Rangal Structural Supermodel 2002

The aim of this project was to build an accessible quantitative three-dimensional (3D) visual information model of the Rangal Coal Measures structure from existing site data. This project targeted the southern mining areas in the vicinity of Blackwater and northwards to Middlemount. This study formed an extension to the Bowen Basin Supermodel research which aimed to access information and knowledge for all the coal sequences in the basin. To date the Moranbah-German Creek sequence was modelled in the 2000 study (ACARP C9021), and this 2002 research component focuses on the central portion of the Rangal Coal Measures.

The study area extends approximately 160km north to south and 65km west to east. Over 28,000 drillholes from exploration and mining activity intersect the coal measures in the study area.

A uniform seam coding system (Unicode) has been designed as a means of transcending the difficulties encountered with disparate seam naming and coding schemes used by the different mines. It is designed to run in parallel with existing coding schemes.

Maps have been constructed that show the distribution of the coal sequence around the flanks of an elongate low-profile basement dome-like structure, the Comet Ridge. The sedimentary sequence dips away to the west, south and east of this structure and extend northwards along the centre and eastern parts of the Bowen Basin.

The project's core deliverable was a series of 8 detailed site-specific interactive 3D information models, which are installed at a combination of contributing operating sites, company and consultants offices and a short open report.

Data was specifically sourced and integrated from mine-scale databases. Data consisted of mine and exploration site drilling in which coal seams had been intersected (drillhole lithology and geophysical logs), and a varied mix of fault mapping that was mostly only in two dimensions, inconsistent and substantially incomplete. A wealth of information exists in legacy data but is not readily accessible. Participants were not able to provide any joints and coal cleat data.

To the extent data was made available, the information for individual mines and exploration tenements was processed into separate models and then visually integrated into respective 3D information models. These 3D models include a combination of drillhole logs and geophysics, seam structure surfaces, fault locations, maps of structure interpretation and hazards, highwall imaging, and mine plans. Many mining issues are geologically derived and controlled by the geological history of the coal sequence during sediment deposition and subsequent burial and coalification. Geological skills are essential to rigorously scout, map and characterise the subsurface terrain, and maintain the secure knowledge foundation required for mining to proceed effectively.

Sites that participated in the study and which have 3D information models are:

1. Blackwater-South Blackwater (BHP-Billiton);
2. Curragh; (CQML)
3. Curragh North; (CQML)
4. German Creek East; (Anglo Coal)
5. Jellinbah;
6. Oak Park; (Anglo Coal)
7. Togara South; (BHP-Billiton)
8. Togara North; (Xstrata)
9. Yarrabee.

The results include:

• Regional correlations of seams and a series of 2D isopach maps of coal seam elevation and thickness, and the thickness of inter- seam partings. These show regions of stability and areas where deposition was more influenced by structure, which provide preferential pathways for subsequent structural reactivations and seam disruptions.
• 3D imaging of drillhole wireline geophysics logs (sourced from LAS files) that show seam names and auto-interpretations of rock-type and rock-strength and present a more standardised and rigorous basis for enhanced characterisation of rock units in advance of mining.
• 3D displays of drillhole bedding and structure dip and dip-direction by depth derived from post-processing of Reeves wireline dipmeter logs. This facilitates identification of structures and potential hazards ahead of mining.
• The Supermodel 2000 structural interpretation of Bowen Basin faulting style, severity and timing within the coal measures that is underpinned by an assessment of regional basement structure and available stress measurements;
• The results do not incorporate any coal quality information although it is anticipated that profound relationships will exist between coal quality and the regional and local structural and sedimentary frameworks outlines in this study.