Pub Date : 2026-03-20DOI: 10.1016/j.coal.2026.104992
Ferian Anggara, Shifeng Dai, Tim A. Moore, Auvanda Ivan Muhammad, Ofentse M. Moroeng, Jingjing Liu, Aldian Fahrialam, Himawan Tri Bayu Murti Petrus, Aulia Agus Patria
{"title":"Organic petrological and geochemical controls on critical element distribution in peat influenced by rhyolitic basement rocks from the Sebangau Peatland, Central Kalimantan: An analogue model for critical element enrichment in coals","authors":"Ferian Anggara, Shifeng Dai, Tim A. Moore, Auvanda Ivan Muhammad, Ofentse M. Moroeng, Jingjing Liu, Aldian Fahrialam, Himawan Tri Bayu Murti Petrus, Aulia Agus Patria","doi":"10.1016/j.coal.2026.104992","DOIUrl":"https://doi.org/10.1016/j.coal.2026.104992","url":null,"abstract":"","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"49 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147496258","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}
Achieving safe and efficient CO₂ injection into deep, low-permeability coal seams is a critical challenge for carbon storage and enhanced coalbed methane recovery (CO₂-ECBM). However, field-scale data from deep (>1000 m), low-permeability (<0.1 mD), high-rank coals using horizontal wells remain scarce, representing a critical knowledge gap for global carbon storage deployment, and the relative contributions of multiple trapping mechanisms under in situ conditions are poorly constrained. This study presents China's first thousand-tonne-scale pilot trial of liquid CO₂ injection into a deep anthracite seam (No. 3 coal, depth ~ 1040 m, permeability 0.03 mD) using a repurposed U-shaped well (one vertical injector/producer and one 720-m horizontal well) in the Qinshui Basin. The trial integrated comprehensive “downhole-surface-wellbore” monitoring (pressure, geochemistry, tracers) and history-matched numerical simulation. Results demonstrate technical feasibility: a cumulative injection of 1001.28 t of liquid CO₂ was achieved over 64 operational days at a stable rate of 18 t/d, with bottomhole pressure maintained at ≤14.42 MPa (below the fracture gradient of 26.8 MPa), ensuring caprock integrity throughout. Monitoring and simulation consistently indicate that the injected CO₂ plume was effectively confined within ~10 m of the horizontal wellbore. No tracer breakthrough was detected at a monitoring well 27.5 m away, and HCO₃−/CO₃2− concentrations remained unchanged. Rapid adsorption onto the coal matrix (>90%) was the dominant trapping mechanism, while solubility and mineral trapping were negligible within the trial period. The 720-m horizontal section was essential for achieving viable injectivity in this low-permeability reservoir. This study confirms that CO₂-ECBM in deep, low-permeability anthracite is technically viable, and establishes that storage security is governed by rapid adsorption immobilization supported by effective geological containment. The findings provide a crucial technical benchmark and an integrated geology-engineering-monitoring framework for scaling up secure CO₂ storage in deep, low-permeability coal basins globally.
{"title":"Feasibility of CO₂-ECBM in deep, low-permeability anthracite: Insights from a successful horizontal well pilot","authors":"Songhang Zhang, Shuheng Tang, Zanwei Wang, Zhiming Fang, Jinyi Wang, Jianxin Li, Zhaodong Xi","doi":"10.1016/j.coal.2026.104991","DOIUrl":"https://doi.org/10.1016/j.coal.2026.104991","url":null,"abstract":"Achieving safe and efficient CO₂ injection into deep, low-permeability coal seams is a critical challenge for carbon storage and enhanced coalbed methane recovery (CO₂-ECBM). However, field-scale data from deep (>1000 m), low-permeability (<0.1 mD), high-rank coals using horizontal wells remain scarce, representing a critical knowledge gap for global carbon storage deployment, and the relative contributions of multiple trapping mechanisms under in situ conditions are poorly constrained. This study presents China's first thousand-tonne-scale pilot trial of liquid CO₂ injection into a deep anthracite seam (No. 3 coal, depth ~ 1040 m, permeability 0.03 mD) using a repurposed U-shaped well (one vertical injector/producer and one 720-m horizontal well) in the Qinshui Basin. The trial integrated comprehensive “downhole-surface-wellbore” monitoring (pressure, geochemistry, tracers) and history-matched numerical simulation. Results demonstrate technical feasibility: a cumulative injection of 1001.28 t of liquid CO₂ was achieved over 64 operational days at a stable rate of 18 t/d, with bottomhole pressure maintained at ≤14.42 MPa <ce:bold>(</ce:bold>below the fracture gradient of 26.8 MPa<ce:bold>),</ce:bold> ensuring caprock integrity throughout. Monitoring and simulation consistently indicate that the injected CO₂ plume was effectively confined within ~10 m of the horizontal wellbore. No tracer breakthrough was detected at a monitoring well 27.5 m away, and HCO₃<ce:sup loc=\"post\">−</ce:sup>/CO₃<ce:sup loc=\"post\">2−</ce:sup> concentrations remained unchanged. Rapid adsorption onto the coal matrix (>90%) was the dominant trapping mechanism, while solubility and mineral trapping were negligible within the trial period. The 720-m horizontal section was essential for achieving viable injectivity in this low-permeability reservoir. This study confirms that CO₂-ECBM in deep, low-permeability anthracite is technically viable, and establishes that storage security is governed by rapid adsorption immobilization supported by effective geological containment<ce:bold>.</ce:bold> The findings provide a crucial technical benchmark and an integrated geology-engineering-monitoring framework for scaling up secure CO₂ storage in deep, low-permeability coal basins globally.","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"38 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2026-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465731","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}
Pub Date : 2026-03-14DOI: 10.1016/j.coal.2026.104990
Dalibor Matýsek, Jakub Jirásek, Juraj Majzlan, Jan Filip, Michal Osovský, Jörg Göttlicher
The Czech part of the Upper Silesian Basin is still a home of bituminous coal mining in Europe. The underground mines there feature rich assemblages of evaporite minerals that precipitate from the water flowing through the mines. The minerals occur in stalactites, rarely as cave pearls. The predominant minerals of the stalactites is halite (NaCl). The first group consists of halite stalactites with sylvite (KCl), carnallite (KMgCl<ce:inf loc="post">3</ce:inf>·6H<ce:inf loc="post">2</ce:inf>O), and rare gypsum (CaSO<ce:inf loc="post">4</ce:inf>·2H<ce:inf loc="post">2</ce:inf>O) and baryte (BaSO<ce:inf loc="post">4</ce:inf>) on their surface. Orange coloration may be caused by lepidocrocite or akageneite (both Fe-oxyhydroxides). In the second group, halite is covered by carnallite, králíkite (BaCl<ce:inf loc="post">2</ce:inf>·2H<ce:inf loc="post">2</ce:inf>O), and SrCl<ce:inf loc="post">2</ce:inf> hydrates. In the third group, halite is associated with burkeite [Na<ce:inf loc="post">6</ce:inf>(CO<ce:inf loc="post">3</ce:inf>)(SO<ce:inf loc="post">4</ce:inf>)<ce:inf loc="post">2</ce:inf>], blödite [Na<ce:inf loc="post">2</ce:inf>Mg(SO<ce:inf loc="post">4</ce:inf>)<ce:inf loc="post">2</ce:inf>·4H<ce:inf loc="post">2</ce:inf>O], kainite [KMg(SO<ce:inf loc="post">4</ce:inf>)Cl·3H<ce:inf loc="post">2</ce:inf>O], thénardite (Na<ce:inf loc="post">2</ce:inf>SO<ce:inf loc="post">4</ce:inf>), and trona [Na<ce:inf loc="post">3</ce:inf>H(CO<ce:inf loc="post">3</ce:inf>)<ce:inf loc="post">2</ce:inf>·2H<ce:inf loc="post">2</ce:inf>O]. Some of the stalactites are dominated by sulfates, with starkeyite, hexahydrite, epsomite (all representing MgSO<ce:inf loc="post">4</ce:inf> hydrates), or thénardite. The fourth group comprised a single sample, a stalactite with α‑calcium formate and králíkite. All these minerals precipitate from brines that acquire their dissolved load primarily from Early Badenian groundwater bodies, frequently in direct contact with the Carboniferous basement rocks. These are fossil marine waters with total mineralization >10 g·l<ce:sup loc="post">−1</ce:sup>, rich in NaCl, locally also in CH<ce:inf loc="post">4</ce:inf> and CO<ce:inf loc="post">2</ce:inf>, and enriched in Sr<ce:sup loc="post">2+</ce:sup>, Ba<ce:sup loc="post">2+</ce:sup>, I<ce:sup loc="post">−</ce:sup> and Br<ce:sup loc="post">−</ce:sup>. These types of water also led to precipitation of the newly described mineral králíkite. Owing to the low solubility of baryte, králíkite can only form from water strongly depleted in sulfate. The brines are locally mixed with sulfate-rich acid mine drainage water, resulting in some sulfate-rich compositions observed in this work. Our study highlights some processes tightly linked to coal and coal mining, namely formation of secondary mineralization underground and its possible environmental impact during and after the mining. As the coal mines are being successively shut down, this aspect should be prominent for the middle- to long-term e
{"title":"Evaporite minerals from the coal mines of the Czech part of the Upper Silesian Basin, including a new mineral králíkite (BaCl2·2H2O)","authors":"Dalibor Matýsek, Jakub Jirásek, Juraj Majzlan, Jan Filip, Michal Osovský, Jörg Göttlicher","doi":"10.1016/j.coal.2026.104990","DOIUrl":"https://doi.org/10.1016/j.coal.2026.104990","url":null,"abstract":"The Czech part of the Upper Silesian Basin is still a home of bituminous coal mining in Europe. The underground mines there feature rich assemblages of evaporite minerals that precipitate from the water flowing through the mines. The minerals occur in stalactites, rarely as cave pearls. The predominant minerals of the stalactites is halite (NaCl). The first group consists of halite stalactites with sylvite (KCl), carnallite (KMgCl<ce:inf loc=\"post\">3</ce:inf>·6H<ce:inf loc=\"post\">2</ce:inf>O), and rare gypsum (CaSO<ce:inf loc=\"post\">4</ce:inf>·2H<ce:inf loc=\"post\">2</ce:inf>O) and baryte (BaSO<ce:inf loc=\"post\">4</ce:inf>) on their surface. Orange coloration may be caused by lepidocrocite or akageneite (both Fe-oxyhydroxides). In the second group, halite is covered by carnallite, králíkite (BaCl<ce:inf loc=\"post\">2</ce:inf>·2H<ce:inf loc=\"post\">2</ce:inf>O), and SrCl<ce:inf loc=\"post\">2</ce:inf> hydrates. In the third group, halite is associated with burkeite [Na<ce:inf loc=\"post\">6</ce:inf>(CO<ce:inf loc=\"post\">3</ce:inf>)(SO<ce:inf loc=\"post\">4</ce:inf>)<ce:inf loc=\"post\">2</ce:inf>], blödite [Na<ce:inf loc=\"post\">2</ce:inf>Mg(SO<ce:inf loc=\"post\">4</ce:inf>)<ce:inf loc=\"post\">2</ce:inf>·4H<ce:inf loc=\"post\">2</ce:inf>O], kainite [KMg(SO<ce:inf loc=\"post\">4</ce:inf>)Cl·3H<ce:inf loc=\"post\">2</ce:inf>O], thénardite (Na<ce:inf loc=\"post\">2</ce:inf>SO<ce:inf loc=\"post\">4</ce:inf>), and trona [Na<ce:inf loc=\"post\">3</ce:inf>H(CO<ce:inf loc=\"post\">3</ce:inf>)<ce:inf loc=\"post\">2</ce:inf>·2H<ce:inf loc=\"post\">2</ce:inf>O]. Some of the stalactites are dominated by sulfates, with starkeyite, hexahydrite, epsomite (all representing MgSO<ce:inf loc=\"post\">4</ce:inf> hydrates), or thénardite. The fourth group comprised a single sample, a stalactite with α‑calcium formate and králíkite. All these minerals precipitate from brines that acquire their dissolved load primarily from Early Badenian groundwater bodies, frequently in direct contact with the Carboniferous basement rocks. These are fossil marine waters with total mineralization >10 g·l<ce:sup loc=\"post\">−1</ce:sup>, rich in NaCl, locally also in CH<ce:inf loc=\"post\">4</ce:inf> and CO<ce:inf loc=\"post\">2</ce:inf>, and enriched in Sr<ce:sup loc=\"post\">2+</ce:sup>, Ba<ce:sup loc=\"post\">2+</ce:sup>, I<ce:sup loc=\"post\">−</ce:sup> and Br<ce:sup loc=\"post\">−</ce:sup>. These types of water also led to precipitation of the newly described mineral králíkite. Owing to the low solubility of baryte, králíkite can only form from water strongly depleted in sulfate. The brines are locally mixed with sulfate-rich acid mine drainage water, resulting in some sulfate-rich compositions observed in this work. Our study highlights some processes tightly linked to coal and coal mining, namely formation of secondary mineralization underground and its possible environmental impact during and after the mining. As the coal mines are being successively shut down, this aspect should be prominent for the middle- to long-term e","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"10 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2026-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465058","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}
Pub Date : 2026-02-28Epub Date: 2026-02-11DOI: 10.1016/j.coal.2026.104965
Xiaodong Liu , Wanglu Jia , Qiang Wang , Jinbu Li , Jian Chen , Ping'an Peng
<div><div>Hydrogen derived from organic-rich sedimentary rocks plays important roles in conventional and green energy applications, energy utilization, and atmospheric pollution. Although thermal simulation experiments have preliminarily revealed the mechanisms of hydrogen generation, the understanding of its migration from source rocks and accumulation processes remains scarce, which severely constrains exploration practices. This study conducted high-pressure gold-tube (closed-system) pyrolysis at 600 °C to investigate three series of source rocks with different maturities, obtained by artificial maturation. The work examined the amount of hydrogen generated during pyrolysis of source rocks. We carefully quantified hydrogen in its multiple phases and evaluated the influencing factors of hydrogen-bearing gases and H<sub>2</sub> generation potential. Firstly, organic hydrogen (TOH) contents for up to 36.2–72.2% of total hydrogen (TH) in low-mature original source rocks. When thermally evolved to a high maturity (Easy %Ro 1.98), a significant reduction in TOH is observed (by 62–76% of the original TOH), while the inorganic hydrogen (TIH) remains relatively stable. Moreover, when source rocks evolved to Easy %Ro 4.45, hydrogen is primarily converted into CH<sub>4</sub> (up to 40.8% relative to the TH of original source rocks), much higher than H<sub>2</sub> (up to 1.2%). In contrast, in high‑sulfur source rocks, due to the competition of sulfur for hydrogen, the percentage of hydrogen in H<sub>2</sub>S generated (5.8%) exceeds that of H<sub>2</sub>. Secondly, the yields of H<sub>2</sub> and CH<sub>4</sub> exhibit a strong positive linear correlation with HI values of Rock-Eval analysis, whereas H<sub>2</sub>S yields also depend on the source rock's sulfur content. For type I kerogen with significantly higher HI, the H<sub>2</sub> yield is greater than that of type II. However, for samples classified as type II kerogen, the HI value alone does not fully indicate the magnitude of H<sub>2</sub> yield. The thermal maturation process alters the organic matter structure, thereby changing the H<sub>2</sub> generation characteristics of different source rocks. Moreover, H<sub>2</sub> and CH<sub>4</sub> generation is influenced by the pyrolysis conditions. Open-system pyrolysis generally exhibits higher H<sub>2</sub>/CH<sub>4</sub> molar ratios than closed-system pyrolysis, which may be due to much higher temperatures adopted in open-system pyrolysis, as well as the occurrence of hydrogenation reactions in closed systems. Finally, hydrogen distribution analysis indicates that source rocks retain significant H<sub>2</sub> generation potential even with thermal evolution to a post-mature stage (Easy %Ro > 4.45), with a maximum yield of approximately 7.4–25.5 mg/g TOC upon complete conversion of residual organic hydrogen to H<sub>2</sub>. Notably, post-mature source rocks, initially having type II kerogen rich in condensed aromatic structures, demonstrate a
{"title":"Hydrogen distributions during thermal maturation of organic-rich sedimentary rocks: Generation potentials and influencing factors of hydrogen-bearing gases revealed by pyrolysis","authors":"Xiaodong Liu , Wanglu Jia , Qiang Wang , Jinbu Li , Jian Chen , Ping'an Peng","doi":"10.1016/j.coal.2026.104965","DOIUrl":"10.1016/j.coal.2026.104965","url":null,"abstract":"<div><div>Hydrogen derived from organic-rich sedimentary rocks plays important roles in conventional and green energy applications, energy utilization, and atmospheric pollution. Although thermal simulation experiments have preliminarily revealed the mechanisms of hydrogen generation, the understanding of its migration from source rocks and accumulation processes remains scarce, which severely constrains exploration practices. This study conducted high-pressure gold-tube (closed-system) pyrolysis at 600 °C to investigate three series of source rocks with different maturities, obtained by artificial maturation. The work examined the amount of hydrogen generated during pyrolysis of source rocks. We carefully quantified hydrogen in its multiple phases and evaluated the influencing factors of hydrogen-bearing gases and H<sub>2</sub> generation potential. Firstly, organic hydrogen (TOH) contents for up to 36.2–72.2% of total hydrogen (TH) in low-mature original source rocks. When thermally evolved to a high maturity (Easy %Ro 1.98), a significant reduction in TOH is observed (by 62–76% of the original TOH), while the inorganic hydrogen (TIH) remains relatively stable. Moreover, when source rocks evolved to Easy %Ro 4.45, hydrogen is primarily converted into CH<sub>4</sub> (up to 40.8% relative to the TH of original source