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Abstract

AAPG Bulletin, V. 86, No. 9 (September 2002), P. 1531-1542.

Copyright ©2002. The American Association of Petroleum Geologists. All rights reserved.

Quantitative evaluation of the oil-leg potential in the Oliver gas field, Timor Sea, Australia

M. Lisk,1 G. W. O'Brien,2 P. J. Eadington3

1CSIRO Petroleum, P.O. Box 1130, Bentley, Western Australia, 6102, Australia; email: [email protected]
2Australian Geological Survey Organisation-Marine Petroleum and Sedimentary Resources Division, G.P.O. Box 378, Canberra, Australian Capital Territory, 2601; email: [email protected]
3Commonwealth Scientific and Industrial Research Organisation Petroleum, P.O. Box 1130, Bentley, Western Australia, 6102, Australia; email: [email protected]

AUTHORS

Mark Lisk graduated from the University of Auckland in 1990 with B.Sc. (1988) and M.Sc. (1990) degrees in geology. After working briefly on epithermal gold systems he joined the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in 1990 and is currently employed as a geologist with their Petroleum Division. His research interests center on the application of fluid inclusion technologies to petroleum exploration, particularly fault seal analysis and hydrocarbon charge histories. He is a member of the Petroleum Exploration Society of Australia, the Formation Evaluation Society of Western Australia, and AAPG.

Geoffrey O'Brien is a senior principal research scientist with the Petroleum and Marine Division (PMD) of Geoscience Australia and is presently the research group leader of the Marine Zone Geoscience Program. His present work is focused on the application of multidisciplinary research strategies to basin analysis on the Australian margin. O'Brien has previously worked for BHP and for Western Mining Corporation. He is a member of the Petroleum Exploration Society of Australia (PESA) (PESA Australian Lecturer, 1992), AAPG, and the American Geophysical Union.

Peter Eadington has a B.Sc. degree and Ph.D. in geology from the University of Newcastle, New South Wales, Australia, and a graduate diploma in business administration from Maquarie University, New South Wales, Australia. He worked with BHP and Geophysical Service International and is currently a principal research scientist at CSIRO Petroleum. He introduced fluid inclusion and hydrothermal geochemical techniques to CSIRO for applications for uranium, copper, and tin exploration. Since 1987 he has investigated petroleum migration and is a member of the Petroleum Exploration Society of Australia and AAPG.

ACKNOWLEDGMENTS

This article forms part of the Fill-Spill project, a collaborative initiative between the Australian Geological Survey Organisation (AGSO) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) aimed at characterizing charge histories on the North West Shelf. The assistance and comments of research and support staff at CSIRO and AGSO is gratefully acknowledged. The constructive comments of Colin Barker and an anonymous reviewer helped improve the quality of this article, and their efforts are warmly appreciated.

ABSTRACT

Oil-bearing fluid inclusions in sandstone cores and cuttings represent hidden oil shows. The frequency of quartz grains containing these inclusions (the GOI number) reflects the maximum paleo-oil saturation experienced in a sandstone reservoir irrespective of the present fluid phase. Samples that have been exposed to high oil saturation have GOI numbers at least one order of magnitude greater than samples that have demonstrably low oil saturation. In this way, these fluid inclusion data can be used to identify paleo-oil columns and to map original oil-water contacts in wells where oil has been displaced by a later gas charge. Moreover, the use of detailed GOI mapping to accurately define the location of the original oil-water contact allows the height of the paleocolumn to be determined and an estimate to be made of original oil in place.

The Oliver oil and gas discovery, located in the Timor Sea, Australia, presently contains a hydrocarbon column of 178.5 m, composed of 164 m of gas over a 14.5 m oil leg, and is filled to spillpoint. In well Oliver-1, GOI mapping has delineated a gross paleo-oil column of between 99 and 132 m within the present gas leg. This corresponds to original oil in place of up to 200 million bbl, considerably greater than the 45 million bbl of oil presently reservoired. The displacement of up to 155 million bbl of oil from this structure has high-graded the prospectivity of tilted fault blocks updip from the Oliver structure.

GOI mapping is an innovative approach to reservoir characterization that can reliably detect paleo-oil accumulation in hydrocarbon traps that are presently filled by gas. These data allow the oil-leg potential of both gas discoveries and nearby untested structures to be addressed in a quantitative manner before additional drilling is commissioned.

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