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Sedimentary Modelling (Sedsim) Of The M. Australis Sediments On The Southern Enderby Terrace - Lewis Trough Area, Carnarvon Basin, Western Australia.

Baker, Darren Leigh

Honours Degree, 1997

University of South Australia

Abstract

The aim of this study was to develop and utilise a systematic approach for the production of various sedimentary input parameters to the 3D stratigraphic forward modelling package (SEDSIM). High-resolution sequence stratigraphic concepts were used to define the input for the 3D sedimentary modelling of the sandstones within the M. australis palynozone, southern Enderby Terrace - Lewis Trough area, Carnarvon Basin. Controlled simulations were run to monitor the formation of various depositional frameworks over specified intervals of time in order to predict reservoir and sealing potential away from well control and in areas of low seismic resolution.

In this study, simulated models were developed for a stable shelf (Enderby Terrace) and an adjacent major depocentre (Lewis Trough) in the Early Cretaceous.

The area of interest lies within the Carnarvon Basin, Western Australia, under WA-209-P and adjacent permits, and covers an area of ~30 by 30 km. The sandstone located within the M. australis palynozone is considered to be the basal part of the Upper Muderong Shate Fm and contains a stratigraphic section consisting of glauconitic sandstones, siltstones and claystones. During the Barremian to Aptian, these sediments were deposited as part of an overall transgression. Analysis of the area using seisrnic stratigraphy indicates shoreface sands, highstand shelfal progrades, shelf break, sediment by-pass zones, slope fans and basin-floor fans.

To increase the reliability of prediction in the study area, a budget of sediment deposition and probable input localities was made. Palynological, seismic and lithostratigraphic studies were also incorporated into the simulation procedures of SEDSIM to constrain the proposed geological processes. These parameters were modified over the palaeotopographic surface by manual interaction with SEDSIM.

Factual input came from well completion reports (sidewalls and cuttings), palynology reports and seismic surveys. The depositional surface was generated by the interpretation of seismic data.

Data were generated in order to clone areas of factual data, and also to provide highest order accuracy predictions away from those areas. Using grid dimensions of 250 by 250m, 20 simulations made within the study area were tested for geological credibility by comparisons of model-derived cross sections to similar oriented seismic sections. The interrelationships between sedimentary sequences and intrasequencial geometries represented in these sections by downlap and onlap features, angular unconformities and phase variations in reflectors were ordered by interpreting systems tract sets for each sequence.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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