Coal Macerals Research Articles

Distribution of Germanium in Coals of the Pavlovsk Deposit

The concentration and distribution of germanium in coals from the Spetsugli section of the Pavlovsk brown coal deposit in Primorskii krai was studied using mass spectrometry and laser microanalysis. The maximum concentrations of germanium in low-ash coals were established. The distribution of germanium in the vitrinite group macerals of coals and in mineral impurities was studied. A conclusion on the accumulation of germanium in coals at the stage of ancient peat accumulation was made.

FTIR spectroscopic features of the pteridosperm Ruflorinia orlandoi and host rock (Springhill Formation, Lower Cretaceous, Argentina)

Ruflorinia orlandoi (Pteridospermophyta) fronds are chemically analyzed for the first time by semi-quantitative Fourier transform infrared (FTIR) spectroscopy. This analysis allows the chemical characterization of the mesophyll and cuticle revealing the functional groups preserved in different frond parts (pinnae and rachis). The specimens collected in the Springhill Formation at the Río Correntoso locality (Lower Cretaceous, Santa Cruz province, Argentina) are compressions with very well-preserved cuticular features. The R. orlandoi remains (pinnae and rachis) are spectroscopically analyzed into two samples: compressions (Cp) and cuticles (Ct). Additionally, a third sample form from the host rock and named associated coal (V) is spectroscopically analyzed. Semi-quantitative data derived from Cp, Ct, and V spectra are evaluated by principal component analysis. The results indicate that Cp samples have a similar chemical composition whereas Ct samples show a greater variability. The latter could be related to intraspecific variability of foliar characters (e.g., trichomes and cuticular striations). Furthermore, Ct samples exhibit high contents of aromatic carbon groups suggesting a distinctive composition, likely including cutin/cutan biomacropolymers and/or phenolic compounds. Considering each specimen, the rachis shows a higher aromatic carbon content than pinnae as a consequence of the presence of more lignified tissues in the former. The V samples have the lowest relative intensity of aliphatic groups. On the other hand, the functional-group composition of R. orlandoi remains and V samples are compared with kerogen types and coal macerals showing a general chemical composition similar to type II kerogen. The latter is related to cuticles, spores, pollen grains, and resins.

Chemical imaging of coal in micro-scale with Raman mapping technology

Raman mapping and petrography analysis of three two-dimensional planes including typical coal macerals in a lignite were done and coupled. The self-correlations between Raman spectral parameters and the relationship between Raman spectral parameters and random reflectivity (Rf) of coal maceral particles were set up. The results indicate that the area ratio of D band to G band (AD/AG) and intensity ratio of D band to G band (ID/IG) should not be equal, and they were not well related to Rf of coal maceral particles. Good self-correlations between full width at half maximum intensity of G band (G FWHM), the total area of first-order Raman spectrum (SAll) and fluorescence interference degree defined as drift coefficient α were found. G FWHM, SAll and α are also well related to Rf and can act as good indicators for chemical structure characteristics of coal maceral particles. With the increase of Rf, the relative amount of polyolefin, small aromatic rings, C–H, C-O, O–H etc. substitutional groups in vitrinite and liptinite decreases drastically, while the increase of aromatic ring size mainly takes place in inertinite. Chemical imaging of two-dimensional coal planes at a very high resolution was realized by drift coefficient α, and reproduction of the distribution of coal macerals in micro-scale is reasonable. The Raman mapping technology developed can be further used to deeply study the chemical structures of detailed coal macerals. This study can be further extended for rapid identification and detection of coal macerals by micro-Raman spectroscopy.

The Classification of Inertinite Macerals in Coal Based on the Multifractal Spectrum Method

Considering the heterogeneous nature and non-stationary property of inertinite components, we propose a texture description method with a set of multifractal descriptors to identify different macerals with few but effective features. This method is based on the multifractal spectrum calculated from the method of multifractal detrended fluctuation analysis (MF-DFA). Additionally, microscopic images of inertinite macerals were analyzed, which were verified to possess the property of multifractal. Simultaneously, we made an attempt to assess the influences of noise and blur on multifractal descriptors; the multifractal analysis was proven to be robust and immune to image quality. Finally, a classification model with a support vector machine (SVM) was built to distinguish different inertinite macerals from microscopic images of coal. The performance evaluation proves that the proposed descriptors based on multifractal spectrum can be successfully applied in the classification of inertinite macerals. The average classification precision can reach 95.33%, higher than that of description method with gray level co-occurrence matrix (GLCM; about 7.99%).

