Impacts of Diagenesis on Reservoir Quality in a Sedimentary Geothermal Play

Abstract

Geothermal resources hosted within sedimentary basins, also described as Hot Sedimentary Aquifers, have been targeted 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 that permeability in the Hutton Sandstone in Celsius-1 was extremely low. Petrographic studies show that diagenetic effects, including compaction and neoformation of quartz (syntaxial overgrowths) and kaolinite have destroyed the porosity and permeability in the formation. This study integrated a range of analytical techniques including petrography, SEM, and QEMSCAN. The result of this integrated study gives a robust evaluation of the diagenetic history in a deep burial environment, its effects on the flow properties of the Hutton Sandstone, and implications for the geothermal potential of siliclastic formations.