Petroleum systems model for source-rock-reservoir evaluation in the Beetaloo Sub-basin

The Beetaloo Sub-basin comprises one of the oldest petroleum systems in the world with the Middle Velkerri and Lower Kyalla shales considered as key unconventional source-rock-reservoir targets. The basin is relatively under-explored with only few wells penetrating potential source rocks in deeper parts of the basin. In order to aid further exploration in the basin a comprehensive 3D petroleum system model has been developed. The model also includes detailed lithofacies and organic content information derived from stratigraphic forward modelling. The sedimentary sequence was subjected to multiple burial and uplift events including in the Mesoproterozoic, Neoproterozoic, Palaeozoic and the Mesozoic. Thermal maturity modelling suggests that maximum burial of the Precambrian section occurred during the Palaeozoic. Significant uncertainty exists in constraining the burial depths associated with the early events and therefore multiple scenarios were tested. Overall, however, the models suggest that in deeper parts of the basin, liquid hydrocarbon generation from the Velkerri shale began during the Mesoproterozoic further generation and secondary cracking to gas occurring during the Neoproterozoic and Palaeozoic burial episodes. In the shallower regions of the basin, where the Velkerri and Kyalla shales are liquids and wet gas mature, hydrocarbon generation mostly occurred during the Palaeozoic. The properties of reservoir hydrocarbons predicted by the model is consistent with the data from production wells testing the Middle Velkerri and Lower Kyalla shales in different parts of the basin. The model also computes petrophysical properties and adsorbed gas content as a function of lithology, temperature, pressure, organic content, and thermal maturity which have been calibrated against laboratory measurements. The model is readily updatable as new data become available and outputs can be directly used for reservoir modelling and to conduct detailed geomechanical analyses.