International Journal of Coal Geology最新文献

{"title":"Advancing shale geochemistry: Predicting major oxides and trace elements using machine learning in well-log analysis of the Horn River Group shales","authors":"Ammar J. Abdlmutalib ,&nbsp;Korhan Ayranci ,&nbsp;Umair Bin Waheed ,&nbsp;Nicholas B. Harris ,&nbsp;Tian Dong","doi":"10.1016/j.coal.2025.104767","DOIUrl":"10.1016/j.coal.2025.104767","url":null,"abstract":"<div><div>This study evaluates machine learning algorithms for predicting geochemical compositions in the Middle to Upper Devonian Horn River Group shales. The minor textural variations within shale successions necessitate a detailed understanding of their geochemical composition for accurate interpretation of depositional environments and stratigraphic relationships. Geochemical analysis is essential for unconventional reservoir shales but is traditionally labor-intensive. Machine learning offers a cost-effective alternative, streamlining geochemical interpretation and stratigraphic correlation. Five models, Random Forest Regressor, Gradient Boosting Regressor, XGBoost, Support Vector Regressor, and Artificial Neural Networks (ANN), were assessed using well-log data to predict major oxides and trace elements. Training and validation used data from two wells, with model performance tested on an unseen well to evaluate generalizability. Tree-based models, particularly Random Forest Regressor, demonstrated high accuracy for major oxides such as K₂O and CaO, while Gradient Boosting Regressor excelled for Al₂O₃ and TiO₂. However, SiO₂ and Na₂O were less predictable due to their complex origins and low concentrations. For trace elements, Random Forest Regressor effectively predicted Th, Zr, Co, and total rare earth elements (∑REE). Redox-sensitive elements such as Mo, Cu, U, and Ni had lower accuracy due to their weaker correlation with well-log data; however, Random Forest Regressor still achieved the best performance among the models for these elements. Blind tests confirmed the generalizability of the models, with tree-based models maintaining strong predictive performance for several major oxides, trace elements, and REEs, while ANN and Support Vector Regressor exhibited robustness in Al₂O₃, K₂O, and TiO₂ predictions. This study highlights tree-based models as reliable tools for predicting geochemical compositions, supporting chemostratigraphy and reservoir characterization. Integrating machine learning with well-log data offers a promising solution for efficient geochemical analysis and subsurface characterization in Devonian shale reservoirs.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"304 ","pages":"Article 104767"},"PeriodicalIF":5.6,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143817711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reconstructing the late Permian-early Triassic environment of a coal-bearing succession in the Maniamba Basin, Mozambique (Central Gondwana): A multiproxy palynological and geochemical approach","authors":"N. Nhamutole ,&nbsp;M.K. Bamford ,&nbsp;P.A. Souza ,&nbsp;C.M. Felix ,&nbsp;E. Pereira ,&nbsp;L. Bastos ,&nbsp;L. Mendes ,&nbsp;O. Deus ,&nbsp;M. Nopeia ,&nbsp;D.A. Carmo","doi":"10.1016/j.coal.2025.104755","DOIUrl":"10.1016/j.coal.2025.104755","url":null,"abstract":"<div><div>The Maniamba Basin is an intracratonic, Karoo-aged basin located in northern Mozambique. Recent studies have reported the occurrence of organic-rich units in the Maniamba Basin, based on Rock Eval data. However, detailed characterization of the palaeoenvironments in the basin is still lacking. In this study, detailed palynological, palynofaciological, XRD and organic geochemical techniques (TOC, total sulphur, and biomarkers) were performed in order to understand past environments that prevailed in the basin. The palynological data reveal the dominance of gymnosperm taxa (striate and non-striate bisaccate, and praecolpate pollen grains) followed by lycopsids, sphenopsids and ferns suggesting hypautochthonous sedimentation characterized by warm and humid palaeoclimate. The palynological results indicate a Permian and Triassic age for the strata. The organic-rich units unveiled a dominance of phytoclasts and palynomorphs, and to a lesser extent by terrestrial and bacterially derived organic matter with no fluorescence, indicating high maturity. Swamp, river and lake dominated environments with oxic-suboxic-anoxic conditions, reflecting shifting of depositional conditions overtime, are inferred in the Maniamba Basin. The deposition and accumulation of organic-rich units were mainly controlled by palaeoredox conditions linked to basin infill during different rifting episodes. The biomarkers mainly consist of saturated compounds that suggest terrestrial organic matter with freshwater algal contribution.