Developing Australian Enhanced Geothermal Systems and Hot Sedimentary Aquifer Models for Reducing Risk

Abstract

Reducing uncertainty at an early stage of resource development is a key aspect to attract project finance. Risk analysis frameworks exist in the petroleum industry for quantifying risk and expected returns (Newendorp, 1975; Suslick et al., 2009). For deep Enhanced Geothermal Systems (EGS), there is insufficient knowledge and experience available to make informed estimates of the likelihood of outcomes for incorporation into a risk analysis framework. Australia has low heat flow relative to ‘traditional’ geothermal countries, requiring deep reservoirs in order to attain sufficient temperature, but this comes at the expense of matrix permeability. In Australia, estimating temperature at depth has so far proven to be robust using heat flow or extrapolation of temperature – where a temperature measurement point is available. Approaches such as Thermap (Haynes et al. 2013) will facilitate exploration in areas with no temperature data by allowing target generation in areas with favourable market conditions. Predicting permeability is a much more difficult task. A range of fracture detection methods exist or are being further developed, but at depths of interest (3500 – 4000 m) these have limited resolution, meaning that drilling will remain to be the only way to test predictions of reservoir properties. An outstanding issue is the lack of examples of working deep EGS reservoirs. A study is needed to compile the fracture characteristics of existing projects in Australia and internationally. A conceptual study using discrete fracture network modelling in a Monte Carlo sensitivity analysis will provide constraints on what sort of geological environments (lithologies, geodynamic history including uplift, compaction, metamorphism, thermal history, previous deformation, present stress regime) may be favourable for the development of optimal fracture networks for geothermal exploitation. Haynes, M.W., Gerner, E.J., Kirkby, A.L., Petkovic, P., Budd, A.R., and Harris-Pascal, C., 2013, Thermal Map from Assessed Proxies (THERMAP): a pilot study to estimate subsurface temperatures for the Australian continent. Australian Geothermal Energy Conference, Brisbane, 14-15 December, available at: http://www.geothermal-energy.org/pdf/IGAstandard/AGEC/2013/Haynes.pdf Newendorp, P., 1975. Decision Analysis for Petroleum Exploration, PennWell Publishing Company, Tulsa, Oklahoma, 668pp. Suslick, S.B., Schiozer, D. and Rodriguez, M.R., 2009. Uncertainty and Risk Analysis in Petroleum Exploration and Production, TERRÆ 6(1):30-41.