Bed Scale Reservoir Heterogeneities and Compartmentalization in Salt Mobilized Deepwater Sediments - Donkey Bore Syncline, Flinders Ranges, South Australia

Blaise I. Fernandes
Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia

Comparision of reservoir data with good outcrops for a given rock type or suite can lead to major advances in the understanding of reservoir characteristics. Therefore geoscience depends extensively on analogues. Outcrop data have been used to model facies geometry, size and distribution, which have implications on reservoir behaviour. Cambrian deepwater mini-basin fill sediments which lie in the zone of influence of an adjacent salt diapir, uniquely outcrop in the Donkey Bore Syncline, Flinders Ranges, South Australia. The low dipping strata and structural disposition of the syncline present a fine opportunity for detailed field analyses. The sediments in question are over 400 m thick and have an area of around 20 km².

Field data comprising of highly representative measured sections and lateral bed evaluations from walking of beds along the syncline flanks furnish significant insights into possible reservoir compartmentalization. The presence of slumping and slump pinch-out as well as pinch-outs due to change in sedimentation, possibly influenced by the adjacent diapir were frequently recognised. Slumping tends to be the most common cause of discontinuities and geometry changes, which varies with proximal-distal situation from the diapir. One of the main sand units shows lateral thickness variations in individual constituent beds typically from 30 cms over a distance of 750 m to 80 cms over just 50 m. In minor slumps with a maximum thickness of a couple of tens of centimetres, pinch-outs occur over a distance of only a couple of meters.

The distribution of compartmentalizing effects associated with stratigraphic heterogeneities is a key to understanding connectivity. Most of these features are below seismic resolution and their recognition is paramount for the characterisation of such deposits.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas