Geothermal energy prospectivity in the Hutton Sandstone, Eromanga Basin, Australia

Abstract

The Cooper and Eromanga Basins of Australia, with old and hot basement rocks, offer promise for geothermal exploration. The basement rock radioactive decay has high radiogenic heat production exceeding 5 microwatts per cubic meter. The basement structure transitions from the 3.6 km deep Patchawarra Trough in the west with 3–4 μW/m3 radiogenic heat production to the 4.7 km deep Nappamerri Trough having 5–7 μW/m3 radiogenic heat production in the east (Beardsmore in Explor Geophys 35(4):223–35, 2004). This study integrates petrophysical analysis, seismic interpretation, and thermal energy assessment to evaluate the geothermal viability and prospectivity in the Hutton Sandstone formation of the Eromanga Basin in the vicinity of an unsuccessful geothermal well. The Hutton Sandstone is a potential geothermal aquifer where it contains temperatures exceeding 120 °C, high thermal conductivity of 5 W/mK (Beardsmore in Explor Geophys 35(4):223–35, 2004), net sand thickness over 60 m, and effective porosities > 10%. The 120 ºC isotherm occurs in several areas downslope of gas fields along the Warra–Merrimelia NE–SW ridge system. The highest Hutton net sand thickness (~ 50 m) and porosity thickness (~ 30) occur near the Gashnitz-001 well, where there are good reservoir characteristics and high thermal energy. Seismic interpretation indicates probable lateral reservoir continuity up to 11 km east of the well. A prospective area of 100–683 km² is interpreted as having over 50 m net sand in the Hutton with over 16% average effective porosity and temperatures exceeding 120 °C. The in-place potential thermal energy is as high as 245 MWth with a mean of 164 MWth. The Gashnitz-001 well drilled outside of structural closure benefited from high total heat content and less geological risk in terms of porosity thickness in the Hutton formation.