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Considering the urgency of resource utilization and environmental protection, the geochemistry of anomalous trace transition metal elements in coal formed in terrestrial environments has been studied using methods such as inductively coupled plasma atomic emission spectrometry analysis, electron probe micro-area analysis, sequential chemical extraction procedures, and correlation analysis. The results indicate that minerals in the coal samples included pyrite, kaolinite, quartz, dolomite, calcite, and celestite. Furthermore, compared with the average values of coals in China and the upper continental crust, the coal samples were rich in transition metal trace elements such as Ni, Cr, and Sr and were deficient in Be, Cd, Cu, Co, Ga, Mo, Sb, Tl, V, Zn, and Ti. We found that Ni preferentially occurred in the organic matter over minerals, while Cr primarily bonded with sulfide minerals and to a lesser extent with the iron-manganese oxide minerals. Sr had a low correlation with organic matter but adhered to clay minerals and celestite. Ni enrichment in coal samples was the result of terrigenous input, while the Cr enrichment was related to intrusion of magmatic hydrothermal fluids. Sr enrichment was caused by the presence of SO42- in the terrigenous debris and the influence of Sr-rich water underground. [ABSTRACT FROM AUTHOR]

The Ecca equivalent coal deposits in the Morupule, Mmamabula, and Mabesekwa coalfields exist within the Kalahari Karoo Basin of the Karoo Super Group. Only the Morupule coal has proved its potential for power generation; while, the utilization value of the Mmamabula and Mabesekwa coals is yet to be determined. The current study presents petrographical characteristics of the three seams from each coalfield. Reflected light microscopy combined with scanning electron microscopy was used in the study. The analyses revealed that the Morupule and Mabesekwa coals are rich in inertinite; while, the Mmamabula coal is rich in vitrinite. The vitrinite reflectance indicates that the coal rank stretches between high volatile bituminous B and high volatile bituminous A. The compositions of macerals and coal facies indicate variations in the depositional conditions for the three studied coalfields. The Morupule and Mabesekwa coals were accumulated in a terrestrial bedmont dry forest swamp through fluvial vegetation transportation; while, the Mmamabula coal was deposited in a limnic upper plain wet forest swamp through alluvial vegetation transportation. Hydrological conditions were rheotrophic except in the Mmamabula South, which had ombrotrophic conditions. Based on petrographic compositions, coals from the Mmamabula East, Mmamabula South, Morupule East Main, Morupule West Main and Morupule South would be suitable for carbonization, gasification and liquefaction processes. However, several challenges with coals from the Mmamabula South, Mabesekwa Seam B, Mabesekwa Seam C and Mabesekwa Seam E would be encountered during carbonization, gasification and liquefaction due to high ash content and inert semifusinite content. [ABSTRACT FROM AUTHOR]

ABSTRACT The study investigated 50 Permian coals from the Singrauli Coalfields in the Son Valley Basin, India, using advanced petro‐geochemical techniques to assess their source rock properties, energy and utilisation potential and to reconstruct the paleodepositional environment. Petrological analysis indicated vitrinite reflectance values between 0.39% and 0.49%, classifying the Singrauli coals as sub‐bituminous to high volatile bituminous rank and indicating a thermally immature state. The results of geochemical analysis (volatile matter: 36.8%–46.5% and Tmax: 420°C–425°C) further support the above contention. High carbon content (average 77.89%), low sulphur content (average 0.46%) and varying nitrogen and oxygen levels in studied coal enhance its environmental suitability. The hydrogen index (HI: 163–279 mg HC/g TOC) values suggest a predominance of type‐III kerogen with mixed type‐II–III kerogen, further supported by petrographic data. Moreover, geochemical and petrographic data suggested the suitability of Singrauli coals for gasification. The high total organic carbon (TOC ≥ 38 wt%) indicated admirable potential as a source rock for hydrocarbon generation, particularly within the gas‐source rock zone, highlighting their suitability for energy production. Petrographic indices indicated a wet forest swamp origin with a telmatic source and bog region under ombrotrophic to mesotrophic hydrological circumstances. The association of macerals and total sulphur content further supported the conclusion of a freshwater environment during peat deposition. [ABSTRACT FROM AUTHOR]

Differences in the pore and fracture systems of four marcolithotypes (bright，semi‐bright, semi‐dull and dull) in coal reservoirs affect the quality of coalbed methane (CBM) and constrain exploration and development of CBM. In this paper, vitrinite reflectance (RO), maceral composition, proximate analysis, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), low‐field nuclear magnetic resonance (NMR) and high‐pressure isothermal adsorption experiments and the mathematical method of fractal dimension were carried out on high‐rank coal samples of different marcolithotypes from the Weizhou mining area in the western margin of Ordos Basin. The results show that from bright coal to dull coal, the RO and vitrinite content gradually decrease, while the mineral content and Aad gradually increase. SEM images show that the bright and semi‐bright coals develop open fractures, whereas semi‐dull and dull coals develop closed fractures. According to pore size distribution established by MIP and NMR, the proportion of seepage pores gradually increased from bright coal to dull coal, and MIP fractal dimension of seepage pores (DM2; 2.3352, 2.3532, 2.3755 and 2.4727, respectively) and NMR fractal dimension of seepage pores (DN2; 2.8767, 2.9142, 2.9297 and 2.9981, respectively) show that the structure of the seepage pore is progressively more complex from bright coal to dull coal. In addition, percentage of NMR adsorption pores progressively increases from bright coal to dull coal (64.96%, 76.64%, 82.04% and 89.67%, respectively), but total porosity of bright coal (6.74%) is much greater than that of dull coal (1.34%), which results in that bright coal also has the strongest CH4 adsorption capability (Langmuir volume is 22.898 cm3/g). [ABSTRACT FROM AUTHOR]

Efficient enrichment of macerals improves the liquefaction efficiency of low-rank coal. The paper studied the characteristics of Shendong low-rank coal, including proximate and ultimate analyses, size and density compositions, and petrographic analysis, as well as the migration regularity of narrow particle size of low-rank coal macerals in the enhanced gravity field. On this basis, a novel classification separation process for low-rank coal macerals using Krebs hydrocyclone and enhanced gravity separator was proposed. The classification size was determined to be 0.074 mm and Krebs hydrocyclone achieved a satisfactory classification effect with a classification efficiency of 84.72%. Based on the enhanced gravity separation results of macerals from hydrocyclone underflow and overflow, the optimal sorting solutions for underflow and overflow were obtained through response surface analysis, respectively. Through the novel classification separation process, the vitrinite content of clean coal has been increased from 46.60% to 61.33% with an outstanding recovery of 77.40%. The novel classification separation process using hydrocyclone and enhanced gravity separator develops an excellent enrichment effect for low-rank coal macerals, which also provides a prospective approach for the cleaner utilization of low-rank coal. [ABSTRACT FROM AUTHOR]

The Carboniferous-Permian coal measure strata in the Qinshui Basin exhibit highly lithium (Li) enrichment, with substantial exploitation potential. To further explore the enrichment mechanism of lithium in coal measure strata, the No. 15 coal of the Taiyuan Formation from the Gaoping mine is taken as the research object, and its mineralogical and geochemistry characteristics are evaluated using optical microscopy, X-ray diffraction, scanning electron microscopy, inductively coupled plasma mass spectrometry, X-ray fluorescence, and infrared spectral. The results show that the No. 15 coal is semi-anthracite coal with low moisture, low ash, low volatility, and high sulfur. Organic macerals are primarily vitrinite, followed by inertinite, and liptinite is rare; the inorganic macerals (ash) are dominated by clay minerals (predominantly kaolinite, cookeite, illite, and NH4-illite), calcite, pyrite, quartz, siderite, gypsum, and zircon. The average Li content in the coal is 66.59 μg/g, with higher content in the coal parting (566.00 μg/g) and floor (396.00 μg/g). Lithium in coal occurs primarily in kaolinite, illite, cookeite, and is closely related to titanium-bearing minerals. In addition, Li in organic maceral may occur in liptinite. The No. 15 coal was formed in the coastal depositional system, and the deposition palaeoenvironment is primarily a wet–shallow water covered environment in open swamp facies; the plant tissue preservation index is poor, and aquatic or herbaceous plants dominate the plant type. The reducing environment with more terrestrial detritus, an arid climate, and strong hydrodynamic effects is favorable for Li enrichment in coal. The results have important theoretical significance for exploring the enrichment and metallogenic mechanisms of Li in coal. [ABSTRACT FROM AUTHOR]

