Detection of palaeo-oil columns in the offshore northern Perth Basin: extension of the effective Permo-Triassic charge system

Abstract

A widespread charge system for oil accumulation in the offshore northern Perth Basin, Western Australia, is revealed by specialised fluid inclusion technologies. Palaeo-oil columns are detected in about three of four exploration wells, including those at the Cliff Head, Dunsborough, Frankland and Perseverance fields, and in dry wells at Flying Foam–1, Hadda–1, Houtman–1, Leander Reef–1, Lilac–1, Livet–1, Mentelle–1 and Morangie–1. A high incidence of palaeo-oil charge into Permian reservoirs below the Kockatea Shale confirms that the conventional oil shows are, in part, residues of palaeo-oil. Oil migration is suggested at Vindara–1 and Leander Reef–1 and is below detection limits in Batavia–1, Charon–1, Fiddich–1 Geelvink–1A, Gun Island–1 and South Turtle Dove–1B, Twin Lions–1 and Wittecarra–1. New geochemical data from fluid inclusion oil at Hadda–1 shows evidence for a contribution from the Hovea Member of the Kockatea Shale, including: high wax content; low pristane/phytane ratio; high abundance of extended tricyclic terpanes; and, the highly diagnostic C33 n-alkylcyclohexane biomarker. This key component of the petroleum system acted as both source and seal, and extends further offshore than previously realised. Possible co-sourcing from terrestrial organic matter is indicated by high abundances of C29 steranes and diasteranes, C19 tricyclic, and C24 tetracyclic terpanes, which may be sourced from Permian rocks. The high incidence of palaeo-oil and residual columns suggests that trap integrity is likely to be an important preservation risk, with elements of gas displacement. Screening of prospects for structural and hydrocarbon charge characteristics, which are favourable for retention of oil, is key in future exploration of the offshore northern Perth Basin.

Cenozoic uplift of south Western Australia as constrained by river profiles

“…Changes in intraplate stresses across the Australian plate (Müller et al, 2012) could induce surface uplift over short (~1--5 Myr) time periods. Indeed, Miocene fault inversion and north--south anticlinal folding, attributed the collision of the Indo--Australian and Eurasian plates (Borissova et al, 2010, Iasky, 2003, Harris, 1994, occurs offshore Western Australia, but only north of ~28ºS (Kempton et al, 2011, Iasky, 2003. Onshore, the east--west orientation of the maximum horizontal stresses in the Yilgarn Craton should result in preferential reactivation of north-south striking structures, which is at odds with the Neogene seismic quiescence of the Darling Fault (Quigley et al, 2010, Clark andLeonard, 2003), a Cambrian tectonic feature bounding the eastern margin of the Perth Basin (Fig.…”

CO2geosequestration potential in the Northern Perth Basin, Western Australia

“…It was also noted that a large number of dry wells exist within structural closures, where hydrocarbon loss is thought to be owing to local reactivation of faults (Kempton et al 2011). Additionally, the high cost of offshore operations limits the attractiveness of offshore CO 2 storage options where onshore options are available (APCRC 2000).…”