</div><div>Overall, the integration of mineralogical composition with palynofacies, biomarkers and palynology indicate the presence of potential source rocks that were thermally influenced. Additionally, the petroleum fluids known from younger strata in the Rovuma and Mozambique basins did not show any link with the source rock reported previously.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"304 ","pages":"Article 104755"},"PeriodicalIF":5.6,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143767826","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Domestic combustion of biomass pellets: Example from Poland","authors":"Agnieszka Drobniak ,&nbsp;Zbigniew Jelonek ,&nbsp;Kamila Widziewicz-Rzońca ,&nbsp;Maria Mastalerz ,&nbsp;Arndt Schimmelmann ,&nbsp;Iwona Jelonek","doi":"10.1016/j.coal.2025.104757","DOIUrl":"10.1016/j.coal.2025.104757","url":null,"abstract":"<div><div>In the context of the European Union's intensified efforts to curb greenhouse gas emissions and meet climate targets, wood pellets have emerged as a pivotal element in the renewable energy strategy. Yet, biomass pellet combustion has been linked to a range of pollutants impacting air quality and public health. As biomass utilization gains popularity as a fuel for residential heating, it is important to determine this impact and enhance sustainable practices throughout the entire biomass energy production cycle.</div><div>This study investigates the intricate dynamics of biomass pellet properties on their combustion emissions, with a specific focus on the differences observed between pellets of woody and non-woody origins. The data reveal a variation in pellet characteristics, especially regarding their ash yield and fines contents, mechanical durability, and impurity levels, and significant differences in the type and amount of utilization emissions. The results highlight potential health risks posed by the combustion of biomass fuels, particularly non-woody (agro) pellets, due to elevated concentrations of emitted particulate matter (PM), carbon monoxide (CO), nitrogen dioxide (NO₂), hydrogen sulfide (H₂S), ammonia (NH₃), chlorine (Cl₂), sulfur dioxide (SO₂), and formaldehyde (HCHO), all surpassing recommended limits.</div><div>Moreover, the study reveals that emissions from pellet combustion could be partially predicted by analyzing pellet characteristics. Statistical analysis identified several key variables—including bark content, fines content, mechanical durability, bulk density, heating value, net calorific value, sulfur, and nitrogen content—that impact emissions of CO, NO₂, H₂S, SO₂, HCHO, and respiratory tract irritants. These findings underscore the need for proactive measures, including the implementation of stricter standards for fuel quality and emissions, alongside public education initiatives promoting the cleanest and safest fuels possible.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"304 ","pages":"Article 104757"},"PeriodicalIF":5.6,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143791168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"","authors":"Gregory Smith","doi":"10.1016/j.coal.2025.104756","DOIUrl":"10.1016/j.coal.2025.104756","url":null,"abstract":"","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"304 ","pages":"Article 104756"},"PeriodicalIF":5.6,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143817710","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The role of geological fluids on the distribution of lithium in anthracite, an example from the Yangquan Mining District, Qinshui Basin, northern China","authors":"Huidi Hao ,&nbsp;Bo Jiu ,&nbsp;Wenhui Huang ,&nbsp;Chunlan Yu ,&nbsp;Zhaoguo Wang ,&nbsp;Binchao Qin ,&nbsp;Linghao Huang","doi":"10.1016/j.coal.2025.104754","DOIUrl":"10.1016/j.coal.2025.104754","url":null,"abstract":"<div><div>Coal with abundant kaolinite and illite has become an important target for the exploration of potential coal-hosted lithium deposits. The No.15 coal from the Xinjing Mine, northern China, is rich in kaolinite, illite, and NH₄-illite. This study comprehensively applied multi-scale mineral analysis and in-situ micro-regional characterization methods to analyze the lithium content distribution in clay minerals, while elucidating the genetic mechanisms of clay minerals and their interactions with geological fluids. The genesis of these minerals and their interaction with geological fluids during thermal evolution were analyzed using whole-rock and in-situ geochemical methods. Lithium is enriched in the No.15 coal (42.2 μg/g). The Li concentration in clay minerals in the No.15 coal seam follows a descending