Changes

The Velkerri Formation is formally subdivided into three members: Kalala, Amungee and Wyworrie in ascending stratigraphic order, distinguished in the subsurface by their lithology, organic content, geochemistry, and petrophysical characteristics<ref>Munson, T. J., and D. Revie, 2018, Stratigraphic subdivision of the Velkerri Formation, Roper Group, McArthur Basin, Northern Territory: Northern Territory Geological Survey, Record 2018-006.</ref>. The Amungee Member is the main target for hydrocarbon exploration within the Velkerri Formation, it represents the deepest and most distal depositional environment and contains the highest proportion of fine-grained sediments. It is further subdivided informally into three organic-rich shale units (A, B and C organofacies, in ascending stratigraphic order) separated by two clay-rich, organically lean intervals. The A-C organofacies are laterally continuous with strong, ubiquitous gas shows<ref name=Cls2017>Close, D., A. Côté, E. Baruch, C. Altmann, F. Mohinudeen, B. Richards, R. Ilett, R. Evans, and S. Stonier, 2017, Exploring the Beetaloo: will Australia’s first viable shale play be sourced by billion year old gas?: The APPEA Journal, vol. 57, no. 2, p. 716-721.</ref>.   

The Velkerri Formation is formally subdivided into three members: Kalala, Amungee and Wyworrie in ascending stratigraphic order, distinguished in the subsurface by their lithology, organic content, geochemistry, and petrophysical characteristics<ref>Munson, T. J., and D. Revie, 2018, Stratigraphic subdivision of the Velkerri Formation, Roper Group, McArthur Basin, Northern Territory: Northern Territory Geological Survey, Record 2018-006.</ref>. The Amungee Member is the main target for hydrocarbon exploration within the Velkerri Formation, it represents the deepest and most distal depositional environment and contains the highest proportion of fine-grained sediments. It is further subdivided informally into three organic-rich shale units (A, B and C organofacies, in ascending stratigraphic order) separated by two clay-rich, organically lean intervals. The A-C organofacies are laterally continuous with strong, ubiquitous gas shows<ref name=Cls2017>Close, D., A. Côté, E. Baruch, C. Altmann, F. Mohinudeen, B. Richards, R. Ilett, R. Evans, and S. Stonier, 2017, Exploring the Beetaloo: will Australia’s first viable shale play be sourced by billion year old gas?: The APPEA Journal, vol. 57, no. 2, p. 716-721.</ref>.   

Biomarkers studies indicate that the depositional organic matter is derived from biomass dominated by bacteria with minor input from archaea and eukaryotes (Jarrett et al., 2019). Total organic carbon (TOC) content of the Amungee Member varies across the basin: along the northern margin of the basin where the formation is shallowly buried, TOC can be as high as 20 wt% and thermal maturity indicators are consistent with early liquid hydrocarbon generation. In the deeper central parts of the basin TOC of the organic-rich intervals reduced to ca. 2-4 wt% and maturity indicators are consistent with dry gas generation (Faiz et al., 2016; Delle Piane et al., 2020; Hall et al., 2020). Organic geochemistry laboratory results summarized by Hall et al. (2020) indicate excellent source rock potential for the oil-prone organic-rich intervals of the Velkerri Formation with hydrogen index as high as 800 mg HC/g TOC. Peak hydrocarbon generation is estimated to occur at thermal maturity quantified by average equivalent vitrinite reflectance of 0.95 %EqVR (equivalent vitrinite reflectance) and onset of generation occurs at maturities between 0.44 %EqVR and 0.82 %EqVR (Hall et al., 2020).

Biomarkers studies indicate that the depositional organic matter is derived from biomass dominated by bacteria with minor input from archaea and eukaryotes<ref>Jarrett, A. J., G. M. Cox, J. J. Brocks, E. Grosjean, C. J. Boreham, and D. S. Edwards, 2019, Microbial assemblage and palaeoenvironmental reconstruction of the 1.38 Ga Velkerri Formation, McArthur Basin, northern Australia: Geobiology, vol. 17, no. 4, p. 360-380.</ref>. Total organic carbon (TOC) content of the Amungee Member varies across the basin: along the northern margin of the basin where the formation is shallowly buried, TOC can be as high as 20 wt% and thermal maturity indicators are consistent with early liquid hydrocarbon generation. In the deeper central parts of the basin TOC of the organic-rich intervals reduced to ca. 2-4 wt% and maturity indicators are consistent with dry gas generation (Faiz et al., 2016; Delle Piane et al., 2020; Hall et al., 2020). Organic geochemistry laboratory results summarized by Hall et al. (2020) indicate excellent source rock potential for the oil-prone organic-rich intervals of the Velkerri Formation with hydrogen index as high as 800 mg HC/g TOC. Peak hydrocarbon generation is estimated to occur at thermal maturity quantified by average equivalent vitrinite reflectance of 0.95 %EqVR (equivalent vitrinite reflectance) and onset of generation occurs at maturities between 0.44 %EqVR and 0.82 %EqVR (Hall et al., 2020).

Mineralogical analyses, geo-mechanical laboratory tests and down-hole fracture tests conducted so far indicate that the organic rich mudstones of the Amungee Member have good reservoir and completion qualities that should result in brittle behavior conductive to fracture propagation (e.g. Santos 2017).

Mineralogical analyses, geo-mechanical laboratory tests and down-hole fracture tests conducted so far indicate that the organic rich mudstones of the Amungee Member have good reservoir and completion qualities that should result in brittle behavior conductive to fracture propagation (e.g. Santos 2017).

* Faiz, M., Altmann, C., Dunne, M., Baruch, E., Close, D., Cote, A., Richards, B. and Ranasinghe, P., 2016, June. Precambrian organic matter and thermal maturity of the Beetaloo Basin, Northern Territory, Australia. In Australian Earth Sciences Convention, Adelaide, South Australia (pp. 26-30).

* Faiz, M., Altmann, C., Dunne, M., Baruch, E., Close, D., Cote, A., Richards, B. and Ranasinghe, P., 2016, June. Precambrian organic matter and thermal maturity of the Beetaloo Basin, Northern Territory, Australia. In Australian Earth Sciences Convention, Adelaide, South Australia (pp. 26-30).

* Hall L.S., Wang L., Bailey A.H.E., Orr M.L., Owens R., Jarrett A.J.M., Lech M.E., Skeers N., Reese, B. and Woods M. (2020) Petroleum prospectivity of the Beetaloo Sub-basin. Technical appendix for the Geological and Bioregional Assessment Program: Stage 2. Department of the Environment and Energy, Bureau of Meteorology, CSIRO and Geoscience Australia, Australia.

* Hall L.S., Wang L., Bailey A.H.E., Orr M.L., Owens R., Jarrett A.J.M., Lech M.E., Skeers N., Reese, B. and Woods M. (2020) Petroleum prospectivity of the Beetaloo Sub-basin. Technical appendix for the Geological and Bioregional Assessment Program: Stage 2. Department of the Environment and Energy, Bureau of Meteorology, CSIRO and Geoscience Australia, Australia.