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The application of the hydrodynamic method has enhanced the extraction of coal bed methane (CBM). In this method, fracturing fluid rapidly penetrates the coal reservoir, altering its intrinsic pore structure and microscopic mechanical properties. These changes impact the properties of the coal reservoir and CBM depletion. It is, therefore, crucial to explore how these micro-characteristics evolve following water invasion. In this context, using nanoindentation tests, the microscopic characteristics of three coal samples were measured under dry conditions and at water saturations corresponding to 44% and 75% relative humidity. The influence of water immersion on the pore structure was also assessed using mercury injection experiments. Moreover, cluster analysis was used to categorize the extensive measured data into three sub-components: fractures (large pores), inertinite, and vitrinite, to investigate the impact of water saturation on microscopic properties. The findings indicate that cluster analysis is well-suited to these data, showing excellent agreement with porosity and maceral tests. The relationship between the elastic modulus and hardness of dry and wet coal samples varies across the sub-components. There is a notable dependency in the case of vitrinite, whereas water content tends to reduce this dependency. It is also found that water content negatively affects elastic modulus and hardness and reduces the anisotropy ratio. The mechanical properties of inertinite are highly responsive to water immersion, whereas vitrinite exhibits lesser sensitivity. The softening mechanisms of coal when immersed in water, such as calcite phase dissolution, swelling stress fracturing, and weakening of macerals, are identified. This study offers new perspectives on the impact of moisture on the alteration of micromechanical properties in coal. [ABSTRACT FROM AUTHOR]

In this study, the compositional, structural, mineralogical and thermal characterisation of the newly discovered Duduguru (DDG) coal from Nasarawa State was conducted to examine its fuel and energy utilisation potentials. The compositional examination involved elemental, proximate, and calorific analyses, whereas microstructure/morphology and mineralogy were determined by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX), respectively. The thermal examination involved heating the pulverised DDG coal from 25-900 °C using air (flowrate ɸ = 20 mL/min) to examine its combustion characteristics. Results revealed DDG contains high carbon (>60 wt.%) and hydrogen (>5 wt.%), fixed carbon (>52 wt.%) and higher heating value (>28 MJ/kg) but relatively low nitrogen (< 1.5 wt.%) and sulphur (<1 wt.%) contents. TGA revealed that DDG experienced significant thermal degradation, resulting in high weight loss (~83%) and low residual mass (~17%). Weight loss was ascribed to the degradation of macerals in DDG. The TG plot indicated onset, midpoint, and offset temperatures of 335.54°C, 538.72°C, and 708°C, respectively. The DTG plot revealed thermal degradation occurred in two major phases: stage I (25-200°C) and stage II (200-900°C), which was ascribed to drying/low-temperature degradation and macerals degradation, respectively. Overall, the findings demonstrate that the newly discovered DDG coal is suitable for energy recovery and utilisation in future power plants. Future studies could investigate the kinetic and thermodynamic properties of DDG coal often required in reactor design and optimisation for energy generation. [ABSTRACT FROM AUTHOR]

The hydrocarbon generation potential of the Campano-Maastrichtian to Paleogene shales from the Benin Flank (located in SW Nigeria) of the Anambra Basin, has been previously investigated mostly by studying outcrops and by relatively few subsurface data-based studies. Thus, it is expedient undertaking an assessment of the hydrocarbon generation potential of this frontier area from subsurface samples. Campano-Maastrichtian to Paleogene shale samples obtained from Egoli-1 borehole in the Benin Flank of the Anambra Basin are studied by means of HAWK programmed pyrolysis, organic petrography, and mineralogy (XRD), with the aim to explore the petroleum-generating potential and the thermal maturity. The obtained results display a significant variation of the TOC content ranging from very low (<0.5%) to significant (>5%), indicating poor to excellent oil potential based on S2 values under the condition, of course, the studied formations reached the oil window. The shales of the Nsukka and Imo Formations display lower petroleum-generating potential than these of the Mamu Formation. All the studied samples are dominated by gas-prone (type III) and inert (type IV) kerogens, with few displaying mixed II/III (oil- and gas-prone). The organic-petrography observations support partly the results of the HAWK programmed pyrolysis, as they reveal an organic-richer Mamu Formation in comparison to the Nsukka and Imo Formations; huminite/vitrinite particles (both indigenous and recycled) along with variable contents of liptinite (mostly alginite and bituminite) and inertinite macerals (mostly inertodetrinite) are hosted in the shales. The latter display a typical composition for fine-grained clastic sediments; mostly kaolinite, illite/montmorillonite, quartz, and subordinately, anatase. In terms of thermal maturity, huminite/vitrinite reflectance data points to immature stage; however, the occurrence of solid bitumens, displaying equivalent vitrinite reflectance values within the oil window, points to an active petroleum system in sequences deeper than the examined ones. [ABSTRACT FROM AUTHOR]

Geochemical analysis was performed on the Cretaceous sequence of the Azhar‐A‐2 well in the West Beni Suef Basin (WBSB), Western Desert, Egypt, utilizing data on total organic carbon (TOC), kerogen composition, vitrinite reflectance (Ro%) and Rock‐Eval pyrolysis. In addition, a 1D basin model was built to investigate the burial and temperature history of the study area. The most important Cretaceous source rocks are predominantly reported within the Albian Kharita Formation and Late Cenomanian‐Santonian Abu Roash (AR) Formation. Based on visual kerogen tests and Rock‐Eval pyrolysis, AR Formation (A, E, F, and G) are mixed oil‐ and gas‐prone source rocks with kerogens ranging from type II to type III, where A/R 'A and F' Members show dominant oil‐prone kerogen with the highest generative potential, while A/R 'E and G' Members are more gas‐prone kerogen. Most samples of the lower Kh Formation were interpreted as gas‐prone kerogen type III with low generative potential. On the other hand, the high amount of liptinite in the visual kerogen macerals is a strong indicator that the lower Petroleum Formation is an oil‐prone rather than gas‐prone source rock. The thermal maturity of the studied members increases consistently with depth, ranging from immature at the top of the AR Formation to the main/peak oil window at the base of the Lower Kharita Formation, which served as an active source rock for the hydrocarbons generated in the WBSB. The high value of the heat flow in the Beni Suef Basin (57 and 60 mW/m2) is a good indicator for the shallowing of the active source rock depth limit depth. From the study of the basin modeling, the main mature zone reached between 9811 and 11,090 ft in the middle of the Late Cretaceous (84.3–82.5 Ma) is through the L. Kharita Formation with three phases of hydrocarbon generation according to transformation ratio, where the second phase is the main stage in which TR is 5%–50%, showing the beginning of oil expulsion (Ro: 0.73%–0.78%, possibly 0.81%). [ABSTRACT FROM AUTHOR]

The consumption of coals without coking properties in coal blends for coke production is a challenge, precisely because of their lack of coking properties, and in some cases, high contents of macerals from the inertinite group, which are known to contribute to a reduction in the mechanical strength of coke when present in high size dimensions. With the constant search for the use of non-coking coal in the coal blends, the main objective of the study was to investigate the effect of increase inertinite-rich coal content in multi-component coal blends. To achieve this, selective crushing was performed to obtain 1.5 mm as the critical inertinite size for the coke’s mechanical strength, decreasing the amount of microcracks at the boundary between reactive maceral-derived components (RMDC) and inert maceral-derived components (IMDC). The microstructural characterization for the industrial metallurgical coke was studied using optical microscopy associated with image analysis (ImageJ software). It was established that a 25 % content of inertinite-rich coal addition in the blend caused systematic changes in the coke’s microstructural features, decreasing the mechanical strength. Additionally, the segmentation between RMDC and IMDC was studied to achieve better correlation from the coke’s microstructural parameters, predicting mechanical strength (DI150/15). A new equation was proposed describing both microstructural features from reactive and inert components. [ABSTRACT FROM AUTHOR]

