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Diagenetic Controls And Reservoir Evaluation Of The Eastern View Group, Bass Basin, Tasmania Australia.

Cubitt, Chris

Honours Degree, 1992

University of Adelaide

Abstract

The Bass Basin is situated between Tasmania and mainland Australia. It covers an area of approximately 65000 km2. There are approximately eight kilometres of sediments accumulated in this intracratonic extensional basin since the Late Jurassic-Early Cretaceous.

From the drilling activity undertaken between 1985 and 1986, deep sands appear to display good reservoir qualities.

This study analyses the thermal history of the basin, controls on diagenetic adjustments and the effects of these adjustments on reservoir quality.

The fine grained sands have been effected by compaction to the extent of having all porosity occluded. Medium to coarse grained sands display the most favourable reservoir quality. Good quality reservoir sands are found at depth. The formation of late stage silica that occludes minor amounts of porosity at depth, is controlled by the onset of high temperatures. The formation of porosity in the sediments is mainly from the dissolution of siderite. Some primary porosity is preserved. Feldspar dissolution is a minor contributor to creation of sediment porosity. Dolomite and ankerite form in a coarse to medium grained sediments predominantly in areas near the basin margin. The diagenetic sequence seen in the sediments is: Early siderite cement

Early silica cement

Kaolin development

Siderite and kaolin dissolution

Dolomite and ankerite cements (Coarse to medium- grained sediments)

Illite development

Secondary silica cementation stage

Organic acids dissolving fractures in rock

Numerous extrusive and intrusive igneous bodies have heated large areas of basin sediments, possibly affecting petroleum maturation and preservation in the basin.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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