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The Relationship Between Volcanics, Associated Intrusives And Carbon Dioxide Within The Otway Basin, South Australia.

Chatfield, Kim

Honours Degree, 1992

University of Adelaide

Abstract

The relationship between volcanics, associated intrusives and carbon dioxide within the Otway Basin of South Australia has been investigated. Magmatically derived carbon dioxide, existing within the hydrocarbon province of the Otway Basin, presents a risk for petroleum exploration.

Trends of volcanic centres and faulting are related to regional structures and stratigraphy. Seventeen main eruptive centres of two distinct ages are represented by the northern Mt Burr Range, of Pleistocene age, and the southern Mounts Gambier and Schank, Holocene in age.

Magmatic material, in the form of sheet-like dykes 1 to 100m wide and 1 to 8km long, originates from deep magma bodies in the rift zone. The magma has intruded and probably widened pre-existing faults and fractures, using them as conduits to the surface. The orientation of the volcanics and associated dykes is likely to be northwest-southeast along the trend of existing fault planes. Faults may act as either seals or conduits for the migration of carbon dioxide and hydrocarbons.

Carbon dioxide exsolution from intrusions in the Otway Basin has resulted in the concentration within structures of large amounts of carbon-dioxide with possible partial or total displacement of pre-existing hydrocarbons. For example, carbon dioxide has been encountered in the Caroline #1, Ladbroke Grove #1 and Kalangadoo #1 wells.

Avoidance of high concentrations of carbon dioxide is a priority in delineating petroleum exploration targets. The risk of striking carbon dioxide can be minimized by magnetic and seismic reflection surveys to locate `blind' vertical intrusives and therefore potential carbon dioxide plays.

Selected seismic reflection lines, aeromagnetic survey data, surface magnetic susceptibility measurements and drilling results, have been integrated in order to locate basaltic intrusions and therefore evaluate possible carbon-dioxide migratory pathways and traps.

The poor quality and paucity of available geophysical data imposes limitations upon accurate interpretation within the volcanic province of the Otway Basin. New high quality geophysical data sets are necessary for future exploration. The author has recommended parameters for future surveys carried put within the volcanic province.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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