Palaeogeographic reconstructions of the Early Cretaceous South Perth Supersequence in the offshore Vlaming Sub-Basin, southwest Australia: implications for CO2 storage  

Authors / CoAuthors

Lech, M.E. | Southby, C. | Lescinsky, D.T. | Wang, L. | Borissova, I.

Abstract

As part of the Australian Government's National CO2 Infrastructure Plan (NCIP), Geoscience Australia undertook a CO2 storage assessment of the Vlaming Sub-basin. The Vlaming Sub-basin a Mesozoic depocentre within the offshore southern Perth Basin located about 30 km west of Perth, Western Australia. The main depocentres formed during the Middle Jurassic to Early Cretaceous extension. The post-rift succession comprises up to 1500 m of a complex fluvio-deltaic, shelfal and submarine fan system. Close proximity of the Vlaming Sub-basin to industrial sources of CO2 emissions in the Perth area drives the search for storage solutions. The Early Cretaceous Gage Sandstone was previously identified as a suitable reservoir for the long term geological storage of CO2 with the South Perth Shale acting as a regional seal. The Gage reservoir has porosities of 23-30% and permeabilities of 200-1800 mD. The study provides a more detailed characterisation of the post Valanginian Break-up reservoir - seal pair by conducting a sequence stratigraphic and palaeogeographic assessment of the SP Supersequence. It is based on an integrated sequence stratigraphic analysis of 19 wells and 10, 000 line kilometres of 2D reflection seismic data, and the assessment of new and revised biostratigraphic data, digital well logs and lithological interpretations of cuttings and core samples. Palaeogeographies were reconstructed by mapping higher-order prograding packages and establishing changes in sea level and sediment supply to portray the development of the delta system. The SP Supersequence incorporates two major deltaic systems operating from the north and south of the sub-basin which were deposited in a restricted marine environment. Prograding clinoforms are clearly imaged on regional 2D seismic lines. The deltaic succession incorporates submarine fan, pro-delta, delta-front to shelfal, deltaic shallow marine and fluvio-deltaic sediments. These were identified using seismic stratigraphic techniques and confirmed with well ties where available. The break of toe slope was particularly important in delineating the transition between silty slope sediments and fine-grained pro-delta shales which provide the seal for the Gage submarine fan complex. As the primary reservoir target, the Gage lowstand fan was investigated further by conducting seismic faces mapping to characterise seismic reflection continuity and amplitude variations. The suitability of this method was confirmed by obtaining comparable results based on the analysis of relative acoustic impedance of the seismic data. The Gage reservoir forms part of a sand-rich submarine fan system and was sub-divided into three units. It ranges from canyon confined inner fan deposits to middle fan deposits on a basin plain and slump deposits adjacent to the palaeotopographic highs. Directions of sediment supply are complex. Initially, the major sediment contributions are from a northern and southern canyon adjacent to the Badaminna Fault Zone. These coalesce in the inner middle fan and move westward onto the plain producing the outer middle fan. As time progresses sediment supply from the east becomes more significant. Although much of the submarine fan complex is not penetrated by wells, the inner fan is interpreted to contain stacked channelized high energy turbidity currents and debris flows that would provide the most suitable reservoir target due to good vertical and lateral sand connectivity. The middle outer fan deposits are predicted to contain finer-grained material hence would have poorer lateral and vertical communication.

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nonGeographicDataset

eCat Id

78747

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• External PublicationAbstract

( Theme )

• palaeogeography

( Theme )

• geological storage of CO2

( Theme )

• sequence stratigraphy

( Theme )

• marine

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

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2014-01-01T00:00:00

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