Constraining Late Cretaceous exhumation in the Eromanga Basin using sonic velocity data
Mitchell Keany A , Simon Holford A and Mark Bunch AAustralian School of Petroleum, The University of Adelaide
The APPEA Journal 56(1) 101-126 https://doi.org/10.1071/AJ15009
Published: 2016
Abstract
Exhumation in sedimentary basins can have significant consequences for their petroleum systems. For example, source rocks may be more mature than their present-day burial depths suggest, increased compaction can result in reduced reservoir quality, and seal integrity problems are commonly encountered. The Eromanga Basin in central Australia experienced an important phase of exhumation during the Late Cretaceous, though the magnitude and spatial distribution of exhumation is poorly constrained. In this study exhumation magnitudes have been determined for 100 petroleum wells based on sonic transit time analyses of fine grained shales, siltstones and mudstones within selected Cretaceous stratigraphic units.
Observed sonic transit times are compared to normal compaction trends (NCTs) determined for suitable stratigraphic units. The Winton Formation and the Bulldog Shale/Wallumbilla Formation were chosen for analysis in this study for their homogenous, fine-grained and laterally extensive properties. Exhumation magnitudes for these stratigraphic units are statistically similar. Results show net exhumation in the southern Cooper-Eromanga Basin (<500 m [~1,640 ft]) and higher net exhumation magnitudes (up to 1,400 m [~3,937 ft]) being recorded in the northeastern margins of the basin. Gross exhumation magnitudes show significant variation across short distances suggesting different tectonic processes acting upon the basin. Independent vitrinite reflectance and apatite fission track analysis data, available for a subset of wells, give statistically similar exhumation magnitudes to those that have been calculated through the compaction methodology, giving confidence in these results. The effect on source rock generation is illustrated through 1D basin modelling where exhumation is shown to impact the timing and type of the hydrocarbons generated. The improved quantification of this exhumation permits a better understanding of the Late Cretaceous tectonics and palaeogeography of central Australia.
Mitchell Keany is a 2015 petroleum geoscience and geophysics honours graduate from the Australian School of Petroleum (University of Adelaide After completing a bachelor’s degree in 2008 with majors in geology, geophysics and environmental geoscience at the University of Adelaide, Mitchell worked as geophysical wireline operator at Borehole Wireline. He gained experience on projects in the central Queensland coalfields, Rio Tinto Pilbara iron ore operations, Leigh Creek Coal Mine, Ranger Uranium Mine, and on exploration projects spanning various commodities (coal, iron ore, uranium and rare earths) throughout Australia, from Kalgoorlie to Mt Isa. Mitchell transitioned to working as a geophysicist with Borehole Wireline, where his duties included image interpretation (acoustic and optical), tool calibration and verification, and the development of processing techniques using WellCAD’s automation capabilities. Mitchell’s interests include petrophysics, geomechanics, basin analysis and reservoir modelling, and he is excited to be embarking on a career in the petroleum industry. He is an active member of PESA and the AAPG, and a past committee member of the Adelaide University Geological Society. mitchell.keany@student.adelaide.edu.au |
Simon Holford is a Senior Lecturer at the Australian School of Petroleum, University of Adelaide, where he is co-leader of the Stress, Structure and Seismic (S3) Research Group. Simon has published around 55 papers and has received more than $3 million in research funding. Simon’s research interests encompass the formation and evolution of rifted margins; quantifying uplift, subsidence, structural permeability and contemporary stresses in sedimentary basins; and, understanding the impacts of magmatic activity on petroleum systems. Simon has won numerous awards, including the 2012 APPEA Best Paper award. He has a first-class Honours degree from Keele University (2001), and a PhD from the University of Birmingham (2006). He is the present president of the SA/ NT branch of PESA. Member: AAPG, AGU, GSA, GSL, PESA and PESGB. simon.holford@adelaide.edu.au |
Mark Bunch is a Senior Lecturer in Petroleum Geoscience at the Australian School of Petroleum, University of Adelaide. His present research activities are concerned with formation evaluation and seismic geomorphology. Prior to his present role, he spent seven years with the CO2CRC as a Research Associate in reservoir characterisation, during which he worked on geological carbon storage site selection, capacity estimation and geological modelling projects in the onshore Canterbury Basin (NZ), the Gippsland and Otway basins of Victoria, the Surat Basin of Queensland, and the Darling Basin of NSW. Mark spent a period of time as acting head of geomodelling for the CO2CRC Otway Basin Pilot Project and led CO2CRC storage research projects for five years. Mark holds degrees in geology and geophysics (BSc Hons), hydrogeology (MSc), and a PhD in stratigraphic forward modelling. Mark has also worked for the North Sea Palaeolandscapes Project and as a developer of shallow groundwater flow models to guide excavation planning. mark.bunch@adelaide.edu.au |