Perchloroethylene (PCE) adsorption on coal macerals as derived from micro-FTIR spectroscopic analysis and mapping of the C=C bonds from PCE

ABSTRACT Organic liquids are used to prepare the density medium to produce clean coal composites for coal quality and coking test evaluations during the coal exploration stage. Perchloroethylene (PCE) is commonly used as a density medium for this procedure; however, it has been shown before that PCE affects Gieseler Fluidity and Ruhr Dilatation indices of coal, as well as the quality of the resulting coke. It was also found that PCE has a negative effect on the coking properties of coals with a high inertinite content. This paper investigates the adsorption of PCE on various coal maceral surfaces using micro-Fourier Transform Infrared Spectroscopy (micro-FTIR) analysis to observe the changes in the absorbance of the double carbon bond C = C (C = C absorbance peak is used as a marker to indicate the presence of PCE) before and after PCE was applied onto their surfaces. The micro-FTIR mapping of absorbance intensity of the C = C bond on coal macerals showed an increasing trend in the presence of these bonds on the surface of all macerals with the time after exposure to the PCE. The SEM- energy-dispersive X-ray spectroscopy was used to analyze the composition of minerals associated with fusinite and semifusinite, as they were filling the pores in these macerals.

Strain-Induced Graphitization Mechanism of Coal-Based Graphite from Lutang, Hunan Province, China

Anthracite and coal-based graphite (CBG) samples were collected at varying distances from a granite intrusion. Optical microscopy, X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structural evolution of CBG at different scales. The results indicated differences in the graphitization rates of coal macerals and crystallization degree of different graphite-like particles. Differentiated graphitization of coal was caused by deformation, which led to the discontinuous distribution of CBG. This indicates that samples located at the same distance from the intrusion were graphitized to different degrees or that CBG with a similar graphitization degree occurred at varying distances from the intrusion. A possible mechanism for graphitization is strain-induced graphitization, where the local stress concentration leads to preferred orientations of the basic structure units (BSUs), as well as the motion and rearrangement of structural defects, resulting in the formation of a locally ordered structure. The graphitization degree is enhanced as the local graphite structure spreads.

Coal seam development characteristics and distribution predictions in marginal sea basins: Oligocene Yacheng Formation coal measures, Qiongdongnan Basin, northern region of the South China Sea

Coal measures located in marginal sea basins are important hydrocarbon source rocks. For the purpose of effectively guiding future oil and gas exploration, the characteristics and distribution patterns of coal seams in coal measures of a marginal sea basin are systematically outlined. Coal measures in marginal sea basins can have large thicknesses, but the individual coal seams can be very thin and lack lateral continuity. In the study area, the organic micro-components of the coal are dominated by vitrinite, with very low amounts of inertinite and liptinite. The amount of inorganic microscopic components is large, but with limited drilling results, few cores and thin coal seams, which are easily overlooked during logging activities, a comprehensive analysis of the logging data may improve efficiency in coal-seam identification and thickness determination. The development and distribution of coal seams in marginal sea basins are controlled by various factors, including (1) paleoclimatic and paleobotanic conditions, which could fundamentally limit coal formation, (2) coal-forming sedimentary environmental conditions that may limit the scope of coal-seam development from a macroscopic perspective, and (3) paleotectonic and paleotopographic conditions that define the coal-forming structures. Therefore, the descending and rising cycles of base-levels, along with changes in the growth rates of the accommodation spaces, can be used to determine the horizons that are potentially favourable for coal formation and can also indicate the migration trends of coal-forming environments on the structural plane. Seismic wave impedance inversion methods could be utilised for semi-quantitative assistance for prediction of coal seams. In summary, for models of coal-seam development in marginal sea basins, the grades should be divided according to reliability, and the different reliability levels should be predicted separately.The characteristics of coal seams developed in marginal sea basins are described.The macerals of coals developed in marginal sea basins have been ascertained.A development model and distribution prediction method for coal seams are assessed according to the control factors.A model for the prediction of coal-seam distribution is presented.

