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Wireline log investigation of CO2-induced diagenesis, Katnook and Ladbroke Grove fields, South Australia

Efthymiou, Efthymios

Honours Degree 2007

University of Adelaide

Abstract

CO2-related diagenesis has been well documented in the Ladbroke Grove gas field. Diagenetic reactions include formation of kaolinite and siderite at the expense of chlorite, feldspar, calcite and volcanogenic lithic clasts. The mineralogy of the Pretty Hill Formation was reviewed with the aim of investigating the wireline response to CO2-related diagenesis. Cored sections were also examined and observations from the core were compared to the wireline response.

The study used previously identified depositional facies common to the Katnook and Ladbroke Grove gas fields and examined their individual wireline response to see if diagenetic changes could be observed. The wireline response of the Pretty Hill Formation did not show significant changes between the Katnook and Ladbroke Grove wells with the exception of the spectral gamma ray log and a matrix identification (MID) crossplot using data from the Litho-Density log and a core
calibrated Sonic Porosity. The Spectral Gamma Ray log showed low levels of thorium in Ladbroke Grove compared with Katnook. This could be related to the removal of thorium by CO2-induced diagenesis. The MID crossplot shows a relative increase in dolomitic cement in Ladbroke Grove. This could be due to CO2-related diagenetic precipitation of carbonates.

The effects of CO2-related diagenesis in the Ladbroke Grove field are subtle and relating to the relatively low concentrations of authigenic cements, particularly siderite. As such it is difficult to assess the net mineralogical storage of CO2 from the wireline response alone. However, the methods used in this study should be investigated further in any future study.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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