Reservoir Modelling, Structural History and Volumetrics of the Jerboa Area, Eyre Sub-Basin

Abstract

The Eyre Sub-basin is situated in the Bight Basin in the Southern Margin. It covers an area of approximately 8,000km2. It is one of several half-graben in the Bight Basin that formed during the initial rifting between Australia and Antarctica. Sediments have accumulated in these depocentres from the Middle Jurassic to present. The initial environments of deposition were a series of fluvial, lacustrine and floodplain sequences before becoming open marine environments in the Cretaceous to Recent. Structural, Property and Reservoir Facies Models were created using the seismic interpretation and well logs from Jerboa-1. The models suggest the sequences on the Jerboa high thicken down-flank away from the well. Source rocks capable of generating hydrocarbons complete with oil stains and oil inclusions were found in the Middle Jurassic-Early Cretaceous non-marine sequences. There are several potential stacked reservoir sections in the sequences from the Middle Jurassic to the Berriasian. These have high porosities between 14-30% and clean channel sands as indicated on the Jerboa-1 logs. The Valanginian-Barremian shale dominated sequence is mapped as laterally extensive and has the best potential of sealing the underlying reservoirs. Across fault seal assessment indicates the fault throws potentially seal the reservoirs, although fault reactivation in the Late Cretaceous resulted in a collapsed graben complex along the apex of the Jerboa high and is potentially the cause of the hydrocarbons escaping. Sections in the Eyre Sub-basin that have stacked channel reservoirs, source rocks with adequate burial and traps that have not been breached have the potential to hold an accumulation of hydrocarbons. The Eyre Sub-basin is a working petroleum system.