BARROW ISLAND OIL FIELD

Abstract

The Barrow Island Field in the Barrow Sub-basin of the Carnarvon Basin was discovered in 1964 by West Australian Petroleum Pty Limited. It is the largest oil field in Western Australia. Appraisal drilling has defined in-place oil of 200 GL (1,250 MMBBL) and in-place gas of 16.5 Gm3 (580 BCF) primarily in the Lower Cretaceous Windalia Sand Member of the Muderong Shale and in- place gas of 14.5 Gm3 (515 BCF) in Middle Jurassic Biggada Formation. Additional hydrocarbon reservoirs have been discovered, including oil and gas in the Upper Jurassic Dupuy Formation, the Lower Cretaceous Malouet Formation, Flacourt Formation and Tunney Member, Mardie Greensand Member and M zones of the Muderong Shale and in the Upper Cretaceous Gearle Siltstone. Approximately 850 wells have been drilled to appraise and develop these accumulations, and to provide water source and water injection wells to enhance recovery. Production commenced in December 1966, with the first shipment of oil in April 1967. Although numerous hydrocarbon reservoirs have been developed, 95% of the 44 GL (278 MMBBL) of produced oil has been from the Windalia Sand.

Structural development of the Barrow Island anticline occurred initially during the Middle Jurassic and continued intermittently during the Cretaceous and Tertiary. Initial charging of the Dupuy and Malouet formations with oil from the Upper Jurassic Dingo Claystone occurred in the Early Cretaceous prior to the development of the shallower closures. Periodic wrench- related movement on the Barrow Fault during the Early to Late Cretaceous produced closures at the Lower Cretaceous reservoirs and provided a catalyst for oil migration and charging of these closures. Significant amounts of an extremely biodegraded component, and several less biodegraded phases are present in the oil in the Windalia Sand, indicating several phases of oil charging of the Barrow structure from Middle and Upper Jurassic sediments. In the Tertiary, gas sourced from Triassic and Jurassic sediments migrated into the Barrow structure via a dilated Barrow Fault, charged the Middle Jurassic Biggada Formation and displaced some of the oil in the Lower Cretaceous reservoirs.