Seven Cretaceous Low-Order Depositional Sequences From the Browse Basin, North West Shelf, Australia: A Framework for CO2 Storage Studies

Abstract

The Browse Basin Cretaceous succession comprises seven low order depositional sequences (K10-K50, K60a and K60b). Sequence development was controlled by tectonic events associated with the separation of Greater India and Antarctica from Australia. These events punctuated a long-term accommodation trend that combined thermal subsidence and first-order eustasy. Sediment sourced from the Kimberly Basin hinterland was delivered to the basin via entrenched drainage systems. The main direction of sequence progradation varies from WNW in the Early Cretaceous to N in the Late Cretaceous. The updated sequence analysis presented here underpins a recent CO₂ storage study by Geoscience Australia. Sequence K10 (late Tithonian-early Valanginian) is a sand-rich, deltaic package that includes a distinctive lowstand wedge. Deep water sands are present in the lower part of the sequence, especially in the lowstand wedge (Brewster Member). K20 (early Valanginian-late Hauterivian) and K30 (late Hauterivian-early Aptian) display aggradational and back-stepping stratal geometries. They are mud-prone and sands were mainly trapped inboard. Deep-water sands (Asterias Member) that occur in both sequences are known only in the north. K40 (early Aptian-late Cenomanian) is marked by a basinward shift in facies indicated by a basal sand (Aptian Windalia Sandstone equivalent) present in some inboard wells and a sand-rich progradational package on the Yampi Shelf. Rapid transgression followed, resulting in a condensed interval (Aptian Windalia Radiolarite equivalent) and a thick, mud-dominated Albian-Cenomanian section. K50 (late Cenomanian-early Campanian) coincides with a peak in eustasy and is incised by the K60 sequence boundary. The remnant outboard part of K50 comprises mainly mudstone and marl, and foreset to bottomset stratal geometries. K60a (early Campanian-mid Maastrichtian) and K60b (mid to end Maastrichtian) represent a change to regressive architecture associated with falling eustasy and lower subsidence rates. Fluvio-deltaic sediments prograde over deep water fan complexes sourced from lowstand channel systems. The Sequence analysis has refined relationships between stratigraphic play elements both within and between sequences. Deep water sands in K10, K20, K30, K60a and K60b are prospective storages because they are well sealed by downlapping muds. After application of risk criteria, deep water sands in K60a and b have been high-graded as potential CO₂ storages.

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