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