Coal facies studies in Australia

Despite the economic importance of coal to the Australian economy, detailed studies of controls on variation in coal type are remarkably few. However, important contributions have been made in the understanding of coal facies development. Tertiary lignite deposits of the Gippsland Basin provide key insights into the development of lithotype cyclicity and its relationship to relative sea-level changes, with individual paling-up cycles being correlated to parasequences. Studies of Permian hard coals have identified relationships between coal type and surrounding sediments. Unfortunately, these relationships have been widely over-interpreted in a manner that has diminished their real value

Controls on methane sorption capacity of Indian coals

Details of methane sorption properties of some Indian coals ranging in rank from high-volatile bituminous C (0.62% Ro max) to medium-volatile bituminous coal (1.46% Ro max) were investigated to determine the major factors influencing gas adsorption capacity and desorption rate. Variables studied included moisture content, mineral-matter content, rank, and coal type (maceral composition).\ud \ud Adsorption isotherm analysis of dry coals showed that adsorption capacity followed a second-order polynomial trend with rank. Equilibrium moist samples showed a linear increase in adsorption capacity with rank and had a significantly reduced adsorption capacity compared to the dry coals, with the reduction being related to the moisture content. Mineral matter acted as a simple diluent to the gas adsorption capacity of the coals and was found to be nonadsorbent. Adsorption capacity (moist) was reduced by 0.32 cm3/g (10 ft3 gas/t) for every 1% increase in the ash yield.\ud \ud Bright and dull coal lithotypes showed strong separation in their adsorption capacities on an as analyzed basis, with the bright coals adsorbing greater quantities of gas. On a dmmf basis, however, no relationship was observed between coal type and gas storage capacity. Comparison of maceral composition with adsorption capacity (dry) confirmed this observation.\ud \ud Effective diffusivity (De) of methane through the coal was seen to be affected by coal type and rank. Effective diffusivity, De, decreased as rank increased, which is related to the increasing microporous nature of the coal. Bulk coals tested had 2-3 times larger effective diffusivities than bright coals, and dull coals had intermediate rates. The larger De values for the bulk coals may be related to the presence of collodetrinite coupled with mineral matter, which acts as higher permeability pathways for the gas compared with the high-ash dull coals dominated by inertinite macerals.\ud \ud Differences were noted with similar-age (Permian) Australian coals, where methane adsorption capacities were larger and coal type had a stronger influence on adsorption capacity

Facies architecture and depositional dynamics of the Upper Permian Rangal Coal Measures, Bowen Basin, Australia

The Upper Permian Rangal Coal Measures in the northern Bowen Basin, Australia, accumulated during rapid basinal aggradation in a retroarc foreland basin setting. They reflect peatland deposition towards the close of a long-lived climatic regime that came to an abrupt termination at the Permian-Triassic boundary, which is well developed in the Newlands mine highwall and adjoining borefield. Six lithofacies are represented in the Newlands district: (1) erosionally based, vertically stacked, ribbon and sheet-like sandstone bodies (up to 30 m thick and 1000 m wide); (2) heterolithic lobes and wedges; (3) interbedded siltstone and sandstone sheets; (4) interlaminated claystone and coal stringers; (5) laterally extensive bituminous coal sheets; and (6) laterally extensive laminated carbonaceous siltstone sheets. This facies assemblage is interpreted to correspond to six alluvial, cold-climate depositional environments: (1) trunk river channels and crevasse feeder channels; (2) levee bank-proximal crevasse splay; (3) distal splay-overbank; (4) marsh; (5) peat mire and (6) floodbasin lake, respectively. The sequence architecture at Newlands reveals that a prolonged period of peat deposition was progressively terminated by northward-stepping lobes of fluvial sediment in the south and by lacustrine drowning in the north. Exceptionally well developed, composite, elongate crevasse splay microdeltas, up to 26 m thick and >3000 m long, indicate that crevassing was responsible for the localized emplacement of thick sediment packages on the proximal floodplain. In the absence of active siliciclastic sedimentation, peat mire environments expanded from the distal floodplain, extending across abandoned depositional lobes. The geometry of these deposits reflects in large part accommodation space developed by the compaction of the peat precursor of the thick and laterally extensive Upper Newlands Seam. Sequential compaction of peat by clastic overburden controlled the nucleation and location of succeeding clastic packages. The behavior of the peat under compactional load largely controlled the lateral facies mosaic and stacking pattern of depositional units on a district scale

