Reservoir lithofacies study of the Toolebuc Formation, Eromanga Basin, Australia as a potential unconventional target

Open file data and new laboratory data were integrated with different lithofacies from gamma-ray (GR) response and core to interpret reservoir properties that would lead to a hydrocarbon potential targeting model for the Toolebuc Formation (Fm). The Toolebuc Fm is divided into an upward deepening cycle (UDC) followed by an upward shallowing cycle (USC), in which silica-rich argillaceous mudstone (Facies 1), mixed argillaceous mudstone (Facies 2) and interbedded calcareous mudstone and shelly thin beds/horizons (Facies 3) occur. Facies 1 is enriched in clay and silica component with relatively low Total Organic Carbon (TOC). Facies 2 has a mixed mineralogical composition with high TOC. Facies 3 is enriched in carbonates (coccoliths and shelly debris). The TOC value is high and shows large variation. The organic matter (OM) in the Toolebuc Fm corresponds to Type II kerogen and exhibits variability in maturity indicators but has arguably entered the early oil window. The dominant pore types of the Toolebuc Fm are intraparticle mineral pores and interparticle mineral pores while OM pores are rare. Samples collected from the basin centre show evidence of hydrocarbon generation.