ABSTRACT: Depositional Systems, Petrography, and Reservoir Quality of Cores from the Chinook and Griffin Fields, Block WA-210-P, North Carnarvon Basin, Australia

McPHERSON, JOHN G., Mobil R&D Corporation, Dallas, TX and IAN A. RUSSELL,* Mobil E&P Australia Pty Ltd., South Melbourne, Australia

Mobil and Inpex have resulted in the discovery of oil reserves in the Barrow and Mardie formations within the Chinook and Griffin structures. These structures are drape anticlines of the Barrow/Mardie reservoir over the underlying Triassic of the Alpha Arch. Seal is provided by the Muderong shale. The wells were notable for their recovery by DST of oil at high flow rates from both the expected permeable Barrow sandstone (up to 7800 BOPD), but also from fine-grained sandstones within the Mardie Formation (up to 4060 BOPD). Detailed core descriptions and petrography were done to evaluate the depositional setting, quality, and likely lateral extent of these two reservoir units.

The Barrow reservoir comprises the fluvial topset sequence of the extensive Neocomian Barrow braiddelta system. Much of the reservoir is composed of thick units of large-scale cross-bedded, coarse-grained sandstone representing channel-fill and bar-top deposits of a sandy braided-river system. Some intervals contain crudely developed fining-upwards cycles interpreted as the deposits of lower delta-plain meandering distributary channels. Delta-plain subenvironments include crevasse-splay and coaly interchannel/marsh facies. The quartzose Barrow sands have good lateral and vertical continuity and exceptional reservoir quality (mean 0 = 19%; mean k = 2000 md).

The overlying Mardie Formation was deposited during a period of regional transgression across the thick Barrow delta. The Mardie comprises typical transgressive systems tract deposits, namely glauconitic lower-shoreface and offshore facies of a shallow-shelf, open-marine environment. Reservoir quality in the Mardie is locally good, but highly variable.

The existence of reservoir facies in the Mardie has allowed for an increase in potential producible reservoir under closure, and has resulted in a sizable reservoir addition. Evaluation of the two reservoir units in the Chinook and Griffin structures has necessitated a fully integrated approach, incorporating detailed core description and analysis, wireline-log analysis, RFT data, and DST results.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)