The Story of the Carrara Sub-Basin - Biomarker Distribution and Thermal Maturity of Source Rocks from NDI Carrara 1

Abstract

The NDI Carrara 1 drill hole was drilled as part of the Mine Ex CRC National Drilling Initiative in September-December 2020 in collaboration with Geoscience Australia and the Norther Territory Geological Survey. In this project, 17 rock samples and 3 oil stains from the Carrara 1 drill core were analysed using Gas Chromatography and Mass Spectrometry (GC/MS) to provide a comprehensive assessment of biomarkers and the thermal maturity of the Carrara Sub-basin in Northern Australia. According to aromatic hydrocarbon maturity assessment of phenanthrenes and methylphenanthrenes, the interval from the top of the core to 630 m is in the peak oil window and the source rocks are likely highly generative in terms of liquid hydrocarbons. In addition, prokaryote and eukaryote biomarkers are detected in high abundance providing valuable insights into life during the Cambrian period. In contrast, biomarkers are below detection limits in the Proterozoic section of the core (630-1750.85 m) with the notable exception of acyclic saturated hydrocarbons which are detected in some of the shallower Proterozoic samples. Thermal maturity estimates computed using aromatic hydrocarbons illustrate that maturity increases downcore indicating that these compounds are syngenetic and that the source rocks are overmature in terms of liquid hydrocarbon generation and are likely in the late stages of wet gas generation or a producing dry gas. In addition, the distribution of biomarkers and thermal maturity is consistent with an unconformity at 630 m and a fault repeated sequence between 630-800 m from 925-1130 m. Finally, the distribution of acyclic saturated hydrocarbons and polyaromatic hydrocarbons provide evidence for secondary migration of liquid hydrocarbons in at least one sample of the Carrara 1 drill core Show more