rocks), much higher than H<sub>2</sub> (up to 1.2%). In contrast, in high‑sulfur source rocks, due to the competition of sulfur for hydrogen, the percentage of hydrogen in H<sub>2</sub>S generated (5.8%) exceeds that of H<sub>2</sub>. Secondly, the yields of H<sub>2</sub> and CH<sub>4</sub> exhibit a strong positive linear correlation with HI values of Rock-Eval analysis, whereas H<sub>2</sub>S yields also depend on the source rock's sulfur content. For type I kerogen with significantly higher HI, the H<sub>2</sub> yield is greater than that of type II. However, for samples classified as type II kerogen, the HI value alone does not fully indicate the magnitude of H<sub>2</sub> yield. The thermal maturation process alters the organic matter structure, thereby changing the H<sub>2</sub> generation characteristics of different source rocks. Moreover, H<sub>2</sub> and CH<sub>4</sub> generation is influenced by the pyrolysis conditions. Open-system pyrolysis generally exhibits higher H<sub>2</sub>/CH<sub>4</sub> molar ratios than closed-system pyrolysis, which may be due to much higher temperatures adopted in open-system pyrolysis, as well as the occurrence of hydrogenation reactions in closed systems. Finally, hydrogen distribution analysis indicates that source rocks retain significant H<sub>2</sub> generation potential even with thermal evolution to a post-mature stage (Easy %Ro > 4.45), with a maximum yield of approximately 7.4–25.5 mg/g TOC upon complete conversion of residual organic hydrogen to H<sub>2</sub>. Notably, post-mature source rocks, initially having type II kerogen rich in condensed aromatic structures, demonstrate a","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"316 ","pages":"Article 104965"},"PeriodicalIF":5.7,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146160593","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}
Pub Date : 2026-02-28Epub Date: 2026-01-15DOI: 10.1016/j.coal.2026.104945
Jorge Eliecer Mariño-Martinez , Tim A. Moore , Juan Sebastian Gomez-Neita
Coalbed methane (CBM) has garnered growing attention in Colombia due to declining conventional energy resources and reserves, persistent mining accidents caused by methane explosions, and climate regulations aimed at reducing greenhouse gas (GHG) emissions. This study provides a review of the current status of CBM in Colombia, synthesizing geological, geochemical, and technical data to assess its development potential. Despite the significant coal reserves of Colombia, early CBM resource estimates were overly optimistic. Updated evaluations reveal that most coal seams exhibit low gas contents (<200 ft3/ton - 5.66 m3/ton), having gas saturations typically less than 50%. This level of gas content poses particular challenges for commercial development. In Colombia, four provinces or coal zones—Cundinamarca, Boyacá, Cesar, and La Guajira—show localized potential, with some samples exceeding 300 ft3/ton. However, reservoir modeling, particularly from the Umbita-Chinavita area (Boyacá), demonstrates that low permeability (<10 mD), thin and discontinuous coalbeds, and structural complexity may inhibit development. The gas quality in these areas also varies, with a methane content averaging 75%, which also places additional pressure on commerciality. Isotopic and hydrogeological analyses suggest a predominantly biogenic origin of methane, often linked to meteoric recharge of the aquifers. Despite technical promise, development faces significant barriers, including inconsistent laboratory standards for existing historical data, a lack of clear legal frameworks, insufficient infrastructure, and limited investor interest and research. Regulatory and institutional fragmentation between coal and gas authorities further complicates the management of CBM resources. To unlock the CBM potential, Colombia must implement standardized exploration practices, develop robust incentive structures, and conduct comprehensive feasibility studies incorporating desorption, adsorption, and isotopic data. This work concludes that while Colombia possesses notable CBM resources, substantial technical, economic, and regulatory challenges must be overcome before near-term commercial production can be realized. The findings provide a foundation for future exploration, policy reform, and sustainable energy strategies aligned with national safety and environmental goals.