Salinized lacustrine shale (SLS) represents a frontier in the global quest for unconventional hydrocarbon resources. The impact of terrigenous input, which includes terrigenous organic matter (OM) and detrital matter, on the deposition and hydrocarbon potential of SLS is still controversial. Here, we examine this issue using the newly discovered SLS within the Paleogene Biyang Depression, employing a combination of organic petrographic and geochemical analyses. A high influx of terrigenous input (terrigenous OM and detrital matter) promotes the formation of SLS. On the one hand, terrigenous higher plants emerge as the primary source of OM in the SLS, as indicated by the dominance of terrigenous macerals (e.g., terrigenous liptinite) and the abundance of plant-derived biomarkers (e.g., tricyclic terpanes). Additionally, a portion of the OM may originate from bacteria. On the other hand, the rapid input of detrital matter improves the preservation of OM, resulting in the deposition of SLS with high total organic carbon (TOC) contents and low hydrogen index (HI) values. The findings of this study contribute to a deeper understanding of SLS deposition and provide guidance for regional hydrocarbon exploration. [ABSTRACT FROM AUTHOR]

Two hundred and fifty single first-order Arrhenius reactions are simulated to generate S2 pyrograms at three heating rates 25, 15, and 5 °C·min−1. The activation energy (E) and pre-exponential factor (A) of the reactions simulated follow a long-established trend of those variable values displayed by shales and kerogens. The characteristics of the transformation fraction (TF) profiles (product generation window temperatures) of the simulated single reactions are compared to the TF profiles of recorded shale pyrograms generated by multiple reactions with different E-A values lying near the defined E-A trend. Important similarities and differences are observed between the TF profile values of the two datasets. The similarities support the spread of E-A values involved in shale pyrogram best fits. The differences are most likely explained by the complexity of the multiple kerogen first-order and second-order reactions contributing to the recorded shale pyrograms versus the simplicity and crispness of the single first-order reactions simulated. The results also justify the validity of using the previously described "variable E-A pyrogram-fitting method" of multi-heating-rate shale pyrograms enabling optimizers to choose multiple reactions from an unlimited range of E-A values. In contrast, further doubt is cast on the validity of the constant-A pyrogram-fitting method used by the Easy%Ro technique, in that a distribution of reactions with a single A value is unlikely to represent the complex variety of kerogen macerals observed in shale formations. TF profiles generated by the variable E-A pyrogram-fitting method lie close to the established E-A trend and are likely to provide more realistic TF generation window temperatures than TF profiles generated by the constant-A pyrogram-fitting method. [ABSTRACT FROM AUTHOR]

There is a lack of published literature on coal deposits in Madagascar. The Imaloto Basin is a sub-basin of the Morondava Basin, Southwestern Madagascar, and hosts the Sakoa Coal Measures. The aim of this study was to increase our understanding of the petrography, geochemistry, and mineralogy of coal deposits hosted in the Imaloto Basin. Three coal seams (from the bottom: Main Seam, Upper Seam, and Top Seam) were intersected during a drilling program conducted by the Lemur Holdings in 2019. Coal samples were characterized using organic petrography (type and rank determination); the ash chemistry was assessed (XRF), and the mineralogy was considered using X-ray diffraction. The depositional environment at the time of peat accumulation was considered. The Main Seam samples are of better quality compared to the Upper Seam and Top Seam samples in terms of calorific value (CV) and ash yield. The coals are borderline Sub-bituminous Low Rank A to Bituminous Medium Rank D. An abundance of inertinite macerals was determined in the Main Seam, while the Upper and Top Seams are more vitrinite-rich. An unusual mineral, possibly albite or analcime, was determined in samples with a high Na content. The Imaloto coal samples show varied depositional settings (dry forest swamp, wet forest swamp, and piedmont plain), which influences coal quality. [ABSTRACT FROM AUTHOR]

The porosity characteristics of coal seams serve as a pivotal factor in assessing the development potential of coalbed methane (CBM) resources, significantly influencing the adsorption and permeability capabilities of coal reservoirs, as well as the accumulation, entrapment, and preservation of CBM. In this study, we focused on the coal seams of the Xishanyao Formation in the western part of the southern Junggar Basin (NW China). By leveraging the complementarity of nuclear magnetic resonance (NMR), low-temperature liquid nitrogen experiments, and high-pressure mercury intrusion porosimetry (MIP) in spatial exploration range and precision, we conducted a comprehensive analysis to achieve a fine description of porosity characteristics. Furthermore, we explored the coal petrology factors controlling the pore characteristics of the Xishanyao Formation, aiming to provide geological evidence for the selection of favorable areas and the development potential evaluation of CBM in the study area. The results indicate the following: (1) The total pore volume of the coal samples is 6.318 × 10−3 cm3/g on average, and the micropore volume accounts for a relatively high proportion (averaging 44.17%), followed by the fine pores (averaging 39.41%). The average porosity is approximately 3.87%, indicating good gas storage and connectivity of the coal seams, albeit with some heterogeneity. The coal reservoir is dominated by micropores and fine pores with diameters less than 100 nm, and the pore structure is characterized by low pore volume and high pore area. (2) The pore structure is influenced by both the coalification degree and the coal maceral. Within the range of low coalification, porosity increases with the increase in coalification degree. Building upon this, an increase in the vitrinite content promotes the development of micropores and fine pores, while an increase in the inertinite content promotes the development of meso–macropores. The clay mineral content exhibits a negative correlation with the adsorption pore volume ratio and a positive correlation with the seepage pore volume ratio. [ABSTRACT FROM AUTHOR]

The Bozburun coalfield hosts a late Miocene 1.1 m thick coal seam. This study aims to determine coal quality, mineralogy, petrography and geochemistry, and controlling factors of elemental enrichments. The coals are generally black and greyish black in colour, and the low part of the seam commonly includes fossil shell remains. The ash yield displays a decreasing trend towards the upper part of the seam; in turn, gross calorific and total C values increase upwards. The total S content being generally higher than 5% (on dry basis), displays an increasing trend towards the upper part. In the entire seam, huminite is the most common maceral group, while inertinite and liptinite display variable proportions. The identified minerals by XRD are mainly quartz, clay minerals, calcite, pyrite, and aragonite (in fossil shell remains-bearing samples), whereas feldspars and marcasite determined in a few samples. Furthermore, in the coal samples, celestine and barite were identified by SEM-EDX. This study indicates that precipitation of celestine and Sr-bearing barite grains during diagenetic stage and Sr-uptake by mollusc within the palaeomire caused Sr enrichment in the entire seam. Overall, the water influx and redox conditions controlled the mineralogical and the elemental compositions of the coal seam.

In this paper, based on a geochemical study of rock samples and fluids, it is proven that carbon-bearing deposits of the Lower and Middle Jurassic complex of Western Siberia on the southern outskirts of the Khanty-Mansiysk and Yamalo-Nenets Autonomous Okrug can generate liquid hydrocarbons. It has been established that the oil-generation potential of carbon-bearing deposits depends on the paleogeographic conditions of burial of the organic matter and the enrichment of rocks with macerals of the liptinite group. The complex of studies included pyrolysis of coals, coal-rich shale of Lower and Middle Jurassic rocks, study of maceral composition and measurement of reflectivity indicators, hydrocarbon and isotopic composition of extracts from rocks, as well as study of the composition of oils from the studied area, selected both within the Jurassic and Cretaceous complexes. The studied area is located in the Frolov megadepression and the South Nadym megamonoclise. The result of the research was the identification of significant geochemical characteristics of an additional source of hydrocarbons – coals, coal-rich shale of the Lower and Middle Jurassic, which had not previously been proven on the studied area, the contribution of which to the formation of oil and gas potential was confirmed by the correlation of hydrocarbon and isotopic characteristics of fluids and extracts from source rocks. Сluster and the principal component analysis were used for genetic correlation of extracts and oils. The conclusions obtained from geochemical studies suggest the possible prospects of Lower and Middle Jurassic deposits from the point of view of detecting hydrocarbon accumulations.

