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. |
References
Beach Energy Ltd (2013). Sawpit No. 2 well completion report. South Australia. Department for Mines and Energy (unpublished). Available at http://mer-wcr.s3.amazonaws.com/SAWPIT 002.zip [Verified 19 April 2020].Bendall, B., Forbes, A., Revie, D., Eid, R., Herley, S., and Hill, T. (2020). New insights into the stratigraphy of the Otway Basin. The APPEA Journal 60, 691–696.
| New insights into the stratigraphy of the Otway Basin.Crossref | GoogleScholarGoogle Scholar |
Boult, P., and Hill, A. (2002). Source rock distribution. In ‘The Petroleum Geology of South Australia. Vol. 1: Otway Basin’. 2nd edn. (Eds P. J. Boult and J. E. Hibburt.) (South Australia Department of Primary Industries and Resources: Adelaide.)
Forbes, A., Munday, S., and Revie, D. (2020). An elemental chemostratigraphic study, Onshore Otway Basin, Victoria. Victorian Gas Program Technical Report 12. Geological Survey of Victoria. Department of Jobs, Precincts and Regions. Melbourne, Victoria.
Geomark Research Ltd, (2020). Sawpit source rock extract summary sheets. Interim results for South Australia Department for Energy and Mining (unpublished).
Hannaford, C. (2020). Palynological analysis of infill core and cuttings from Sawpit 2, Otway Basin, South Australia. Unpublished Report prepared for South Australia Department for Energy and Mining.
Intertek (2018). Sawpit 1 Source Rock Analysis. Unpublished Report prepared for South Australia Department for Energy and Mining.
Lavin, C. J., and Muscatello, T. (1997). ‘The Petroleum Prospectivity of the Casterton Petroleum System in the Victorian Onshore Otway Basin. Victorian Initiative for Minerals and Petroleum Report 41.’ (Department of Natural Resources and Environment: Melbourne.)
Martin, M. A., Wakefield, M., Macphail, M. K., Pearce, T., and Edwards, H. E. (2013). Sedimentology and stratigraphy of an intra-cratonic basin coal seam gas play: Walloon Subgroup of the Surat Basin, eastern Australia. Petroleum Geoscience 19, 21–38.
| Sedimentology and stratigraphy of an intra-cratonic basin coal seam gas play: Walloon Subgroup of the Surat Basin, eastern Australia.Crossref | GoogleScholarGoogle Scholar |
Oil Company Of Australia Ltd (1992). Sawpit No. 1 well completion report. South Australia. Department for Mines and Energy (unpublished). Available at http://mer-wcr.s3.amazonaws.com/SAWPIT 001.zip [Verified 19 April 2020].
Price, P. L. (1993). Palynostratigraphy, organic facies and geochemistry of Sawpit-1 Otway Basin. Unpublished Report prepared for Oil Company of Australia. Appendix 10 in Sawpit 1 Well Completion Report.