--> ABSTRACT: Top Seal Facies and Capacity as First-Order Controls on the Distribution and Composition of Hydrocarbon Accumulations and Seeps, Yampi Shelf, Browse Basin, North-Western Australia, by Geoffrey William O'Brien, A. Barrett, M. Lisk, G. Lawrence, and A. Williams; #90906(2001)

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Geoffrey William O'Brien1, A. Barrett1, M. Lisk2, G. Lawrence3, A. Williams4

(1) Australian Geological Survey Organisation, Canberra, ACT, Australia
(2) CSIRO Division of Petroleum Resources, Bentley, WA, Australia
(3) TREICOL Limited, Knebworth, Hertfordshire, United Kingdom
(4) Nigel Press & Associates, Crockham Park, Edenbridge, Kent, United Kingdom

ABSTRACT: Top Seal Facies and Capacity as First-Order Controls on the Distribution and Composition of Hydrocarbon Accumulations and Seeps, Yampi Shelf, Browse Basin, North-Western Australia

The northern Yampi Shelf is located at a margin-scale relay system (the juncture between the Bonaparte and Browse Basins) and is presently a focus for active hydrocarbon migration and entrapment, as well as being a key input corridor for silici-clastics through time. Traps, charged with both oil (Cretaceous source) and gas (pre-Jurassic source), comprise Cretaceous seal-reservoir couplets developed around, and over, a rugose, basement ramp topography. Interaction between basement topography, relative sea-level and silici-clastic input history produced a heterogeneous regional seal which becomes markedly thinner and sandier margin-ward. A detailed study of the area, using a combination of 3D seismic data, oil seep remote sensing data (SAR, sniffer etc), fluid inclusion-based charge history analysis and capillary measurements, has revealed that hydrocarbon accumulation and seepage on the Yampi Shelf are controlled principally by the top seal facies (and their attendant capacity). In more basinal areas, where seal capacity is higher, hydrocarbon seepage is minimal and oil accumulations tend to be progressively gas-flushed. In more inboard locations, prolific gas seepage is common, with progressive failure of the seal resulting in "leaky" traps in which much of the gas bleeds off. This scenario provides an opportunity to reduce gas-flushing and preserve oil columns. Further inboard, the seal thins and shales out, significant oil seepage occurs, and no accumulations are present. The Yampi Shelf provides a classic example of how seal facies can act, via differential seal capillary failure, as a first-order control on the distribution and composition of hydrocarbon accumulations and seeps.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado