Lila W. Gurba

Mineral matter and trace elements in coals of the Gunnedah Basin, New South Wales, Australia

Abstract The concentrations of major and trace inorganic elements in a succession of Permian coals from the Gunnedah Basin, New South Wales, have been determined by X-ray fluorescence techniques applied to both whole-coal and high-temperature ash samples. The results have been evaluated in the light of quantitative data on the minerals in the same coals, determined from X-ray diffraction study of whole-coal samples using a Rietveld-based interpretation program ( Siroquant ™), to determine relationships of the trace elements in the coals to the mineral species present. Comparison of the chemical composition of the coal ash interpreted from the quantitative mineralogical study to the actual ash composition determined by XRF analysis shows a high degree of consistency, confirming the validity of the XRD interpretations for the Gunnedah Basin materials. Quartz, illite and other minerals of detrital origin dominate the coals in the upper part of the sequence, whereas authigenic kaolinite is abundant in coals from the lower part of the Permian succession. These minerals are all reduced in abundance, however, and pyrite is a dominant constituent, in coals formed under marine influence at several stratigraphic levels. Calcite and dolomite occur as cleat and fracture infillings, mostly in seams near the top and bottom of the sequence. The potassium-bearing minerals in the detrital fraction are associated with significant concentrations of rubidium, and the authigenic kaolinite with relatively high proportions of titanium. Zirconium is also abundant, with associated P and Hf, in the Gunnedah Basin coal seams. Relationships exhibited by Ti, Zr, Nd and Y are consistent with derivation of the original sediment admixed with the seams from an acid volcanic source. Pyrite in the coals is associated with high concentrations of arsenic and minor proportions of thallium; no other element commonly associated with sulphides in coals, however, appears to occur in significant proportions with the pyrite in the sample suite. Small concentrations of Cl present in the coal are inversely related to the pyrite content, and appear to represent ion-exchange components associated with the organic matter. Strontium and barium are strongly associated with the cleat-filling carbonate minerals. Ge and Ga appear to be related to each other and to the coals organic matter. Cr and V are also related to each other, as are Ce, La, Nd and Pr, but none of these show any relationship to the organic matter or a particular mineral component.

Effects of igneous intrusions on coalbed methane potential, Gunnedah Basin, Australia

Abstract The Gunnedah Basin, NSW, Australia, contains more than 500 Gt of coal, and has been the subject of recent coalbed methane exploration. Large areas of the basin contain igneous intrusions and large areas of coal have been heat-affected as a consequence. A detailed study has been undertaken of coal seams intersected in a cored coalbed methane exploration drillhole in which two sill-form igneous intrusions are present. Comparisons are made between coals that are unaltered and coals that have been heat-affected, using petrographic and chemical data, coal seam gas desorption data, and gas chemical analysis data. Results demonstrate that the two igneous intrusions have had a very positive effect on coalbed methane development. The gas content in a number of heat-affected coal seams within thermal aureoles above and below the sills is substantially higher than in adjacent unaffected coal seams. In addition, the intrusions have had little effect on gas quality. The coals in the heat-affected zone were found to contain gas with approximately 95% methane. The coals in the thermal aureoles were found, under the microscope, to contain characteristic micropores and slits, which collectively may serve to enhance gas adsorption capacity, permeability, and gas desorption. Gas contents below each of the sills is substantially higher than above the sill, confirming earlier results that the sills appear to have acted as a reservoir seal, during and for some time after intrusion. The background coal rank in ACM Yannergee DDH 1 is in the high-volatile bituminous range. The igneous intrusions have resulted in an increase in rank such that large areas of coal have moved into the optimal thermogenic gas generation window. This rank increase has affected a major part of the coal-bearing sequence.

Vitrinite reflectance anomalies in the high-volatile bituminous coals of the Gunnedah Basin, New South Wales, Australia

Abstract The rank of the Permian coals in the Gunnedah Basin has been analyzed using both petrographic and chemical methods. Apart from the effects of local igneous intrusions, a number of seams in the sequence have vitrinite reflectance values (Rv max) that deviate significantly from the trend expected with a steady downward increase in coalification. Correlation of these anomalies with interpreted depositional environments suggests that abnormally low vitrinite reflectance values in the sequence occur in seams either overlain by or intimately associated with marine strata. The three-dimensional distribution of such low reflectance values, in part of the section at least, can be related either to the lithofacies pattern or post-depositional groundwater flow associated with a major fan-delta system. Coals with anomalously high vitrinite reflectance values appear to contain material described elsewhere as pseudovitrinite, a component not previously reported in Australian Permian bituminous coals. Both low-value and high-value anomalies need to be taken into account when interpreting maturation patterns from vitrinite reflectance data. In some cases other rank indicators such as air-dried moisture may be useful to complement vitrinite reflectance in rank studies of high volatile bituminous coals. Abnormally low vitrinite reflectance values due to environmental factors such as marine influence, on the other hand, may be used to identify flooding-surface sequence boundaries in the basin for stratigraphic and sedimentological investigations.

