F. E. Burns¹, J. Thompson², R. B. Ainsworth³, R. Seggie³

(1) University Western Australia, Perth, Australia
(2) Ichron Ltd, Cheshire, United Kingdom
(3) Woodside Energy Ltd, Perth, Australia

ABSTRACT: Depositional Modelling of a Deltaic System Using Ichnofabric Analysis: Middle Jurassic Plover Formation, Sunrise-Troubadour Gas-Condensate Fields, Bonaparte Basin, Timor Sea

Reservoir quality and distribution in the Sunrise-Troubadour Fields are directly related to primary depositional processes. Facies and sequence stratigraphical interpretations, derived from sedimentological and ichnofabric analysis of cored intervals, and constrained by biostratigraphical and well-log data, are therefore crucial to reservoir architecture and sand-body geometry prediction in the study area.

The ichnofabrics identified in core are grouped into 6 broad ichnofabric associations: Ophiomorpha; Palaeophycus; Teichichnus; Phycosiphon; Planolites and Chondrites. As ichnofabrics are environmentally specific, the integration of ichnological studies with facies analysis enables 7 facies associations to be identified: fluvial channel; prograding mouthbar complex; barrier bar; restricted embayment; upper shoreface; lower shoreface and shelf. Low diversity trace fossil assemblages dominated by Planolites and Teichichnus are characteristic of restricted embayment facies. Shelf deposits display higher diversity trace fossil assemblages, with Phycosiphon-, Teichichnus-, Chondrites-, Ophiomorpha-, and Diplocraterion-dominated ichnofabrics evident. Prograding and retrograding shoreface sandstones are identified through the vertical juxtaposition of ichnofabrics, for example the transition from lower shoreface, HCS sandstones with Teichichnus, through sandstones with Palaeophycus, to upper shoreface, cross-bedded sandstones with Ophiomorpha indicate a shoaling-upward stacking pattern. Significant stratal surfaces are identified through changes in ichnofabrics, ichnofabric-stacking patterns, and by the presence of omission colonisation surfaces marked by concentrations of Diplocraterion and Skolithos.

Two depositional models are proposed: a lower bay-head delta complex, and an upper linear shoreface model. Bay-head delta complex deposits exhibit the highest degree of heterogeneity, due to abundant lateral and vertical facies shifts, while shoreface and shelf deposits are correlatable field-wide.

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