Publication Date:
2006-09-01
Description:
Paleo-oil-water contacts (paleo-OWCs) defined in eight wells from the Griffin, Chinook, and Scindian fields, Barrow Subbasin, Australian North West Shelf, are 47–147 m (154.2–482.3 ft) deeper than the current OWCs. The paleo-OWCs are deeper than the spillpoints separating the fields and are consistent with the existence of a single large paleo-oil accumulation. A plane of best fit projected through these paleo-OWCs describes an inclined surface with a northwesterly dip of approximately 1.5°. Assuming that this paleo-OWC was horizontal at the time of charge, three-dimensional structural restoration was used to assess the trap geometry at that time and the impact of subsequent post-charge structuring. The paleo-OWC tilt is reduced to 0.6° by restoration to the middle Miocene, and by the base Tertiary, the paleo-OWC became over-rotated by 0.1°. A horizontal paleo-OWC plane occurred some time between these periods and is broadly consistent with oil-charge estimates derived from fluid-inclusion paleotemperature data combined with one-dimensional basin modeling. The restored paleostructure and the approximate position of the paleo-OWC are consistent with the combined trap having initially been filled to spill. The bulk rock volume of the paleo-accumulation is more than 10 times larger than the current accumulation, indicating the loss of significant oil volumes as post-charge westerly tilting progressively reduced the trap capacity. Based on the current oil volumes (about 200 million bbl), nearly 2 billion bbl of oil was spilled from the trap by the relative shallowing of the eastern spillpoint. The region to the east and north of the Griffin area fields is lightly drilled, and remigration of such large volumes of oil to this area provides great incentive for future exploration. New targets are also inferred on the hanging wall of the main Griffin fault, which could represent bypassed pay. Mark Brincat graduated from the University of Adelaide with a B.Sc. (hons) degree in 1992 in petroleum geology from the Australian School of Petroleum. After a short-term contract with Santos Australia Ltd. as a development geologist, he joined Geoservices and later Baker Hughes Inteq. In 1995 he joined the Commonwealth Scientific and Industrial Research Organization (CSIRO) Petroleum as a research geologist, focusing on the application of multidisciplinary techniques to help predict fault-seal and trap prospectivity. In mid-2006, he joined Strike Oil Limited as a geoscientist. Anthony Gartrell graduated with a B.Sc. (hons) degree in geology from the University of Western Australia (UWA) in 1993. After a short period as a research officer at UWA, he joined the Western Mining Corporation Resources Petroleum Division as a structural geologist. He then completed a Ph.D. in structural geology at UWA in 2000 and now works with CSIRO Petroleum as a research scientist. His recent work focused on structural controls on hydrocarbon charge and leakage histories. Mark Lisk graduated from the University of Auckland in 1990 with a B.Sc. degree (1988) and an M.Sc. degree (1990) in geology. After working briefly in New Zealand on epithermal gold systems, he joined CSIRO Petroleum in 1990 as a research geologist, developing new technologies for petroleum exploration and appraisal, in particular directed toward seal analysis and the assessment of petroleum systems. In 2005, he joined Woodside Energy Ltd. as a senior geologist in their Australian and New Ventures Team. Wayne Bailey graduated in 1997 with a Ph.D. in structural geology from Durham University, United Kingdom. From 1997 to 2002, he was a research associate with the Fault Analysis Group, University College Dublin (formerly Liverpool). He later joined CSIRO Petroleum as a researcher focusing on seismic-scale fault-seal analysis. In 2006, he joined Woodside Energy Ltd. as a coordinator of the Traps, Seals, and Pressure Team. Luke Johnson graduated from Curtin University with a B.Sc. (hons) degree in applied geology. He was later employed as a geologist with CSIRO Petroleum, investigating hydrocarbon migration and accumulation, paleotemperature and salinity, and basin hydrodynamics. In late 2005, he joined Chevron Australia Ltd. as a geologist. Dave Dewhurst is a principal research scientist with CSIRO Petroleum in Perth. From the early 1990s, his research has been concentrated on compaction, faulting, and fluid flow in mudstones. He currently works on top- and fault-seal issues, overpressure, and CO2 storage, as well as the application of rock physics and geomechanics to petroleum systems.
Print ISSN:
0149-1423
Electronic ISSN:
1943-2674
Topics:
Geosciences
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