This study investigates the paleodepositional conditions of the No. 6 Seam of the Madzaringwe Formation in Makhado and Voorburg south area of the Soutpansberg Coalfield (Limpopo Province, South Africa) utilizing organic petrography and inorganic geochemical proxies. The coals are predominantly high-volatile bituminous B-A rank with high ash yields (avg. 36.1 wt%), characterized by high-vitrinite (~ 41.5 vol%), moderate-to-high inertinite (9.8 vol%–33.7 vol%) and low liptinite (~ 2.3 vol%). The distribution of inertinite varies among different coal horizons (from bottom-lower to middle-upper), suggesting differential oxidation conditions and/or paleofire occurrence. Vitrinite-to-inertinite (V/I) ratio, tissue preservation–gelification index (TPI–GI), and groundwater–vegetation index (GWI–VI) plots, indicate that the peat-forming forest-swamp vegetation accumulated under mesotrophic-to-rheotrophic hydrological conditions. The presence of structured macerals (i.e., telinite, collotelinite, fusinite, and semifusinite) suggests well-preserved plant tissues, whereas framboidal pyrite and sulphur content (0.24 wt%–2.16 wt%) point to brackish-water influence at the peat stage. The coals contain quartz, kaolinite, siderite, muscovite, dolomite, calcite, and pyrite minerals, most of which were likely sourced from felsic igneous rocks. The Al/(Al+Fe+Mn) and (Fe+Mn)/Ti ratios for the studied samples range between 0.24–0.97 and 0.57–70.10, respectively. The ratios, Al–Fe–Mn plot, and presence of massive botryoidal-type pyrite imply some influence of meteoric waters or fluids from hydrothermal activity post-deposition. Moreover, the chemical index of alteration (CIA: 98.25–99.67), chemical index of weathering (CIW: 92.04–97.66), and A–CN–K ternary diagram suggest inorganic matter suffered strong chemical weathering, indicating warm paleoclimatic conditions during the coal formation. [ABSTRACT FROM AUTHOR]

This study investigated the differences and correlation between the occurrence characteristics of alkali and alkaline earth metals (AAEMs) among different maceral groups in high-alkali, high-inertinite coal, and provides scientific guidance for the co-separation of AAEMs and inertinite groups in Xinjiang coal. The total AAEMs of inertinite-enriched samples were significantly higher than those in raw coals and vitrinite-enriched samples. Five-step sequential extraction showed that Na mainly occurs as water-soluble sodium (Na-Water) in raw coal and inertinite-enriched samples, accounting for about 53% of the total content, while it exists as organic sodium (Na-NH4Cl and Na-EDTA) in vitrinite-enriched samples, accounting for about 52% of the total content. Ca and Mg are both mainly present in organic form (Ca/Mg-NH4Cl and Ca/Mg-EDTA) in all the samples, with slightly higher proportions present in vitrinite-enriched samples. The contents of K are low in all the samples, which exist in an insoluble state (K-I). Combined microscopy and SEM-EDS analyses have revealed that the localized enrichment of Na in raw coal and inertinite-enriched samples occurs in the inertinite cell cavity, which primarily exists as NaHCO3 combined with quartz crystals, with a maximum content of up to 5.85 wt%. In this study, although EDS spectra could not directly characterize organic Ca and Mg, dolomite and calcite minerals were repeatedly found in the inertinite cell cavity. Moreover, the contents of Ca and Mg in the vitrinite-enriched samples were significantly lower than those in the other samples, which suggests that Ca and Mg are enriched with the inertinite groups. The localized enrichment of AAEMs could not be detected in any of the vitrinite-enriched samples. In summary, though there are significant differences between the occurrence modes of AAEMs in different maceral groups of high-alkali coal, AAEMs have a strong affinity with inertinite, which may be due to the inertinite's abundant pore structures. [ABSTRACT FROM AUTHOR]

The comprehensive quality enhancement and grading of coal are crucial methods for unlocking the high value-added and low-carbon utilization of coal resources. In this work, the influence of oily bubbles on the flotation of Shendong Jurassic vitrinite-rich coal and inertinite-rich coal was studied via flotation tests, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle detection, and induction time measurements. FT-IR and XPS analyses demonstrated that the surface of inertinite-rich coal contains more hydrophilic oxygen-containing functional groups. Contact angle and induction time measurements showed that the vitrinite-rich coal is more hydrophobic than inertinite-rich coal, and that for both air and oily bubbles, the induction time on the surface of vitrinite-rich coal is shorter than that on the surface of inertinite-rich coal. In addition, rather remarkably, the induction times for both vitrinite-rich coal and inertinite-rich coal are significantly reduced by oily bubbles. Finally, a better flotation performance for oily bubble flotation of vitrinite-rich coal and inertinite-rich coal was found. It appears that oily bubble flotation is an efficient method for enhancing the recovery of vitrinite-rich coal and inertinite-rich coal. [ABSTRACT FROM AUTHOR]

Coal is a solid combustible mineral, and coal-bearing strata have important hydrocarbon generation potential and contribute to more than 12% of the global hydrocarbon resources. However, the deposition and hydrocarbon evolution process of ancient coal-bearing strata is characterized by multiple geological times, leading to obvious distinctions in their hydrocarbon generation potential, geological processes, and production, which affect the evaluation and exploration of hydrocarbon resources derived from coaly source rocks worldwide. This study aimed to identify the differences on oil-generated parent macerals and the production of oil generated from different coaly source rocks and through different oil generation processes. Integrating with the analysis of previous tectonic burial history and hydrocarbon generation history, high-temperature and high-pressure thermal simulation experiments, organic geochemistry, and organic petrology were performed on the Carboniferous-Permian (CeP) coaly source rocks in the Huanghua Depression, Bohai Bay Basin. The oil-generated parent macerals of coal's secondary oil generation process (SOGP) were mainly hydrogen-rich collotelinite, collodetrinite, sporinite, and cutinite, while the oil-generated parent macerals of tertiary oil generation process (TOGP) were the remaining small amount of hydrogen-rich collotelinite, sporinite, and cutinite, as well as dispersed soluble organic matter and unexhausted residual hydrocarbons. Compared with coal, the oil-generated parent macerals of coaly shale SOGP were mostly sporinite and cutinite. And part of hydrogen-poor vitrinite, lacking hydrocarbon-rich macerals, and macerals of the TOGP, in addition to some remaining cutinite and a small amount of crude oil and bitumen from SOGP contributed to the oil yield. The results indicated that the changes in oil yield had a good junction between SOGP and TOGP, both coal and coaly shale had higher SOGP aborted oil yield than TOGP starting yield, and coaly shale TOGP peak oil yield was lower than SOGP peak oil yield. There were significant differences in saturated hydrocarbon and aromatic parameters in coal and coaly shale. Coal SOGP was characterized by a lower Ts/Tm and C31-homohopane22S/ (22Sþ22R) and a higher Pr/nC17 compared to coal TOGP, while the aromatic parameter methyl dibenzothiophene ratio (MDR) exhibited coaly shale TOGP was higher than coaly shale SOGP than coaly TOGP than coaly SOGP, and coal trimethylnaphthalene ratio (TNR) was lower than coaly shale TNR. Thus, we established oil generation processes and discriminative plates. In this way, we distinguished the differences between oil generation parent maceral, oil generation time, and oil production of coaly source rocks, and therefore, we provided important support for the evaluation, prediction, and exploration of oil resources from global ancient coaly source rocks. [ABSTRACT FROM AUTHOR]

