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Geological history of the western Barrow Sub-basin: Implications for hydrocarbon entrapment at Woollybutt and surrounding oil and gas fields

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Geological history of the western Barrow Sub-basin: Implications for hydrocarbon entrapment at Woollybutt and surrounding oil and gas fields

 

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Publication Name: The Sedimentary Basins of WA

Authors: D.J. Hearty, G.K. Ellis & K.A. Webster

Publication Volume: 3

Date Published: December 2002

Number of Pages: 39

Reference Type: Book Section

Abstract:

The Woollybutt Oil Field, discovered in 1997, is located approximately 50 km west of Barrow Island in the Barrow Sub-basin of the Northern Carnarvon Basin, Western Australia. The under-saturated oil accumulation occurs in sandstones of the Early Cretaceous, deltaic Barrow Group and the overlying porous unit of the Mardie Greensand. The field comprises a north and southwest lobe, each having a different oil-water contact and a
different structural history.
During the break-up of Gondwana, deep-seated structures influenced the Triassic and Jurassic fault styles and basin geometry. The resulting structural trends, in conjunction with deep-seated, northwest-trending structural lineaments, have in turn influenced both the depositional form of the Early Cretaceous Barrow Group delta progrades, and wrench-related deformation in the Turonian and Late Tertiary, forming a focus for development of closures at the Top Barrow Group level at the Woollybutt Oil Field. Turonian tectonism initially created the Woollybutt southwest lobe, whereas Tertiary movement, resulting from the collision of the Australian and Asian plates, further enhanced the southwest lobe and formed the Woollybutt north lobe. These Late Cretaceous and Late Tertiary tectonic movements created traps for other Top Barrow Group oil and gas fields in the Barrow Sub-basin. Fields located on the Alpha Arch and Barrow Island Trend initially formed during the Early Cretaceous and were structurally enhanced or altered by subsequent tectonism during the Late Cretaceous and Late Tertiary. The Spar and East Spar gas fields are located on a major northwesterly-plunging fold that shielded the Woollybutt
structure from any gas migrating from further north in the sub-basin. The source for the Woollybutt oil is interpreted to be from the Late Jurassic Dingo Claystone in the southern part of the Barrow Sub-basin.

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