Authors / CoAuthors
Ambrose, G.J. | Liu, K. | Deighton, I. | Eadington, P.J. | Boreham, C.J.
Abstract
The northern Pedirka Basin in the Northern Territory is sparsely explored compared with its southern counterpart in South Australia. Only seven wells and 2500 km of seismic data occur over a prospective area of 73,000 km2. In this basin three petroleum systems have potential related to important source intervals in the basal Jurassic (Poolowanna Formation), Triassic (Peera Peera Formation) and Early Permian (Purni Formation). They are variably developed in three prospective depocentres, the Eringa Trough, the Madigan Trough and the northern Poolowanna Trough. New basin modelling techniques indicate oil and gas expulsion responded to increasing early Late Cretaceous temperatures in part due to sediment loading (Winton Formation). Using a composite kinetic model, oil and gas expulsion from coal rich source rocks were largely coincident at this time when source rocks entered the wet gas maturation window. The Purni Formation coals provide the richest source rocks and equate to the lower Patchawarra Formation in the Cooper Basin. Widespread well intersections indicate that glacial outwash sandstones at the base of the Purni Formation, herein referred to as the Tirrawarra Sandstone, have regional extent and are an important exploration target as well as providing a direct correlation with the prolific Patchawarra/ Tirrawarra petroleum system found in the Cooper Basin. An integrated investigation into the hydrocarbon charge and migration history of Colson-1 was carried out using CSIRO Petroleum's OMI (Oil Migration Intervals), QGF (Quantitative Grain Fluorescence) and GOI (Grains with Oil Inclusions) technologies. In the basal Jurassic Poolowanna Formation between 1984 and 2054 mRT, elevated QGF intensities, evidence of oil inclusions and abundant fluorescencing material trapped in quartz grains and low displacement pressure measurements collectively indicate the presence of palaeo-oil and gas accumulation over this 70 m interval. This is consistent with the current oil show indications such as staining, cut fluorescence, mud gas and surface solvent extraction within this reservoir interval. Multiple hydrocarbon migration pathways are also indicated in sandstones of the lower Algebuckina Sandstone, basal Poolowanna Formation and Tirrawarra Sandstone. This is a significant upgrade in hydrocarbon prospectivity, given previous perceptions of relatively poor quality and largely immature source rocks in the Basin. Conventional structural targets are numerous but the timing of hydrocarbon expulsion dictates that those with an ?older? drape and compaction component will be more prospective than those dominated by Tertiary reactivation which may have resulted in remigration or leakage. Preference should also apply to those structures adjacent to generative source ?kitchens? on relatively short migration pathways. Early formed Tirrawarra Sandstone and Poolowanna Formation stratigraphic traps are also attractive targets. Cyclic sedimentation in the Poolowanna Formation results in two upward fining cycles which compartmentalise the sequence into two reservoir ? seal configurations. Basal fluvial sandstone reservoirs grade upwards into topset shale/ coal lithologies which form effective semi-regional seals. Onlap of the basal cycle onto the Late Triassic unconformity offers opportunities for stratigraphic entrapment.
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nonGeographicDataset
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40076
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- External PublicationArticle
- ( Theme )
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- petroleum geology
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- AU-NT
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2002-01-01T00:00:00
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42
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