This contribution focuses on the organic rich intervals of the prospective Mesoproterozoic Velkerri Formation from the Beetaloo Sub-basin, part of the greater McArthur Basin (Northern Territory). It is based on the integration of petrophysical measurements, high resolution petrographic observations from scanning and transmission electron microscopy, organic and inorganic geochemical analyses, and sequence stratigraphy. Specifically, we show how intervals of intense diagenetic quartz cementation are widespread throughout the Amungee Member of the Velkerri Formation and preferentially affect the organic-rich intervals of the formation. At the micro-scale, these intervals show a pervasive, quartz dominated nano-crystalline matrix interspersed with clays. The presence of this diagenetic matrix also shows at the well scale through 1D geochemical profiles and is well correlated with intervals of high organic content in all the wells where organic and inorganic profiling has been acquired. Using sequence stratigraphy to explain these consistent vertical patterns, we infer that the organic-rich and diagenetic quartz-rich layers are associated with detrital sediment starved intervals overlying transgressive surfaces. These are capped by maximum flooding surfaces and progressively leaner high-stand system tracts. The vertical patterns can be laterally correlated to map organic-rich and silica-rich strata with desirable reservoir properties like stiffness and storage potential.

Open-Access Online Publication: March 03, 2023