The recently drilled deep stratigraphic drill hole NDI Carrara 1 penetrates the carbonate formations of the Cambrian Georgina Basin as well as the underlying Proterozoic successions of the Carrara Sub-basin. The Proterozoic section consists predominantly of tight shales, siltstones, and calcareous clastic rocks. This study aims to assess the petrophysical properties of the Proterozoic shales using conventional wireline logs. Gamma ray and neutron-density crossplots were used to calculate shale volume fraction, and neutron-density crossplots were applied to compute the total and effective porosity of non-shale rocks. Total organic carbon (TOC) content was interpreted using artificial neural networks, and was used to derive the volume of organic matter was converted from TOC content. Bulk density logs were corrected by removing the kerogen effect in the organic-rich shales. Matrix and kerogen densities were obtained by correlating the reciprocal of grain density with TOC content. Total shale porosity was calculated from kerogen-corrected density porosity and organic porosity. Effective porosity was estimated by removing the shaliness effect. Water saturation was derived using the Simandoux equation. The Proterozoic Lawn Hill Formation in NDI Carrara 1 exhibits petrophysical properties that indicate a favourable potential for shale gas resources. Herein, we define three informal intervals within the intersected Lawn Hill Formation; the upper Lawn Hill, the Lawn Hill shale, and the lower Lawn Hill. The net shale thickness of the upper Lawn Hill and Lawn Hill shale intervals are 165 m and 149 m, respectively. The increased TOC content and organic porosity of the upper Lawn Hill and Lawn Hill shale implies higher adsorbed gas content potential. The Lawn Hill shale has the highest gas saturation (average of 31.1%) and the highest potential for free gas content, corresponding to the highest methane responses in logged mud gas profiles. This extended Abstract was submitted to/presented at the Australasian Exploration Geoscience Conference (AEGC) 2023, Brisbane (https://2023.aegc.com.au/)

The Palaeoproterozoic Fraynes Formation in the Birrindudu Basin is a chronostratigraphic counterpart to the highly prospective Barney Creek Formation in the McArthur Basin. However, there is limited understanding of its source potential in comparison. As part of Geoscience Australia’s Exploring for the Future program, this study aims to assess the hydrocarbon generating potential and shale gas prospectivity of the Fraynes Formation in the exploration drillhole Manbulloo S1 through the reconstruction of original source-rock generating potential and well log interpretation. Internal units inside the Fraynes Formation were defined according to sedimentary facies. The hydrocarbon generation potential was estimated using the original TOC content, hydrogen index and thermal maturity data. The shale total porosity was re-interpreted from bulk density logs by removing the organic matter effect and adding organic porosity for the organic-rich shales. The water saturation was then updated accordingly. The maximum amount of generated gas of the organic-rich source rocks are 3969 Mcf/a-ft, 2769 Mcf/a-ft and 1912 Mcf/a-ft when assuming the kerogen compositions of 100 Type I, mix of 50-50% Type I and II, and 100% Type II, respectively. The richness of organic matter and interpreted water saturation (<100%) imply favourable shale gas prospectivity in the Fraynes Formation. This work expands our knowledge on the unconventional energy resources in the west of the greater McArthur Basin. Paper presented at the 2024 Australian Energy Producers (AEP) Conference &amp; Exhibition (https://pesa.com.au/events/2024-aep-conference-exhibition/)

The ca. 1.5–1.3 Ga Roper Group of the greater McArthur Basin is a component of one of the most extensive Precambrian hydrocarbon-bearing basins preserved in the geological record, recently assessed as of 429 million bbl oil (68 million cubic meters of oil) and between 8 and 118 TCF (222.56 billion cubic meters) of gas (in place). It was deposited in an intracratonic sea, referred to here as the McArthur-Yanliao gulf. The Velkerri Formation forms the major deep-water facies of the Roper Group. Trace metal redox proxies from this formation indicate that it was deposited in stratified waters, in which a shallow oxic layer overlay suboxic to anoxic waters. These deep waters became episodically euxinic during periods of high organic carbon export. The Velkerri Formation has organic carbon contents that reach ∼10 wt. %. Variations in organic carbon isotopes are consistent with organic carbon enrichment being associated with increases in primary productivity and export, rather than flooding surfaces or variations in mineralogy. Although deposition of the Velkerri Formation in an intracontinental setting has been well established, recent global reconstructions show a broader mid to low latitude gulf, with deposition of the Velkerri Formation being coeval with the widespread deposition of organic-rich rocks across northern Australia and northern China. The deposition of these organic-rich rocks may have been accompanied by significant oxygenation associated with such widespread organic carbon burial during the Mesoproterozoic. <b>Citation:</b> Grant M. Cox, Alan S. Collins, Amber J. M. Jarrett, Morgan L. Blades, April V. Shannon, Bo Yang, Juraj Farkas, Philip A. Hall, Brendan O’Hara, David Close, Elizabeth T. Baruch; A very unconventional hydrocarbon play: The Mesoproterozoic Velkerri Formation of northern Australia. <i>AAPG Bulletin</i> 2022;; 106 (6): 1213–1237. doi: https://doi.org/10.1306/12162120148