Elemental composition of coal macerals in relation to vitrinite reflectance, Gunnedah Basin, Australia, as determined by electron microprobe analysis

Abstract The elemental composition of macerals in high-volatile bituminous coals from the Gunnedah Basin, New South Wales, Australia, has been analysed by light-element electron microprobe techniques. The results have been evaluated in relation to maximum vitrinite reflectance trends in vertical section, including the effects of marine influence and igneous intrusions on the coal-bearing sequence. Mean maximum vitrinite (telocollinite and desmocollinite) reflectance for the analysed samples ranges from 0.63% to 0.99%, and to 2.2% for coal affected by igneous intrusions. The carbon content of the vitrinite, as determined by electron microprobe, ranges from 79.74% to 86.07%, and up to 89.06% for the heat-affected coal studied. A simple relationship cannot be established between the reflectance of the vitrinite and its carbon content over this range of coal samples. Vitrinite in marine influenced coals (with suppressed reflectance) appears to have a slightly higher carbon content than vitrinite in isorank coals without marine influence. The increase in carbon may be due to incorporation of carbon and sulphur–rich lipoid material into the vitrinite component. Notwithstanding these differences, the carbon content of vitrinite (telocollinite) seems to be affected only slightly by the depositional changes that cause suppression of vitrinite reflectance in marine-influenced coals. Telocollinite carbon content may therefore be a useful alternative to vitrinite reflectance as a rank indicator in maturation studies. The carbon content of whole-coal samples, determined by ultimate analysis, shows in vertical section a trend intermediate between the carbon of the vitrinite determined by electron microprobe and that of the associated inertinite macerals. Whole-coal analysis data in this range depend on the relative proportions of the different macerals present, as well as the rank of the coal concerned. Coals affected by igneous intrusion show a different relationship between carbon and oxygen of vitrinite (telocollinite), relative to coals where the rank is determined by depth of burial alone. The difference in C–O relationships suggests that the short-term heating associated with intrusions produces chemical changes in macerals that are not paralleled in more normal rank advance.

Chemical composition of macerals in bituminous coals of the Gunnedah Basin, Australia, using electron microprobe analysis techniques

Abstract The chemical composition of the organic matter in the principal macerals of high-volatile bituminous coals from the Gunnedah Basin, New South Wales (Rvmax of telocollinite between 0.6 and 1.1%) has been evaluated from polished section specimens using an electron microprobe technique. Highest proportions of carbon occur in the inertinite macerals, especially fusinite and secretinite (formerly resino-sclerotinite), as well as in sporinite; lowest proportions of carbon occur in the different macerals of the vitrinite group. Oxygen shows the reverse trend, being most abundant in vitrinite and least abundant in the inertinite components, whereas sulphur is lowest in the inertinites and highest in the liptinite (mainly sporinite) present. Evaluations of maceral composition, using the carbon content of telocollinite as a rank indicator, show that carbon is more abundant in both sporinite and semifusinite, relative to vitrinite, in low-rank high-volatile bituminous coals. The difference decreases with increasing rank, and the proportion of carbon in telocollinite becomes essentially the same as that in sporinite and semifusinite at carbon contents of about 89 and 91%, respectively. The carbon content of fusinite and secretinite, on the other hand, does not seem to vary appreciably with rank advance. No significant difference in composition occurs in the rank range studied between the three vitrinite varieties present, desmocollinite, telocollinite and a more highly reflecting telocollinite resembling pseudovitrinite. No evidence was found to indicate a higher hydrogen content, relative to telocollinite, for the vitrinite matrix of desmocollinite.

Occurrence and distribution of organic sulphur in macerals of Australian coals using electron microprobe techniques

The organic sulphur content of the individual macerals in Permian high volatile bituminous coals from the Gunnedah Basin of New South Wales, has been studied using an electron microprobe technique. Liptinite (chiefly sporinite) in the coal has the highest organic sulphur content and inertinite (mainly semifusinite) the lowest; the vitrinite macerals have intermediate sulphur contents. These variations are responsible for the relatively low overall organic sulphur in inertinite-rich coals, typical of Australian Permian deposits. Neither marine influence on coal formation nor increases in coal rank appear to be associated with significant changes in organic sulphur of the individual macerals concerned.

Determination of nitrogen in coal macerals using electron microprobe technique-experimental procedure

This paper discusses nitrogen determination with the Cameca SX50 electron microprobe using PC0 as an analyzing crystal. A set of conditions using differing accelerating voltages, beam currents, beam sizes, and counting times were tested to determine parameters that would give the most reliable nitrogen determination. The results suggest that, for the instrumentation used, 10 kV, current 20 nA, and a counting time of 20 s provides the most reliable nitrogen determination, with a much lower detection limit than the typical concentration of this element in coal. The study demonstrates that the electron microprobe technique can be used to determine the nitrogen content of coal macerals successfully and accurately.

The Influence of Depositional and Maturation Factors on the Three-Dimensional Distribution of Coal Rank Indicators and Hydrocarbon Source Potential in the Gunnedah Basin, New South Wales

Three-dimensional modelling of vitrinite reflectance has been used to enhance the understanding of lateral and vertical rank variations in the Permian coals of the Gunnedah Basin, New South Wales, Australia. The level of organic maturity of the coals has been investigated using both petrographic (vitrinite reflectance and fluorescence) and chemical methods (proximate and ultimate analyses, and electron microprobe data). The coal is of high-volatile bituminous rank, with a mean maximum vitrinite reflectance of between 0.56 and 1.1%. In addition to maturation-induced trends, a significant influence of depositional environment has been identified on vitrinite reflectance and other coal rank indicators in different parts of the sequence.

Greenhouse gas reduction options for Australian coal-fired power plants—An integrated approach

Publisher Summary This chapter discusses the research undertaken by the cooperative research centre for coal in sustainable development (CCSD) in the context of sustainable development and greenhouse gas (GHG) mitigation strategies for Australian coal fired power plants. With the active participation of power generators and coal producers the CCSD research program investigates a range of greenhouse gas mitigation options for current and future coal-fired power stations. The assessment of the most prospective electricity generation technology options that are available for Australia to 2050 has shown that no single technological solution exists, and an integrated approach needs to be undertaken in order to reduce greenhouse gas emissions. The best combination for Australia will not necessarily be the same as for other regions, given differences in coal properties, coal intensity, and coal export. An increase in renewable energy technologies and fossil fuelled power generation efficiency is required, along with significant developments in, and CO 2 capture and storage technologies.