New insights into the organic geochemistry of the Otway Basin
Tony Hill A C , Betina Bendall A and Andrew Murray BA South Australia Department for Energy and Mining, GPO Box 320, Adelaide, SA 5001, Australia.
B Murray Partners PPSA Pty Ltd., Perth, WA, Australia. Email: amurraypartners@gmail.com
C Corresponding author. Email: tony.hill@sa.gov.au
The APPEA Journal 60(2) 712-717 https://doi.org/10.1071/AJ19092
Accepted: 7 April 2020 Published: 15 May 2020
Abstract
The Penola Trough of the Otway Basin in South Australia has enjoyed over 20 years of commercial hydrocarbon production from the sandstones of the Early Cretaceous Otway Group with 71.46 PJ sales gas and 65 840 kL of condensate produced from five fields until production ceased in 2011. Recent success in Haselgrove 3, where a newly discovered deeper reservoir underlying depleted reservoirs of the Pretty Hill Formation flowed 25 MMscfd on test heralds a new phase of exploration and appraisal with a 2C Contingent Resource of 87 PJ assigned to the discovery. These hydrocarbons are considered to have been principally derived from lacustrine, floodplain and back swamp facies of the Pretty Hill Formation and lacustrine facies of the underlying Casterton Formation. The South Australia Department for Energy and Mining is currently investigating an unnamed Late Jurassic syn-rift sequence of interbedded metasediments, tuffaceous sediments and organically-rich shale, first identified as fractured basement in Sawpit 1, located on the northern flanks of the Penola Trough and which unconformably underlies the Casterton Formation. A low-sulfur medium-gravity paraffinic oil was recovered from drill stem tests from this well and subsequent total organic carbon and Rock-Eval analyses for the same unit in nearby Sawpit 2 identified a source rock containing algal organic matter and thought to be deposited in a deep anoxic lake setting. In this paper, we will present the preliminary results of detailed geochemical analyses of rocks and rock extracts from this previously unrecognised syn-rift sequence and discuss implications for hydrocarbon prospectivity in the deeper portions of the Penola Trough.
Keywords: Casterton Formation, chemostratigraphy, Penola Trough, source rocks.
Tony Hill graduated with a BSc in Applied Geology from the Royal Melbourne Institute of Technology in 1980. He has worked extensively in several petroleum basins across Australia and also worked in the fields of hydrogeology and geothermal energy. He is currently Deputy Director within the Energy Resources Division of the South Australian Department for Energy and Mining (SA-DEM). |
Betina Bendall has a BSc (Hons) and PhD in Geology from the School of Earth and Environmental Sciences at the University of Adelaide and a PGrad Dip in Environmental Management from Charles Sturt University. She currently holds the position of Chief Geoscientist in the Energy Resources Division in the South Australia Department for Energy and Mining and has previously worked in the minerals and geothermal industries in Australia and the petroleum industry in the United Arab Emirates. |
Andrew Murray holds BAppSc, MSc and PhD degrees in Applied Chemistry, Environmental Chemistry and Petroleum Geochemistry and was Principal Petroleum Systems Analyst at Woodside Energy for 18 years. After semi-retirement in 2016 he started his own company (Murray Partners PPSA Pty Ltd) to provide training and consulting services to industry. |
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