Geosequestration of CO₂ in Low-Permeability Sedimentary Systems: Opportunities and Challenges in the Sydney Basin, Eastern Australia

Mario Werner¹, Faiz Mohinudeen², and John Kaldi^1
1Australian School of Petroleum, CO₂CRC & University of Adelaide, Adelaide, SA, Australia
²Petroleum Geoscience, CO₂CRC & Commonwealth Scientific and Industrial Research Organisation, North Ryde, NSW, Australia

The Sydney Basin region contains the largest concentration of stationary CO₂ emitters in Australia, with the major sources, such as coal-fired power stations, oil refineries and coke ovens, contributing about 34% of the total national stationary emissions. CO₂ emissions from these point sources over the next 20 years are anticipated to be around 1350 Mt. Because of this large emissions profile the CO₂ sequestration potential of the Sydney Basin is being addressed by a systematic basin-scale evaluation to identify, characterise and prioritise potential CO₂ storage areas. The Sydney Basin contains a number of Permian reservoir-seal pairs in deep saline formations which are potentially suitable for CO₂ storage and containment. However, their distribution in the subsurface is poorly constrained due to the limited number of deep petroleum wells and the paucity of high quality seismic data. As a consequence many potential structural traps are poorly defined. In contrast, Permian coal seams are abundant and have been extensively drilled in the various coal fields. Preliminary work suggests that the major challenge for geosequestration in the Sydney Basin is the low permeabilities of the potential storage rocks. Target sandstones and coals commonly have permeabilities of less than 10 mD. Despite these low permeabilities, considerable amounts of coal seam methane are produced from about 70 wells in the southern part of the basin. Methane flow rates from wells drilled in a high production fairway range up to 900 Mcf/day which suggest possibilities for favourable permeabilities for CO₂ injection. Furthermore, major advances have been made in understanding the behaviour of CO₂ in coal-bearing successions through both natural analogue and laboratory studies. These insights will be applied to improve quantification of CO₂ storage capacities for coal seams in the Sydney Basin.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas