Characterisation of the cleat network serves as the basis for estimating the hydraulic and mechanical seam properties which in turn are fundamental for flow and geomechanical modelling in the context of underground coal mining. Cleat and cleat network geometry can be described as a function of frequency, aperture, size, orientation relative to in situ stresses, connectivity and porosity, with mineralised and un-mineralised cleats occurring. To describe these properties, CTscans of core samples of a Bowen Basin coal in central Queensland, Australia, are analysed.A unique image processing workflow method is introduced to extract the key statistical parameters of perpendicular butt and face cleats present in a two-dimensional image. As face and butt cleats have different characteristics, the presented method distinguishes face cleats and butt cleats by direction and present detailed data for both cleat types. The results comprise cleat length, apertures, sizes, intensities, densities, shape parameter, spacing, orientation and connectivity and are therefore more comprehensive than previous cleat descriptions. Three generally different cleat geometries are considered within this study, one sample shows perpendicular face and butt cleats, the second two sets of face cleats intersected by butt cleats and the third parallel face cleats only.

A large extent of groundwater flow in fractured aquifers follows fractures and cleats. The heat pulse flow meter allows the localisation and quantification of in-and outflow along borehole profiles through field measurements and subsequent inverse modelling. In this paper the method is presented and its feasibility is discussed based on the experiences gained from two different field sites. Field work was undertaken on two sites on the East Coast of Australia under different conditions leading to different outcomes. The experiences with the heat pulse flow meter method and concluding recommendations are reported to help improve the performance of the method.

The planning and design of any coal mine development requires among others a thorough investigation of the geological, geotechnical and hydrogeological subsurface conditions. As part of a coal mine exploration program we conducted heat pulse vertical flow meter testing. The flow data were combined with absolute and differential temperature logging data to gain information about the hydraulic characteristics of two different coal seams and their over-and interburden. For the strata that were localised based on geophysical logging data including density, gamma ray and resistivity hydraulic properties were quantified. We demonstrate that the temperature log response complements the flow meter log response. A coupling of both methods is therefore recommended to get an insight into the hydraulic conditions in a coal seam and its overburden.

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Coal is characterised by its unique microstructure made up of a porous matrix intersected by a network of face and butt cleats. Together with mining-induced fractures and faults caused by geological activities, these small scale cleats provide the principal source of permeability for groundwater and gas flow within a coal seam. The coal seam permeability plays a crucial role in mine stability, minability, gas well performance, and seam drainage behaviour. Therefore, a fundamental understanding of the fracture and cleat characteristics is essential for safe and efficient coal mining and coal seam gas production.Due to the various structural parameters of coal varying widely in size, the permeability of coal is highly scale-dependent. This thesis investigates the permeability of coal fractures and cleats on the example of Bowen Basin coals over a range of scales. The investigation of permeability is carried out using field studies, laboratory work, and numerical modelling.The relationship between permeability results gathered across scales is investigated to determine the Representative Element Volume and thus the smallest volume over which a measurement can be made that will yield a value representative of the whole.Field work has been undertaken at the Hail Creek Coal Mine in Central Queensland, Australia. A Heat Pulse Flow Meter, a downhole wireline tool, was utilised to test for permeability of macro-scale (metres to kilometres) fractures frequently associated with fault structures intersecting the coal measures at the mine site. Coal samples were taken for subsequent laboratory work. Laboratory investigations of permeabilities cover the meso-scale (centimetres to decimetres). The coal samples taken at two coal seams, the Elphinstone and the Hynds seam, were tested for permeability in a triaxial cell using the constant head test method. Based on Computer Tomography scans of the coal, the samples were numerically reconstructed to allow for investigations on the micro-scale The University of Queensland has provided me with a well-equipped work environment to conduct my PhD studies using a wide range of techniques and instruments.