A very unconventional hydrocarbon play: The Mesoproterozoic Velkerri Formation of northern Australia

Abstract

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 containing 429 million barrels of oil and eight trillion cubic feet of gas (in place). It was deposited in an intra-cratonic 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 organicrich rocks across northern Australia and North 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.

Low‐temperature thermal history of the McArthur Basin: Influence of the Cambrian Kalkarindji Large Igneous Province on hydrocarbon maturation

“…Source rocks within the basin have been identified as the Velkerri and Kyalla formations of the Roper Group within the Wilton Package, and the Barney Creek, Lynott and Yalko formations of the underlying McArthur Group of the Glyde Package (Crick et al, 1988;Jackson et al, 1988). Of these, the Velkerri and Barney Creek formations are considered the most prospective, preserving total organic carbon values up to 12% (e.g., Cox et al, 2022;Crick et al, 1988;Lanigan et al, 1994).…”

“…Intriguingly, the basin hosts considerable hydrocarbon reserves derived from Mesoproterozoic source rocks, which have been preserved to the present day (Cox et al, 2016(Cox et al, , 2022Jackson et al, 1986). While extensive research has been undertaken characterising the hydrocarbon source, chemistry and maturity (e.g., Cox et al, 2022;Crick et al, 1988;George et al, 1994;Jackson & Raiswell, 1991;Lanigan et al, 1994;Summons et al, 1988), the timing of hydrocarbon maturation remains poorly resolved. Consequently, the preservation of hydrocarbons produced from Mesoproterozoic source rocks in the McArthur Basin remains a fundamental and unresolved question.…”

“…Overlying Palaeoproterozoic basement of the North Australian Craton, the McArthur Basin is an unmetamorphosed and largely undeformed sequence of sedimentary and volcanic rocks deposited over a period of more than 500 million years (e.g., Ahmad & Munson, 2013;Rawlings, 1999;. Intriguingly, the basin hosts considerable hydrocarbon reserves derived from Mesoproterozoic source rocks, which have been preserved to the present day (Cox et al, 2016(Cox et al, , 2022Jackson et al, 1986). While extensive research has been undertaken characterising the hydrocarbon source, chemistry and maturity (e.g., Cox et al, 2022;Crick et al, 1988;George et al, 1994;Jackson & Raiswell, 1991;Lanigan et al, 1994;Summons et al, 1988), the timing of hydrocarbon maturation remains poorly resolved.…”

Petroleum supersystems in the greater McArthur Basin, Northern Territory, Australia: prospectivity of the world’s oldest stacked systems with emphasis on the McArthur Supersystem

“…Collaborations between NTGS, CSIRO, government, industry and academia have led to an enhanced understanding of the regional geology, architecture and resource potential of the basin (e.g. Munson 2016;Revie 2017;Collins et al 2018;Jarrett et al 2019;Cox et al 2022). Herein, we highlight some of the results of this ongoing program with a primary focus on a new petroleum supersystems framework to better document and correlate the distribution of petroleum systems across the components of the greater McArthur Basin, before focusing on individual play types within the McArthur supersystem as a way to highlight the utility of this nomenclature at regional through to play scales.…”

“…Revie 2017;Cox et al 2022). Conventional oil and gas, as well as shale hydrocarbon discoveries, shows and fracture-stimulated flows are known from this supersystem(Côté et al 2018;Altmann et al 2020;Riddle 2021;Underwood 2021;Scrimgeour 2022).…”