Difference in structural chemistry of non-coking and coking coal using acid treatment demineralization technique

ABSTRACT Recently, the structural information about non-coking and coking coal has attracted pronounced interest for sustainable utilization of poor coking coal in different industries specifically for steel industry like Tata Steel. In the present work, demineralization techniques via acid treatment (HCl-HF) are effective to remove mineral phase from coal. The difference in carbon chemistry of non-coking (CDPCI), weakly coking (Curragh SS), and prime coking coals (Illawarra and Jamadoba) has been studying through advanced characterization methods like petrography, TGA-DTG, FTIR spectroscopy, X-ray diffraction, Raman, 13C solid-state NMR, FESEM, and TEM. These advanced characterization techniques offer comparative structural information of different coal through the distribution of individual coal maceral and mineral grains with their rank (petrographic study), functional group study along aliphatic-aromatic structural relationship measurement (FTIR), crystalline/graphitic nature of carbon (XRD & Raman) with oxygenated carbon skeletal structural information (Solid State 13C NMR), aromatic-aliphatic cross-linking behavior (FESEM) and their orientation toward lattice fringe structure (TEM).

Impact of tectonic deformation on coal methane adsorption capacity

Tectonic deformation can cause significant changes in the physical and chemical structures of coal by damaging the macrostructure and macromolecular composition. For thorough research on the coal tectonic deformation impacts on gas adsorption capacity, this paper collected and summarized the parameters of experimental adsorption isotherms and coal macerals, conducted proximate and ultimate analyses, and systematically discussed the adsorption properties of different structures of coals and the influence of temperature and pressure on coal adsorption. Furthermore, the semi-quantitative relationships between the structural parameters of coal and its methane adsorption capacity are explored. The results show that (1) due to different tectonic stresses, the molecular and porous structures of different types of tectonic coal exhibit significant differences (e.g. sample N25, which is in a fault zone, has the highest methane adsorption capacity), and (2) coal methane adsorption capacity decreases along with increasing temperature. At a pressure of 12 MPa, primary coal (N32) showed Langmuir volume (VL) values of 15.38, 9.58, and 7.86 cm3/g and Langmuir pressure (PL) values of 3.82, 2.07, and 1.81 MPa at temperatures of 30°C, 50°C, and 70°C, respectively. (3) The Langmuir volume appears to have a linear relationship with parameters ID1/IG, Al/OX, and A-factor, as well as a parabolic curve relationship with fa, thereby illustrating that increases of apparent aromaticity can raise CH4 adsorption on coal.

Chemometric approach to the foliar cuticle of Ptilophyllum micropapillosum sp. nov. from the Springhill Formation (Lower Cretaceous, Argentina)

Ptilophyllum micropapillosum sp. nov. is a new bennettitalean frond recovered from the Lower Cretaceous Springhill Formation, Patagonia, Argentina. The foliar cuticle is herein characterized by means of light and scanning electronic microscopy along with its preserved chemistry. The aim of the chemical study is to reveal mesophyll and cuticle chemical structures (functional groups) preserved in different frond parts (apical, middle, and basal) as well as their relation with kerogen types and coal macerals. Fronds of P. micropapillosum sp. nov. are bipinnate, the abaxial epidermis has different papillae types: (1) abundant, small and simple, (2) scarce compound papillae, and (3) few big simple papillae. For the first time, plant fossil remains from the Springhill Formation are studied by semi-quantitative Fourier transform infrared (FTIR) spectroscopy. Two sample forms are included: compressions (Cp) and cuticles (Ct). Additionally, the host rock is analyzed through concentrate kerogen and entire rock samples. From these, thermal indices (Ro%, TAI, and VRE) and organic and inorganic matter characterization are derived. Semi-quantitative data (area ratios), derived from the Cp and Ct FTIR spectra, are interpreted by principal component analysis. Results indicate differences between Cp and Ct, revealing a high content of aromatic compounds in P. micropapillosum sp. nov. foliar cuticle. This is most likely attributed to the presence of aromatic monomers in cutin/cutan biomacropolymers. The chemical composition is similar among apical, middle, and basal frond parts. This fact probably implies a distinctive frond construction pattern where the energy investment and the metabolic cost are similar throughout the analyzed fronds.

