Challenges for Geothermal Energy Utilisation

The Queensland Government recently awarded A$15 million to the University of Queensland to establish a new “hot rocks” research and development centre, called the Queensland Geothermal Energy Centre of Excellence. The vision for the Centre is to provide urgent, forward looking research, development and support for establishment of geothermal energy as a clean energy option through a program of research, development and skills capacity building that will be linked with other major research providers nationally and internationally. The Centre is currently developing a road map for its next five years. This paper will report on that process and should be recognised as “work in progress.” Geothermal Energy in Australia Numerous past studies estimate existence of substantial geothermal resources for Australia, e.g.. In many areas of Australia, the estimated temperatures at a depth of 5 km exceeds 250 C as shown in Figure 1 extrapolated from a database of temperatures recorded in 3291 wells. While the Great Artesian Basin appears as the largest hot rock area in Figure 1, there are other areas, e.g. the area labelled as A in the figure which is in the heart of a major coal mining district and close to large coalfired power stations. Figure 1: The estimated temperature at a depth of 5 km in the Australian continental crust calculated from the database of (Somerville et al. 1994) by (Swenson, Chopra & Wyborn 2000) There are nine Australian companies listed on the stock exchange with a combined market capitalisation of over A$700m. The most significant advancement in terms of the potential of hot rock geothermal energy in Australia is the drilling of the Habanero wells by Geodynamics. The Australian geothermal energy industry is described in greater detail in another paper presented in this workshop(Goldstein et al. 2008). The bulk of the Australian geothermal resource seems to be under a horizontal stress regime with both the major and intermediate principal stresses defining a near-horizontal plane. Such a stress field would suggest a subhorizontal (close to horizontal) reservoir zone after the stimulation. Early seismic results from Habanero-1 seemed to support this hypothesis. A horizontal reservoir is favoured because of the relative ease of adding new wells to an existing network of cells and the ability of the reservoir to contain water. On the downside, higher injection pressures might be necessary to open up against the subvertical minimum principal stresses, which are expected to be roughly equal to the lithostatic pressures at that depth. The experience with Habanero-1 so far has confirmed these predictions. An examination of the induced seismicity during hydraulic stimulation indicates the existence of a large subhorizontal fracture zone dominating the stimulated reservoir(Baisch et al. 2006). Queensland Geothermal Energy Centre of Excellence In September 2007, responding to a proposal from The University of Queensland (UQ), the Queensland State Government committed A$15 million to the Queensland Geothermal Energy Centre of Excellence at UQ, Brisbane. This is being met by a A$3.3 million contribution of expertise and other resources from UQ, making this the largest investment in geothermal energy research in Australia. The Centre will carry out original R&D and will work with Australian and overseas universities and research institutions to expedite the development and adoption of geothermal energy in Australia. The Centre is currently developing a road map for its next five years with a focus on surface plant and power generation and transmission technologies and equipment while maintaining a watching brief on the subsurface issues. This choice of focus does not necessarily reflect the ranking of surface and subsurface issues for the Australian or global geothermal industry but to fill in significant gaps in the existing research line-up in Australia and around the world. The work will be conducted under four program headings: o Power conversion o Air-cooled heat exchangers o Reservoir management o Power generation and transmission This paper will try to develop some concepts for these four programs, with an emphasis on the first one.