Hyperspectral logging of middle Cambrian marine sediments with hydrocarbon prospectivity: a case study from the southern Georgina Basin, northern Australia

The Georgina Basin is a Neoproterozoic'Paleozoic basin that spans parts of the Northern Territory and Queensland in northern Australia. The basin is prospective for petroleum, phosphate and base metals (copper, lead and zinc). The Dulcie and Toko synclines in the southern part of the basin are prospective for petroleum, where a thick Cambro-Ordovician succession of marine carbonates hosts several source rocks and associated oil and gas shows. The key source rock units occur within the middle Cambrian Narpa Group including both the Thorntonia Limestone (Series 2 and 3) and the Arthur Creek Formation (Series 3). The base of the Arthur Creek Formation is characterised by organic-rich 'hot' shales (associated with a prominent gamma spike in well logs) that have been targeted by petroleum explorers for both conventional and unconventional oil and gas. For this study, hyperspectral logging data collected by HyLoggerTM instruments were evaluated from 13 wells in the southern Georgina Basin, including petroleum, mineral and stratigraphic wells. Formation boundaries are often (but not always) characterised by distinctive changes in mineralogy, as determined by spectral and X-ray diffraction data. Key source rock units in the southern Georgina Basin were characterised and mapped in terms of their mineralogy, and other spectral properties (e.g. short-wave infra-red 'SWIR' reflectance and spectral contrast). Interpretation of the hyperspectral data alongside wireline log data supports the differentiation of two organic-rich shale units within the Arthur Creek Formation, previously distinguished on the basis of biostratgraphy and well log data. The older shale unit in the Dulcie Syncline, is characterised by quartz and carbonate mineralogy. A younger shale unit, distributed across the eastern part of the Dulcie Syncline and the Toko Syncline, is characterised by quartz, carbonate and variable white-mica contents. Key associations are observed between HyLogger mineralogy and geophysical log data. Peaks in the gamma log intensity in the middle Cambrian sediments often correspond to elevated measured total organic carbon contents, decreased carbonate contribution, Short-Wave Infrared reflectance and spectral contrast, and relatively-increased proportions of white micas and quartz. This study demonstrates that HyLogging data can provide an improved understanding of the sedimentological, mineralogical and diagenetic characteristics, as well as associated spatial heterogeneity, of prospective hydrocarbon formations in sedimentary basins.