Influence of depositional environment on coalbed methane accumulation in the Carboniferous-Permian coal of the Qinshui Basin, northern China

Based on analyses of the lithofacies palaeogeography of the Taiyuan and the Shanxi Formations in the Qinshui Basin, the spatial variations of the coal seam thickness, coal maceral composition, coal quality, and gas content, together with the lithofacies of the surrounding rocks in each palaeogeographic unit were investigated. The results show that the thick coals of the Taiyuan Formation are mainly distributed in delta and barrier island depositional units in the Yangquan area in the northern part of the basin and the Zhangzi area in the southeastern part of the basin. The thick coals of the Shanxi Formation are located within transitional areas between delta plain and delta front depositional units in the central southern part of the basin. The Taiyuan Formation generally includes mudstone in its lower part, thick, continuous coal seams and limestones in its middle part, and thin, discontinuous coal seams and limestone and sand-mud interbeds in its top part. The Shanxi Formation consists of thick, continuous sandstones in its lower part, thick coal seams in its middle part, and thin coal seams, sandstone, and thick mudstone in its upper part. From the perspective of coal-bearing sedimentology and coalbed methane (CBM) geology, the lithology and thickness of the surrounding rocks of coal seams play more significant roles in controlling gas content variation than other factors such as coal thickness, coal macerals, and coal quality. Furthermore, it is found that the key factors influencing the gas content variation are the thicknesses of mudstone and limestone overlying a coal seam. At similar burial depths, the gas content of the Taiyuan coal seams decreases gradually in the lower delta plain, barrier-lagoon, delta front, barrier-tidal flat, and carbonate platform depositional units. The CBM enrichment areas tend to be located in zones of poorly developed limestone and well-developed mudstone. In addition, the gas content of the Shanxi Formation is higher in the coals of the delta front facies compared to those in the lower delta plain. The CBM enrichment areas tend to be associated with the thicker mudstones. Therefore, based on the lithologic distribution and thickness of the rocks overlying the coal seam in each palaeogeographic unit of the Taiyuan and Shanxi Formations, the areas with higher gas content are located in the north-central basin for the Taiyuan coals and in the southern basin for the Shanxi coals. Both of these areas should be favorable for CBM exploration in the Qinshui Basin.

The fracture anisotropic evolution of different ranking coals in Shanxi Province, China

This work aims to reveal the relationship between fracture anisotropic characteristics and coal rank by considering aperture, length, intensity, density, spacing and connectivity. In addition, coal component heterogeneity, P-wave velocity, pattern, orientation and anisotropic index were studied. A set of 5 coal samples with varying degrees of coalification from Hedong Coalfield, Huoxi Coalfield and Qinshui Coalfield were used for this study. P-wave velocity tests, microscopy tests and stereomicroscopy tests were applied in this study. Based on the experimental results, the following conclusions were drawn: P-wave velocities present a U-shaped trend with the increaseing coal rank, which in its various directions is ordered X < Y < Z. The results show that the heterogeneity of coal macerals varies with coal rank and can be divided into three stages: rapid increase (0.68% < Ro,avg < 0.97%), rapid decline (0.97% < Ro,avg < 1.28%), and stable stage (1.28% < Ro,avg < 2.61%). The relationship between microfractures and submicrofractures is ‘wane and wax or increase and decrease’. Microfractures and submicrofractures with the coalification increases are U-shaped and inverted U-shaped. The bf/bb ratio initially shows a downward trend and then an upward trend. All of the break points occur near Ro,avg = 1.5%. The X direction has the greatest aperture, followed by the Y direction, and then by the Z direction. Contrary to fracture spacing, submicroscopic fracture length, intensity, and density with increasing coal rank are divided into two stages: rapid increase (0.68% < Ro,avg < 1.73%) and rapid decline (1.73% < Ro,avg < 2.61). The average connectivity of samples (mean values for the X, Y, and Z directions) with the coalification displays a linearity relationship of “y = 7.32x + 38.48”. With the increase in coal rank, the anisotropic fracture characteristics show two forms: inverted U-shaped (aperture) and U-shaped (length, intensity, density, spacing and connectivity).

