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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 63 (1979)

Issue: 3. (March)

First Page: 539

Last Page: 539

Title: Generation and Occurrence of Hydrocarbons Related to Structural and Geothermal History of Onshore Perth Basin, Western Australia: ABSTRACT

Author(s): B. M. Thomas

Article Type: Meeting abstract

Abstract:

The Perth basin, an elongate rift basin along the southwestern coast of Australia, contains over 15,000 m of mainly continental clastic sediments which range in age from Silurian to Holocene. Organically rich sediments are widely distributed throughout the Permian, Triassic, and Jurassic sections of the basin. However, as a result of the proximity of the Precambrian shield in the east and the predominance of terrestrial organic matter in the largely continental to marginal-marine sedimentary fill of the basin, the kerogen type is mainly humic and gas-prone. Hydrocarbon accumulations are therefore mainly gas and/or condensate, although a secondary light, highly paraffinic oil is of economic significance. Present commercial fields are restricted to the northern part of the asin and appear to be related to Permian, Triassic, and Jurassic mature source beds in the Dandaragan trough. In the Bunbury trough in the south, mature source beds are limited to a very deeply buried Permian coal measures sequence 2,000 m thick, from which significant but noncommercial gas flows and some condensate have been recorded.

Vitrinite reflectance data suggest that the uplift and erosion of the northwestern flank of the Perth basin were accompanied by higher geothermal gradients than are measured today in exploratory boreholes. In contrast, low geothermal gradients in the axis of the Dandaragan and Bunbury troughs (<2.0°C/100 m) mean that generative temperatures are reached in these areas at relatively great depths. Producible accumulations often depend on a delicate balance between depth needed to generate hydrocarbons and the level at which porosity declines to unacceptable levels for gas production.

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Copyright 1997 American Association of Petroleum Geologists