Mapping the geothermal potential of Cenozoic aquifers in Gippsland, Victoria

Category: Geothermal Reports	Product Code: MP-R-169360
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Executive Summary
Geothermal energy is used around the world for direct heating of buildings, greenhouses, aquaculture ponds and swimming pools, and in industrial processes. The Gippsland Smart Specialisation Strategy (GS3) identified direct use geothermal energy as a potential competitive advantage to help with the economic transition away from fossil fuel power generation in the Latrobe Valley (The University of Melbourne, 2021). Direct use geothermal can replace gas in many heating applications, reducing CO2 emissions and costs. As part
of the Geothermal Innovation Group of GS3, the Geological Survey of Victoria (GSV) has collaborated with the University of Melbourne (UoM) to deliver the preliminary geological mapping necessary to establish an online geothermal investigation tool.

This report presents geological datasets that underpin assessments of geothermal energy potential across Gippsland. It details the collection of new geothermal data, the collation of historical geothermal data, and the methods used to create maps of aquifer temperature and geothermal gradient (the rate at which temperature increases with depth). The data are intended to support a future on-line geospatial cost-benefit tool that will allow landowners or other stakeholders to investigate the temperature and depth of underlying geothermal aquifers and to view examples and cost estimates of potential uses.

This study is intended to reduce the geological uncertainty, and thereby the risk, for uptake of direct use geothermal energy in Gippsland by mapping the temperature of aquifers alongside other properties including depth, thickness, water quality and transmissivity. The study builds on previous work by King et al. (1987), Driscoll (2006), and Taylor & Mather (2015), combining knowledge from a diverse range of studies including heat flow modelling (Taylor & Mather, 2015), groundwater modelling (Hocking et al., 2020), the Victorian Aquifer Framework (GHD, 2012 & SKM, 2009), previously unpublished and newly collected geothermal data.

Twenty-six new precision borehole temperature logs were collected throughout Gippsland as part of this project, increasing the total number of precision temperature logs in the region to 60. These continuous temperature profiles have resulted in accurate definition of aquifer temperatures and calculation of geothermal gradients. In addition, historical temperature measurements from known depths were attributed to specific aquifers and corrected to a top of aquifer equivalent. Temperature data from petroleum wells were
also assessed and included in the database, where appropriate, to increase knowledge of aquifer temperatures at locations and depths inaccessible for present day temperature logging.

New maps were produced detailing the temperature, geothermal gradient, depth to the top of aquifers, transmissivity and groundwater quality (dissolved solids) of the Gippsland region. The study confirms that the Lower Tertiary Aquifer is the largest and most prospective of the geothermal aquifers in Gippsland, with a maximum observed temperature commonly exceeding 60°C from a depth of 600 m in the Latrobe Valley and 1000 m in the Lake Wellington Depression. Prospectivity for direct use geothermal energy is highest within the Latrobe Valley between Morwell and Sale, and parallel to Ninety Mile Beach between Lake Wellington and Metung. Prospectivity also appears relatively high near Seaspray and east of Yarram.

The cause of the elevated aquifer temperatures appears to be associated with regionally extensive, thick, thermally insulating formations which decrease the slow outward conduction of the Earth’s internal heat, resulting in a build-up of ‘trapped’ heat. Brown coal acts as the thermal insulator beneath the Latrobe Valley and around Yarram, whereas thick limestone sequences act as the insulator between Lake Wellington and Metung. The potential for hot upwelling groundwater along major faults, and its impact on local aquifer temperatures, remains unconfirmed.

Bibliographic Reference
C.D. O’Neill, M.J. Hocking, and C.P. Riley 2022. Mapping the geothermal potential of Cenozoic aquifers in Gippsland, Victoria. Geological Survey of Victoria. Department of Jobs, Precincts and Regions. Melbourne, Victoria. 81p.

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The downloadable version of this report is supplied in PDF format (173 MB) and Attachment A1 data package (ZIP 99MB).