An investigation of the molecular change in coal maceral concentrates prepared under dimensional heating condition

Three maceral samples with vitrinite content of 88, 77 and 66 vol% (mmf) obtained from an Australian coking coal were investigated to understand the difference in their thermoplastic development. Each sample was packed in a quartz tube and heated from the bottom by a heating plate of which temperature was set to slowly ramp from room temperature to 900 °C. A thermocouple was inserted at 55 mm from the base to monitor the temperature change at this position as heat transferred through via thermal conduction. At the end of the experiment, the thermocouple measured temperatures at 469, 485 and 495 °C for the three respective maceral samples, suggesting a greater thermal gradient existed in samples with higher vitrinite concentration.The heated samples were then analysed by laser desorption/ionization time of flight imaging mass spectrometry (LDI-TOF-IMS) to track the change in molecular weight distribution across the sample length. Significant intensity of ionisable species was recorded in regions close to the thermocouple position for all maceral samples. Samples with higher vitrinite content displayed a greater molecular weight discrepancy (∆m/z) in the plastic region compared to that in samples with lower vitrinite content, indicating a larger molecular variation occurred in these samples.

The characteristic and evolution of coal-forming swamp in Hanshuiquan district, Santanghu Coalfield, Xinjiang, NW China, during the Middle Jurassic: evidence from coal petrography, coal facies and sporopollen

Santanghu Coalfield is the largest integrated coalfield exploration area in China. The major coal seams developing in Xishanyao Formation (Middle Jurassic) are the high-quality steam coals characterized by large thickness, favorable horizontal continuity and high coal quality. In this paper, twenty-two samples were collected from the three typical boreholes in Hanshuiquan district, representing the 11 coal seam sequences (7#, 8#, 9#, 13#, 14#, 15#, 17#, 18#, 19#, 20#, 22#), respectively. The petrographic characteristics of the coal-bearing sequence in Xishanyao Formation were firstly summarized systematicly, and then the coal-forming swamp characteristics and succession mechanism of the coal seam in Xishanyao Formation were defined by analyzing the samples. The maceral composition, structure, geochemical and geophysical characteristics of coal are included in original genetic criteria of coal-forming swamp analysis. And the composition of coal petrography, maceral and microlithotype are the most frequently used parameters. Coal is composed of microscopic constituents and inorganic substances. The Xishanyao Formation maceral mainly consists of vitrinite (65.74%–97.01%), inertinite (1.93%–34%), and the exinite shows the mode of regular change. The coal-forming swamp in Xishanyao Formation possesses the characteristics of mainly marsh, wet forest swamp facies, and shallow water covered forest swamp facies, and a few of coal seams distribute in the deep water covered forest swamp facies. In addition, the sporopollens in Xishanyao Formation are mainly Pinaceae evergreen broad leaf and needle-leaved plants, Osmundaceae, Cyatheaceae and Lygodiaceae, indicating that the warm and humid tropic-subtropical climate conductive to the persistent growth of coal-forming plants in the Middle Jurassic. The coal-forming swamp shows the characteristics of vertically upward fluctuation through the periodic transition. It indicates a shallow-deep-shallow change process of the water covered depth in the swamp. This is the principal factor for the formation of the high-quality and continuous coal seam in Hanshuiquan district, Santanghu Coalfield.

Reflectance increase from broad beam ion milling of coals and organic-rich shales due to increased surface flatness

Broad ion beam (BIB) milling is useful in organic petrology because it can yield flat sample surfaces and avert the ‘smearing’ of organic matter (OM) that results from traditional mechanical polishing. This potentially makes BIB especially useful in the study of nano-porosity, where even minor mechanical disruption of the sample surface distorts the sample characteristic of interest—the pore structure. However, several studies have observed an OM reflectance increase after BIB milling, concluding that ion milling may cause thermal alteration to OM surfaces. To better understand ion milling effects on organic matter, coal (subbituminous, high volatile bituminous, medium volatile bituminous, anthracite) and shale [Bakken Formation, Ohio Shale-Huron Member (5), Kimmeridge Clay Formation, Alum Shale, New Albany Shale] samples were prepared using traditional mechanical polishing methods. Reflectance measurements (% Ro) were gathered on all maceral types present before BIB milling, followed by re-measurement of OM reflectance at the same locations after milling. Most OM increased in reflectance after BIB milling, with some exceptions in high maturity samples. Liptinite macerals in both coal and shale samples showed the greatest percent reflectance increase on average (+133%; n = 338), followed by solid bitumen (+49%; n = 313), vitrinite (+26%; n = 413), and inertinite (+9%; n = 220). Despite the increases to OM reflectance caused by BIB milling, no evidence was found for kerogen conversion (e.g., change in maceral abundances), or for migration of newly generated petroleum (e.g., pseudomorphic replacement of kerogen by solid bitumen). Such changes occur when samples are thermally altered from immature conditions into the oil window (e.g., by hydrous pyrolysis), and, if the increases in OM reflectance were thermally driven (by BIB milling), they should have been observed in the above experiments. Herein, we also used atomic force microscopy to document a decrease in surface roughness of correlative locations of OM on pre- and post-ion milled samples. This improved surface polish caused by BIB milling appears to be the root cause of increased OM reflectance, as no other supporting evidence of thermal alteration could be found. That is, the fraction of light formerly lost to oblique scatter in diffuse reflectance from a mechanically polished surface is converted to specular reflectance after BIB ion milling. Thus the light leaves the surface at a near normal angle and returns to the detector, resulting in increased OM reflectance.

