Geelong
Geothermal Exploration Permit (GEP) 10
Location
GEP 10 comprises the Daylesford area in the north to the Bellarine Peninsula/Surf Coast Shire Council area in the south. It contains the major industrial centre of Geelong and the western half of suburban Melbourne. Within GEP 10 is the coal fired power station at Anglesea owned by Alcoa of Australia.
Geothermal Description
GEP 10 contains insulating sediments overlying Palaeozoic basement. The base of the cover rocks reach depths in excess of 4km, and have known porosity and possible reservoir potential, while the tight overlying sediments provide a good thermal seal.
North of the Geelong area the rocks generally consist of outcropping Palaeozoic basement (sediments and granite). The southern and coastal areas of the permit contain the eastern margin of the Cretaceous-Tertiary aged Otway Basin. This area contains thick sediments overlying basement.
The regional structural setting of the Otway Basin shows that there is significant displacement/disruption in the Palaeozoic/Cretaceous contact at the basin margins. Compressional and tensional features are probably present with the latter having the potential to provide conduits for deeper geothermal waters.
The basal parts of the insulating sedimentary cover - (the porous Pretty Hill Sandstone) reaches a depth of 4000-5000 m in the south of the permit. Just to the west of the permit boundary Pretty Hill Sandstone is 615 m thick. This thick porous unit is a geothermal target at depth greater than 3000 m.
The Victorian Department of Primary Industries has published a temperature depth map covering the basin part of the permit area (figure 1). It shows the shallowest areas for temperature of 150oC are located near Geelong.
FIGURE 1: Temperature vs Depth Map GEPs 10
The Company carried out thermal mapping work in 2007. Hot Dry Rocks Pty Ltd was contracted to produce a heat flow map of GEP 10 (figure 2). Data for this area is limited. South of Geelong the three northern most wells Bellarine 1, Hindhaugh Creek 1 and Geelong Flow Oil-1 have an average heat flow of 80 mW/m2. Jan Juc 8215 (bore hole) returned the highest value of 101 mW/m2 with the remaining two wells drilled close to the ocean shore displaying lower heat flow values. These results point to an area of high heat flow and supports the independent temperature depth modeling that indicates 150oC should be encountered below 4000 m in the Anglesea area and below 3000 m in the Hindhaugh Creek area.
FIGURE 2: Heat Flow Map GEPs 10 (Prepared by Hot Dry Rocks Pty Ltd)
It is possible that granite occurs beneath the insulating sediments in the Hindhaugh Creek area at around 3000 m. With temperature estimated at around 150oC at 3000 m this area has possible conventional hydrothermal potential.