Geothermal heat flow map of Victoria D. Taylor & B. Mather Geothermal Atlas Report 1 Geological Survey of Victoria Technical Record 2015/2 Authorised by the Director of the Geological Survey of Victoria Disclaimer: Department of Economic Development, Jobs, Transport and This publication may be of assistance to you but the authors Resources and the State of Victoria and its employees do not guarantee 1 Spring Street Melbourne Victoria 3000 that the publication is without flaw of any kind or is wholly Telephone (03) 9651 9999 appropriate for your particular purposes and therefore © Copyright State of Victoria, 2015. disclaim all liability for any error, loss or other consequence Except for any logos, emblems, trademarks, artwork and which may arise from you relying on any information in this photography this document is made available under the terms publication. of the Creative Commons Attribution 3.0 Australia license. For more information about Earth Resources Programs and This document is also available in an accessible format at Policy visit the website at economicdevelopment.vic.gov.au www.energyandresources.vic.gov.au/earth-resources Bibliographic reference: Taylor D. & Mather B., 2015. Geothermal Heat Flow Map of Victoria: Victorian Geothermal Atlas Report 1. Geological Survey of Victoria Technical Record 2015/2. Geological Survey of Victoria. ISSN 1324 0307 ISBN 978-1-74146-940-0 (pdf) GSV Catalogue Record #107532 Acknowledgements: David Taylor prepared the text and basic data tables with the heat flow modelling done in conjunction with Ben Mather who also prepared the map figures. Geothermal explorers GeoGen/AGL, Granite Power, Greenearth Energy and MNGI (Petratherm) generously made available their basic data. Quite a number of honours and postgraduate students from the University of Melbourne and Monash University contributed their study results. DELWP provided access to the State observation groundwater bore network for temperature measuring and Lakes Oil provided access to Wombat-4 that was logged in collaboration with Geoscience Australia, who also collected some data from the Murray Basin. Kate Bassano assisted on contract from SRK for much of the early data management and collection and Michelle Ayling internally assisted later in the project. Louise Goldie-Divko of the Geological Survey of Victoria peer reviewed this report. Emma Cordon and Damia Ettakadoumi from Straight Up Marketing edited and formatted this report. Contents 1. Introduction ........................................................................1 2. Previous work ......................................................................2 3. New data collection ................................................................3 4. Method for estimating heat flow ....................................................4 5. Results .............................................................................9 6. Discussion .........................................................................12 7. Ground surface temperature ......................................................13 References ...........................................................................14 Appendix 1 Heat flow summary sheet .................................................16 Appendix 2 Heat flow calculations ................................................... 30 Appendix 3 Inaccessible bores ........................................................41 Appendix 4 Average Annual Ground Temperature ................................... 42 Figures Figure 1. Heat flow uncertainty.. ............................................................................................5 Figure 2. Example of a Good Confidence heat flow estimate from Narrawaturk-6 in the Otway Basin. .6 Figure 3. Example of a Moderate Confidence heat flow estimate from Berrook-1 in the Murray Basin... 7 Figure 4. Example of a Poor Confidence heat flow estimate from Lillimur 15004 in the Murray Basin. .................8 Figure 5. Historic heat flow data treated with same methodology as the new data and rated for confidence as good (green), moderate (orange), poor (red) and unreliable (black). ...................................10 Figure 6. Heat flow map of Victoria. ...................................................................................... 11 Figure 7. Average annual ground temperature.. 13 Tables Table 1. Compilation of the ten historic heat flow estimates stating original data source. ..............................2 Table 2. Heat flow results and attributed confidence ratings. .............................................................9 Table 3. Examples of large variance between legacy temperature data taken during drilling operations compared to later precision measurements. .................................................................9 Geothermal heat flow map of Victoria – Geothermal Atlas Report 1 I i ii I Geothermal heat flow map of Victoria – Geothermal Atlas Report 1 1. Introduction Geothermal energy is naturally occurring heat energy stored within rocks of the earth. Under the right circumstances, geothermal energy can be extracted and used directly for heating and cooling at moderate temperatures, or converted into electricity at higher temperatures (e.g. Duffield & Sass, 2003). Geothermal energy resources are attractive due to their 2015. During this time, extensive geothermal data was minimal greenhouse gas emissions and ability to directly collected by GSV and compiled from exploration provide energy security from a local source. Knowledge companies and university research. Precision of the geothermal heat flow allows the temperature of temperature logs from 242 bores (totalling the crust to be modelled at increasing depths (even approximately 74,000 logged metres) resulted in 175 below the depth of direct measurement) so that the full heat flow estimates considered to be of reliable quality. crustal temperature regime and deep geothermal This significantly expands on the ten previously resources can be estimated. In Victoria, previous work published geothermal heat flow estimates drawn from documented shallow geothermal energy resources from similar temperature logs and thermal conductivity direct temperature measurements (King et al., 1987; measurements. Driscoll, 2006). Although this work remains valid, the nature of collected data (mainly bottom hole Over much of western and central Victoria, the close temperature point data sourced from bores) and a lack spacing of the expanded new data allows for of rock thermal conductivity measurements have meaningful interpolation between the data points to limited its value in terms of providing the right create a map of surface heat flow. This new data will information to create a geothermal heat flow map. assist in better understanding geothermal resource potential and also hydrocarbon maturity modelling for To assess Victoria’s geothermal resource potential, GSV oil and gas prospectivity. led the Geothermal Atlas Project between 2010 and ii I Geothermal heat flow map of Victoria – Geothermal Atlas Report 1 Geothermal heat flow map of Victoria – Geothermal Atlas Report 1 I 1 2. Previous work The Oil Shock Crisis in the 1970s led to the first appraisal of Victorian geothermal resources (King et al., 1987), which drew on historic temperature point data collected from numerous water and petroleum bores across the state. The quality of much of this temperature data is somewhat degraded because many measurements were carried out soon after drilling, when the natural geothermal gradient was still disturbed by the introduction of surface temperature drilling fluids into the bore. Nevertheless, this data showed that the thick, porous appraised the basic geological framework relevant to (and thermally insulating) sediments of the Gippsland geothermal potential in further support of geothermal and Otway basins often reached temperatures of about exploration (Driscoll, 2006). This research showed that 50 – 70 degrees Celsius at a depth of approximately one deep petroleum bores in some parts of the Gippsland kilometre. Such geothermal temperatures could be used and Otway basins were reaching 150 degrees Celsius at directly for some industrial and direct heating approximately three kilometres depth, suggesting that applications in preference to burning fossil fuels. electricity generation from geothermal energy could be possible. The return of cheap oil prices throughout the 1980s and 1990s suppressed interest in geothermal energy. The Before this new phase of geothermal interest, there were rapid rise in oil prices in the early 2000s, combined with only ten historic heat flow estimates for Victoria from concerns over greenhouse gas emissions, renewed precision downhole temperature logs with thermal interest in geothermal energy. The Victorian conductivity, most collected by academia from the Government created the Geothermal Energy Resources 1970s to the 1990s (see Table 1). Many of these estimates Act (2005) to allow the exploration of deeper and hotter had relatively poor geothermal gradient control geothermal energy. An initial report aimed at predicting because of widely spaced downhole measurements and deeper, hotter temperatures was limited by a lack of limited amounts of rock thermal conductivity data. dedicated heat flow data and a paucity of rock thermal Many of the historic estimates are considered unreliable conductivity information (Cull, 2005). Another report or of low confidence in light of the expanded data set updated the historic