International Journal of Coal Geology最新文献

{"title":"Electron microbeam investigations of the spent ash from the pilot-scale acid extraction of rare earth elements from a beneficiated Kentucky fly ash","authors":"Debora Berti ,&nbsp;John G. Groppo ,&nbsp;Prakash Joshi ,&nbsp;Dorin V. Preda ,&nbsp;David P. Gamliel ,&nbsp;Todd Beers ,&nbsp;Michael Schrock ,&nbsp;Shelley D. Hopps ,&nbsp;Tonya D. Morgan ,&nbsp;Bernd Zechmann ,&nbsp;James C. Hower","doi":"10.1016/j.coal.2025.104738","DOIUrl":"10.1016/j.coal.2025.104738","url":null,"abstract":"<div><div>Fly ash derived from the combustion of an eastern Kentucky high volatile bituminous coal blend was, as discussed in previous studies, beneficiated to yield a − 75-μm product with a reduction in the carbon and spinels. The beneficiated fly ash was reacted with a strong acid in a pilot-scale unit to extract rare earth elements (REE) and other major and minor elements. In this study, polished, epoxy-bound pellets of the beneficiated and acid-extracted ashes were examined via scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Selected slices of the polished section were extracted using a focused ion beam (FIB) technology and further examined via transmission electron microscopy (TEM) and EDS. The bulk chemistry of the original feed ash (not studied by microbeam methods), the beneficiated ash, and the acid-extracted ash exhibit similar Upper Continental Crust-normalized REE patterns. The bulk chemistry indicates that the concentrations of the major oxides (aside from SiO₂), REE, V, Cr, Mn, Ni, As, Rb, Sr, Zr, Ba, and Pb are less in the processed ash compared to the beneficiated ash. The fly ashes have H-type distributions (La_<em>N</em> &lt; Lu_<em>N</em>) with a strong M-type (medium type: La_N/Sm_N &lt; 1, Gd_N/Lu_N &gt; 1) contribution. Among the REE and Y, SEM-EDS and TEM-EDS showed the presence of zircon with Y (and Ce, Nd, and Gd, perhaps from an adjacent monazite); xenotime; a Dy-rich xenotime-structure mineral: and monazite with light REE (La, Ce, Pr, Nd, and Sm), Gd, Dy, Er, and Th. Glassy Al-Si-rich fly ash spheres showed the presence of Ce, Nd, Sm, and Dy but no discernable minerals at the scale of the SEM view. Certain spheres showed 2- to 4-μm amorphous rims surrounding nano-crystalline cores. As with the depletion of elements in the bulk fly ash, the amorphous rims showed a relative increase in Si and a depletion or apparent elimination of other elements, including the REE. It is possible that the apparent absence of 2- to 4-μm particles may mean that these particles were totally or largely dissolved by the acid or as a consequence of multiple wash-filtration cycles to remove leachate from the spent ash. Processing of a combination of a finer size than processed in this pilot-scale investigation and/or more fractured particles, perhaps via a pre-processing step, would permit a greater penetration of the acid into the interior of the fly ash particles, leading to a greater recovery of REE.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"303 ","pages":"Article 104738"},"PeriodicalIF":5.6,"publicationDate":"2025-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143549085","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":"Reassessment of the Pennsylvanian bio- and chronostratigraphy of the Saar-Lorraine Basin using high-precision UPb ages of volcanic ashes","authors":"Alain Izart ,&nbsp;Stanislav Opluštil ,&nbsp;Raymond Michels ,&nbsp;Sebastian Voigt ,&nbsp;Christoph Hartkopf-Fröder ,&nbsp;Jocelyn Barbarand ,&nbsp;Thomas Blaise ,&nbsp;Jiří Laurin ,&nbsp;Mark Schmitz ,&nbsp;Salim Allouti ,&nbsp;Romain Hemelsdael ,&nbsp;Jacques Pironon","doi":"10.1016/j.coal.2025.104724","DOIUrl":"10.1016/j.coal.2025.104724","url":null,"abstract":"<div><div>Chronostratigraphic calibration of the Westphalian and early Stephanian succession in the Saar-Lorraine Basin of Germany and France has been improved using high-precision U<img>Pb zircon dating of intercalated tonsteins (volcanic ashes) in coal seams. The clay mineralogy and elemental composition were determined to specify the source of these volcanic ashes and the post-depositional weathering processes. Samples selected for dating were tonsteins with homogeneous zircons without zoning to avoid the inherited ages from the volcanic chamber. Four of them provided concordant ages in agreement with their stratigraphic position. New radiometric ages constrain the hiatus below the Holz Conglomerate approximately between 307.9 and 306.0 Ma, that corresponds to the early and mid-Cantabrian substage as defined in its type area, the NW Spain. The age of T600 tonstein, which corresponds in Saar-Lorraine Basin to the Duckmantian/Bolsovian boundary is fully in agreement with ages of that boundary determined in the Ruhr Basin of the Variscan foreland and in continental basins of the Bohemian Massif. T10 tonstein on top of the Westphalian succession confirms its late Asturian age previously determined from macroflora. T00 tonstein in the Ottweiler Group provided a mid-Barruelian age, which allowed to re-define macrofloral biozones in the lower part of that group from <em>Alethopteris zeilleri</em> of Saberian substage to <em>Crenulopteris lamuriana</em> of Barruelian substage. New U<img>Pb ages further improved correlation of local lithostratigraphic units with other basins in Europe and also with global marine-based stages. These new ages allow us to compare radioisotopically constrained Bayesian age model to metronomic age models from Bolsovian to Barruelian and show that the high frequency sequences fall in the range of the precession and obliquity. The sources of the volcanic ashes were probably volcanoes in the Vosges and Black Forest massifs. Considered could be also volcanic centers at a larger distance, e.g., the Teplice-Altenberg volcanic complex for Westphalian, Gothard and Aar massifs in Alps and the Thüringian Forest in Saxony for Stephanian and Autunian tonsteins. The detrital zircons extracted from the sandstones of the Bolsovian deposits and Holz Conglomerate (late Cantabrian) show a wide range of ages from Precambrian to Ordovician that confirms the northward source of these zircons (Rhenohercynian zone) mixed with a local source from the Mid-German Crystalline High.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"302 ","pages":"Article 104724"},"PeriodicalIF":5.6,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143479072","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":"Evolution of pore structure in the Upper Cretaceous Second White Speckled Shale during thermal maturation: Insights from artificial and naturally matured samples","authors":"Haiping Huang ,&nbsp;Hong Zhang ,&nbsp;Zhongliang Ma ,&nbsp;Xiangrong Yang ,&nbsp;Yong Ma ,&nbsp;Lunju Zheng","doi":"10.1016/j.coal.2025.104728","DOIUrl":"10.1016/j.coal.2025.104728","url":null,"abstract":"<div><div>The evolution of pore structures in marine shale during thermal maturation was investigated using naturally matured samples (Ro 0.46–1.26 %) from the Upper Cretaceous Second White Speckled Shale and artificially matured samples in a semi-open system (200–450 °C). Analytical techniques, including Rock-Eval pyrolysis, FIB-FESEM, and nitrogen adsorption, revealed key trends in pore volume (PV) and specific surface area (SSA). Immature samples exhibited high PV and SSA, which decreased during early oil generation (Ro ∼0.98 % or 350 °C) due to compaction and oil infill. PV and SSA rose significantly between Ro 0.98 % and 1.26 % (350–400 °C), driven by mesopore development, and remained elevated at higher temperatures. Artificially matured samples showed higher PV and SSA compared to naturally evolved samples, reflecting the absence of compaction and cementation processes in laboratory conditions. Naturally evolved samples demonstrated greater heterogeneity due to expulsion dynamics and geological factors, developing complex pore networks during hydrocarbon generation. Organic matter (OM) composition, dominated by Type II kerogen with terrestrial inputs, played a critical role in pore evolution. Amorphous organic matter (AOM) and solid bitumen were the primary OM components, with liptinite macerals and terrigenous vitrinite and inertinite also contributing. Clay minerals dominated the rock matrix, while pyrite framboids contributed dissolution-induced secondary porosity. SEM imaging identified five pore types, with OM-hosted pores forming predominantly in bitumen rather than kerogen. Mesopores (2–50 nm) were the dominant pore type, while micropores (&lt; 2 nm) were negligible. Fluorescence microscopy and pyrolysis experiments confirmed increasing maturity with depth, accompanied by significant intraparticle pore formation in migrated bitumen at higher