Publication Name: The Cooper & Eromanga Basins Australia
Authors: J.W. Hunt, R.S. Heath, and P.F. McKenzie
Date Published: June 1989
Number of Pages: 29
Reference Type: Book Section
Abstract:
The Permo-Triassic Cooper Basin is Australia's major onshore hydrocarbon province. Hydrocarbons discoveredin the Basin to date comprise mainly gas (approximately 6 TCF recoverable) although one large oil pool, in the
Tirrawarra Sandstone of the Tirrawarra Field, is present (27 MMSTB recoverable) and substantial gas-liquids reserves are associated with the gas in the Basin (280 MMSTB of liquids recoverable). The composition of the hydrocarbons reflects the nature of the source material, which consists of a rich, mainly gas-prone, higher plant (woody) material but with significant liquids potential.
The distribution of hydrocarbons in the Basin is closely related to source maturity, measured in terms of vitrinite
reflectance (Rv%). There is a sharp onset of significant accumulation when the source reaches a maturity of 0.95% Rv in the drainage area. It is only beyond this level of maturity that traps may be filled to structural spill. For maturities between Rv 0. 70% and 0.95%, hydrocarbons may be found in partly filled traps due to either early
expulsion from locally rich source rocks, or longer distance migration (up to 10 km) from mature down-dip areas. The distribution of oil in the Cooper Basin coincides with the distribution of wet gas with respect to source maturity, which suggests both are derived from the same source type. Significant oil has been found in the Permian and, with further understanding of the source of Permian oil, more will be found.
The composition of gas is also maturity driven, at least for the hydrocarbon components. Liquid recoveries (C2.)
vary from less than 10 BBL/MMCF of gas in dry gas areas, to more than 120 BBL/MMCF of gas in wet gas areas. The
amount of carbon dioxide present in the gas varies widely from area to area. Hydrocarbon gas composition and gas-liquid recoveries may thus be estimated pre-drill from a consideration of source rock maturity.