Geomechanical evaluation of a middle Cambrian unconventional oil and gas play in the southern Georgina Basin, northern Australia.

Middle Cambrian sediments in the southern Georgina Basin contain multiple organic-rich source rocks and have been suggested to be prospective for both conventional and unconventional hydrocarbons. We present new geomechanical, mineralogical and geochemical data collected from the Arthur Creek Formation and Thorntonia Limestone in four wells (Baldwin 1, MacIntyre 1, Owen 2, Todd 1) in the southern Georgia Basin. Geomechanical test intervals were selected such that geomechanical test results could be directly compared to the mineralogical and geochemical datasets we collected (X-Ray Diffraction, HyLogger and organic geochemistry). Approximately 25 m of core was tested for unconfined compressive strength (UCS) using the scratch technique. Results indicate that most core that was analysed has UCS values in the range of 60¿150 MPa. Triaxial testing was also conducted to measure the poroelastic properties of core and indicated that Young¿s modulus is generally in the range of 45-67 GPa. UCS and Young¿s modulus are positively correlated and also tend to increase with depth through the prospective Arthur Creek Formation. The mechanical properties of the tested core are also comparable to proven shale-gas plays in Australia and internationally. Mineralogically, the Georgina Basin rocks tested have lower clay contents when compared to data from other Australian and international basins. However, no clear correlation between geomechanical properties and mineralogy was observed, suggesting that multiple factors contribute to the poroelastic and strength parameters. For example, parameters such as sonic velocity and porosity appear correlated with rock strength. Such data can be used alongside other datasets (e.g. sedimentological, geophysical and structural data) to better inform predictions of hydrocarbon prospectivity. Citation: Tenthorey, E., & Ayling, B. (2020). Geomechanical evaluation of a middle Cambrian unconventional oil and gas play in the southern Georgina Basin, northern Australia. Australian Journal of Earth Sciences, 68(5), 697–716. https://doi.org/10.1080/08120099.2021.1847733