As part of Geoscience Australia’s Exploring for the Future program, this study aims to analyse the hydrocarbon prospectivity in the Carrra Sub-basin through wireline log interpretation and shale gas reservoir characterisation. NDI Carrara 1 is the first stratigraphic test of the Carrara Sub-basin, a recently uncovered depocentre located within the South Nicholson region of the eastern Northern Territory and northwestern Queensland. Four chemostratigraphic packages were defined according to the informal sub-division of stratigraphy and inorganic geochemical properties. Wireline log interpretation has been conducted to derive the clay mineral compositions, porosity, gas saturation and gas contents for the unconventional shale gas reservoirs in the Proterozoic succession in NDI Carrara 1. The predominant clay minerals include illite/muscovite, mixed-layer clay, smectite, kaolinite, and minor contents of glauconite and chlorite. The average geothermal gradient is estimated to be 35.04 °C/km with a surface temperature of 29.4 °C. The average formation pressure gradient is calculated to be < 10.7 MPa/km from mud weight records. Artificial neural network technology is used to interpret the TOC content from wireline logs for unconventional shale gas reservoirs. TOC content is positively correlated with methane and ethane concentrations in mudlog gas profiles, shale porosity, formation resistivity and gas content for NDI Carrara 1. The organic-rich shales in P2 have favourable adsorbed, free and total gas contents. The organic-rich micrites within P3 have the potential in adsorbed gas, but with very low average gas saturation (< 0.01 m3/m3). Our interpretation has identified potential shale gas reservoirs, as well as tight non-organic-rich shales and siltstones with potential as gas reservoirs. These occur throughout several of the identified chemostratigraphic packages within the Proterozoic section of NDI Carrara 1.

Porosity and permeability data form part of Geoscience Australia’s Reservoir, Facies and Shows (RESFACS) database, which contains depth-based information regarding porosity and permeability measured or interpreted from core, sidewall core and well-log analysis of rocks intersected by offshore petroleum wells. Porosity and permeability are rock properties related to the number, size, and connectivity of openings in the rock. More specifically, porosity of a rock is a measure of its ability to hold a fluid within pore-spaces and the permeability is a measure of the ease of flow of a fluid through a porous solid. Data entered into the porosity and permeability tables are primarily sourced from the Basic and Interpretive volumes of Well Completion Reports (WCR) provided by the petroleum industry to the Commonwealth under the Offshore Petroleum and Greenhouse Gas Storage Act (OPGGSA) 2006 and the previous Petroleum (submerged Lands) Act (PSLA) 1967. Data is also sourced from sedimentologic evaluations and petrophysical studies by Geoscience Australia and its predecessor organisations, the Australian Geological Survey Organisation (AGSO) and the Bureau of Mineral Resources (BMR), as well as from state and territory geological organisations, and scientific publications. The database structure has evolved over time and will keep changing as different types of relevant data become available and the delivery platform changes. Data hosted within Geoscience Australia’s Oracle petroleum wells database was initially delivered through the Petroleum Wells web page, http://dbforms.ga.gov.au/www/npm.well.search, which is in the process of being decommissioned . The porosity and permeability data will now be available to view and download through the Geoscience Australia Portal Core, https://portal.ga.gov.au/. Use Porosity and Permeability as your search term to find the relevant data.