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Abstract

AAPG Bulletin, V. 89, No. 1 (January 2005), P. 27-40.

Copyright copy2005. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/08150403134

Modeling petroleum generation in the Paleozoic of the Carnarvon Basin, Western Australia: Implications for prospectivity

K. Ameed R. Ghori,1 Arthur J. Mory,2 Robert P. Iasky3

1Geological Survey of Western Australia, Department of Industry and Resources, Mineral House, 100 Plain Street, East Perth, Western Australia 6004, Australia; [email protected]
2Geological Survey of Western Australia, Department of Industry and Resources, Mineral House, 100 Plain Street, East Perth, Western Australia 6004, Australia; [email protected]
3Geological Survey of Western Australia, Department of Industry and Resources, Mineral House, 100 Plain Street, East Perth, Western Australia 6004, Australia; [email protected]

AUTHORS

Ameed has M.Sc. degrees in geology from the University of Karachi (1968) and the Curtin University of Technology, Perth, Western Australia (1994). He specializes in petroleum geochemistry and has worked on Pakistani, Libyan, Australian, and Ugandan basins. Ameed joined the Geological Survey of Western Australia as a senior geologist in 1994; he is a member of AAPG, the Formation Evaluation Society of Western Australia, and the Petroleum Exploration Society of Australia.

Arthur graduated from the University of Sydney (B.Sc., 1976; Ph.D., 1980) and joined the Geological Survey of Western Australia in 1980. He has published articles on stratigraphy and sedimentology of all major onshore basins in the state and is a member of the Petroleum Exploration Society of Australia and the Geological Society of America.

Robert graduated from the Western Australia Institute of Technology (B.App.Sc., 1978; Grad.Dip.Sc., 1979) and Curtin University of Technology, Perth, Western Australia (M.App.Sc., 1991) majoring in geophysics. He joined the Geological Survey of Western Australia in 1981 and maintains an active interest in structural interpretation of basins in the state, particularly the Perth, southern Carnarvon, and Officer basins. He is a member of Australian Society of Exploration Geophysicists and Petroleum Exploration Society of Australia.

ACKNOWLEDGMENTS

Reviews by John B. Curtis, Ernest A. Mancini, and Qingming Yang greatly improved this manuscript. This paper is published with the permission of the director of the Geological Survey of Western Australia.

DATASHARE 15

Tables 1–3 are accessible in an electronic version on the AAPG Web site as Datashare 15 at ltwww.aapg.org/datashare/index.htmllt.

ABSTRACT

Maturity and petroleum generation modeling of the Paleozoic succession in the Carnarvon Basin shows that most potential source rock intervals reached their maximum generation migration during the Carboniferous–Permian and could have charged traps developed during rifting in the middle Carboniferous to Early Permian except for the Peedamullah Shelf, where generation peaked during the Cretaceous. However, identification of such traps is challenging because it is difficult to differentiate between the deformation associated with middle Carboniferous–Early Permian rifting and that of the Early Cretaceous breakup rifting. Given the presence of suitable reservoir and sealing units in most of the Paleozoic, the prime risks for this section are the volume of available source rock, trap integrity because of the long period of preservation required, and relative timing of generation vs. trap formation, such that charging of younger traps requires secondary migration.

The best Paleozoic oil-prone source beds identified in the Carnarvon Basin are thin beds in carbonate-dominated Silurian and Devonian units on the Gascoyne Platform, but Devonian source beds are restricted to the northern parts of the platform. The maturity of these units progressively increases from immature in the south-southeast to mature in the north-northwest, following increasing depth of burial in that direction. The best gas-prone source beds lie within the Lower Permian of the Merlinleigh Subbasin, and their maturity ranges from immature along the margins of the subbasin to overmature toward the center. Within the Upper Permian, the best source beds for oil and gas are in the Peedamullah Shelf, where they range from immature in the southeast to mature in the northwest.

Commercial Paleozoic petroleum has yet to be discovered in the Paleozoic of the Carnarvon Basin, but the assessment of this part of the basin is limited because few, if any, of the exploration wells drilled to date were valid tests of these objectives.

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