Mechanical testing of anthracite to assess its surface energy and temperature dependence

In order to assess the applicability of mechanical method for testing the surface energy of coal, the surface energy of ten coal specimens of two macroscopic lithotypes (semidull and semibright) with metamorphic degree in anthracite stage and a carbonaceous mudstone specimen from a certain mine were tested and analyzed at different temperatures. The results showed that the measurements of surface energy are affected by the test methods, test temperature, coal macerals and minerals, and coal surface roughness. For coal and rock solid materials with strong heterogeneity, the mechanical method is simpler than the optical method and the error is smaller. The surface energy of coal specimens varies from 22.08 to 28.08 mJ·m−2 at room temperature of 293 K by mechanical method. With the increase of temperature, the surface energy of the specimens decreases linearly, and the coefficient of variation of the measured surface energy of various specimens exponentially increased. The surface energy of carbonaceous mudstone specimen is the largest, followed by semidull coal specimens and semibright coal specimens. In contrast, the order of decrease rate of surface energy with temperature increases is semibright coal, semidull coal and carbonaceous mudstone. The surface energy of the specimens exhibited a negative exponentially decreasing trend as the surface roughness increased. The study results provide a basis for further improving the test methods of the surface energy of heterogeneous solid materials, and the application of engineering methods to improve the extraction efficiency of coalbed methane by changing temperature.

Using δ15N and δ13C and nitrogen functionalities to support a fire origin for certain inertinite macerals in a No. 4 Seam Upper Witbank coal, South Africa

Fires are likely to have been central to the formation of certain inertinite macerals in South African coals. To investigate this hypothesis, a Permian, medium rank C bituminous Witbank coal (No. 4 Seam Upper) was density fractionated to yield an inertinite-rich and a vitrinite-rich sample, and assessed using stable nitrogen and carbon (δ15N and δ13C) isotopes in conjunction with nitrogen functionalities. The parent coal comprises of 41.6 vol% vitrinite and 48.5 vol% inertinite. The vitrinite-rich sample is dominated by collotelinite and collodetrinite (81 vol% vitrinite), and the inertinite-rich sample by fusinite, semifusinite, and inertodetrinite (63 vol% inertinite). The δ15N and δ13C values and nitrogen functionalities were used to constrain early coal formation pathways for the dominant macerals in the density fractionated samples. The vitrinite-rich sample has a lower δ13C relative to the inertinite-rich counterpart. However, the inertinite-rich sample has the lower δ15N value, along with a lower concentration of N-quaternary and higher N-pyrrolic compounds. Because these samples are of the same coal maturity, and the major macerals were derived from similar precursors, differences in δ15N and δ13C and nitrogen functionalities reflect differences in coal formation pathways. Degradation of 13C-rich cellulose in wood through either charring or bacterial activity leads to lower δ13C values. The lower 14N content for the vitrinite-rich sample along with higher N-quaternary and N-pyridinic suggests cellulose degradation driven by bacterial activity. In contrast, the higher 14N coupled with higher N-pyrrolic and N-oxide complexes for the inertinite-rich sample, suggests fusinite and semifusinite were formed through charring. Inertodetrinite is attributed to the disintegration of the charred matter.

