PETROLOGICAL AND PETROPHYSICAL STUDY OF PERMIAN ARENITES FOR POTENTIAL SUBSURFACE STORAGE OF NATURAL GAS, SYDNEY BASIN, NEW SOUTH WALES, AUSTRALIA

The expanding natural gas market in New South Wales during the next decades will require guaranteed back-up supplies in the event of insufficient deliverability through the Moomba-Sydney pipeline and/or cut-off of the pipeline. Subsurface storage of natural gas in natural reservoirs near the market area offers one solution for ensuring continuity of supply to this market. A petrological, wireline log, structural and reservoir-engineering study has been conducted of water-bearing arenites of the Permian Nowra Sandstone, Muree Sandstone and Snapper Point Formation in the Sydney Basin. This has resulted in the delineation of seven potential natural gas storage reservoirs near Sydney. The cap-rocks to the seven reservoirs are Permian impermeable arenites, siltstone, claystone and shale beds of the Berry Formation, Mulbring Siltstone, Wandrawandian Siltstone and Snapper Point Formation. Porosity in the Nowra and Muree Sandstone ranges from 5.5 to 12.2 percent and in the Snapper Point Formation from 5.4 to 6.8 per cent. Permeability is estimated to range from 0.47 to 5.00 millidarcies. The structures of these potential reservoirs include both faulted and unfaulted, gently folded anticlines, and an irregular dome. Their areal extent and vertical closure range from 1 to 45 sq km and 20 to 225 respectively. Total potential storage capacity for the seven reservoirs is estimated to be 21.3 x 109m3 of natural gas, and their deliverability potential, based on permeabilities of 1.0 and 5.0 millidarcies, ranges from 0.002 to 0.103 x 106m3 of natural gas per day per well.