The ability to understand and predict the distribution of the primary organic content in a basin is key when exploring for unconventional hydrocarbons. Many pathways lead to the formation of organic-rich rocks through combinations of primary production, organic matter preservation, and dilution rates. It is likely that: (1) primary productivity will vary temporally and spatially, (2) preservation will be affected by the basin's physiography (e.g., open vs. restricted) and the burial efficiency, and (3) dilution will be a function of the stratigraphic evolution. If the vertical and lateral variations of each of these factors are not understood, it is difficult to quantify the impact of their interaction on organic matter accumulation, thus making the accurate prediction of the distribution of organic matter difficult. In the present work, we focus on the Mesoproterozoic Velkerri Formation, an unconventional hydrocarbon selfsourced shale reservoir that is currently the target of exploration and appraisal activities in the Beetaloo Subbasin. Using stratigraphic modelling, we simulate the evolution of the basin in the Proterozoic and calibrate the results to key wells located in the basin. We then run multiple realisations of the model while changing the input parameters that affect organic primary productivity, oxygen renewal in the water column, and sediment supply. This allows the effects of each parameter on organic matter accumulation to be quantified. This study emphasizes that deposition during the Mesoproterozoic required high primary productivity for organic-rich shales to form in the basin. In addition, this study shows that the controls on organic matter distribution vary spatially, both laterally and with stratigraphic depth within the Velkerri Formation/Beetaloo basin.

Open-Access Online Publication: March 01, 2023