The Middle Jurassic Walloon Subgroup coals in Australia's Surat Basin are extremely rich in low-medium rank coal seam gas (CSG) resources, making it one of the world's most productive CSG development basins. The desorption, diffusion and seepage behaviors of CSG are remarkably influenced by the pore–fracture structure characteristics of coals; therefore, their detailed characterizations are greatly significant for CSG exploration and development. There are, however, currently few researches on the pore–fracture structure characteristics of Surat Basin coals. Thus, 12 low-medium rank coals ( R ¯ r: 0.42–0.60%) from the Walloon subgroup of Eastern Surat Basin were obtained for this study, and then coal petrology analyses, field emission scanning electron microscopy and nuclear magnetic resonance (NMR) experiments were performed on these samples. The results show that the organic macerals of Surat coals are dominated by vitrinite, followed by liptinite, and the inertinite is generally rare. The average porosity, movable porosity and movable water saturation of the coal samples were 5.08%, 1.01% and 22.47%, respectively. The coal samples' pore–fracture structure was characterized by an overwhelming predominance of MIT (micropores and transition pore) and relatively less developed ME (mesopore) and MAF (macropore and fracture), with average volume proportions of 74.58%, 14.06% and 11.36%, respectively. The movable porosities of different pore–fracture structure types were obtained, and the average values were presented as MAF > ME > MIT. The NMR experiments showed that the average movable spaces in the MIT, ME and MAF of the coal samples were 6.6%, 41.8% and 97.9%, respectively. The pore–fracture structure of the sampled coals was influenced by coal maturity, as well as the coal macerals. The coal facies have some impacts on the porosities of coal samples, and the coals with higher texture preservation index and vegetation index, and lower gelation index overall have higher porosities. [ABSTRACT FROM AUTHOR]

The hydrocarbon generation potential of the Campano-Maastrichtian to Paleogene shales from the Benin Flank (located in SW Nigeria) of the Anambra Basin, has been previously investigated mostly by studying outcrops and by relatively few subsurface data-based studies. Thus, it is expedient undertaking an assessment of the hydrocarbon generation potential of this frontier area from subsurface samples. Campano-Maastrichtian to Paleogene shale samples obtained from Egoli-1 borehole in the Benin Flank of the Anambra Basin are studied by means of HAWK programmed pyrolysis, organic petrography, and mineralogy (XRD), with the aim to explore the petroleum-generating potential and the thermal maturity. The obtained results display a significant variation of the TOC content ranging from very low (5%), indicating poor to excellent oil potential based on S2 values under the condition, of course, the studied formations reached the oil window. The shales of the Nsukka and Imo Formations display lower petroleum-generating potential than these of the Mamu Formation. All the studied samples are dominated by gas-prone (type III) and inert (type IV) kerogens, with few displaying mixed II/III (oil- and gas-prone). The organic-petrography observations support partly the results of the HAWK programmed pyrolysis, as they reveal an organic-richer Mamu Formation in comparison to the Nsukka and Imo Formations; huminite/vitrinite particles (both indigenous and recycled) along with variable contents of liptinite (mostly alginite and bituminite) and inertinite macerals (mostly inertodetrinite) are hosted in the shales. The latter display a typical composition for fine-grained clastic sediments; mostly kaolinite, illite/montmorillonite, quartz, and subordinately, anatase. In terms of thermal maturity, huminite/vitrinite reflectance data points to immature stage; however, the occurrence of solid bitumens, displaying equivalent vitrinite reflectance values within the oil window, points to an active petroleum system in sequences deeper than the examined ones.

Opencast coal mining produces trash of soil and rock containing various minerals, that are usually dumped nearby the abandoned sites which causes severe environmental concern including the production of acid mine drainage (AMD) through oxidation pyrite minerals. The current study entailed assessing the potential production of AMD from an opencast coal mining region in Northeast part of India. In order to have a comprehensive overview of the AMD problem in Makum coalfield, the physico-chemical, geochemical, and petrological characteristics of the coal and overburden (OB) samples collected from the Makum coalfield (Northeast India) were thoroughly investigated. The maceral compositions reveal that coal features all three groups of macerals (liptinite, vitrinite, and inertinite), with a high concentration of liptinite indicating the coal of perhydrous, thereby rendering it more reactive. Pyrite (FeS2) oxidation kinetics were studied by conducting the aqueous leaching experiments of coal and (OB) samples to interpret the chemical weathering under controlled laboratory conditions of various temperature and time periods, and to replicate the actual mine site leaching. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) was operated to detect the disposal of some precarious elements from coal and OB samples to the leachates during our controlled leaching experiment. The Rare earth element (REE) enrichment in the samples shows the anthropogenic incorporation of the REE in the coal and OB. These experiments reveal the change in conductivity, acid producing tendency, total dissolved solid(TDS), total Iron(Fe) and dissolved Sulfate(SO42−) ions on progress of the leaching experiments. Moreover, the discharge of FeS2 via atmospheric oxidation in laboratory condition undergoes a significant growth with the rise of temperature of the reaction systems in the environment and follows pseudo first order kinetics. A bio-remediative strategies is also reported in this paper to mitigate AMD water by employing size-segregated powdered limestone and water hyacinth plant in an indigenously developed site-specific prototype station. Apart from neutralisation of AMD water, this eco-friendly AMD remediation strategy demonstrates a reduction in PHEs concentrations in the treated AMD water. [ABSTRACT FROM AUTHOR]

To investigate the influence of organic matter conversion on the evolution of organic matter pores, fractional conversion (TRHI) and loss of TOC (TOCL) from the organic matter conversion of Middle Jurassic Dameigou Formation shale samples were calculated using petrographic analysis. The TRHI of organic matter varies from 0.30 to 0.88 and TOCL content ranges from 0.62% and 4.09%. Relative to samples of Type III organic matter in shales, type II samples exhibit higher TRHI and TOCL values. Petrographic calculations of TRHI reveal that the fractional conversion of different kerogens differs for the same thermal maturity level. The specific surface area (SBET) ranges between 1.25 and 6.63 m2/g and micropore surface area (Smic) ranges between 4.16 and 21.27 m2/g. Correlations between pore structure parameters and TOCL content are higher than those between pore structure parameters and TOC content. The original TOC content decreases with increasing maturity level owing to hydrocarbon generation from organic matter conversion. The development of organic matter pores depends mainly on organic matter conversion, which is influenced by the richness, organic maceral compositions, and thermal maturity of the organic matter. The contents of kaolinite, illite, and mixed-layer illite/smectite (I/S) in the studied shales are 17.83%–37.05%, 5.36%–11.31%, and 5.27%–14.36%, respectively. Pore structure parameters (SBET and Smic) exhibit moderate positive correlations with illite content and I/S content, and moderate negative correlations with kaolinite content, indicating that different clay minerals have differential effects on pore structure. [ABSTRACT FROM AUTHOR]

The energy demand increased dramatically owing to the evolution of industrial and domestic requirements and the associated decrease in oil and gas resources. This study aims to evaluate El-Maghara coal (with about 52 MT reserve) as a potential hydrocarbon source. The collect samples were subjected to petrographic, chemical analyses and Rock–Eval pyrolysis to investigate the detailed characteristics of this coal. Chemically, this coal is high volatile bituminous coal with high H and S content. The high H/C ratio indicates the high extraction yield of coal. The main maceral group in the studied samples is vitrinite (62.8%) followed by liptinite (31.3%) and inertinite (5.8%). The content of liptinite indicates the capability of this coal for petroleum production. Based on Rock–Eval Pyrolysis results and TOC content, the coal has excellent petroleum potential. The hydrogen index (HI) and H/C atomic ratio indicate the II kerogen type (oil prone) of this coal. This coal has Tmax and vitrinite reflectance values around 415.8 °C and 0.37%, respectively, indicating the immature stage of kerogen. The high reactive maceral content (94.2%), oil-yield (65.5%) and conversion from coal to oil (95.4%), indicated that this coal has a hydrocarbon generation potential for oil. [ABSTRACT FROM AUTHOR]

