Geochemical Composition of Natural Gases from the onshore Canning Basin, Australia

The onshore Canning Basin in Western Australia is the focus of a regional hydrocarbon prospectivity assessment being undertaken by the Exploring for the Future (EFTF) program; an initiative by the Australian Government dedicated to boosting investment in resource exploration in Australia. The four-year program led by Geoscience Australia focusses on the acquisition of new data and information about the potential mineral, energy and groundwater resources concealed beneath the surface in northern Australia and parts of South Australia. As part of this program, significant work has been carried out to deliver new pre-competitive data including new seismic, drilling of a stratigraphic well and the geochemical analysis of petroleum recovered from exploration wells. Current conventional remaining gas resources of the Canning Basin are deemed limited (0.2 TCF; AERA, 2018), whereas unconventional gas resources are inferred to be extremely high, with estimated recoverable resources for shale gas and tight gas being 452.3 TCF (5% of P50,Table 2; AREA, 2018). This disparity arises from the high degree of uncertainty of key geological factors, particularly the poor constraints on source rock volumetrics, the lack of understanding of the volume of gaseous hydrocarbons generated and the origin and degree of thermal maturity of the gases. Carbon isotopic data are scarce and hydrogen isotopic data are non-existent, even though numerous gas discoveries have been made across the Lennard Shelf, Broome Platform and Fitzroy Trough following the initial discovery at Pictor 1 in 1984 by BHP Petroleum (Cadman et al., 1993; Jonasson, 2001). Indeed, gas samples have only been available for analyses since the drilling campaign by Buru Energy in 2010, and more recently, mud gases collected in IsoTubes are routinely sampled during drilling and presented in well completion reports (e.g. Cyrene 1; Nicolay 1, Paradise Deepening 1, Theia 1, Yulleroo 3 and Yulleroo 4). This component of the EFTF program, evaluates the molecular and isotopic composition of natural gases from petroleum wells and a hot-spring seep at Mount Wynne, to constrain the much publicised resource potential inferred in this basin. Interpretation of these data will also assist with in the determination of their origin, and hence increase our understanding of the Larapintine Petroleum Supersystem, as proposed by Bradshaw (1983) and Bradshaw et al. (1984). All gas analyses in this study were undertaken by Geoscience Australia’s Organic Geochemistry Laboratory.