Geological controls on no. 4 seam roof conditions at New Denmark Colliery, Highveld Coal Field, Karoo Basin, South Africa
- Authors: Stanimirovic, Jasmina
- Date: 2009-01-28T09:43:30Z
- Subjects: Facies (Geology) , Coal , Stratigraphic geology , Sedimentology , Mine roof control , Karoo Supergroup , Mpumalanga (South Africa)
- Type: Thesis
- Identifier: uj:14849 , http://hdl.handle.net/10210/1971
- Description: M.Sc. , The coal-bearing Permian Vryheid Formation of the Ecca Group (Karoo Supergroup) was investigated at New Denmark Colliery, situated in the north east section of the Karoo Basin, South Africa. The lithostratigraphy of the sequence is defined in terms of conventional lithostratigraphic terminology but also by applying detailed genetic stratigraphic schemes that have previously been proposed for the adjacent coalfields. The succession is divided up into depositional sequences named after the underlying and overlying coal seams, the No. 2, 3, 4 and 5 seam sequences. The sedimentary succession was divided up into five facies, namely: conglomerate facies, sandstone facies, interlaminated sandstone-siltstone facies, siltstone facies and coal facies. These were interpreted hydrodynamically. Facies assemblages were then interpreted palaeoenvironmentally. Glacial, fluvial, deltaic and transgressive marine sequences were responsible for forming this sedimentary succession. Attention was then focussed on the main economic No. 4 seam, which is mined underground at the colliery. Detailed subsurface geological cross-sections, core sequences and isopach maps of the No. 4 seam coal and the lithologies above, were used to determine specific aspects of the depositional environment that could contribute to unstable roof conditions above No. 4 seam. Coarsening-upward deltaic cycles, fining-upward bedload fluvial cycles, glauconite sandstone marine transgressions and crevasse-splay deposits are recognized in the overlying strata. Poor roof conditions occur parallel to palaeochannel margins because the interbedded channel sandstone and adjacent flood plain argillites cause collapsing along bedding plane surfaces. Rider coals overlying thin crevasse-splay sequences in close proximity to the No. 4 seam, create one of the most serious roof conditions; complete collapse occurs along the rider coal contact with the underlying splay deposits. Differential compaction of mudrock/shale/siltstone over more competent sandstone causes slickensided surfaces that weaken the roof lithologies. Correct identification of these sedimentological features will enable the prediction of potential poor roof conditions during mining operations and mine planning.
- Full Text:
- Authors: Stanimirovic, Jasmina
- Date: 2009-01-28T09:43:30Z
- Subjects: Facies (Geology) , Coal , Stratigraphic geology , Sedimentology , Mine roof control , Karoo Supergroup , Mpumalanga (South Africa)
- Type: Thesis
- Identifier: uj:14849 , http://hdl.handle.net/10210/1971
- Description: M.Sc. , The coal-bearing Permian Vryheid Formation of the Ecca Group (Karoo Supergroup) was investigated at New Denmark Colliery, situated in the north east section of the Karoo Basin, South Africa. The lithostratigraphy of the sequence is defined in terms of conventional lithostratigraphic terminology but also by applying detailed genetic stratigraphic schemes that have previously been proposed for the adjacent coalfields. The succession is divided up into depositional sequences named after the underlying and overlying coal seams, the No. 2, 3, 4 and 5 seam sequences. The sedimentary succession was divided up into five facies, namely: conglomerate facies, sandstone facies, interlaminated sandstone-siltstone facies, siltstone facies and coal facies. These were interpreted hydrodynamically. Facies assemblages were then interpreted palaeoenvironmentally. Glacial, fluvial, deltaic and transgressive marine sequences were responsible for forming this sedimentary succession. Attention was then focussed on the main economic No. 4 seam, which is mined underground at the colliery. Detailed subsurface geological cross-sections, core sequences and isopach maps of the No. 4 seam coal and the lithologies above, were used to determine specific aspects of the depositional environment that could contribute to unstable roof conditions above No. 4 seam. Coarsening-upward deltaic cycles, fining-upward bedload fluvial cycles, glauconite sandstone marine transgressions and crevasse-splay deposits are recognized in the overlying strata. Poor roof conditions occur parallel to palaeochannel margins because the interbedded channel sandstone and adjacent flood plain argillites cause collapsing along bedding plane surfaces. Rider coals overlying thin crevasse-splay sequences in close proximity to the No. 4 seam, create one of the most serious roof conditions; complete collapse occurs along the rider coal contact with the underlying splay deposits. Differential compaction of mudrock/shale/siltstone over more competent sandstone causes slickensided surfaces that weaken the roof lithologies. Correct identification of these sedimentological features will enable the prediction of potential poor roof conditions during mining operations and mine planning.
