Required steps to develop an enhanced geothermal system – an Australian Basin example

Abstract

Enhanced geothermal system (EGS) research focusses on reservoirs not generally considered for geothermal systems, and a key site for their advancement is the US Department of Energy (DOE) Utah Frontier Observatory for Research in Geothermal Energy (FORGE) site at Milford, Utah. The project’s roadmap is focussed on a 5-year timeline of technology applications appropriate for the geology of the FORGE test site and to develop the knowledge and understanding of how to build future large-scale, economically sustainable EGS systems (i.e. horizontal wells, hydraulic fracturing, etc.). EGS opportunities exist in several Australian Basins, and this paper will explore one potential application to illustrate how the technologies can be applied in an Australian setting. For example, we have identified a potential EGS play in the carbonates of the Middle Cambrian, Lower Kalladeina Formation of the Warburton Basin around the Gidgealpa-Merrimelia-Innamincka Ridge. Karstified dolomites with vuggy fracture porosity have been drilled in the 2500–3000 m depth range and were drill stem tested (DST) in the 1990s. Gidgealpa 5 produced 5200 barrels of water/day on DST testing. The bottom hole temperature (BHT) is estimated to range between 120 and 170°C at the depth intervals. Fracture orientations are published for these strata in multiple wells, and stress conditions are estimated from historical data. They can be used to plan the optimal orientation of horizontal well paths to connect as many of these conductive structures as possible and, like FORGE, create ESG pathways using multi-stage hydraulic fracturing between injector and producing wells.