Facies Distribution Within The M. Australis Section On The Enderby Terrace, Carnarvon Basin, Western Australia.
Honours Degree, 1995
University of Adelaide
The study concentrates on the deposition of the Lower Cretaceous (Barremian) sands in the M. australis palynology zone, on the Enderby Terrace, within the Barrow-Dampier Sub-basins of the Carnarvon Basin, Western Australia.
The unit was mapped using seismic data and well-to-well correlations to determine thickness and variation in the sand quality.
The thickest section corresponds with the cleanest sand and occurs near Hampton #l, Wandoo #1 and Enderby #1. On the Enderby Terrace, the M. australis sand thins against the Mermaid Fault, before thickening in the central region, then thinning once more onto the basin edge. A region of non-deposition of the M. australis sand near Arabella #1 and Emma #l, separates the better quality reservoir sand in the northeast from sand in the Barrow Sub-basin. In the Barrow Sub-basin and some areas of the northern Barrow-Dampier region, the equivalent to the Lower and Mid M australis sand is probably the glauconitic Mardie Greensand. The greensand is transgressive at the base of the Muderong Shale but becomes a clean, more quartzose sand as it laps onto the shelf areas near the basin margin.
Glauconitic sands can reservoir oil, but the glauconite pellets must be a part of the framework, maintaining support, not hindering effective porosity as it does when a matrix constituent. Two possible reservoir locations are evident, between the Stag and Wandoo Fields on the Enderby Terrace, and where thickening of the unit occurs between the Mermaid Fault and basin edge. Both are dependant upon migration pathways and an adequate seal in the area. The Windalia Sandstone, a proven reservoir in the Barrow Island Oil Field, is present on the Enderby Terrace, but its potential as a reservoir on the Enderby Terrace is yet to be proven.
It was difficult to distinguish a pinchout on regional paper seismic lines corresponding with geological data. The strike line, although structurally good, did not reveal any isochron variations of the M. australis horizon.