The Walloon Coal Measures (WCM) in the Clarence-Moreton and the Surat basins in Qld and northern NSW contain up to approximately 600 m of mudstone, siltstone, sandstone and coal. Wide-spread exploration for coal seam gas (CSG) within both basins has led to concerns that the depressurisation associated with the resource development may impact on water resources in adjacent aquifers. In order to predict potential impacts, a detailed understanding of sedimentary basins hydrodynamics that integrates geology, hydrochemistry and environmental tracers is important. In this study, we show how different hydrochemical parameters and isotopic tracers (i.e. major ion chemistry, dissolved gas concentrations, 13C-DIC, 18O, 87Sr/86Sr, 3H, 14C, 2H and 13C of CH4) can help to improve the knowledge on groundwater recharge and flow patterns within the coal-bearing strata and their connectivity with over- or underlying formations. Dissolved methane concentrations in groundwaters of the WCM in the Clarence-Moreton Basin range from below the reporting limit (10 µg/L) to approximately 50 mg/L, and samples collected from nested bore sites show that there is also a high degree of vertical variability. Other parameters such as groundwater age measurements collected along distinct flow paths are also highly variable. In contrast, 87Sr/86Sr isotope ratios of WCM groundwaters are very uniform and distinct from groundwaters contained in other sedimentary bedrock units, suggesting that 87Sr/86Sr ratios may be a suitable tracer to study hydraulic connectivity of the Walloon Coal Measures with over- or underlying aquifers, although more studies on the systematic are required. Overall, the complexity of recharge processes, aquifer connectivity and within-formation variability confirms that a single tracer that cannot provide all information necessary to understand aquifer connectivity in these sedimentary basins, but that a multi-tracer approach is required.

This presentation will provide an overview of geological storage projects and research in Australia.

Abstract: The onshore Georgina Basin in northern Australia is potentially prospective for unconventional hydrocarbons, however, like many frontier basins it is under-explored. A well-connected hydraulic fracture network has been shown to be essential for the extraction of resources from the tight reservoirs that categorise unconventional plays, as they allow for economic flows of fluid from the reservoir to the well. One of the fundamental scientific questions regarding hydraulic stimulation within the sub-surface of sedimentary basins is the degree to which local and regional tectonic stresses act as a primary control on fracture propagation. As such, an understanding of present-day stresses has become increasingly important to modern petroleum exploration and production, particularly when considering unconventional hydrocarbon reservoirs. This study characterises the regional stress regime in the Georgina Basin using existing well data. Wellbore geophysical logs, including electrical resistivity image logs, and well tests from 31 petroleum and stratigraphic wells have been used to derive stress magnitudes and constrain horizontal stress orientations. Borehole failure features interpreted from wellbore image and caliper logs yield a maximum horizontal stress orientation of 044°N. Integration of density log data results in a vertical stress gradient of 24.6 MPa km-1. Leak-off and mini-fracture tests suggest that this is the minimum principle stress, as leak-off values are generally shown to be at or above the magnitude of vertical stress. The maximum horizontal stress gradient is calculated to be in the range of 34.0-53.9 MPa km-1. As such, a compressional stress regime favouring reverse/reverse'strike-slip faulting is interpreted for the Georgina Basin.

This data package was preduced in response to a request by Rodney King from Teck Australia for a compilation of GA borehole datasets from the Isa Superbasin, in particular for gamma-ray data. The data set includes drill hole/section location information, and lithological, geochemical and gamma ray data. All data were extracted from GA databases.

The Upper Burdekin Chloride Mass Balance Recharge web service depicts the recharge rates have been estimated at borehole locations in the Nulla and McBride basalt provinces. Using rainfall rates, rainfall chemistry and groundwater chemistry, the recharge rates have been estimated through the Chloride Mass Balance approach.

Thelodont scales recovered from the basal (calcareous) unit of the Cravens Peak Beds in the Georgina Basin, are referable to Turinia australiensis Gross, 1971, T. cf. pagei (Powrie, 1870), and Gampsolepis ? sp. undet. The thelodonts probably lived in a marginal marine environment (as evidenced from the associated ostracods and eridostracans) at about the same time as the placoderm Wuttagoonaspis sp. lived in the freshwater bodies, now represented by the sandstone and conglomerate facies of the Cravens Peak Beds. Scales of Turinia australiensis Gross, 1971, associated with Wuttagoonaspis plates, from the lower part of the Mulga Downs Group in the Cobar/Wilcannia area of New South Wales, are at least as young as late Early Devonian (Emsian), because they post-date the Pragian age of the underlying Amphitheatre Group. By correlation, those parts of the Cravens Peak Beds (Georgina Basin) and the Tandalgoo Red Beds (Canning Basin) that also contain Turinia australiensis are approximately coeval. After reaching Australia in Early Devonian time, the Turinia fauna began an adaptive radiation to give apparently younger (Middle Devonian) stocks that have survived longer in the Australian region than elsewhere, as the youngest known scales come from the Gneudna Formation (Iatest Givetian-earliest Frasnian) in the Carnarvon Basin, Western Australia.

276 km of continuous seismic reflection profiles have been obtained from the inter-reef areas of the Capricorn Reefs. Five reflectors were identified, three being widespread: reflector A, the shallowest, is found only close to modern reefs; reflector C is widespread and varies from flat-lying to irregular; the deepest reflector, D, is limited to the area north and west of Heron Island, where it is flat-lying. All the reflectors are assumed to represent erosional surfaces, and the ages of the intervening sequences are not known. Either reflector C, or the present sea bottom and reflector A, represent the surface of the Holocene transgression.