Underground » Geology
The aim of the Supermodel 2000 project was to deliver a regional three-dimensional model of the Moranbah-German Creek Coal Measures along the western limb of the Bowen Basin from integrated mine-scale databases and regional basement geology. It provides a snapshot of the available data and knowledge as at December 2000 and provides the first set of regional maps showing coal seam thickness and interburden distributions in the context of structure and basin evolution. This model is the framework from which to examine the relationships between structure, interburden character, stress and gas contents that will aid in regional area selection and local hazard recognition for coal resource extraction. The approach is novel in that it is the first time since initial exploration that a formalized approach to data sharing and presentation at this scale has been implemented.
The approach of the project was to quilt together a ?Supermodel? consisting of three regional tiles (Northern: Wards Well to Grosvenor; Middle: Peak Downs to Norwich Park; and Southern: German Creek to Kestrel mines) that display the regional and local structure of the main mineable seams, their thickness and splitting patterns and their interburden thickness distributions. A regional correlation schema of the coal seams across all tiles was developed to implement this approach. Where available, the sedimentary character of the interburden was included to project ground conditions due to the distribution of weak and strong lithologies and their association with tectonic structures. Within this framework, the distribution of virgin gas content and composition was examined to identify domains of similarity with respect to depth and interpreted permeability using coal rank, type and cleat orientation with respect to regional horizontal stress.
Data consisted of mine site drilling (37,250 drill holes) in which coal seams had been logged, open cut and underground mapping of faults, joints and coal cleat, available geophysics (seismic, aeromagnetics, and gravity) and stress measurements. Gas content data came from exploration drilling (415 drill holes) and is presented as full seam composites normalized to 15% ash at 20º C and 101.3 kPa for the Goonyella Middle seam in the northern tile and the German Creek seam in the southern tile.
The results are:
- A structural interpretation of faulting style, severity and timing within the coal measures that is underpinned by an assessment of regional basement structure and available stress measurements;
- The recognition of basement controls on the thickness distribution and splitting patterns of coal seams and their interburden character along the western limb of the basin;
- Predictive relationships between the distributions of weak lithologies and jointed and faulted ground adjacent to strong sandstone dominated roof;
- Predictive relationships between low to high gas domains, seam structure, projected permeability and stress;
- Regional correlations of seams and a series of isopach maps of superseams and interburdens for each of the tiles.
The above relationships are presented in a series of maps and cross sections that are described in this report and contained in a poster set included on CD. Super-seam correlations are provided for the Goonyella Lower-Dysart-German Creek-Lilyvale seam and the Goonyella Middle-Harrow Creek-Aquila/Tieri seam, which are the main mineable seams in this region. Also included in digital format are maps of super-seam structure, thickness and splitting patterns and interburden distributions. Where data were dense enough, seam thickness and interburden maps of the stratigraphically higher intervals to the P-Pleiades seam and the Goonyella Upper seam are also included.
This project had the support of the coal industry, in particular BHP Billiton Mitsubishi Alliance, North Goonyella Coal Pty Ltd, Oaky Creek Coal Pty Ltd, Anglo Coal Pty Ltd, Capricorn Coal Management Ltd, Pacific Coal Pty Ltd, Kestrel Coal Pty Ltd, Santos Ltd and CH4 Pty Ltd, who provided invaluable data, ideas, in-kind support and/or finance. The Queensland Department of Natural Resources and Mines also provided access to regional data and open file information. Geoscience Australia provided access and use of regional gravity data. Invaluable discussions were also held with Chris Fielding of University of Queensland. Two honours theses (Ronan, 2000 and Hill, 2000) were supported as part of this project.