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High Resolution Seismic Sequence Stratigraphy of the Tuna Flounder Channel, Gippsland Basin, Australia

Ross, Ashley

Honours Degree, 2004

University of Adelaide

Abstract

The Gippsland Basin A is mature hydrocarbon province with the major fields nearing the end of their productive lifespan. Declining production rates have prompted increased exploration activity to slow the rate of decline. The recent acquisition of large scale high quality 3D seismic data provides a new resource to investigate for remaining hydrocarbon accumulations and to maximize recovery of existing fields.

The Tuna and Flounder Fields of the Gippsland Basin are 100 mmboe oil fields. The shallowest reservoirs are contained within the Tuna Flounder Channel (TFCh) which links both fields. Despite significant potential, the TFCh remains predominantly unexplored and offer an attractive potential for further discoveries.

The TFCh is a large-scale subaerially eroded canyon formed by a tectonically induced relative sea level fall. Eocene compression arched and uplifted the coastal plain sediments of the Latrobe Group causing fluvial down-cutting. The TFCh fill comprises a series of nine high order sequences deposited in a punctuated transgression.

The nine sequences infill the TFCh as repeated ‘drowned valley’ systems characteristic of incised valleys. Incised lowstand fluvial systems are rapidly flooded during the subsequent transgression and converted to a shallow marine drowned valley environment (estuarine). Highstand bayhead deltas prograde into the central basin while barrier bar sediments are deposited in the channel mouth. Repeated cut and fill sequences have created a complex incised valley fill. Orthogonal incised tributaries etched into the walls of the TFCh act as drainage systems for the surrounding highlands and continuously deposit reworked coastal plain sediment. At the Tuna Field, facies are dominated by fluvial, coastal plain and shore-face sediments, while at the Flounder Field facies are dominated by estuarine and shallow marine sands and shales.

Three potential plays within the TFCh were identified. The sub-crop and base-channel high plays require sealing TFCh sediment of erosional remnants. The intra-channel play comprises of TFCh reservoirs sealed by internal or overlying facies. Erosional remnant plays juxtaposed by floodplain or shallow marine sediment have a high chance of sealing and present significant upside potential. Stacked intra-channel bayhead deltas top sealed by Latrobe Group marine shales provide attractive potential if four-way closure can be identified. Adequate seal is the main risk identified for intra-channel reservoirs, especially proximal to the Tuna Field, while locating large high quality reservoirs is the main risk proximal to the Flounder Field.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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