The Permian Gidgealpa Group of the Cooper Basin in South Australia is the focus of an escalating drilling and evaluation campaign for continuous gas accumulations. At this early stage contingent unconventional gas resources total 4.6 TCF in the South Australian part of the Cooper Basin, comparable to the total sales gas production from conventional accumulations to date. However unconventional gas exploration has only just begun and undiscovered resource estimates are much higher. Beach Energy has stated there is potential for at least 15 to 20 trillion cubic feet recoverable gas in PEL 218. Santos estimates for the South Australian Cooper Basin Joint Venture licences range from a low of 22 trillion cubic feet to a high of 187 trillion cubic feet raw recoverable gas.
The Cooper Basin is a Permo-Carboniferous to Triassic intracratonic basin with an entirely non-marine succession that includes thick coal seams, thick and laterally extensive lacustrine shales and fluvial, shoreface and pro-glacial outwash sands. In the deeper troughs, the Gidgealpa Group is dessicated, gas saturated and overpressured. With tight sands, shales and deep coals potentially contributing to future gas production in the troughs, the accumulations are here described as composite gas resource accumulations.
The Cooper Basin is a Permo-Carboniferous to Triassic intracratonic basin located 800 km north of Adelaide, extending into southwest Queensland (FIG 1). The total area of the Basin exceeds 130 000 km2, of which approximately 35 000 km2 are in north-eastern South Australia.
The Cooper Basin has a long history of exploration with the first commercial gas discovery made at Gidgealpa 2 in 1963. Since then a number of conventional oil and gas fields have been discovered in the Basin. To end June 2012 the South Australian parts of the Cooper Basin and overlying Eromanga Basin have produced around 5 tcf of gas, 77 mmboe of condensate, 158 mmbbl of oil and 78 mmboe of LPG. In addition to the known conventional accumulations, the presence of a basin-centred gas accumulation in the Nappamerri Trough has been suspected for over two decades. However the play was not pursued as gas was not considered an attractive commodity due to the small domestic gas market, and readily available gas supplies from other Australian basins. In fact when Petroleum Exploration Licence (PEL) 218 over the Nappamerri Trough was offered for competitive tender in 2004, no bids were received. The growing international LNG market has now refocused attention on the potential for continuous gas plays in the Cooper Basin. This paper summarises the geology and unconventional gas potential of the Gidgealpa Group in South Australia.