Cretaceous Stratigraphic Play Fairways and Risk Assessment in the Browse Basin: Implications for CO2 Storage

Abstract

The Browse Basin is a major Paleozoic to Cenozoic depocentre on Australia's Northwest Shelf that contains extensive petroleum reserves. Some of the gas accumulations have naturally elevated levels of CO₂ and future development of these gas fields may require sequestration options. A regional sequence stratigraphic analysis and geochemical study, using newly acquired geophysical data (from marine seepage and aeromagnetic surveys) and sediment samples, were undertaken to provide an updated basin framework and a better understanding of the potential of Cretaceous supersequences for both CO₂ storage and hydrocarbons. Updated biostratigraphy, well correlations, seismic, paleogeography interpretation and play fairway mapping were completed for seven supersequences, from the Berriasian to Maastrichtian. This analysis shows that entrenched fluvial systems flowing from the Kimberley Paleoproterozoic Basin on the inner-shelf formed a complex network of sedimentary inputs that operated throughout the Cretaceous. These fluvial systems fed numerous large submarine fan complexes of variable reservoir quality that are potentially isolated from the deltaic systems. These were deposited with N-NW progradation in the central and northern depocentres during sea level falls in the Berriasian, Valanginian, Barremian, Campanian and Maastrichtian. A risk assessment was carried out to better understand the suitability of these fans for CO₂ storage, including reservoir quality characterisation using well log analysis and key containment constraints. The constraints investigated include fault reactivation, connectivity between sand bodies, hydrocarbon presence and indications of present-day or palaeo-seepage. Geochemical analysis and Grains with Oil Inclusions (GOI) techniques were used to assess the seal integrity. Contemporary stress field indicators suggest that the basin is most likely in a strike-slip faulting regime, with the main compression direction oriented E-W. Seal integrity modelling predicts that faults trending WSW–ENE and WNW–ESE are most prone to reactivation in response to CO₂ injection. Common risk element maps allow characterisation of reservoir and seal pairs away from these key containment risks and prioritisation of areas that are located within Upper Cretaceous submarine fans. This study provides a framework for further work which will help determine the suitability of potential CO₂ storage sites, which are not in direct conflict with hydrocarbon prospectivity.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015