Reservoir Quality for Geothermal Energy in the Hutton Sandtsone: from Analysis to Prediction

Abstract

Geothermal resources hosted within sedimentary basins, also described as Hot Sedimentary Aquifers, have been explored as a geothermal play type in Australia. These resources have been targeted as they are thought to have high natural matrix permeability and are not expected to require significant permeability enhancement. However, at the resource temperatures (and depths) required to generate electricity, diagenetic processes may have destroyed permeability. This paper reports on the effects of diagenesis on geothermal reservoir quality in the Hutton Sandstone of the Eromanga Basin, Australia. This formation is a prolific oil and gas producer and is known to have good reservoir quality in oil fields, typically associated with structural highs. The geothermal potential was recently tested by the Celsius-1 well in the Nappamerri Trough. Well tests indicated good temperatures (160 degrees centigrade at 2,400m TVD) but extremely low permeability. Petrographic studies show that diagenetic effects, including compaction and neoformation of quartz (syntaxial overgrowths), kaolinite, and illite have destroyed the porosity and permeability in the formation. This study integrates a range of analytical techniques including petrography, SEM, and QEMSCAN. It results in a robust evaluation of the diagenetic history in a deep burial environment, its effects on flow properties, and implications for the geothermal potential of siliclastic formations.