THE TINTABURRA OILFIELD

Abstract

The Tintaburra oilfield, discovered in December 1983 with the drilling of Tintaburra 1, is situated within Petroleum Lease 29 (previously within Authority to Prospect 299P Part 2) on the southeast margin of the Eromanga Basin, Queensland.

Tintaburra 1 recorded the first flow of oil from the Cretaceous Wyandra Sandstone Member of the Cadnaowie Formation in the Eromanga Basin and established the presence of oil columns in the Murta Member and Hutton Sandstone. The Hutton Sandstone produced 1750 barrels of 44° API gravity oil per day on drill stem test.

The results of six successful appraisal wells show the field to be a simple structural accumulation at the top Hutton level. The top Hutton accumulation is believed to be full to fault-independent closure. The hydrocarbons are trapped on the western upthrown side of the Tertiary reverse faulted Tintaburra Anticline. Approximately 80 per cent of reserves are reservoired in the top Hutton.

The discovery extended the productive limits of the Eromanga Basin 100 km to the north and east from the

Jackson oilfield, and highlighted the potential of Tertiary structures, previously thought by many to be non-prospective.

Channelling at the 'C' horizon (base Wallumbilla Formation) extends across the southern part of the field, complicating depth mapping by virtue of the large velocity contrasts between channel and host sediments. Velocity and raypath distortion below the channel are major geophysical complexities that have been successfully overcome, allowing more accurate location of appraisal wells.

Appraisal drilling, combined with high quality seismic data, has identified the nature of the Early Cretaceous submarine channelling, and has identified new channel-related plays. 'C' horizon channelling imparts a strong stratigraphic component to the Murta and Wyandra accumulations. Integrated core and log studies indicate that every reservoir within fault-independent closure, and overlain by a laterally continuous effective seal, contains oil. Facies variations within the top Hutton/base Birkhead interval have important implications for trap integrity and are generally not resolvable seismically.

The high API gravity, low pour point Wyandra and Murta crudes are distinct from the waxy, paraffinic Hutton crudes, and geochemical analysis of the oils and source rocks indicates a probable Eromanga-sequence origin for all the crudes.