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Geosequestration Potential of The Western Otway Basin in South Australia

Nachiketa Mishra

Honours Degree of Bachelor of Science (Petroleum Geology and Geophysics) - 2013

Australian School of Petroleum

University of Adelaide

Abstract

The Otway Basin is an Early Cretaceous-Tertiary rift basin formed during the separation of
Antarctica from Australia. The South Australian portion of the basin has extensive and deep
fluvio-lacustrine sediment fill with multiple reservoir and seal lithologies conducive to
geosequestration. Several depocenters and sub-basins were picked for geoscientific
characteristation and assessing their suitability for CO2 storage. These included the Early
Cretaceous Penola, St Clair and Robe Troughs, the Late Cretaceous Morum Sub-basin and
the Voluta Trough as well as the Tertiary cover of the Gambier Basin. Several petroleum
fields in the Penola Trough were also selected for assessment. Relevant data was compiled
from well completion reports and open file petroleum geology reports in the study area.

The depth for supercritical CO2 was estimated to be 791 m and this limited the number of
suitable reservoirs in the area to three in particular: the Pretty Hill Formation, the Waarre
Sandstone and the Timboon Sandstone. Although storage potential is significant in these
saline formations, significant uncertainty remains with cap seal geometry, capacity and
integrity especially in the Eumeralla Formation regional seal. Moreover, the hydrocarbon
traps in the region indicate primarily fault-bound closures and fault seal integrity becomes a
significant CO2 containment risk. Present-day compressional forces are likely reactivating
NW-SE trending faults in the area that are optimally oriented to the maximum horizontal
stress, resulting in structural permeability and seal breach.

A quantitative assessment was done for each of the prospective storage sites using simple
volumetric equations to estimate storage capacity. This was followed by a qualitative
assessment using basin-scale screening criteria that considered containment security,
storage capacity and technological as well as economic feasibility to identify the most
suitable sites for storage. The Penola Trough and the Gambier Basin were deemed highly
suitable and it is recommended that further characterisation is done in these sites to reduce
the risk and uncertainty inherent in geosequestration.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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