order of: cryptocrystalline kaolinite (649.9 μg/g) &gt; detrital kaolinite (366.1 μg/g) &gt; cell-filling kaolinite (94.8 μg/g) &gt; illite (16.1 μg/g) and NH₄-illite (21.1 μg/g). Cryptocrystalline and detrital kaolinite are thus the primary hosts of Li. Whole-rock and mineral geochemical data indicate detrital input as the main source of Li. The similarities in the REE distribution patterns between kaolinite in coal and Yinshan granite suggest that kaolinite, a key weathering product of acidic magmatic rocks in humid sedimentary systems, may have originated from the Yinshan Mountain granite. The presence of seawater and organic acids within coal-bearing strata collectively facilitate the illitization of kaolinite at temperatures of 120–140 °C. The negative correlation between Gd anomalies and Sr/Ba ratios indicates that the interaction between groundwater and seawater has established a geochemical barrier, which facilitates the enrichment of Li in coal.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"303 ","pages":"Article 104754"},"PeriodicalIF":5.6,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143704614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Vitrinite reflectance patterns from the Riosa-Olloniego Sector (Carboniferous, Cantabrian Zone, NW Spain): Overburden implications","authors":"Luis Pedro Fernández ,&nbsp;Miguel Allende ,&nbsp;Ángeles G. Borrego","doi":"10.1016/j.coal.2025.104753","DOIUrl":"10.1016/j.coal.2025.104753","url":null,"abstract":"<div><div>Vitrinite reflectance is a parameter of organic matter maturity considered of paramount importance to reconstruct the history of sedimentary basins (palaeotemperature, depth of burial, unconformities, tectonic overprinting, local thermal anomalies). Although sensitive to external factors (vitrinite alteration, maceral composition, lithology) that may harm its reliability, it is still the most robust tool widely applied in sedimentary basins. In this work, vitrinite reflectance is used to study the post-sedimentary evolution of a Carboniferous (Moscovian, Asturian) succession (Riosa-Olloniego Sector, Central Asturian Coalfield) of the Cantabrian Zone foreland basin (NW Spain). Fourteen samples (coals, carbonaceous shales and channel sandstones with rip-up coaly clasts and plant fragments) from an 800-m-thick, mixed continental–marine interval and two localities, underground (coal mine) and on surface, respectively, were subjected to chemical and petrographic analyses. Attention was paid to the influence of the above-mentioned external factors. The organic matter plots in the Kerogen type III field and has a Bituminous C-B coal rank, with generally low S content. Reflectance values range from 0.79 to 1.07 Ro% with a gradient of ∼0.3 Ro%/km for both mine and surface samples, which plot along similar trends but with the latter yielding comparatively lower values. Palaeotemperatures calculated from vitrinite reflectance using the most general models yielded palaeogeothermal gradients of 23–36 °C/km and maximum burial depths of ∼3.9–5.2 km, depending on the model. It was concluded that the vitrinite reflectance was mainly governed by sedimentary burial, with differences between mine and surface values reflecting variable tectonic overburden under a neighbouring nappe (Aramo Nappe).</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"304 ","pages":"Article 104753"},"PeriodicalIF":5.6,"publicationDate":"2025-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143726003","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Enrichment of Al-Li-Ga-Nb(Ta)-Zr(Hf) in the Permo-Carboniferous coal-bearing sequences of the Jungar Coalfield, northern China","authors":"Yuan Wang ,&nbsp;Jing Li ,&nbsp;Daohua Wang ,&nbsp;Xin Luo ,&nbsp;Wei Yuan ,&nbsp;Hongguang Cai ,&nbsp;Han Zhang ,&nbsp;Xiangdong Feng ,&nbsp;Shuai Guo ,&nbsp;Wenhua Li ,&nbsp;Xinguo Zhuang ,&nbsp;Van Long Hoang","doi":"10.1016/j.coal.2025.104752","DOIUrl":"10.1016/j.coal.2025.104752","url":null,"abstract":"<div><div>Coal-hosted critical metal deposits have emerged as a viable alternative to conventional critical metal resources and have garnered significant attention in recent years. Notable enrichments of critical metal assemblages, including aluminum, gallium, lithium, and rare earth elements and yttrium (REY) have been identified in several Permo-Carboniferous coal measures within the Jungar Coalfield and across other coalfields in the Ordos Basin, northern China. Using a number of analytical techniques such as X-ray diffraction analysis (XRD), scanning electron microscopy (SEM-EDX), the TIMA-X integrated mineral analyzer, X-ray fluorescence spectroscopy (XRF), inductively coupled plasma-mass spectrometry (ICP-MS), and LA-ICP-MS, this study systematically investigates the mineralogical and geochemical characteristics of three economically significant coal seams (Nos. 3, 6 upper, and 6 coal) in the Laosangou exploration area of the northern Jungar Coalfield. The study focuses on the modes of occurrence, enrichment mechanisms, and economic potential of critical metal assemblages within the coal deposits.</div><div>Compared to the average for world hard coals, Al-Ga-Li-Nb(Ta)-Zr(Hf) assemblages are generally enriched in the No. 3 coal of the Shanxi Formation and Nos. 6 upper and 6 coals of the Taiyuan Formation, and exhibit much higher values in the lower portion of the No. 6 coal adjacent to or within the tonsteins. Aluminum, Ga, and Li in the studied coals are primarily hosted in kaolinite and/or boehmite, while Nb, Ta, Zr, and Hf primarily occur in zircon and/or anatase embedded within kaolinite. The critical metals in the studied coals all demonstrate promising economic potential and could potentially be extracted from the coal-combustion fly ashes.</div><div>The enrichment of the Al-Li-Ga-Nb(Ta)-Zr(Hf) assemblages in these coals is attributed to contributions from both terrestrial sediment sources and pyroclastic materials, as well as hydrothermal fluid injections. The sediment provenance of the studied coals includes inputs mainly from the Yinshan Oldland, northern Trans North China Orogens (TNCO), and bauxite-rich weathering crusts of the Benxi Formation, which served as initial sources of Al, Li, Ga, and other critical metals. Additionally, the intermediate-felsic alkaline volcanic ash enriched in Li, Ga, Nb, Ta, Zr, and Hf along with the injection of acid groundwater or low-temperature hydrothermal fluids further facilitated the enrichment of these critical metals.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"303 ","pages":"Article 104752"},"PeriodicalIF":5.6,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143678267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tracing highly oxidized events and its response to peat dynamic from the northwest Kapuas coastal wetlands, Indonesia","authors":"Aulia Agus Patria ,&nbsp;Stephen P. Obrochta ,&nbsp;Ferian Anggara","doi":"10.1016/j.coal.2025.104751","DOIUrl":"10.1016/j.coal.2025.104751","url":null,"abstract":"<div><div>Peat deposits are highly sensitive to environmental changes and are well-suited to palaeobotanical investigations. Therefore, we assess the integration between organic petrology, palynology, and microcharcoal distributions to provide a robust interpretation on peatland dynamic and paleoenvironmental reconstruction. In addition, we propose a peat characterization using a quantitative color coordinate (CIELAB) to reduce biases while characterizing peat via qualitative comparisons to the Munsell soil color chart. This study was conducted in low-lying mires in the northwest Kapuas coastal plain, West Kalimantan, Indonesia. Five types of peat were identified: sapric muck, sapric shorts, sapric wood, coarse hemic, and fine hemic. The quantitative color coordinate analysis successfully recognizes the peat physical properties but is not directly related to the peat type. Higher values of the red-green chromaticity index (a*) indicate a greater preservation of plant material. Conversely, lower values represent charcoal or an oxidized layer of organic matter. Higher contents of inertinite or oxidized organic matter are comparable to the microcharcoal abundance, showing the presence of severe fires. At least eight fire events were reported, with decreasing intensity towards top of the core. Variation in microcharcoal abundances led to a degree of preservation changes, nutrient status and paleovegetation shift in the studied area. Four phases of peat dynamics were identified: initiation, early ombrogenous, late ombrogenous, and topogenous phases. In general, past vegetation shows an alternation community of mixed-riparian forest and open vegetation to present day mangrove low-lying topogenous mire. Our findings refer to the vulnerability of vegetation changes and peat dynamics concerning on highly oxidized events related to the fire intensity as an important driver in the northwest coastal wetlands of Kalimantan Island.