Australia has an extremely large total hot dry rock (HDR) resource above
a depth of 5 km, equivalent to 7500 times its present annual energy
consumption, of which 80 per cent underlies the Great Artesian Basin.
The resources most likely to be exploited first are those residing in
homogeneous granitic bodies beneath sedimentary basins containing
insulating rocks such as shales and coal measures. In the Sydney Basin
south of Muswellbrook, an area of high geothermal gradient corresponds
to a gravity low thought to be a buried granite body at a temperature of
possibly 250C. This locality is suspected to have the ideal geological
characteristics for Australia's first hot rock test facility. Australia's high HDR potential is possibly unique in the world, in that
the potential sites satisfy four independent, geological conditions, each
considered as favourable for the creation of a resource, and for the ease of
extracting that resource. They are: Higher crustal heat generating capacity than that of normal
continental crust. Much of the Australian continent is covered by sedimentary basins
which contain a high proportion of shales and coal measures that
have low thermal conductivities, thus providing an insulating blanket
for the heat being generated beneath. The sedimentary basins are in many places underlain by large
untectonised granitic bodies that are not only a major contributor to
heat generation, but also ideally suited to the establishment of HDR
reservoirs. The crustal shortening stress field that is found in the majority of the
Australian continental crust results in a vertical minimum principal
stress orientation which should result in the development of
favourably oriented horizontal stimulation cells necessary for
maximising an HDR resource.