Fifty-four coal clast samples in the siliciclastic rocks (e.g., sandstone and conglomerate) were collected from cores of two-deep research wells (K20H and K20K) drilled at the Kozlu coalfield in Zonguldak Basin, and for the first time, they were evaluated using mineralogy by XRD and SEMEDX and random vitrinite reflectance (%Rr) measurements in order to find out their origin and timing. Petrographic observations on polish surfaces show that the coal clasts are either entirely xylitic/vitrinitic particles or coals including a broader range of macerals. The detected minerals in the samples are mostly derived from the parental coal seams and, to a lesser extent, precipitated from penetrated pore-water in the cleats/fractures of clasts. The %Rr values of coal clasts in Carboniferous sediments are generally relatively higher than those measured in the coal seams due to weak oxidation during transportation. Furthermore, similar mineralogical and maceral compositions between coal clasts and coal seams imply that these clasts were mainly eroded during the peatification and/or early coalification of parental seams and display similar coalification patterns. The close %Rr value of a coal clast sample in the Early Aptian Zonguldak Formation and Carboniferous coal seams could suggest that this coal clast sample is presumably derived from the coal seams eroded during Early Aptian. [ABSTRACT FROM AUTHOR]

The Bozburun coalfield hosts a late Miocene 1.1 m thick coal seam. This study aims to determine coal quality, mineralogy, petrography and geochemistry, and controlling factors of elemental enrichments. The coals are generally black and greyish black in colour, and the low part of the seam commonly includes fossil shell remains. The ash yield displays a decreasing trend towards the upper part of the seam; in turn, gross calorific and total C values increase upwards. The total S content being generally higher than 5% (on dry basis), displays an increasing trend towards the upper part. In the entire seam, huminite is the most common maceral group, while inertinite and liptinite display variable proportions. The identified minerals by XRD are mainly quartz, clay minerals, calcite, pyrite, and aragonite (in fossil shell remains-bearing samples), whereas feldspars and marcasite determined in a few samples. Furthermore, in the coal samples, celestine and barite were identified by SEM-EDX. This study indicates that precipitation of celestine and Sr-bearing barite grains during diagenetic stage and Sr-uptake by mollusc within the palaeomire caused Sr enrichment in the entire seam. Overall, the water influx and redox conditions controlled the mineralogical and the elemental compositions of the coal seam. [ABSTRACT FROM AUTHOR]

A comprehensive petrographic and biomarker study has been performed to evaluate sources, paleoenvironment and maturity of organic matter (OM) in coal samples taken from the borehole BD-4 in the Dubrava block (Aleksinac Basin, Serbia). Studied samples are dominated by vitrinite group macerals, with variable content of liptinite and very low amount of inertinite. The measured random vitrinite reflectance, Rock Eval data and biomarker assemblages confirmed subbituminous rank of coal. The OM is at the late diagenetic and early catagenetic stage. Contents of total organic carbon and mineral matter vary in wide range, indicating frequent changes of depositional settings. Content of sulphur is moderate to very high. The main sources of OM in Aleksinac coal were angiosperms, ferns and aquatic macrophytes, with subordinate contribution of conifer paleovegetation. Diagenetic alteration of OM was governed by methanotrophic bacteria and chemoautotrophic bacteria. Deposition of OM occurred in a low-lying mire environment, showing decreasing concentration of sulphate ions upward the borehole BD-4. The coal deposition was terminated by rise of water level, which led to drowning of the mire and transition to lacustrine environment. [ABSTRACT FROM AUTHOR]

The open-pit exploitation of the Maritsa Iztok lignite field (Bulgaria) generated sedimentary waste rocks of low organic matter content that were deposited in internal dumps. Immediately after deposition the re-deposited sediments underwent weathering, including organic matter oxidation leading in some cases to self-heating. The aims of the research were to study the impact of weathering and self-heating on the maceral alterations in the dump site associated with the sediment re-deposition, and organic compounds identification and distribution. The 27 samples collected from Troyanovo-3 Mine internal dump differed in degree of alteration. The first group contained unaltered macerals and showed normal distribution of n-alkanes, phenols were absent and Rock-Eval Tmax ranged from 420 to 430 °C. The second group contained macerals with irregular cracks, paler oxidation rims, higher reflectance, Gaussian distribution of n-alkanes, high concentration of phenols and PAHs, and lowered Tmax values (below 400 °C). The samples contained elevated amount of pyrite which oxidation might contribute to self-hating. [ABSTRACT FROM AUTHOR]

The petrographic composition of samples from Suhostrel and Bobov Dol coal deposits was studied using optical microscopy. The maceral contents were further used to calculate maceral ratios which were interpreted in terms of environmental condition during peat deposition. Petrographic data of Suhostrel coal is compatible with its organic geochemical characteristics and indicate peat formation under inundated topogenous, meso- to rheotropic, sparsely forested marsh- or fen-type environment. Coal facies diagrams for Bobov Dol coal, however, provide contradictory depositional settings and therefore cannot be used alone for environmental reconstruction. [ABSTRACT FROM AUTHOR]

Macerals are the basic constituents of coal that can be distinguished and identified under the microscope. Depending on the difference in optical properties, the macerals are divided into four maceral groups, including liptinite, vitrinite, huminite and inertinite. These maceral groups not only affect coal mining and utilization but also play different roles in coal beneficiation. According to the different properties of maceral groups, they can be separated (or enriched) to provide high-quality raw materials for the coal industry. This review briefly introduces the international maceral classification system and reviews in detail the role of maceral groups in coal beneficiation combined with their properties. [ABSTRACT FROM AUTHOR]

The work illustrates the physico-chemical, petrographic characteristics and flotation response of low-grade oxidized coking coal containing 39.5% ash. The maceral composition, surface oxidation, and particle liberation are the factors that affect coal flotation. The oxidized coal requires more collectors than the freshly ground coal. The flotation process modeling and optimization of −0.5 mm coal fraction was carried out using response methodology and central composite rotatable design (CCRD). The diesel, MIBC, and sodium hexametaphosphate are used as collectors, frothers, and depressants to maximize the coal grade, yield, and combustible recovery. At an optimum dosage of 1.35 kg/ton collector, 0.2 kg/ton frother, and 0.5 kg/ton depressant, it is possible to achieve 11.3% ash-clean coal with a 50.72% yield from 39% feed ash coal. The ash, yield, and combustible recovery model prediction matched well with the experimental results. The R2 of the ash, yield and combustible recovery model are 0.9676, 0.9662, and 0.9692, respectively. The work highlights that Indian coal can upgrade for metallurgical use using a flotation process. [ABSTRACT FROM AUTHOR]

The Fu 2 Member of the Paleocene Funing Formation in the Gaoyou Depression, Subei Basin is an organic matter-rich formation, and has a high potential for shale oil exploration and exploitation. Total organic carbon (TOC), organic petrography, Rock-Eval pyrolysis, chloroform bitumen “A” extraction, and SARA (saturates/aromatics/resins/asphaltenes) composition analyses of shale samples from one drill core in the studied area spanning a thickness of 257 m were conducted to study the organic matter (OM) richness, kerogen type, maceral composition, hydrocarbon generation potential, and oil content of the Fu 2 Member. Results show that the Fu 2 Member shales in the study area have a Ro of 0.87%, in the peak oil window, suggesting a high potential for hydrocarbon generation. The studied OM in shales mainly belongs to kerogen Type II, with a minor portion of Type I and Type III. Under microscopic observation, macerals in the studied shales are mainly composed of vitrinite, inertinite, alginite, and solid bitumen. The studied shales have an average TOC content of 1.41 wt%, indicating good petroleum potential. The variations of maceral compositions could affect the reliability when the Tmax is used as an indicator of thermal maturity. The lower Shale 4 and upper Shale 5 interval (3650–3700 m), with high TOC and high oil saturation index, is identified as the sweet-spot interval of the Fu 2 Member for shale oil exploration.