{"title":"Coal bed gas in Colombia: Current status","authors":"Jorge Eliecer Mariño-Martinez , Tim A. Moore , Juan Sebastian Gomez-Neita","doi":"10.1016/j.coal.2026.104945","DOIUrl":"10.1016/j.coal.2026.104945","url":null,"abstract":"<div><div>Coalbed methane (CBM) has garnered growing attention in Colombia due to declining conventional energy resources and reserves, persistent mining accidents caused by methane explosions, and climate regulations aimed at reducing greenhouse gas (GHG) emissions. This study provides a review of the current status of CBM in Colombia, synthesizing geological, geochemical, and technical data to assess its development potential. Despite the significant coal reserves of Colombia, early CBM resource estimates were overly optimistic. Updated evaluations reveal that most coal seams exhibit low gas contents (<200 ft<sup>3</sup>/ton - 5.66 m<sup>3</sup>/ton), having gas saturations typically less than 50%. This level of gas content poses particular challenges for commercial development. In Colombia, four provinces or coal zones—Cundinamarca, Boyacá, Cesar, and La Guajira—show localized potential, with some samples exceeding 300 ft<sup>3</sup>/ton. However, reservoir modeling, particularly from the Umbita-Chinavita area (Boyacá), demonstrates that low permeability (<10 mD), thin and discontinuous coalbeds, and structural complexity may inhibit development. The gas quality in these areas also varies, with a methane content averaging 75%, which also places additional pressure on commerciality. Isotopic and hydrogeological analyses suggest a predominantly biogenic origin of methane, often linked to meteoric recharge of the aquifers. Despite technical promise, development faces significant barriers, including inconsistent laboratory standards for existing historical data, a lack of clear legal frameworks, insufficient infrastructure, and limited investor interest and research. Regulatory and institutional fragmentation between coal and gas authorities further complicates the management of CBM resources. To unlock the CBM potential, Colombia must implement standardized exploration practices, develop robust incentive structures, and conduct comprehensive feasibility studies incorporating desorption, adsorption, and isotopic data. This work concludes that while Colombia possesses notable CBM resources, substantial technical, economic, and regulatory challenges must be overcome before near-term commercial production can be realized. The findings provide a foundation for future exploration, policy reform, and sustainable energy strategies aligned with national safety and environmental goals.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"316 ","pages":"Article 104945"},"PeriodicalIF":5.7,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145995726","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}
Pub Date : 2026-02-28Epub Date: 2026-01-30DOI: 10.1016/j.coal.2026.104948
Ibrahim Okunlola , Rona Donahoe , Kalyn Tew , Marcella McIntyre-Redden , Elena Tajuelo Rodriguez
Critical minerals (CM) such as rare earth elements (REE+) and Lithium (Li) are essential to technological innovation, energy transitions, global economic and defense security, necessitating the search for unconventional resources and efficient recovery methods to avert supply chain disruptions. This study evaluates coal-associated sediments (underclay and roof rock) and wastes from the Pennsylvanian Pottsville Formation of the Southern Appalachian Basin (SAB) as potential feedstocks for CM recovery. A total of 34 samples (15 underclays, 12 roof rocks, 5 Acid Mine Drainage (AMD) sludges, and 2 coal mining wastes) were characterized using XRD, XRF, ICP-MS, and μ-XRF analytical methods. The REE+ and Li concentrations of these materials ranged from 46.8 to 334.4 ppm and from 11.1 to 519 ppm, respectively, with one underclay sample (Hendrix 3456) yielding the highest values for both. Bulk mineralogy for all samples was dominated by aluminosilicate clay phases, particularly illite and kaolinite. All samples exhibited REYdef, rel% values >26% and Coutl indices that ranged from 0.69 to 0.94, classifying their REE ore potential as Category II (Promising) as defined by Seredin and Dai (2012). Extractability tests (EPA method 3051 A) yielded low REE+ and Li recoveries, with maximum values of 3.3% and 3.6%, respectively, suggesting associations with resistant minerals like clay and phosphates. Elemental mapping indicates that REE+ is associated with phosphate, whereas statistical analysis suggests that REE+ are associated with aluminosilicates, suggesting heterogeneous associations or minimal phosphate contribution. Li also correlated positively with Al2O3, indicating an aluminosilicate host. This study highlights the potential of coal-associated sediments in the SAB.