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"303 ","pages":"Article 104751"},"PeriodicalIF":5.6,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643156","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Elastic anisotropy and deformation characteristics of Pennsylvania anthracite","authors":"Bodhisatwa Hazra ,&nbsp;Hem Bahadur Motra ,&nbsp;James C. Hower ,&nbsp;Maria Mastalerz ,&nbsp;Chinmay Sethi ,&nbsp;Harold Schobert","doi":"10.1016/j.coal.2025.104740","DOIUrl":"10.1016/j.coal.2025.104740","url":null,"abstract":"<div><div>The mechanical behavior and elastic anisotropy of coal under stress are critical to understanding its structural integrity and performance in subsurface environments. Despite its significance, limited research has systematically analysed the elastic anisotropic responses of coals under such conditions. This study investigates the elastic anisotropy of three anthracite-rank coals, Primrose, Lattimer, and Mt. Carmel, subjected to conventional triaxial loading. P-wave (V_P) and S-wave (V_S) velocities, along with Thomsen parameters (ε and γ), were evaluated to elucidate the effects of increasing vertical stress on the structural integrity and anisotropy of each coal type. The results reveal that the Primrose coal exhibits the highest structural integrity, maintaining elevated V_P and V_S values and stable Thomsen parameters under stress due to its dense microstructure, higher inertinite content, and low porosity, which resist stress-induced microcracking. In contrast, the Lattimer coal demonstrates a significant reduction in VP and ε beyond 45 MPa, indicating greater susceptibility to microstructural damage and a trend towards isotropy as stress increases. The Mt. Carmel coal shows intermediate behavior, with moderate decreases in VP and ε but relatively stable γ values, reflecting a balanced resistance to structural degradation. S-wave anisotropy, as evidenced by shear wave splitting, remains most prominent in the Primrose coal, suggesting its superior ability to retain directional properties and resist stress-induced deformation. Principal component analysis highlights the role of rank, inertinite-to-vitrinite ratio, and aromaticity in influencing the mechanical responses of the coals, with Primrose coal consistently segregating as the most robust and anisotropically stable sample. These findings underscore the critical influence of compositional and microstructural differences on coal's anisotropic behavior under conventional-triaxial loading. They provide valuable insights for applications in subsurface energy extraction and storage, where understanding the mechanical and anisotropic properties of coal is essential for optimizing performance and mitigating risks.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"303 ","pages":"Article 104740"},"PeriodicalIF":5.6,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143609970","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Origin of chemical structure and pore heterogeneity of over-matured organic matter in the Paleozoic marine shales, China","authors":"Yingzhu Wang ,&nbsp;Jijin Yang","doi":"10.1016/j.coal.2025.104742","DOIUrl":"10.1016/j.coal.2025.104742","url":null,"abstract":"<div><div>Organic matter (OM) pores play a leading role in gas storage for many shale formations, and understanding their development mechanism is critical to evaluating the mechanisms of shale gas enrichment. However, an insufficient knowledge of OM compositional and structural complexity makes the origin of pore heterogeneity still unclear. This study correlates high-resolution scanning electron microscopy (SEM) and Raman microscopy to investigate the association of OM molecular structure and pore development in the Cambrian Niutitang shales and Silurian Longmaxi shales, south China. Results show that pyrobitumen, the predominant OM maceral, can be divided into two types (PB1 and PB2) which have differences in petrographic characteristics, Raman parameters, and pore distribution. In the shales with good gas preservation, the pore-filling PB2 shows a lower degree of aromaticity, a higher apparent transformation ratio (15 %–40 %), and larger pore size (peak of 80–90 nm) than that of the less porous PB1. In the poorly-preserved shales, different pyrobitumen exhibit homogeneous molecular structure and smaller pore size (peak of 30–40 nm). The poor development of OM-hosted pores in the Niutitang shale is related to the increased OM graphitization at a Ro &gt; 3.5 %. The heterogeneity of OM structure and porosity in different Longmaxi shales would be originally impacted by a distinction in the degree of oil expulsion under different preservation condition. In the well-preserved shales, a higher retention of aliphatic-rich oil may lead to the more porous and less aromatic pyrobitumen, and thus a higher current gas content. The study provides new insights into the OM chemical controls on nanoscale pore heterogeneity, which is significant for shale gas exploration.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"303 ","pages":"Article 104742"},"PeriodicalIF":5.6,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143576864","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}