Greenearth Energy aims to explore for and develop geothermal resources in Australia and in due course in New Zealand and in the wider Pacific Rim.
In May 2007, Greenearth Energy Limited was awarded 3 geothermal permits in Victoria.
Geothermal Exploration Permit (GEP) 12 and 13
Location
The GEP 12 and 13 permits (which are contiguous and hence are described together) include the Latrobe Valley/Gippsland region and the land running south to the coast. Within the area of GEP 12 and 13 lie four of Victoria's major brown coal fired power stations as well as various existing and potential large consumers of electricity and heat.
Geothermal Description
These permits cover the Palaeozoic basement in the north-west (GEP 12), and to the south (GEP 13) a large part of the onshore Gippsland Basin to the coast. The sedimentary pile, consisting of Tertiary aged sediments (Latrobe Valley Group) overlying Cretaceous sediments (Strzelecki Group), is in the range 3000-4000 m thick or greater. The basal units of the Cretaceous (the Rintouls Creek Sandstone and Tyers Conglomerate), between the Palaeozoic basement and Cretaceous, have known porosity and offer a geothermal reservoir target where they are most deeply buried.
The current modelling suggests that where Latrobe Valley Group (containing thick coals) is 500 m thick then temperatures of 150oC or more can be expected at 3000 m or deeper. Where the Strzelecki Group is overlain by the Latrobe and Seaspray groups (containing only thin coals) temperature of 150oC is expected to occur at a depth from 3250-4000 m. This latter area is located in the south east parts of GEP 13.
The Victorian Department of Primary Industries has published a temperature depth map covering the basin part of the permit areas. It shows the shallowest areas for temperature of 150oC are located in the Latrobe Valley area running east and to the east of Yarram.
FIGURE 1: Temperature vs Depth Map GEPs 12 and 13
The Company carried out thermal mapping work in 2007. Hot Dry Rocks Pty Ltd was contracted to produce heat flow maps of the permit areas (figure 2). For GEP's 12 and 13 the results indicate that there are areas with relatively high heat flow and areas with relatively low heat flow. For descriptive purposes four areas generally above 80 mW/m2 have been defined and named.
- Yallourn High Heat Flow Region: The average heat flow in this region is 87 mW/m2. The wells are dominated by coal sequences. This heat flow region is proximal to the Yallourn Monocline which is a dominant feature in gravity and magnetic images. The region which is open to the north is up to 19 km in lateral extent from current indications.
- Maffra High Heat Flow Region: The three wells average 126 mW/m2. Coal beds are common in these wells. The region is open to the north and east and is up to 23 km in lateral extent from current indications.
- Traralgon South High Heat Flow Region: The average heat flow for this region is 95 mW/m2. Coal Beds are common in these wells. The region is open towards the south and with current knowledge is up to 5.5 km in lateral extent.
- Alberton High Heat Flow Region: the average heat flow is 95 mW/m2. The region is open towards the west where heat flow appears to increase in the Alberton East well and is up 8 km in lateral extent from current understanding.
FIGURE 2: Heat Flow Map GEPs 12 and 13 (Prepared by Hot Dry Rocks Pty Ltd)
Modelling of geophysical data suggests the presence of buried granite. Further buried granite may be present as the detection of granite beneath the thickest parts of the sedimentary cover rocks is difficult given the similarity in geophysical response of thick sediment and some granite bodies. Any granite located beneath thick insulating sedimentary cover would offer Hot Dry Rock potential.
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 3). It shows the shallowest areas for temperature of 150oC are located near Geelong.
FIGURE 3: 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 9). 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 9: 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 and Hot Dry Rock potential.