Diagenesis impact on the reservoir quality of the Hutton Sandstone, Cooper Basin, South Australia

Abstract

The Hutton Sandstone (Cooper-Eromanga Basin, SA) recently became a target for geothermal heat extraction due to its potential for high natural permeability, decent temperatures, and high reservoir volume. However, recent exploratory drilling conducted by Origin Energy Ltd and Geodynamics Ltd at the Celsius-1 well didn’t produce the anticipated flow rates, raising the question of the impact of the diagenesis on the reservoir quality of this sedimentary formation. Previous studies focused on oil and gas fields located on the ridges of the Nappamerri Trough highlighted the good reservoir quality of the upper Hutton Sandstone. Nevertheless, an extensive literature review reveals that the middle part of the Nappamerri Trough – where Celsius-1 is situated – remains poorly investigated. This study aims to better characterize the petrophysical and petrological properties as well as the diagenesis processes occurring within the Hutton Sandstone. It is based on drill cuttings and cores retrieved from Celsius-1 and other existing nearby stratigraphic and petroleum exploration wells (Della-2, Merrimelia-19, Strzelecki-17 and Packsaddle-1). Porosity and pore size distribution of the Celsius-1 drill cuttings were first measured by using a laboratory low field Nuclear Magnetic Resonance (NMR) under water-saturated condition. Permeability was then inferred from NMR transversal relaxation time T2 via the empirical equation of Timur-Coates. The petrology of the Hutton Sandstone was studied via three different analytical tools: i) Basic automated QEMSCAN for phase assemblage mapping and quantitative analysis of the mineralogy; ii) Scanning Electron Microscope for visualizing the pore geometry and secondary mineral growths; iii) Optical Microscopy for high precision characterization of the mineralogy, the micro-structures, the pore connectivity and the diagenetic cements. The integration of these results gives a robust and complementary evaluation of the diagenetic history in a deep burial environment, its effects on the flow properties of the Hutton Sandstone, and its regional extent.