{"title":"Evaluation of coal-associated sediments, wastes, and AMD sludge in the Southern Appalachian Basin as feedstock materials for REE and Li recovery","authors":"Ibrahim Okunlola , Rona Donahoe , Kalyn Tew , Marcella McIntyre-Redden , Elena Tajuelo Rodriguez","doi":"10.1016/j.coal.2026.104948","DOIUrl":"10.1016/j.coal.2026.104948","url":null,"abstract":"<div><div>Critical minerals (CM) such as rare earth elements (REE+) and Lithium (Li) are essential to technological innovation, energy transitions, global economic and defense security, necessitating the search for unconventional resources and efficient recovery methods to avert supply chain disruptions. This study evaluates coal-associated sediments (underclay and roof rock) and wastes from the Pennsylvanian Pottsville Formation of the Southern Appalachian Basin (SAB) as potential feedstocks for CM recovery. A total of 34 samples (15 underclays, 12 roof rocks, 5 Acid Mine Drainage (AMD) sludges, and 2 coal mining wastes) were characterized using XRD, XRF, ICP-MS, and μ-XRF analytical methods. The REE+ and Li concentrations of these materials ranged from 46.8 to 334.4 ppm and from 11.1 to 519 ppm, respectively, with one underclay sample (Hendrix 3456) yielding the highest values for both. Bulk mineralogy for all samples was dominated by aluminosilicate clay phases, particularly illite and kaolinite. All samples exhibited REY<sub>def, rel%</sub> values >26% and C<sub>outl</sub> indices that ranged from 0.69 to 0.94, classifying their REE ore potential as Category II (Promising) as defined by <span><span>Seredin and Dai (2012)</span></span>. Extractability tests (EPA method 3051 A) yielded low REE+ and Li recoveries, with maximum values of 3.3% and 3.6%, respectively, suggesting associations with resistant minerals like clay and phosphates. Elemental mapping indicates that REE+ is associated with phosphate, whereas statistical analysis suggests that REE+ are associated with aluminosilicates, suggesting heterogeneous associations or minimal phosphate contribution. Li also correlated positively with Al<sub>2</sub>O<sub>3,</sub> indicating an aluminosilicate host. This study highlights the potential of coal-associated sediments in the SAB.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"316 ","pages":"Article 104948"},"PeriodicalIF":5.7,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146089707","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}
Pub Date : 2026-02-28Epub Date: 2026-02-12DOI: 10.1016/j.coal.2026.104967
Ahmed Mansour , Eva Geršlová , Dominik Vöröš , Omar Mohamed , Thomas Gentzis , Ahmed Ali
<div><div>Despite widespread organic-rich accumulations in southern Tethyan basins during the Late Cretaceous greenhouse, the relative role of climate-derived weathering, redox regime, paleoproductivity, and regional tectonics in controlling organic matter enrichment and preservation remains poorly constrained. This work investigates how these interacting geological processes governed organic matter richness and redox evolution in Campanian-Maastrichtian strata of the Abu Tartur Plateau, Dakhla Basin (southern Western Desert, Egypt). The study combined bulk-rock elemental and organic geochemical and sedimentological data from phosphates, black and gray shales, limestones, and glauconites of the Phosphate, Liffiya Shale, and Maghrabi Shale members of the Duwi Formation and the overlying Dakhla Formation. Chemical index of alteration (CIA), C-value and other elemental proxies revealed deposition under predominant humid climates and intense continental weathering, interrupted by short-lived arid-semi-arid to semi-humid intervals, corresponding to the development of phosphorite and carbonate beds. These climatic and weathering trends coincide with coeval intervals from the Red Sea and Nile Valley, reflecting the regional geological processes at the near-equatorial southern Tethyan margin during the Campanian-Maastrichtian. Source rock characterization indicates poor to very good with a few intervals of excellent organic matter richness and kerogen Type III with minor Type II. The deposition of the Duwi and Dakhla formations was concurrent with episodic subsidence versus uplift of the Gilf El-Kebir spur and Nubian Swell, consistent with sea-level rise and increased accommodation space and induced upwelling in open shelf settings of the southern Tethys. These conditions governed O<sub>2</sub> replenishment faster than consumption leading to oxic-suboxic environments dominated by organic-rich deposits via organic matter production under enhanced upwelling than persistent anoxia. Conversely, black shales of the Maghrabi Shale Member were deposited under anoxic settings accompanied by elevated biological productivity. Preferential Mo enrichments in black shales compared to limited enrichments of other redox-sensitive metals suggest the operation of a particulate shuttle during short-term redox fluctuations. The mechanism behind enhanced anoxia included episodes of relative sea-level fall and decreased accommodation space along with regional tectonic uplift of adjacent uplands, resulting in a semi-enclosed basin with restricted circulation that promoted nutrient supply and oxygen depletion, favorable for organic matter preservation. The Dakhla Formation was deposited in similar marine environmental conditions to the Liffiya Shale Member; however, intensified weathering and associated terrigenous supply versus limited biological productivity and well-ventilated water column resulted in a strong dilution of labile organic matter and deposition of organic car