Inertinite-rich tertiary coals from the Zeya-Bureya Basin, Far Eastern Russia

Selected Tertiary coals from the Zeya–Buryea Basin, Far Eastern Russia, were investigated for aspects of their coal type, rank, depositional environment and post-depositional history. The coals have been examined in outcrop (lithotype logging), microscopically (maceral, reflectance and fluorescence), and geochemically (proximate analysis).\ud \ud Two laterally extensive coal-bearing horizons occur: one of Palaeocene age and the other of early Miocene age. The Palaeocene coals were investigated in active open-cut mines at Raichikhinsk and Yerkovtsi and the early Miocene deposit in an abandoned open-cut mine at Cergeyevka.\ud \ud Palaeocene coals at Raichikhinsk and Yerkovtsi were indistinguishable from each other macroscopically, microscopically, and geochemically. The deposits were sufficiently coalified that brightness logging could be undertaken. Dull coals, with numerous fusainous wisps, were dominant. Four dulling-up sequences, which represent stacked peat deposits, were observed at Raichikhinsk. At Yerkovtsi, only a small section of the middle of the seam, which was mostly dull and muddy coal, was investigated. Petrographically, these coals were dominated by inertinite group macerals, which is unusual in non-Gondwanan coals and rare in the Tertiary. Rank classification was problematic with volatile matter (VM) content of vitrain (daf), macroscopic appearance, and microscopic textures suggesting subbituminous B rank, but carbon content, moisture content and specific energy indicating a lignite rank.\ud \ud Notwithstanding complications of rank, estimates of the maximum-range burial depths were calculated. Taking the VM (daf) content of vitrain as 48%, burial depth estimates range from 900 m for a high geothermal gradient and long heating time to a maximum of 3300 m for a low geothermal gradient and short heating time. These estimates are maxima as the coal rank may be lower than implied by the VM.\ud \ud The Cergeyevka deposit is a soft brown coal. Limited sampling of the upper-most portion indicated a high moisture content (75% daf) and an unusual, hydrogen-rich geochemistry. Lack of identifiable liptinites using either reflected light or fluorescence microscopy suggested a significant bituminite component. Otherwise, the coals appear to be typical for the Tertiary. An estimate of 125 m maximum burial depth was obtained using the bed-moisture content of the coal, which is around the present burial depth.\ud \ud Comparison of present-day thicknesses with inferred burial depths suggests that at least 500 m of section is missing between the Palaeocene coals and the early Miocene coals.\ud \ud Palaeoenvironmental considerations suggest that fire played a significant role in the accumulation of the peats at Raichikhinsk and Yerkovtsi. At Cergeyevka, peat accumulation ended by drowning of the mire.\ud \ud Two tuff beds were recognised within the seam at Raichikhinsk and one in the seam at Yerkovtsi. Correlation of the tuff beds is uncertain but they should prove useful in regional coal seam correlation and interpreting coal depositional environments. Geochemical analysis by XRF was complicated by high loss-on-ignition (LOI) values. Despite extensive alteration, an acid igneous source is implied from the presence of free quartz and TiO2/Al2O3 ratios of 0.02 to 0.05

Testing reproducibility of vitrinite and solid bitumen reflectance measurements in North American unconventional source-rock reservoir petroleum systems

An interlaboratory study (ILS) was conducted to test reproducibility of vitrinite and solid bitumen reflectance measurements in six mudrock samples from United States unconventional source-rock reservoir petroleum systems. Samples selected from the Marcellus, Haynesville, Eagle Ford, Barnett, Bakken and Woodford are representative of resource plays currently under exploitation in North America. All samples are from marine depositional environments, are thermally mature (T \u3e445 °C) and have moderate to high organic matter content (2.9–11.6 wt% TOC). Their organic matter is dominated by solid bitumen, which contains intraparticle nano-porosity. Visual evaluation of organic nano-porosity (pore sizes \u3c 100 nm) via SEM suggests that intraparticle organic nano-pores are most abundant in dry gas maturity samples and less abundant at lower wet gas/condensate and peak oil maturities. Samples were distributed to ILS participants in forty laboratories in the Americas, Europe, Africa and Australia; thirty-seven independent sets of results were received. Mean vitrinite reflectance (VR ) values from all ILS participants range from 0.90 to 1.83% whereas mean solid bitumen reflectance (BR ) values range from 0.85 to 2.04% (no outlying values excluded), confirming the thermally mature nature of all six samples. Using multiple statistical approaches to eliminate outlying values, we evaluated reproducibility limit R, the maximum difference between valid mean reflectance results obtained on the same sample by different operators in different laboratories using different instruments. Removal of outlying values where the individual signed multiple of standard deviation was \u3e1.0 produced lowest R values, generally ≤0.5% (absolute reflectance), similar to a prior ILS for similar samples. Other traditional approaches to outlier removal (outside mean ± 1.5*interquartile range and outside F10 to F90 percentile range) also produced similar R values. Standard deviation values \u3c 0.15*(VR or BR ) reduce R and should be a requirement of dispersed organic matter reflectance analysis. After outlier removal, R values were 0.1%–0.2% for peak oil thermal maturity, about 0.3% for wet gas/condensate maturity and 0.4%–0.5% for dry gas maturity. That is, these R values represent the uncertainty (in absolute reflectance) that users of vitrinite and solid bitumen reflectance data should assign to any one individual reported mean reflectance value from a similar thermal maturity mudrock sample. R values of this magnitude indicate a need for further standardization of reflectance measurement of dispersed organic matter. Furthermore, these R values quantify realistic interlaboratory measurement dispersion for a difficult but critically important analytical technique necessary for thermal maturity determination in the source-rock reservoirs of unconventional petroleum systems. max o o o