The estimation of the degree of carbonification of coals can be investigated using the Raman microspectroscopy applied for the analysis of grains of selected macerals (altered remains of organic particles). This approach allows for the best control of the analyses such as precise selection and orientation of the maceral grains to be analysed. On the other hand, the miniaturized, especially handheld Raman spectrometers typically offer a significantly less controlled environment with the issues including large laser spot sizes and the focusing issues. However, the advantages of the miniaturized spectrometers include fast analyses and the possibility of in situ analyses. This study illustrates that it is possible to discriminate among the coals of different degrees of maturation of the carbonaceous matter and other types of carbonaceous matter using the data acquired with a portable Raman spectrometer using spectroscopic parameters: D and G band widths and wavenumber positions. The issues inherent to the analyses of such heterogeneous materials such as coals using a portable spectrometer were addressed. Moreover, the variability in the Raman spectroscopic backgrounds of a wide range of coals from lignite to anthracite necessitated the utilization of a robust background removal function. This study shows that modern portable Raman spectrometers with the appropriate excitation are capable of basic discrimination among the different types of carbonaceous matter, with implications towards fast in situ analyses of carbonaceous matter in rocks as an additional tool for a geologist. [ABSTRACT FROM AUTHOR]

The Santanghu Basin is a typical low-rank coal-bearing basin in northwest China, with abundant coalbed methane (CBM) resources. However, the understanding of the main controlling factors and reservoir formation models of CBM in low-rank coal is still insufficient, which has restricted the exploration and development of CBM in this region. In this paper, the CBM enrichment controlling factors and enrichment models are analyzed based on the aspects of sedimentary environment, reservoir characteristics, sealing conditions, and hydrogeological conditions after systematically analyzing the geological characteristics of coal measures. The research results indicate that the coal seams of the Xishanyao Formation in the Santanghu Basin are stably developed, with the main macerals being vitrinite and a lower degree of coalification belonging to low-rank coal; the highest content of CBM can reach 7.17 m3/t, and the methane is mainly composed of biogenic gas supplemented by thermogenic gas; the roof lithology of the coal seam is mainly mudstone and siltstone, with good sealing conditions. Finally, two enrichment modes of coalbed methane in slope zones are proposed, namely, the CBM enrichment in the slope zone and the CBM enrichment by fault-hydraulic plugging. The results of this study can serve as a guide for the exploration and development of the deep-buried coalbed methane in the low-rank coal areas. [ABSTRACT FROM AUTHOR]

Organic‐rich shale samples of the Late Cretaceous Mukalla Formation from the Al‐Fatk1 well in the offshore Jiza‐Qamar Basin, eastern Yemen, were examined using bulk organic geochemistry, microscopic examination, and biomarker measurements combined with 1‐D basin modelling, to evaluate the organic matter characteristics and their ability to generate gas. The studied Mukalla shale samples are characterized by their high organic matter content with total values of up to 14.50 wt.%, and contain mainly hydrogen‐poor Type III kerogen, indicating elevated gas generation potential. The hydrogen‐poor kerogen was also demonstrated by biomarker measurements combined with an abundance of land‐derived organic matter (i.e., vitrinite and inertinite) as established by microscopic investigation. The biomarkers of the studied organic‐rich shales were characterized by a high Pr/Ph ratio, abundance of C29 regular steranes, high C27 17α (H)‐22, 29, 30‐trisnorhopane compared with C27 18α (H)‐22, 29, 30‐trisnorneohopane, all providing evidence for the organic matter being derived primarily from higher land plant organic matter, deposited in fluvial deltaic environments under highly oxic conditions. The bulk carbon isotope data agree with the findings of terrigenous organic matter. The maturity indicators show that the examined organic‐rich shale samples have entered the main oil stage and are at the beginning of wet gas generation windows, exhibiting vitrinite reflectance values that range between 0.73% and 1.20%. Kerogen to gas conversion has been simulated by the basin models and shows that between 10% and 15% of kerogen has transformed into gas during the late Miocene until the present‐day, consistent with the wet gas generation window (1.00–1.20 %Ro). Substantial gas exploration potential may exist in the fluvial deltaic Mukalla source rock system in the deeper structural units of the Qamar‐Jiza Basin, where the Mukalla Formation has reached the high maturity level of the gas generation window. [ABSTRACT FROM AUTHOR]

The present research work attempts to understand the organo-petrological facets of the lignite hosted in the Tertiary successions in Rajasthan. The maceral diversity was analyzed qualitatively and quantitatively which recorded huminite as the dominant microscopic constituent followed by inertinite and liptinite. The rank parameter of coal evaluated through vitrinite reflectance measurement random (VRo) shows the values vary between 0.19 to 0.27% suggesting lignite in rank. The petrographic investigation point towards the primary phase of degradation of organic matter corroborated through the dominance of huminite suggesting frequent flooding and the presence of funginite, demonstrating intense fungal activity in the mire. The paleodepositional model records elevated values of gelification Index (GI) ranging from 1.63 to 3.88 with well-preserved cell structures pointing towards an early phase of coalification. The model and plot of GI and TPI show that the paleomire developed in a limnic setting. [ABSTRACT FROM AUTHOR]

The subject of the study was the No. 116/2 coal seam belonging to the Cracow Sandstone Series of the Upper Silesian Coal Basin. Reflectograms of the samples taking into account all the vitrinite group macerals present in the coal were recorded for ΔR° close to the standard deviation and in the standard range. A careful analysis of vitrinite reflectograms reveals the presence of three or four clearly distinguished peaks. When assessing the rank of coal, only the main maximum, peak No. 4, was considered to be significant. Measurements of the average reflectance of collotelinite were made only on the vitrinite surfaces with a thickness of more than 1 mm. Only two maxima were revealed on detailed reflectograms. These maxima correlate with the peaks marked as No. 3 and 4 in the sample reflectograms taking into account all the vitrinite group macerals. The Cdaf content in the tested coal from the Janina coal mine is between 75.9 and 77.5 wt%, while for vitrain, it ranges from 71.1 to 75.5 wt%. This relationship is an exponential regression with a correlation coefficient of r = 0.95h and can be approximated by a linear correlation of r = 0.94. The correlation strength between the volatile matter content and the coefficient of average reflectance in the vitrinite of the tested coal was also examined. The statistically significant correlation is strong, which is expressed by the exponential correlation coefficient "r" being close to 0.99 and its linear approximation with the correlation coefficient r = 0.98. However, no correlation was found between the measured reflectance values and the GI coefficient calculated for the examined samples. [ABSTRACT FROM AUTHOR]

The paper reports a detailed coal-petrographic and mineralogical–geochemical study of humic coals and coaly rocks in the Upper Devonian Sargaevo deposits in North Timan (Sula River), which are an example of the burial of the oldest coal-forming plants. The following types of organic rocks are identified in the section: "jet-like" coal, liptobiolitic silty–argillaceous coal, and silty–argillaceous–coaly mixtolites. The studied coals and coaly rocks are mainly composed of humic organic components represented by vitrinite and liptinite macerals, with subordinate inertinite group. The vitrinite macerals include gelinite, collotelinite, and telinite (xylenite); the liptinite macerals include sporinite, cutinite, liptodetrinite, bituminite, alginite, and resinite, and the inertinite macerals include inertodetrinite, semifusinite, fusinite, and funginite. The vitrinite reflectance (RV, %) 0.45–0.55% corresponds to the insignificant organic maturity from proto- to meso-catagenesis (rank PC3–MС1). The mineral component of mixtolites and high-ash coals consists of kaolinite, chlorite/smectite (with a predominance of the chlorite component), and quartz. [ABSTRACT FROM AUTHOR]