temperatures. Artificial maturation studies highlight faster hydrocarbon generation and pore development compared to natural systems but fail to replicate long-term burial effects. PV correlated positively with expelled oil in artificial systems, while bitumen content negatively correlated with PV and SSA in both systems. Advanced imaging techniques and integrated natural and experimental models are essential to further understanding pore evolution, connectivity, and hydrocarbon generation mechanisms in shale reservoirs. This study emphasizes the interplay between OM composition, mineralogy, and thermal processes in shaping shale porosity during natural and artificial maturation.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"302 ","pages":"Article 104728"},"PeriodicalIF":5.6,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143479073","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":"Extensive accumulation of organic matter in the Late Permian Dalong Formation, Western Hubei Trough, Southern China","authors":"Lulu Xu ,&nbsp;Saipeng Huang ,&nbsp;Dameng Liu ,&nbsp;Zhiwei Liao ,&nbsp;Kui Wu ,&nbsp;Miankun Chen ,&nbsp;Xianghui Zhou ,&nbsp;Yanlin Zhang ,&nbsp;Bei Liu ,&nbsp;Minglong Li","doi":"10.1016/j.coal.2025.104727","DOIUrl":"10.1016/j.coal.2025.104727","url":null,"abstract":"<div><div>The black shale in the Upper Permian Dalong Formation in the Western Hubei (W<img>H) Trough is characterized by its extreme organic matter accumulation (OMA), and its vertical heterogeneity necessitates more nuanced research. The characteristics of the lithology, conodont, total organic carbon (TOC), mineral composition, silica origin, palaeoenvironmental evolution, and the OMA mechanisms of the Dalong Formation were systematically studied. The results indicate that the Dalong Formation can be subdivided into six distinct members, primarily composed of argillaceous siliceous rocks, siliceous dolomite, siliceous shales, calcareous siliceous rocks, and siliceous limestone, respectively. The silica in the organic-rich shale is predominantly of mixed biogenic and terrigenous origin, with localized contributions from hydrothermal sources. The organic-rich shale (ORS) is primarily distributing below the Wuchiapingian and Changhsingian boundary (WCB), which is deposited under moderate terrigenous input, semi-humid to semi-arid climate, euxinic conditions in a semi-open to the semi-restricted basin, and high palaeoproductivity caused by the upwelling setting and high-frequency volcanic ash layers. The WCB is characterized by the arid climate, oxic conditions in a strongly restricted basin, and low palaeoproductivity. Palaeoproductivity is identified as the principal controlling factor for the OMA. Additionally, the hydrothermal silica is commonly deposited under euxinic conditions, which are conducive to the preservation of organic matter. Evidence suggesting that thicker volcanic ash layer during the Changhsingian Stage may be one of the reasons for the mass extinction in the Late Permian. The north-central of the W<img>H Trough exhibits a higher TOC content (&gt; 4 %), overmature source rock with the vitrinite reflectance (R_o) ranging from 2 % to 3 %, and an euxinic conditions, suggesting more beneficial to shale gas enrichment.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"302 ","pages":"Article 104727"},"PeriodicalIF":5.6,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143474638","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":"Isotopic and hydrochemical evidence for the origins of unconventional gases in the Middle and Lower Jurassic coal measures in the Fukang area of Junggar Basin, NW China","authors":"Jie Xiang ,&nbsp;Jiandong Li ,&nbsp;Xianqing Li ,&nbsp;Xiaomin Ma ,&nbsp;Jie Sun ,&nbsp;Zhuo Zou ,&nbsp;Yuling Qin","doi":"10.1016/j.coal.2025.104726","DOIUrl":"10.1016/j.coal.2025.104726","url":null,"abstract":"<div><div>Extensive coalbed gas exploration has been conducted in the Fukang area of the Junggar Basin in China, but no significant breakthroughs have yet to be achieved, partly due to the unclear origin of coalbed gas. In this study, the compositions and isotopes of coalbed, shale, and tight sandstone gases, along with the chemical characteristics of formation water are reported. The results indicate that the coalbed, shale, and tight sandstone gases are dominated by CH₄. Based on the