CRUDE OIL CORRELATIONS IN THE PERTH AND CARNARVON BASINS

Abstract

It is possible to group oils discovered in the Dandaragan Trough of the Perth Basin and the Barrow and Dampier Sub-basins of the Carnarvon Basin into distinct families according to the nature of the source material and its degree of maturity.

Oils recovered from the Dandaragan Trough are unique and virtually identical in composition, even though they are found in various reservoirs ranging in age from Permian to Jurassic. They are characterised by a high wax content and a low gasoline yield which can be explained by the immaturity of the source material. Condensates from equivalent strati-graphic levels in the Gingin and Walyering fields are similar in composition.

Two families of oils occur in the Barrow Sub-basin of the Carnarvon Basin. Oils recovered from Cretaceous sediments (viz. Windalia Radiolarite, Muderong Greensand and Birdrong Sand) are naphthenic to aromatic whereas those produced from the Jurassic Dingo Group are high wax oils of paraffinic to naphthenic base. A similar grouping of oil families occurs in the Dampier Sub-basin.

Condensates within Jurassic reservoirs in the Angel field are virtually identical in composition to the condensates and oil in Triassic reservoirs along the Rankin trend. In turn they are also similar in composition to the Jurassic oils of the Barrow Sub-basin and it appears likely that a common Jurassic source exists for these hydrocarbons. Oil recovered from the Toolonga Calcilutite in the North Rankin 1 well strongly resembles the Windalia oil at Barrow Island.