Shale sediments were collected from four Cretaceous stratigraphic units across four explorations well locations in South Africa's Orange Basin and analysed to determine organic-matter characteristics, such as amount, quality, thermal maturity, and their viability as gas resources. The geochemical results show that the Cretaceous shales contain moderate organic quantities, as shown by TOC averagely up to 1.29%. The organic facies consist primarily of Type III kerogen, as proven alongside low hydrogen indexes between 40 and 133 mg HC/g TOC. As seen under a reflected light microscope, the dominance of such land plant-rich organic matter is in harmony with the significant amount of Vitrinite macerals. These organic sediments can produce primarily gas when they mature. The geological and geochemical properties of the organic sediments, chiefly Type III kerogen, generate both wet and dry gas, particularly when adequate thermal maturity is enhanced at deeper locations. Thus, the Orange Basin is considered promising for shale gas exploration and production. [ABSTRACT FROM AUTHOR]

The Taranaki Basin in New Zealand presents the most promising territory for strategies of hydrocarbon exploration and development. This basin contains multiple source rock levels in its sedimentary successions formed during syn- and post-rift periods. The deepest source rocks, found in the Rakopi Formation, were deposited in deltaic to deep marine environments and consist of gas-prone coal and organic-rich mudstone lithofacies. However, questions remain about the preservation of their organic carbon. This study integrates various organic geochemical analyses (such as Rock Eval pyrolysis, kerogen petrography, and biomarkers) to assess the hydrocarbon potential of the Rakopi coal and mudstone lithofacies. The organic carbon in Rakopi coals and mudstones originated from oxygenated bottom water, but swift burial during the initial rifting phase facilitated the preservation of organic materials. Rakopi coals are less mature than the mudstone facies and contain a mixture of desmocollinite, suberinite, and resinite macerals. In contrast, the mudstone lithofacies are enriched in liptodetrinite. The maceral mixture in the coal led to its elevated hydrogen index and likely facilitated early expulsion of liquid hydrocarbon phases. Regular steranes, diasteranes, and C29 sterane isomers distribution in the coal and mudstone extracts highlighted a greater terrestrial input in the coals, whereas significant marine input is observed in the mudstone extracts. Biomarkers in the coal and mudstone extracts are similar to some nearby oils discoveries in the Taranaki Basin, thereby confirming oil generation from both coal and mudstone lithofacies in the Rakopi Formation. These findings underscore the potential of liptinite-rich coals to generate liquid hydrocarbon phases at marginal oil maturity levels. [ABSTRACT FROM AUTHOR]

The occurrence and separation relationships of Na and maceral groups in Zhundong coals were investigated in this study. The sequential extraction results indicate that the total Na content of all samples decreased with increasing sampling depth, and the level in inertinite-enriched samples (inertinite content 81.0%–84.0%) was significantly higher than that in corresponding raw coals and vitrinite-enriched samples (vitrinite content 90%). Additionally, H2O-Na (soluble salt species) and insoluble Na (acid-insoluble residues) were found to be concentrated in the inertinite-enriched samples. In combined SEM–EDS and microscope observations, local Na enrichments were detected in all raw coal and inertinite-enriched samples except for the vitrinite-enriched samples, but only inertinite-enriched samples were found to generally have over 10 wt% of Na enrichments, all of which occurred as NaCl. Moreover, Na is mostly filled or associated with cell-filling minerals in cells of fusinite. The maceral separation and Na removal of Zhundong coal were simultaneously achieved using triboelectrostatic separation. The vitrinite content in concentrates increased up to 60%, along with a reduced Na level, while the inertinite and sodium levels were both evidently raised in tailings. The obvious positive occurrence and separation correlation between sodium and inertinite offers new insight into, and a technical reference for, the sodium removal and maceral processing of Zhundong coal. [ABSTRACT FROM AUTHOR]

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Deep coalbed methane (CBM, commonly accepted as >1500 m) has enormous exploration and development potential, whereas the commercial development of deep CBM exploration areas wordwide has been quite limited. The Linxing area, with coals buried approximately 2000 m deep, shows great development potential. Based on a basic geological analysis of structural and hydrodynamic conditions, combining field tests of reservoir temperature and pressure and indoor measurements of maceral composition, proximate analysis, thermal maturity, porosity and permeability, the factors controlling deep CBM accumulations were discussed. The results show that the present burial depth of the No. 8 + 9 coal seam, mainly between 1698 and 2158 m, exhibits a high reservoir temperature (45.0–64.0 °C) and pressure (15.6–18.8 MPa), except for the uplift area caused by the Zijinshan magma event (with coal depth approximately 1000 m). The maximum vitrinite reflectance (Ro,max) of the coal varies from 1.06% to 1.47%, while the magma-influenced areas reach 3.58% with a relatively high ash content of 31.3% (air-dry basis). The gas content calculated by field desorption tests shows a wide range from 7.18 to 21.64 m3/t. The key factors controlling methane accumulation are concluded from regional geological condition variations. The north area is mainly controlled by structural conditions and the high gas content area located in the syncline zones. The center area is dominated by the Zijinshan magma, with relatively high thermal maturity and a high gas content of as much as 14.5 m3/t. The south area is developed with gentle structural variations, and the gas content is mainly influenced by the regional faults. Furthermore, the groundwater activity in the eastern section is stronger than that in the west, and the hydrodynamic stagnant areas in the western are more beneficial for gas accumulation. The coals vary from 3.35% to 6.50% in porosity and 0.08 to 5.70 mD in permeability; thus, hydrofracturing considering high temperature and pressure should be applied carefully in future reservoir engineering, and the co-production of gas from adjacent tight sandstones also should be evaluated. [ABSTRACT FROM AUTHOR]

Analyzing the photomicrographs of coal and conducting maceral analysis are essential steps in understanding the coal's characteristics, quality, and potential uses. However, due to limitations of equipment and technology, the obtained coal photomicrographs may have low resolution, failing to show clear details. In this study, we introduce a novel Generative Adversarial Network (GAN) to restore high-definition coal photomicrographs. Compared to traditional image restoration methods, the lightweight GAN-based network generates more explicit and realistic results. In particular, we employ the Wide Residual Block to eliminate the influence of artifacts and improve non-linear fitting ability. Moreover, we adopt a multi-scale attention block embedded in the generator network to capture long-range feature correlations across multiple scales. Experimental results on 468 photomicrographs demonstrate that the proposed method achieves a peak signal-to-noise ratio of 31.12 dB and a structural similarity index of 0.906, significantly higher than state-of-the-art super-resolution reconstruction approaches. [ABSTRACT FROM AUTHOR]

Coal is usually found in many sandstone-hosted uranium deposits in western China. However, it remains unclear whether coal organic matter is related to the mineralization of uranium in sandstone. In this study, the organic matter of coal containing lenticular carbon plant strips and carbon clastics was analyzed in different alteration zones in the Daying sandstone-hosted uranium deposit located in the northern Ordos Basin. According to geological and geochemical characters, Daying sandstone can be classified into three alteration zones: the oxidation zone, the transition zone, and the reduction zone. The results are as follows. Firstly, the maceral organic matter of the coal at Daying is mostly vitrinite, indicating the characters of humic coal. The maturity of the organic matter is low, which is in the transitional evolution stage of immature lignite or lignite-long-flame coal. Secondly, the kerogen is mainly type III (humic type), which can be easily transformed into humic acid with a strong adsorption capacity for uranium. Thirdly, the vitrinite reflectance (Ro) of the coal organic matter in the transition zone is higher than that of the other alteration zones. Meanwhile, there are bright white bands in the microscopic components of the organic matter of the coal in the transition zone (mineralized zone) and a certain composition of the sapropelite has strong fluorescence. All three aforementioned phenomena are related to the radioactivity of uranium, and each of them possesses the potential for application in mineral exploration. Fourthly, the extraction and separation of humic substances indicates that humic acid plays a key role in organic matter-related uranium mineralization. In the transition zone, uranium can co-precipitate as a humate, and the transition zone's organic carbon content increases. Therefore, the organic matter in coal contributes to sandstone-hosted uranium mineralization, providing a further guide to prospecting methodologies. [ABSTRACT FROM AUTHOR]