- Full Text:
A review of the coalbed methane potential of South Africa's coal deposits and a case study from the north-eastern Karoo basin
- Authors: Sandersen, Andrea
- Date: 2012-03-06
- Subjects: Coalbed methane , Coal mines and mining , Economic geology
- Type: Thesis
- Identifier: uj:2144 , http://hdl.handle.net/10210/4510
- Description: M.Sc. , The potential target areas for coalbed methane in South Africa are reviewed and a case study based on borehole data from the north-eastern Karoo basin was undertaken. The Early Permian coal seams of the Karoo Supergroup occur in several discrete sedimentary basins in South Africa, of which the Karoo basin is the largest. Using screening criteria based on geological, petrographical and analytical data some of the coal deposits can be excluded as potential coalbed methane producers. These include the Molteno Coalfield, large parts of the Karoo basin coal deposits and some of the Northern Province's coal deposits which are structurally disturbed. The traditional mining areas in the Free State, Witbank and Highveld coalfields are excluded from the coalbed methane study because the target seams occur at less than 200 metres below surface, too shallow for gas retention. Some of the coal seams in the Waterberg Coalfield occur at depths of several hundred metres below surface and these are unlikely to be mined by conventional means. These deep coals may be ideal coalbed methane producers. This regional overview was based on available, published data and two important parameters, permeability of coal and coalbed hydrology are unknown but important factors that will need to be taken into account in any future evaluations. The case study focused on an area close to Amersfoort that has a predicted potential for coalbed methane production. The study utilized 465 borehole descriptions from which isopach maps and geological cross-sections were constructed. Limited samples of borehole core provided lithological information from which a facies analyses was undertaken so as to establish the hydrodynamic origin of each facies types. The main lithofacies associated with the coal seams are mudstones, carbonaceous shales and fine- to coarse-grained sandstone. These data were combined with analyses from limited permeability data, petrographical data and proximate analyses for the Gus and Alfred seams. In addition to the sedimentary rocks, the role of dolerite intrusions was found to be significant as these occur as thick sills and dykes that occur below, within and above the coal seams. These may compartmentalize the seams into secondary targets within the study area. Thick sills overlying the coal zone also increase static loading and may be advantageous with respect to reducing the minimum depthbelow- surface requirements. Potential coalbed methane target areas are identified, although the entire study area is not suitable due to structural displacement of the coal seams, thinning of coal in places and devolatization caused by the dolerites.
- Full Text:
- Authors: Sandersen, Andrea
- Date: 2012-03-06
- Subjects: Coalbed methane , Coal mines and mining , Economic geology
- Type: Thesis
- Identifier: uj:2144 , http://hdl.handle.net/10210/4510
- Description: M.Sc. , The potential target areas for coalbed methane in South Africa are reviewed and a case study based on borehole data from the north-eastern Karoo basin was undertaken. The Early Permian coal seams of the Karoo Supergroup occur in several discrete sedimentary basins in South Africa, of which the Karoo basin is the largest. Using screening criteria based on geological, petrographical and analytical data some of the coal deposits can be excluded as potential coalbed methane producers. These include the Molteno Coalfield, large parts of the Karoo basin coal deposits and some of the Northern Province's coal deposits which are structurally disturbed. The traditional mining areas in the Free State, Witbank and Highveld coalfields are excluded from the coalbed methane study because the target seams occur at less than 200 metres below surface, too shallow for gas retention. Some of the coal seams in the Waterberg Coalfield occur at depths of several hundred metres below surface and these are unlikely to be mined by conventional means. These deep coals may be ideal coalbed methane producers. This regional overview was based on available, published data and two important parameters, permeability of coal and coalbed hydrology are unknown but important factors that will need to be taken into account in any future evaluations. The case study focused on an area close to Amersfoort that has a predicted potential for coalbed methane production. The study utilized 465 borehole descriptions from which isopach maps and geological cross-sections were constructed. Limited samples of borehole core provided lithological information from which a facies analyses was undertaken so as to establish the hydrodynamic origin of each facies types. The main lithofacies associated with the coal seams are mudstones, carbonaceous shales and fine- to coarse-grained sandstone. These data were combined with analyses from limited permeability data, petrographical data and proximate analyses for the Gus and Alfred seams. In addition to the sedimentary rocks, the role of dolerite intrusions was found to be significant as these occur as thick sills and dykes that occur below, within and above the coal seams. These may compartmentalize the seams into secondary targets within the study area. Thick sills overlying the coal zone also increase static loading and may be advantageous with respect to reducing the minimum depthbelow- surface requirements. Potential coalbed methane target areas are identified, although the entire study area is not suitable due to structural displacement of the coal seams, thinning of coal in places and devolatization caused by the dolerites.
- Full Text:
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