The Vesta oil and gas field, Vulcan Sub-basin, Timor Sea, Australia
Grant EllisEni Australia Limited
The APPEA Journal 52(1) 163-180 https://doi.org/10.1071/AJ11012
Published: 2012
Abstract
The Vesta oil and gas field is located in the Swan Graben of the Vulcan Sub-basin. The structure consists of a number of separate tilted fault blocks located on a northwest-trending accommodation zone that forms a high, separating the southeast-dipping half-graben of the Swan Graben North from the northwest-dipping half-graben of the Swan Graben South.
Drilled in 2005, Vesta–1 intersected a 17 m thick oil-bearing slope-fan sandstone of the Late Jurassic Elm Sandstone in the Lower Vulcan Formation. Drill-stem testing flowed oil and gas and indicated that the reservoir is normally pressured surrounded above and below by over-pressured claystone. In 2007, Vesta–2 intersected gas-bearing sandstone in a separate fault compartment.
Understanding the geometry of the hydrocarbon-bearing Elm Sandstone reservoir has proved a challenge due to the very poor 3D seismic imaging, the variable sandstone thickness and quality, and abundant evidence of thin steeply-dipping injected sandstones above and below the main reservoir sandstone.
The Lower Vulcan and Upper Vulcan Formation claystone provides the vertical and lateral seal for the Elm Sandstone. This thick seal has protected the Vesta oil and gas accumulations from the effects of the Late Tertiary tectonism, which had a significant effect on the integrity of the palaeo-oil filled closures on the adjacent Eclipse Trend.
Three phases of hydrocarbon charge of the Vesta structure have been identified with oil-source correlation indicating a Lower Vulcan Formation marine source. The source interval intersected in Vesta–1 is presently post-mature, with oil and gas generation associated with high heat flow in the Late Jurassic. Expulsion of hydrocarbons from the source was most likely compaction-driven, with gas expulsion in the Early Cretaceous, and oil expulsion much later with increasing hydrocarbon saturation.
Grant Ellis graduated from the University of SA in 1971 with a Bachelor of Applied Science, and in 1973 with a Graduate Diploma (economic geology), after spending 1972 as a well-site geologist with Core Laboratories Inc. From 1974–78 he worked in sedimentary uranium exploration with Mines Administration Pty Ltd. In 1978, he joined Marathon Petroleum Australia Limited, where he spent the next 16 years, initially in uranium and base metal exploration and subsequently in oil exploration and development. With the closure of Marathon’s Perth office in late 1994, he worked as a consultant before joining Hardy Petroleum Limited in 1997. He is now Timor Sea Exploration project leader and geological coordinator with Eni Australia Limited. grant.ellis@eniaustralia.com.au |
