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ABSTRACT: A sequence stratigraphic approach to reservoir characterisation of the Birkhead Formation, Gidgealpa South Dome, Eromanga Basin, Australia

Lanzilli, Elio , Santos Asia Pacific Pty Ltd, Brisbane, Australia

Within the Mesozoic section of the Eromanga Basin, Central Australia, the Jurassic Birkhead Formation oil accumulation at the Gidgealpa south dome has currently reached the end of its primary production and is now moving into the secondary production phase. For maximum oil recovery reservoir characterisation is required.

This field occurs within quartzose craton-derived to lithic rich, volcanic-arc derived sandstones deposited in a fluvial-deltaic and deltaic-lacustrine environment. In sequence stratigraphic terms, the delta complex was deposited within a transgressive systems tract with the initiation of the Birkhead Formation marked by a transgressive surface separating it from the underlying braided fluvial Hutton Sandstone.

The delta complex at the Gidgealpa south dome consists of a number of isolated and partly isolated sand bodies that represent separate delta lobes. The isolated nature of the sand packages has caused reservoir compartmentalisation that can be more confidently mapped using wells and sequence stratigraphic concepts. Permeability analysis from probe permeability and core plug data indicates that channel fill, over-bank and floodplain facies have good, intermediate and poor reservoir characteristics respectively. This analysis has also allowed for the identification of flow units within the Birkhead Formation reservoir.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia