Maceral Content Research Articles

Organic geochemical and petrological investigations of the upper miocene bongaya formation in the pitas, onshore sabah basin, and its relevance for hydrocarbon potential

The Upper Miocene Bongaya Formation coal, carbonaceous shale, and shale sediments were collected to investigate their origin, types, and maturity. The main objectives of this study were to verify and update previous claim of possible hydrocarbon showings and to gain new insights about the petroleum potential using different geochemical analysis approach. The primary methodology used in this study is the pyrolysis technique and coupled with petrographic analysis. The bulk geochemistry results revealed that the Bongaya sediments serve as favorable source rock, with the total organic carbon (TOC) content ranging from 0.90 to 63.10 wt% by weight, indicating fair to excellent organic richness. The coal samples exhibited the highest TOC values, followed by carbonaceous shale samples, while shale and coal laminated with sandstone samples displayed fair TOC amounts. Most of the Bongaya sediments analyzed in this study exhibited hydrogen index (HI) values of less than 200 mg HC/g TOC, indicating Type III organic matter, which signifies a significant influence of terrestrial organic matter. However, three coals displayed comparatively higher pyrolysis HI values, corroborated by Pyrolysis gas-chromatography (Py-GC) results and maceral types, indicating a mixture of Type II/III kerogen. This suggests that the Bongaya Formation sediment has the potential to generate gas with minor oil. Maceral analysis also revealed that most of the coal samples contained a high content of resinite maceral, which explains the waxy composition of the oil. The organic matter in the analyzed Bongaya sediments was found to be immature for petroleum generation, as evidenced by low huminite reflectance data (lower than 0.50% VR) and Tmax values between 372 and 432 °C. Consequently, the kerogen in the studied onshore Bongaya sediments has yet to enter the hydrocarbon cracking (catagenesis) phase before expelling petroleum. Therefore, it is essential to consider the offshore equivalent Bongaya sediments, which may be laterally extended offshore and buried at deeper depths to attain optimal maturity for hydrocarbon generation.

Pyrolysis characteristics and product distribution of low-rank coal with heat-carrying particles adopting TG-FTIR and a novel self-mixing down tube reactor

A novel self-mixing down tube (SDT) pyrolyzer has been developed, which can separate the heat carrying particles preheated in the fluidized bed from the coal, and the two can be mixed through a specific structure to instantly heat the coal particles to a predetermined temperature. The present study investigated the pyrolysis behavior of low-rank coal with hot silica sand heat-carrying particles adopting TG-FTIR. Identifies optimal conditions for maximum tar production in a laboratory-scale SDT using a significantly larger range of coal feed rates (4 kg/h). An increase in the degree of coal metamorphism increased the initial temperature and the yield of char. The tar yield from Huolinhe lignite coal (6.56 %) and Daliuta bituminous coal (7.48 %) showing a trend of first increased and then decreased with elevating the operating temperature and optimal temperature at 520 °C, respectively. The effect of coal particle size on tar yield mainly comes from the different degrees of secondary cracking caused by contact with solid heat-carrying particles as well as the differences in the content of macerals. GC‒MS spectra of tar and deposited carbon on silica sand indicated that heavy tar can easily deposit on the surface of sand and form char through polymerization reactions.

Hydrocarbon generation potential of Campano-Maastrichtian to Paleogene shales in the Benin Flank of the Anambra Basin, SW Nigeria

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.

Significance of organo-mineralogical constituents on pore distribution, fractals and gas sorption mechanism of Permian shale beds in Korba sub-basin of the Son-Mahanadi Valley, India

In this study, shale samples obtained from the Korbasub-basin of Central India have been evaluated for the significance of organo-inorganic constituents in terms of their source potential of gas genesis, pore-matrix setup, and gas adsorption and desorption. The samples were analysed for various properties, such as megascopic features, lithological variations, depositional facies, and sources of organic and inorganic sediments. Also, maceral content, mineralogical constituents, kerogen type, pore distribution, pore structure, fractal characteristics and gas storage capacity were examined. The analysis revealed a trend of alternating bands of carbonaceous matter, silts, intercalations, and fluvial bedding lithofacies patterns indicating that the sediments were deposited under fluvio-terrestrial-lacustrine depositional conditions. Ternary facies analysis of maceral composition and van Krevelen diagram suggested the evolutionary path of type IV kerogen and are thermally matured source material located within the dry hydrocarbon generation window. Evaluation of pore types and pore structures using BET sorption plots (hysteresis H3 and isotherm type IV) revealed the presence of cylindrical, slit and combined cylindrical-slit pores with two distinct fractal characteristics. The discrete macerals underwent partial decomposition during transportation and mixing with inorganic components (clay and minerals), which influenced organic matter preservation, gas genesis, pore fractals and storage mechanism. The chemical index of alteration (CIA – 88.36 to 91.97), weathering (CIW – 96.60 to 98.80) and compositional variation (ICV – 0.31 to 0.70) demonstrated the influence of partial decomposition and strong weathering patterns on the organo-inorganic matter. A significant correlation was observed between pore fractals and elemental composition, particularly related to the resistance of weathering elements such as MgO, Al2O3, Fe2O3, SiO2, P2O5, TiO2, etc., which partially contributed to the formation of pore rugged surfaces. Microscopic and XRD analyses were employed to determine the mineral type, grain shape and size, and their amount leading to the development of the shales brittleness index (MBI). The importance of brittle characteristics, governed by minerals and clays within the shale, is discussed in relation to the hydro-fracturing technique for permeability enhancement. The results of high-pressure methane sorption indicated a moderate gas storage potential. The variation in sorption capacity (VL – 6.65 to 8.25 cc/g) is described through relationships with the ICV, pore diameter, pore volume, liptinite and total maceral content. Fractal dimensions D1 (2.4571–2.5611) and D2 (2.5804–2.7529) exhibited a direct relationship with adsorption properties, indicating the presence of rugged surfaces associated with meso- and macro-scale pores, which primarily control gas storage in shale. This research offers detailed insights into shale gas, providing valuable information for CBM and petroleum operators engaged in methane gas exploration and production. While commercial CBM production has been ongoing in India for over a decade, the exploration and understanding of shale gas reservoir characteristics are still in progress. This investigation adds significant value and highlights the extensive opportunities for research and potentially commercially recovering shale gas in the Korba sub-basin.

On the interactions between strength and petrology of Pennsylvania anthracite

Six blocks of anthracite, each from a known seam and mine location, were tested for their unconfined compressive strength and elastic modulus. The maceral content and the proximate analysis of the test specimens were examined after the strength tests were completed. The coal rank (2.84 to 5.84%Rmax), the maceral composition (41.9–88.6% vitrinite (mineral-free basis), and as-received ash content (2.76–28.29%) are not good predictors of the strength for these samples. Instead, the highest compressive strength and elastic modulus samples were the anthracites with the highest ash yield. Among the lowest ash specimens, compressive strength decreases with an increase in the ratio of (telovitrinite + fusinite + semifusinite)/detrovitrinite). The cleats and the inorganic (mineral) and organic (maceral) composition of megascopic and microscopic lithologies likely contributed unquantified variables to those determined in this study.

Influence of elevated temperature and gas atmosphere on coke abrasion resistance. Part one: Pilot oven cokes

A novel approach was developed to examine coke abrasion resistance in-situ at temperatures of up to 950 °C and in a controlled gas atmosphere using rotational tribological testing. The originality of this approach lay in the ability to apply tribological testing to the porous coke surface at elevated temperatures under a controlled inert or CO2 reactive atmosphere. Coke wear characteristics were quantified via (i) the application of advanced microscopy and image analysis techniques, and (ii) analysis of the coefficient of friction (COF) during tribological testing.Two pilot oven cokes were examined in this study, which were generated from single coking coals of similar rank but different petrographic composition. The cokes tested showed a deterioration in abrasion resistance even at 400 °C, and this was accentuated at 950 °C.The COF and the severity of the wear as a function of temperature and gas atmosphere were markedly different between the two cokes. Coke C396 from a mid-to-low vol, medium vitrinite coal showed no statistically significant differences between the wear severity results recorded following room temperature testing and high temperature testing in a CO2 environment. Conversely, the more reactive coke C426 with a higher parent coal inertinite content showed clear differences in the extent of abrasive wear at room temperature and at high temperature in both inert and reactive gas atmospheres.This suggests that the reduction in abrasion resistance at elevated temperatures is accentuated in the coke with the highest coke reactivity index (CRI) and the highest content of inertinite maceral derived components (IMDC). Our research has shown that at room temperature, the IMDC show greater resistance to abrasion than the reactive maceral derived components (RMDC). This has implications for understanding the relevance of room temperature testing to the abrasion resistance of coke under practical blast furnace operation conditions. For example, a coke from a coal or blend with a comparatively high inertinite content may show lower resistance to abrasion in the blast furnace than would be expected from tumble drum indices. Larger sample numbers and cokes from a variety of single coals need to be tested in further work to verify these assertions.Finally, a novel method using micro-CT image analysis was developed to examine the wear path generated at the coke surface during tribological testing. The purpose of this was to assess the extent of the abrasive wear by comparing the rendered micro-CT images before and after tribological testing. A colour gradient scale was used to facilitate the quantitative assessment, whereby the colour of each voxel was based on the distance from the nearest voxel that is associated with solid phase.As expected, the specific surface area (SSA) calculated for the upper 1 mm of each sample decreased following tribological testing due to the generation of a wear track which is smoother than the initially rough, porous coke surface. In the C426 coke type examined, the SSA decreased the most for the sample tested in an argon atmosphere at 950 °C, matching the COF and quantified wear severity results, which showed there was a notable increase in abrasive wear to this coke as the temperature was raised from room to elevated temperature.Coupling this method of analysis with 3D visualisation techniques in further work would provide a powerful approach to examine and quantify mechanisms of coke surface breakage and the microstructural and/or microtextural features responsible for the breakage.

Relationship between coal composition, coal facies, and desorbed methane gas content: Thermal histories and exhumation processes in the middle Magdalena Valley basin, Colombia

We analyzed a total of 25 coal samples from high volatile bituminous to medium volatile bituminous range from 2 wells drilled in the Landázuri area of the Middle Magdalena Valley Basin at the Eastern Colombia Cordillera. This study reveals the relationship between the measured gas concentration, petrographic characteristics, and coal facies. We identify that gas desorption in coal seams is related to maceral composition.Three coal seam groups were defined in Landázuri 1 based on petrographic and statistical evaluation. Two groups were identified in Landázuri 2 based on gas content.The evaluation of maceral content and preservation of reflectance vitrinite found that the highest desorbed gas values correlate with the abundance of inertinite and structured inertinite macerals, followed by the percentage of vitrinite. Structured inertinite lumens may serve as macro/mesopores which allow for higher gas desorption because they are free of mineral matter or other macerals.Using existing coal facies diagrams, two types of coal facies were differentiated: lower delta plain (fen, marsh) and back-barrier low moor developed in a humid environment, where reotrophic conditions prevail and herbaceous and aquatic/marginal vegetation predominate.The relationship of these transitional facies with gas content shows are not directly related to the higher gas values measured at Landázuri. Instead, the relationship between the high degree of destruction of organic matter in these facies (marine incursions and other flows) and the measured gas content shows the importance of quantifying the structured macerals as potential gas retainers.Using low-temperature thermochronometers apatite fission-track, and (U–Th)/He in zircon, combined with vitrinite reflectance data, we reconstructed time-Temperature histories for areas near the wells. Differences in gas content can be explained by an asynchronous behaviour of the burial-cooling processes in this part of the Colombian Eastern Cordillera. Our work shows it is possible to distinguish gas desorption in coal seams based on the maceral composition.

Carbon isotopic composition and organic petrography of thermally metamorphosed Antarctic coal: Implications for evaluation of δ13Corg excursions in paleo-atmospheric reconstruction

Large, globally documented negative δ13C excursions that occur across the Permian-Triassic transition are thought to represent the isotopic fingerprint of considerable releases of isotopically light carbon into the atmosphere, with the largest of these excursions (as much as −22.2‰) measured in bulk organic matter in coals and carbonaceous shales from Antarctica. Previous studies have attributed the carbon isotopic excursion (CIE) at the Permian–Triassic boundary to the release of CH4 from organic-rich rocks intruded by dikes and sills associated with the Siberian Traps flood basalts (Russia) and Longwood-Bluff (New Zealand) intrusions. However, any assessment of paleoatmospheric conditions based on this or other δ13Corg excursions must consider the multiple controls on isotopic composition, including maceral content and post-depositional diagenetic and maturation processes. Permian-age coal seams and associated sediments in Antarctica were extensively altered after burial by localized high heat flow and, in some cases, by contact metamorphism associated with Jurassic dikes and sills. Levels of organic maturation reach anthracite, meta-anthracite, and even graphite; such intense thermal alteration had the potential to change the carbon isotopic composition of the bulk organic matter (δ13Corg). To evaluate the Permian–Triassic isotopic excursion in Antarctica, it is important to understand the inherent variability in δ13Corg in Permian-age coal and organic-rich sedimentary rocks prior to the CIE; thus, 128 samples representing pre-boundary coals and shales were selected from the United States Polar Rock Repository for analysis. Petrographic (maceral analysis and vitrinite reflectance), geochemical (C, H, N), and carbon isotopic analyses were performed. Based on the presence of coarse-grained circular and fine-grained lenticular mosaic in the anisotropic cokes found in samples in close proximity to intrusions, the rank of the samples prior to intrusion is estimated to have been medium volatile bituminous (∼1.2% Rmax). These highly altered coals and cokes can have random vitrinite reflectances (Rr) exceeding 6%. Subsequent to intrusion, alteration beyond the contact aureoles continued due to high heat flow, producing high rank coals with Rr > 2%. Values of δ13Corg range between −26.5 and –21.1‰ (5.4‰ difference). Significant relationships (at the 1 and 5% levels) exist between δ13Corg and the level of organic maturity, organic carbon (Corg) content (i.e., size of the carbon reservoir), and total inertinite content, suggesting variability due to these factors should be considered when assessing isotopic excursions and interpretation of Permian-Triassic atmospheric conditions. These findings highlight the importance of incorporating organic petrography into δ13Corg studies.

Geochemistry and depositional environment of the Mesoproterozoic Xiamaling shales, northern North China

The Mesoproterozoic Xiamaling shales from Xiahuayuan area, southeastern Xuanlong sag, Northern China, were examined the elemental analysis by applying the inductively coupled plasma-mass spectrometry (ICP–MS). The Xiamaling shales have good to excellent oil hydrocarbon generation potential with type II kerogenas demonstrated by high content of alginate macerals, TOC, HI, S1 + S2 and extractable organic matter (EOM). The Xiamaling shales were deposited under a marine environment according to boron (B) (56–111 ppm) and other trace elements concentration, which is consistent with the geological settings. These shales can be classified into three types: (1) Type I is a coastal facies, which is influenced by fresh riverine water and has low B content of 56–61 ppm; (2) Type II is a marginal marine with B content of 73–79 ppm; and (3) type III has high B content of 111 ppm, typical of a brackish, and open marine environment.The Xiamaling shales have high B (>50 ppm), low Na, Ca, Ce, Mn, and rare earth elements (REEs). According to the elemental composition and ratios, the Xiamaling sediments were derived from the felsic source, which has suffered from moderate to strong chemical weathering based on the CIA, ICV, and PIA values. The Xiamaling marine shales were mostly deposited under dysoxic-anoxic conditions. The paleoclimate during the deposition of the Xiamaling shales was warm and humid based on the cross plots of Sr/Ca vs Mn/Ca values and Sr/Cu vs Rb/Sr ratios. Their total REE (ΣREE) contents increase from coastal towards the open marine zone. The Xiamaling shales display a negative Ce anomaly, representative of marine shale, and show a negative Eu anomaly, which is representative of lacustrine oil shale and the Post-Archean Australian Shale (PAAS) and is different from typical marine shale of younger age, indicating the influx of terrestrial sediment.

Perhydrous organic carbon logging evaluation method in shore and shallow lacustrine shale formations: A case study of the Mesozoic lacustrine shale in the western Sichuan Basin, China

The types of organic carbon in shore and shallow lacustrine shales are more diverse than those in marine formations. It is of great importance to establish log interpretation models of the separate types of organic carbon content for hydrocarbon generation potential estimation. First, we summarize the main rock types and their logging characteristics in the shore and shallow lacustrine shale reservoirs and analyze the types of organic carbon in shore and shallow lacustrine shales using core pyrolysis analysis and kerogen maceral microscopic identification. Second, we establish the calculation method of the total organic carbon (TOC) content in the lacustrine shale formation by regression analysis. Third, we divide the organic matter in shore and shallow lacustrine shales into two parts: perhydrous organic carbon (perhydrous macerals) with a higher hydrogen index, higher H/C atomic ratio, and stronger hydrocarbon generation potential and subhydrous organic carbon (subhydrous macerals) with a lower hydrogen index, lower H/C atomic ratio, and poorer hydrocarbon generation potential. Furthermore, we introduce the concept of the mixed skeleton, combined with the formation component triangular chart, and establish calculation methods for perhydrous and subhydrous organic carbon contents. Finally, we apply this method to the Mesozoic shore and lacustrine shale in the western Sichuan Basin, China. The application indicates that the kerogen types of the Mesozoic shore and shallow lacustrine formations in the western Sichuan Basin are mainly type III and type IIB kerogen with a low content of perhydrous macerals. The perhydrous organic carbon content calculated by the logging evaluation model is positively correlated with the perhydrous maceral content obtained by kerogen maceral microscopic identification and the oil generation potential S2 obtained by core pyrolysis analysis. Logging analysts should use the perhydrous organic carbon content to estimate the hydrocarbon generation potential of shore and shallow lacustrine shale formations.

Effects of contact metamorphism on the lithium content and isotopic composition of kerogen in coal

Lithium isotopes (δ7Li) in coals have been shown to increase with thermal maturity, suggesting preferential release of 6Li from kerogen to porefluids. This has important implications for paleoclimate studies based on δ7Li of buried marine carbonates, which may incorporate Li from porefluids during recrystallization. Here, the Li content and isotopic composition of macerals from two coal seams intruded by dikes, were studied as a function of temperature across a thermal gradient into the unmetamorphosed coal. Samples were collected in Colorado (USA) from a Vermejo Fm. coal seam intruded by a mafic-lamprophyre dike and compared to a Dutch Creek No.2 coal seam intruded by felsic-porphyry dike; a potential source of Li-rich fluids.The Li-content and Li-isotope compositions of coal macerals were measured in situ by Secondary Ion Mass Spectrometry (SIMS). The macerals of the Vermejo coal samples, buried to VRo 0.68% (Tmax = 104 °C), contained <1.5 μg/g Li with an average vitrinite δ7Li of −28.4 ± 1.6‰, while liptinite and inertinite were heavier, averaging −15.4 ± 3.6‰ and − 10.5 ± 3.7‰, respectively. The contact metamorphosed vitrinite/coke showed the greatest change with temperature with δ7Li 18 to 37‰ heavier than the unmetamorphosed vitrinite.The Dutch Creek coal, buried to VRo 1.15% (Tmax = 147 °C), prior to dike emplacement, may have released Li during burial, as less isotopic change was observed between contact metamorphosed and unmetamorphosed macerals. Overall, Li contents were < 1 μg/g, and the vitrinite in metamorphosed coal had δ7Li values 8 to 21‰ heavier than the unmetamorphosed coal. SIMS measurements on macerals near the dike did not show an increase in Li-content indicative of Li derived from dike fluids, however previous bulk measurements that included silicates showed slightly higher (2-3 μg/g) Li-contents near the dike, suggesting possible Li incorporation from dike fluid into metamorphic silicates. A negative correlation was observed between Li-content and 12C+/30Si+ count ratios, indicating that at metamorphic temperatures Li becomes concentrated in silicates.

Novel Thermal and Microscopic Techniques To Determine the Causes of Suboptimal Combustion Performance at Colombian Stoker Furnaces.

This study presents the application of a novel approach, using thermal and optical techniques, to identify the causes of poor burnout performance of Colombian stoker furnaces in the Cauca Valley State. The four coals used in these furnaces were characterized to obtain particle size distribution, particle and tapped density, elemental and proximate composition, mineral composition, and maceral content. Up to 80% incomplete combustion was noted in macro-TGA tests compared to complete combustion in a micro-TGA. Reflectance and intrinsic reactivity measurements were for chars prepared in three different particle sizes (<6, 6–19, and 19 mm), three temperatures (700, 900, and 1050 °C), and three residence times (10, 30, and 120 min). Two of the coals produced char samples with reflectance values above 6%, which matched those seen in the stoker, indicating that the furnace temperature was not the cause of poor combustion and that only two of the four coals were likely to be present in the furnace bottom ash. These tests were also able to prove that oxygen diffusion limitation was the root cause of the poor burnout where the carbon inside the furnace bottom ash was shielded from oxygen ingress through the formation of a nonpermeable slag layer. Thus, this study demonstrates the potential of both thermal profiling and optical reflectance as a tool for forensically evaluating the thermal history and operational performance of furnaces.

Enhancement of dewatering performance of vitrinite-rich and inertinite-rich coals by surfactants: Experiment and simulation

The high moisture content of fine coals, especially flotation clean coals has affected the production of coal processing plants for a very long time. The two main components of fine coals are vitrinite and inertinite. The percentage of these two macerals present in the coal has an impact on the dewatering process. In this paper, the influence of surfactants on the dewatering effect of two samples with different maceral contents is studied. The results demonstrate that non-ionic surfactants have an excellent dewatering effect on vitrinite-rich coal, and it reduced the filter cake moisture by 1.84%, while cationic surfactants have an outstanding dewatering effect on inertinite-rich coal, and it reduced the filter cake moisture by3.81%. For both the coals, surfactant adsorption reduces the hydrophobicity of the coal. The best dewatering effect corresponds to the lowest filtrate surface tension and the loosest filter cake structure. Surfactants can reduce the pressure required to remove water from the filter cake by lowering the surface tension of the filtrate. In addition, surfactants have an agglomeration effect on fine coals, which increases the porosity of the coal and facilitates a low-moisture product. This study will help engineers select the suitable filter aid for the maceral content of coal and contribute to the development of efficient filter aids.

The Characteristics and Main Controlling Factors for the Formation of Micropores in Shale from the Niutitang Formation, Wenshuicun Section, Southwest China

The characteristics of shale micro-pore development and its main influencing factors have important theoretical guiding significance for shale gas exploration and resource evaluation. In order to clarify the micro-pore development characteristics of lower Cambrian shale and the main controlling factors of micro-pore development, we used the lower Cambrian Niutitang formation shale, in the Wenshuicun section of the Guizhou Province in southwest China. The micro-pore development characteristics of the shale in the region were studied by argon ion profile field emission scanning electron microscopy and a low-temperature liquid nitrogen adsorption and desorption experimental system. The relationship between micro-pore and kerogen maceral composition, total organic carbon (TOC) content and different mineral content was analyzed in combination with mineral and geochemical characteristics. Inorganic pores (clay mineral pores, dissolution pores and pyrite intergranular pores) and micro-fractures (clay mineral shrinkage crack, tectonic fractures and overpressure fractures) were the main type of pore developed in the shale of the Niutitang formation in the Wenshuicun section, and no organic pores had developed. The pore size of shale is usually 2–50 nm, accounting for 58.33% of shale pores, e.g. mesopores. Clay mineral content has an obvious positive correlation with macropore volume and average pore diameter, and an obvious negative correlation with micropore volume. In addition, the content of feldspar in brittle minerals has a strong negative correlation with macropore volume and average pore diameter, and a strong positive correlation with micropore volume and BET-specific surface area. TOC content and the content of different kerogen macerals have no obvious correlation with the development of shale micropores in this region. It is concluded that inorganic mineral composition is the main controlling factor of micro-pore development within lower Cambrian shale, and organic matter abundance and maceral content have little influence on the micro-pore development. This study provides a case study for the characteristics of micropores in lower Cambrian shale in China.

Geochemistry and petrology of selected sediments from Bukit Song, Miri, Sarawak, Malaysia, with emphasis on organic matter characterization

The aim of this study is to provide a better understanding of the type of source input, quality, quantity, the condition of depositional environment and thermal maturity of the organic matter from Bukit Song, Sarawak, which has not been extensively studied for hydrocarbon generation potential. Petrological and geochemical analyses were performed on 13 outcrop samples of the study location. Two samples, having type III and mixed kerogen, showed very-good-to-excellent petroleum potential based on bitumen extraction and data from Rock–Eval analysis. The rest of the samples are inert—kerogen type IV. In terms of thermal maturity based on vitrinite reflectance, the results of this paper are akin to previous studies done in the nearby region reported as either immature or early mature. Ph/n-C18 versus Pr/n-C17 data showed that the major concentration of samples is within peat coal environment, whilst two samples were associated with anoxic marine depositional environment, confirmed by maceral content as well. Macerals mainly indicated terrestrial precursors and, overall, a dominance of vitrinite. Quality of the source rock based on TOC parameter indicated above 2 wt. % content for the majority of samples. However, consideration of TOC and S2 together showed only two samples to have better source rocks. Existence of cutinite, sporinite and greenish fluorescing resinite macerals corroborated with the immaturity of the analysed coaly samples. Varying degrees of the bitumen staining existed in a few samples. Kaolinite and illite were the major clays based on XRD analysis, which potentially indicate low porosity. This study revealed that hydrocarbon-generating potential of Bukit Song in Sarawak is low.

SHAP-based interpretation of an XGBoost model in the prediction of grindability of coals and their blends

ABSTRACT The Hardgrove Grindability Index (HGI) is a measure of coal’s resistance to crushing. HGI is influenced by many factors due to the complex structure of coal. This study examines the effect of the proximate and ultimate analysis and maceral content on HGI, based on 329 samples of Polish coals. In this study, a machine learning technique XGBoost (Extreme gradient boosting regressor) was used to develop a predictive model of HGI with satisfactory accuracy (R2 = 0.86). The Shapley additive explanations (SHAP) technique was used to explain the relationship between the predicted value and the input data. Studies have shown that the moisture (negative impact), carbon (positive), volatile matter (negative), vitrinite (positive) and liptinite (negative) content have the greatest impact on HGI. Additionally, three experimentally obtained coal blends that differ significantly in the degree of grindability were selected for testing the model. The results confirmed the effectiveness of the method when used also for blends. The influence of individual coal parameters on the predicted grindability of the blends has been thoroughly examined.

Constraints of biomethane generation yield and carbon isotope fractionation effect in the pathway of acetotrophic with different coal-rank coals

Biomethane is a clean, renewable, and environment-friendly resource, arousing wide attention worldwide. Eleven coals with vitrinite reflectance ranging from 0.18% to 2.50% were collected from underground coal mines; biomethane production process and carbon isotope fractionation effect in the 123 days biodegradation experiment were implemented. Results show that different coal-rank coals can be degraded by microorganisms and produce specific amounts of biomethane. However, the biomethane yield is related to the maceral contents rather than coal rank. The generation processes of methane and carbon dioxide exhibit the three-phases characteristics. The carbon isotope composition of biodegraded coal is lighter than that of raw coal. The liptinite inhibited biomethane production when the content of vitrinite is higher than 80%. The mineral promotes biomethane production when the content of vitrinite ranges from 60%~80%. The biomethane production yield is low, with vitrinite content less than 60%. The carbon isotope composition of coal organic matter is about −24.0‰, the carbon isotope compositions of CH4 (δ13C-CH4), CO2 (δ13C-CO2) and acetic acid (δ13C-ac) are −52.6‰~–22.1‰, −29.5‰~−24.5‰, and −40.7‰~−20.15‰, respectively. The CO2-CH4 isotope fractionation coefficient (αCO2-CH4) and its fractionation factors (εC) range from 1.001 to 1.025 and 0.50 to 23.80, proving that biomethane mainly generated from acetotrophic. The carbon isotope fractionation effect in the coal-methane conversion was jointly controlled by the anaerobic methane oxidation, multi-stage degradation, and substrate consumption.

Thermal Behavior of Some Indian Coals: Inferences from Simultaneous Thermogravimetry–Calorimetry and Rock–Eval

In this work, thermal behaviors of ten coal samples (across different thermal maturity levels) collected from five different open cast mines in the Jharia and Raniganj basins, India, were examined using differential scanning calorimeter (DSC), thermogravimetry (TG–DTG), Rock–Eval, and organo-petrographic techniques. Rank played a critical factor in controlling their thermal behavior, and with increasing coal rank the combustion parameters shifted towards higher temperatures. The oil-window mature non-coking coals were marked by least ignition and burnout temperatures, least DSC Tpeak, DTG Tpeak, and maximum reactivity. In contrast, the coking-coal samples of peak-oil window and condensate wet–gas window stages of maturity, because of their higher thermal maturity level and lower reactivity, required higher temperatures for combustion. Among the peak-oil window mature coking coals, one sample (C4) showed distinct lower combustion parameters relative to others, although vitrinite reflectance (Ro; %) and Rock–Eval pyrolysis Tmax showed similar results as the other coals. This sample was marked by higher reactive maceral content. Highest combustion parameters and least reactivity were shown by the Jhama sample (baked coal), followed by the condensate wet–gas window mature coking coals. The Rock–Eval S4 Tpeak clearly resolved the coal samples with distinct maturities and complemented the results from TG–DTG–DSC thermograms. Our results indicate that Rock–Eval S4Tpeak can be used to decipher convincingly the thermal maturity level of coals.

Density - A contentious issue in the evaluation and determination of Resources and Reserves in coal deposits

SYNOPSIS The initial evaluation of a coal deposit often raises uncertainty with regard to the accuracy of the reported Resources and Reserves. Reconciliation of results from mining and beneficiation with the original raw field data highlights deficiencies in original estimations. Credible Resource and Reserve estimation forms the basis on which an entire mining enterprise is motivated, initiated, funded, and established as a commercially viable proposition. This is required for sustainable extraction purposes and to support vital downstream industries such as power generation. Accurate determination of the density of the matrix of the material being evaluated is the key to credible values being obtained for Resources and Reserves. Losses between 15% and 20% of the Resource/Reserve can be realized if incorrect densities are applied to the tonnage derivation. Coal plies and particles have different relative densities, determined by the maceral composition, rank, and mineral and moisture content. These factors in turn contribute to the moisture, volatile matter, ash and carbon contents of a coal, which affect the overall density of the raw coal. More specifically, the relationship of ash to density and the effective matrix porosity were found to be critical in solving the greater majority of the problems in predictive calculations. A major deficiency identified is the inability to determine effective porosity, allowing absorption of adventitious moisture and altering the mass of the core sample. Although the volume of the raw material is altered through crushing, the change in mass after controlled air-drying, used with the original geometrical volume of the raw material, provides a credible air-dry density and allows the determination of the volumetric change related to effective porosity. This parameter can be validated through the evaluation of proximate ash using the ash-adjusted algorithm and a correction for the inherent moisture applied to also give a credible relative density value for an air-dried sample. A combination of theoretical, empirical, and reconciliatory evaluations of the available data, taken from the exploration phase through the mining process to final production, has shown that an integrated approach using the ash-adjusted density (AAD) methodology, in conjunction with other evaluative techniques, provides credible results with a considerably higher degree of accuracy than is currently possible. Keywords: coal, deposit evaluation, Resources, Reserves, density determination, ash-adjusted density.

Research of wetting selectivity and wetting effect of imidazole ionic liquids on coal

In order to reduce the amount of coal dust, it is necessary to select the optimal concentration of ionic liquid to achieve the most significant wetting effect for a specific coal sample. In this paper, different concentrations of imidazole ionic liquids [Bmim][Cl], [Bmim][BF4] and coal samples were selected. Through proximate analysis, ultimate analysis, coal micro-component analysis, the DSA25 optical droplet morphology analysis system, and Scanning electron microscope was used to study the wetting selectivity and wetting effect of ionic liquid on coal. The results show that the magnitude of the surface tension of the ionic liquid affects the size of the contact angle, and the key ion [Cl]− or [BF4]− that reduces the contact angle is not a single role but requires [Bmim]+ synergy. The change of the contact angle shows that [Bmim][Cl] has a significant wetting effect on #I (hvBb) when the concentration is 6%, and [Bmim][BF4] on #II (sa) and #III (hvAb) at 8% has the best wetting effect. Besides, the less vitreous group in the maceral content of coal sample, the more oxygen content in the element, the stronger wettability, meanwhile, the rougher the surface morphology of coal samples treated with ionic liquid, the stronger the water storage capacity and the better the wetting effect. This article provides the basis for different imidazole ionic liquids to select specific coal samples to improve coal mine wetting efficiency, which is of special significance to actual production.