Publication Name: PESA's Eastern Australasian Basin Symposium II
Authors: L. Kramer, D.M. McKirdy, K.R. Arouri, L. Schwark and D. Leythaeuser
Date Published: December 2004
Number of Pages: 31
Reference Type: Book Section
Abstract:
The Strzelecki oil and gas field is located on the southern margin of the Nappamerri Trough, a major hydrocarbonkitchen in the Cooper/Eromanga petroleum province of central Australia. Its oil-bearing sandstones (Hutton, Birkhead, Namur) are all of Mesozoic age. With a view to reconstructing their respective charge histories, core plugs of each reservoir at Strzelecki-4, 5 and 6 were extracted in a high-pressure solvent flow-through cell. This device sequentially recovers individual oil charges from the intact pore systems of a reservoir rock, in the reverse order of their arrival at the trap. Initial extraction with dichloromethane retrieves the oil that is freely mobile in the pore network ('free oil' = final charge). The subsequent chloroform/methanol extracts represent the part of the oil that is immobile due to adsorption on pore walls ('adsorbed oil'= initial charge) or retained in smaller, less accessible pores.
The residual oils exhibit systematic variations in yield and bulk composition within each oil column. A minor upward decrease in thermal maturity (-0.02-0.03% R,) is evident in the Hutton and Namur oil pools. However, at any given level, there is generally no significant difference in either maturity or source affinity between the 'free' and 'adsorbed' oils. On a larger scale, the 'free' oils display a field-wide maturity differential: Hutton, 0.87%; Birkhead, 0.86%; and Namur, 0.94% R,. In terms of their source affinity, the relative Araucariacean input is Birkhead> Hutton> Namur. All three oil pools comprise mixtures of intra-Jurassic (probably Birkhead) and Permian hydrocarbons. The major contribution (65-80%) appears to have come from source rocks in the Toolachee Formation of the underlying Cooper Basin.