carbon isotopes of CH₄ and CO₂, the coalbed gas in the Fukang area is primarily biogenic gas via CO₂ reduction pathway, whereas the shale and tight sandstone gases are mainly biogenic gas via acetate (methyl-type) fermentation pathway. The formation water is chiefly derived from glacial meltwater with the chemical type of Na-HCO₃. High concentrations of Na⁺, Cl⁻, and HCO₃⁻ and low concentrations of Mg²⁺, Ca²⁺, and SO₄²⁻ indicate that the study area is distant from the water recharge area. In the contact area between the recharge runoff and the stagnant area, microbial modification of thermogenic gas is enhanced, leading to an enrichment of secondary biogenic gas. The findings of this study contribute to the geological understanding of coalbed, shale, and tight sandstone gases, providing valuable insights for future exploration efforts in the Fukang area.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"302 ","pages":"Article 104726"},"PeriodicalIF":5.6,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143479070","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":"Spatial and temporal variation in coal fire emissions: Examples from two eastern Kentucky coal fires","authors":"Donald R. Blake ,&nbsp;Jennifer M.K. O'Keefe ,&nbsp;Trent Garrison ,&nbsp;Gregory C. Copley ,&nbsp;James C. Hower","doi":"10.1016/j.coal.2025.104725","DOIUrl":"10.1016/j.coal.2025.104725","url":null,"abstract":"<div><div>Organic gases were collected at the Truman Shepherd and Lotts Creek coal fires, both developed in high volatile A bituminous coals, several times over the course of five to six months. Carbon dioxide and CO, exceeding 102,800 ppmv and 11,000 ppmv, respectively, at two of the vents studied, dominate the gas chemistry. Methane, ethane, and propane dominate the aliphatic gases and benzene dominates the aromatic gases. The aliphatic gases, exclusive of the latter three gases vary between vents and between months at both sites, with the Lotts Creek vents exhibiting a greater variation. At both fires, there was a tendency for decrease in methane/(methane + ethane + propane + butane) and an increase in benzene/(Σ BTEX [benzene + toluene + ethylbenzene + xylene]) across the sampling times.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"302 ","pages":"Article 104725"},"PeriodicalIF":5.6,"publicationDate":"2025-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143453434","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":"Correlations between metapelitic zones and graptolite reflectance in Ordovician successions from northwestern Argentina depicting a complex postdepositional history","authors":"Nexxys C. Herrera Sánchez ,&nbsp;Margarita Do Campo ,&nbsp;Blanca A. Toro ,&nbsp;Fernando Nieto García","doi":"10.1016/j.coal.2025.104723","DOIUrl":"10.1016/j.coal.2025.104723","url":null,"abstract":"<div><div>Correlations between metapelitic zones and organic proxies of thermal maturity, like coal rank, vitrinite reflectance and color alteration index in conodonts, were developed several decades ago and have been widely applied with satisfactory results. In contrast, comparisons between graptolite reflectance and metapelitic zones defined by Kübler Index values, clay mineral assemblages and chlorite geothermometry are scarce. In this study, samples from Ordovician successions in northwestern Argentina, where graptolite reflectance had been previously measured, were analyzed for clay mineral assemblages using X-ray diffraction, Scanning Electron Microscopy with Backscattered Electrons, and Electron Probe. Additionally, the Kübler Index was determined, and a chlorite geothermometer was applied to compare the response of these proxies for diagenetic-metamorphic temperatures and thermal maturity. The studied material was selected from two sections: Los Colorados, in the western part of the Cordillera Oriental, which mainly comprises the Acoite Formation (Early-Middle Ordovician), and Muñayoc, in the eastern part of the Puna highland, corresponding to the Cochinoca-Escaya Magmatic-Sedimentary Complex (Early-Middle Ordovician). The samples coming from the Los Colorados section reveal a clay mineral assemblage consisting of dioctahedral mica, kaolinite, along with scarce chlorite-bearing mixed-layers and chlorite in few cases, exhibiting Kübler Index values indicative of diagenesis (≥ 0.52 Δ°2θ), and corresponding temperatures