Publication Name: The Sedimentary Basins of WA
Authors: Giovanni A.E. di Toro
Publication Volume: 1
Date Published: July 1994
Number of Pages: 27
Reference Type: Book Section
Abstract:
The reservoir in the Wanaea and Cossack fields is the Upper Jurassic Angel Formation which was deposited in the eastern Dampier Sub-basin as a sand-dominated submarine fan sequence.Log-correlation between the Wanaea wells show a good degree of lateral continuity of the main reservoir sands;
this is confirmed by high resolution palynostratigraphy which allows fine scale correlation of beds within the
Angel Formation. This has been particularly useful between the fields because of the lack oflog-correlatable markers in the Cossack area.
Detailed geological studies on Wanaea and Cossack well data have revealed depositional trends which control
the reservoir properties.
Systematic changes in net-to-gross ratio, permeability and, to a lesser degree, porosity are detected along the
palaeotransport direction, with the proximal part of the submarine fan (Cossack area) exhibiting the best
reservoir characteristics, and the distal area (Wanaea-4 and Madeleine-! area) showing a distinct decrease in netto- gross ratio and permeability.
One of the contributing factors to the decrease in permeability is the appearence of diagenetic chlorite. This, in turn, can be related to lithological changes between the proximal and distal part of the submarine fan.
Outcrop and subsurface analogues strongly support the proposed depositional model for this area which consists of laterally extensive sheet sands deposited by high-density, sandy turbidites. The most appropriate
outcrop analogue is provided by the Miocene Laga Formation in central Italy and further outcrop examples
are the Miocene Marmoso Arenacea Formation of the Italian Appennines and the Cretaceous Gault Formation
of the eastern Alps and Carpathians. An excellent subsurface analogue is afforded by the Pliocene Cellino
Formation of central Italy.