Another focus of the study was an update to the Cretaceous sequence stratigraphy across the basin. A play fairway mapping approach using the revised tectonostratigraphic framework was applied to assess, identify, risk and high-grade areas for their potential suitability for geological storage of CO2. The main constraints for geologic CO2 storage and containment analysed in this study, other than the distribution of reservoirs, seals and reservoir'seal pairs, were reservoir depth range, fault distribution, and hydrocarbon resource conflicts. Common risk element maps were produced for each supersequence through the overlay of mapped constraints (or risk elements) with the play fairway mapping, thus enabling the high-grading of potential CO2 storage play fairways. The results indicate that the Lower Cretaceous basin margin plays and the Upper Cretaceous (early Campanian) confined submarine fan play are potentially more prospective for CO2 storage. However, these plays are subject to potential resource conflict from up-dip migration of hydrocarbons from Cretaceous and older source rock units in the basin depocentres. This major risk requires further assessment for the high-graded priority areas identified in this study. This study provides a revised basin framework and a regional-scale preliminary prospectivity assessment for the geological storage of CO2 in the Browse Basin. The results will guide future, targeted, site-specific assessments, and identify the main geologic risks warranting more detailed investigation. The study findings will also assist in reducing the risk of conflict between CO2 storage and exploration and utilisation of hydrocarbon resources, as well as in identifying new opportunities in these activities.

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