between 109 and 282 °C. In contrast, samples from the Muñayoc section present a clay mineral assemblage, comprising mainly dioctahedral mica illite, subordinate kaolinite and smectite, associated with chlorite in few samples; Kübler Index values agree with the epizonal zone (≤ 0.32 Δ°2θ), and temperatures ranging from 177 to 321 °C. Notably, these findings show improved correlation with the temperatures derived from graptolite reflectance when considering updated equations between graptolite and vitrinite reflectance. On the other hand, most of the samples from Muñayoc show non equilibrium clay assemblages, as smectite and kaolinite are not stable in the epizone. This fact, along with the absence of chlorite in several samples, is probably a consequence of the hydrothermal alteration that affected the Ordovician rocks in several localities of the Puna region. As any of these approaches has its own limitation factors and sources of uncertainty, the combination of inorganic and organic proxies provide a more robust methodology to outline low-temperature burial pathways. Moreover, the correlation between Kübler Index and equivalent vitrinite reflectance revealed higher geothermal gradients in Puna than in Cordillera Oriental.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"302 ","pages":"Article 104723"},"PeriodicalIF":5.6,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143453435","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":"Petrological, mineralogical, and geochemical compositions of the Eocene coals from Senakin Peninsula, South Kalimantan, Indonesia","authors":"Ferian Anggara ,&nbsp;Donatus Hendra Amijaya ,&nbsp;Tim A. Moore ,&nbsp;Azmii Nanda Fadhillah ,&nbsp;Aulia Agus Patria","doi":"10.1016/j.coal.2025.104722","DOIUrl":"10.1016/j.coal.2025.104722","url":null,"abstract":"<div><div>Samples from the Senakin coal bed (Eocene age, Pasir Sub-basin) were analyzed to study the concentration of critical elements and investigate genetic types and enrichment processes. Of particular interest was to determine if an overlying mafic volcanic unit dated to the same age as the overlying Eocene sediments and tonstein layers withing the coal, affected the geochemical composition of the coal bed. Five partings were identified as being mafic-alkali tonsteins. The lower and upper tonsteins are interpreted to originate both from volcanic ash-fall material intermingled with water-borne detrital sediments. The middle tonstein is thought to have originated primarily as an ash-fall. A consistent feature of all partings, however, is that they are characterized by a graupen texture with additional vermicular and vitroclastic textures. The coal samples from the Senakin coal bed are dominated by vitrinite (64 vol%) with subordinate proportions of liptinite (29 vol%), and inertinite (7 vol%). Optical and SEM-EDX measurements of the coal samples showed that the inorganic material is dominantly pyrite, marcasite, quartz, kaolinite, illite, apatite, calcite, Ti oxides, Ti-V-bearing minerals, and a Mo-bearing mineral. Some coal samples from the Senakin coal bed have total rare earth element and yttrium (REY) concentrations up to 283.53 ppm. Furthermore, coals are enriched in REY and some trace elements (e.g., Zr (Hf), Nb (Ta), Ga, Sr, and V). It is hypothesized that the critical enrichments of the Senakin coal bed may be controlled primarily by three factors: (1) mafic-intermediate volcaniclastic rocks whose provenance are possibly from the Pitap and Haruyan Formations, (2) marine water infiltration from overlying sediments into recently buried peat, and/or (3) the occurrence mafic-alkali tonstein layers.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104722"},"PeriodicalIF":5.6,"publicationDate":"2025-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143422165","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":"Organic matter content and its role in shale porosity development with maturity: Insights from Baltic Basin Silurian shales","authors":"Grzegorz P. Lis ,&nbsp;Tomasz Topór ,&nbsp;Maria Mastalerz","doi":"10.1016/j.coal.2025.104713","DOIUrl":"10.1016/j.coal.2025.104713","url":null,"abstract":"<div><div>Porosity, pore size distribution, and surface area are the main petrophysical characteristics indicative of gas storage capacity in shales. This paper investigates the influence of organic matter (OM) content on the evolution of these parameters at different stages of thermal maturity. Ninety-six samples of Silurian shales from the Baltic Basin ranging in maturity from immature to overmature were selected for this study. Porosity evolution was evaluated using N₂ and CO₂ low-pressure gas adsorption. At the immature stage, the samples with high OM content are characterized by lower porosity than the organic-matter-lean samples. At this stage, high OM content leads to the disruption of stiffer mineral framework; mixed organic-mineral framework is more prone to mechanical compaction than mineral framework. At the oil window stage, porosity of OM-rich samples declines due to pore-throat plugging and pore filling by bitumen. At the wet and dry gas generation stage, porosity of OM-rich samples increases mainly due to pore-throats unplugging. Absent or weak correlation between porosity and OM content at the wet and dry gas stages indicates poor development of OM-hosted secondary porosity. High contents of clay minerals in the studied samples fail to provide the rigid mineral framework and pressure shadows necessary for OM-hosted secondary porosity development.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104713"},"PeriodicalIF":5.6,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143387891","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":"Characteristics of in-situ stress field of coalbed methane reservoir in the eastern margin of Ordos basin","authors":"Kaichao Zhang ,&nbsp;Song Li ,&nbsp;Guanghao Zhong ,&nbsp;Peng Feng ,&nbsp;Chuang Chang ,&nbsp;Hao Li","doi":"10.1016/j.coal.2025.104715","DOIUrl":"10.1016/j.coal.2025.104715","url":null,"abstract":"<div><div>The eastern margin of the Ordos Basin in China holds substantial coalbed methane resources. Nevertheless, coalbed methane production in this region is significantly constrained due to the unclear characteristics of the in-situ stress field within the coal reservoirs. Drawing on extensive coal seam test data, including well testing and hydraulic fracturing, and uses hydraulic fracturing calculation methods, this study conducts a comparative analysis of the in-situ stress characteristics across various CBM blocks in the region. Results indicate that the in-situ stress of the coal reservoirs along the eastern margin of the Ordos Basin predominantly exhibits medium-high stress, with stress levels higher in the south and lower in the north. The stress field is dominated by the inverse fault stress field (<span><math><msub><mi>σ</mi><mi>H</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>) in the north while in the south, it is characterized by a normal fault stress field (<span><math><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>H</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>). The in-situ stress characteristics of the coal seams are primarily governed by burial depth and local structural factors, with the three principal stresses showing a strong linear positive correlation with burial depth. The vertical stress field distinctly exhibits a “three-zoned” distribution. At a depth of 750 m, the in-situ stress relationship is <span><math><msub><mi>σ</mi><mi>H</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>, indicating that the coal reservoir is predominantly under compressive stress. At depths between 750 and 1500 m, the coal seam stress state follows the relationship <span><math><msub><mi>σ</mi><mi>H</mi></msub><mo>≈</mo><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>, transitioning into a stress regime characteristic of a transition zone. At a depth of 1500 m, the in-situ stress relationship is <span><math><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>H</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>, and the coal reservoir is predominantly characterized by tensile stress. Despite the relatively deep burial depth of the coal seams in the Hancheng block, its location within the Tongchuan-Hancheng fault zone, where north-south faulting is significantly developed, causes substantial local structural effects. As a result, the coal seam stress field in this area remains dominated by reverse faulting.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104715"},"PeriodicalIF":5.6,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143422164","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}