Effect of multi-intensification on the liberation of maceral components in coal

In order to achieve high-quality coal resources in western China, this study focused on a coal sample from the Shangwan Coal Mine, owned by the China Shendong Group, and employed scanning electron microscopy (SEM), mineral liberation analysis (MLA), and maceral component quantitative analysis for investigating the coal sample’s liberation characteristics and crack distribution patterns after pre-grading and microwave processing. The results show that the physical properties of coal maceral components significantly affected the related enrichment performances, and many intra-group and inter-group cracks were produced under the induction of microwave radiation. The cracks then developed and stopped growing among the different maceral components and mineral components, thereby inducing selective and random pulverization along the crack growth direction in further pulverization process and effectively enhancing the liberation properties of different components. Using the Sandbox method, the fractal dimension of the cracks on the particle surface was calculated to be 1.01, which confirmed the self-similarity of the cracks on the coal surface. Multi-intensification maceral liberation also yielded favorable grading performances. The inertinite content was the highest (75.23%) in grade-3 product, while the vitrinite content was the highest (66.3%) in grade-1 product; the corresponding enrichment ratios were 2.15 and 1.59, respectively. Moreover, the ash content in grade-2 product was the lowest, which dropped by 3.61% compared with that in raw coal sample.

Study on geological controls and enrichment models of coalbed methane in the Wuwei Basin in eastern North Qilian, northwestern China

The Wuwei Basin is located in the Gansu Corridor, which has abundant coalbed methane resources of 2.75 × 1011 m3. However, a low degree of coalbed methane exploration exists, and only a few wells have been drilled in local regions due to insufficient understanding of coalbed methane enrichment and its main controlling factors. This study analyzed the controlling factors of coalbed methane enrichment, including coal reservoir characteristics, hydrogeological conditions, and the original sedimentary environment of the coal-bearing strata. The results showed that the main coal seams were developed in the Taiyuan Formation, and were mostly concentrated in the Yingpan Sag in the south and the Ermahu Sag in the north of the study area. The macrolithotype of the coals in this basin was mainly semi-bright coal with a medium to high rank. Coal macerals were mainly vitrinite, ranging between 65.1% and 91.6% (averaged 81.70%), followed by liptinite, ranging between 1.9% and 29.5% (averaged 8.82%), and inertinite, ranging between 0.2% and 16.5% (averaged 3.66%). Mineral contents varied from 2.5% to 15.1% (averaged 6.16%). The macrolithotype and microlithotype of the Taiyuan Formation coals were favorable for coalbed methane formation. Through comparative analysis of moisture content, ash yield, gas content, and coal-forming sedimentary environments, it was found that the coal formed in the lagoon environment had a higher gas content and lower ash yield than that of the coal formed in the tidal flat environment. The high contents of total dissolved solids in aquifers around coal seams (1.75–16.70 g/L) reflected the closed hydrodynamic environment and were favorable for the preservation of coalbed methane in the Yingpan Sag. Considering various controlling factors (i.e., structure, sedimentation and hydrogeology), three coalbed methane enrichment models were proposed. The model of coalbed methane enrichment in the synclinorium was the most favorable for the enrichment of coalbed methane in the Yingpan Sag.

Nanoindentation study of macerals in coals from the Ukrainian Donets Basin

Abstract. This article discusses the mechanical properties of macerals in Carboniferous coals from the Ukrainian Donets Basin, covering a maturity range from 0.62 to 1.47 %Rr (vitrinite reflectance). The inherent inhomogeneity of geological samples requires characterization at the micro-/nanoscale, and hence material parameters, such as hardness H and reduced elastic modulus Er, were obtained from twelve coal specimens via nanoindentation tests. Different material properties and maturity trends were acquired for the individual maceral groups (vitrinite, inertinite, liptinite). The results indicate that apart from maturity, multiple factors like microstructural features and depositional environment control the mechanical properties of macerals in coals. H and Er of vitrinites show a complex relationship with maturity due to additional influence of microstructural features such as nanoporosity or mineral inclusions and complex changes in the organic matter structure with increasing rank. The mechanical behaviour of inertinites is mainly controlled by the prevailing conditions (temperature, exposure) during paleo-wildfires. Er and H of liptinites are strongly influenced by transformational processes related to devolatilization at low to medium rank, as well as later hydrocarbon generation. Variations in the depositional environment (e.g. increased organic S content due to marine influence) might play an additional role.