{"title":"Tectonic and climatic controls on organic matter accumulation and redox dynamics in Campanian-Maastrichtian strata of the Abu Tartur Plateau, southern Tethys (Egypt)","authors":"Ahmed Mansour , Eva Geršlová , Dominik Vöröš , Omar Mohamed , Thomas Gentzis , Ahmed Ali","doi":"10.1016/j.coal.2026.104967","DOIUrl":"10.1016/j.coal.2026.104967","url":null,"abstract":"<div><div>Despite widespread organic-rich accumulations in southern Tethyan basins during the Late Cretaceous greenhouse, the relative role of climate-derived weathering, redox regime, paleoproductivity, and regional tectonics in controlling organic matter enrichment and preservation remains poorly constrained. This work investigates how these interacting geological processes governed organic matter richness and redox evolution in Campanian-Maastrichtian strata of the Abu Tartur Plateau, Dakhla Basin (southern Western Desert, Egypt). The study combined bulk-rock elemental and organic geochemical and sedimentological data from phosphates, black and gray shales, limestones, and glauconites of the Phosphate, Liffiya Shale, and Maghrabi Shale members of the Duwi Formation and the overlying Dakhla Formation. Chemical index of alteration (CIA), C-value and other elemental proxies revealed deposition under predominant humid climates and intense continental weathering, interrupted by short-lived arid-semi-arid to semi-humid intervals, corresponding to the development of phosphorite and carbonate beds. These climatic and weathering trends coincide with coeval intervals from the Red Sea and Nile Valley, reflecting the regional geological processes at the near-equatorial southern Tethyan margin during the Campanian-Maastrichtian. Source rock characterization indicates poor to very good with a few intervals of excellent organic matter richness and kerogen Type III with minor Type II. The deposition of the Duwi and Dakhla formations was concurrent with episodic subsidence versus uplift of the Gilf El-Kebir spur and Nubian Swell, consistent with sea-level rise and increased accommodation space and induced upwelling in open shelf settings of the southern Tethys. These conditions governed O<sub>2</sub> replenishment faster than consumption leading to oxic-suboxic environments dominated by organic-rich deposits via organic matter production under enhanced upwelling than persistent anoxia. Conversely, black shales of the Maghrabi Shale Member were deposited under anoxic settings accompanied by elevated biological productivity. Preferential Mo enrichments in black shales compared to limited enrichments of other redox-sensitive metals suggest the operation of a particulate shuttle during short-term redox fluctuations. The mechanism behind enhanced anoxia included episodes of relative sea-level fall and decreased accommodation space along with regional tectonic uplift of adjacent uplands, resulting in a semi-enclosed basin with restricted circulation that promoted nutrient supply and oxygen depletion, favorable for organic matter preservation. The Dakhla Formation was deposited in similar marine environmental conditions to the Liffiya Shale Member; however, intensified weathering and associated terrigenous supply versus limited biological productivity and well-ventilated water column resulted in a strong dilution of labile organic matter and deposition of organic car","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"316 ","pages":"Article 104967"},"PeriodicalIF":5.7,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146172368","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}
Pub Date : 2026-02-28Epub Date: 2026-02-11DOI: 10.1016/j.coal.2026.104966
Sami Nabhan , Christoph Heubeck , Don E. Canfield
The degree of structural order of carbonaceous matter (CM) in metasedimentary rocks is thought to largely depend on the maximum temperature the host rock experienced. This led to the widespread use of Raman spectroscopy of carbonaceous matter (RSCM) as geothermometer to determine maximum burial or metamorphic temperatures. The analytical certainty of most geothermometers based on RSCM is given as ±30–50 °C and the structural order of CM is often shown to be heterogeneous within individual samples, geological beds and units. To better understand the influence of authigenic mineral growth on CM maturation and heterogeneity we analyzed samples from three Precambrian CM-bearing stratigraphic units. Raman spectroscopic results indicate large heterogeneities in the degree of structural order of CM, resulting in ranges of up to 190 °C in calculated temperature within individual samples. Generally, within each sample, CM within authigenic minerals shows a significantly higher degree of structural order than CM in areas devoid of authigenic minerals. This results in calculated average temperatures from CM within authigenic minerals that are 27–94 °C higher than temperatures calculated from CM in neighboring areas devoid of authigenic minerals. Our results indicate that the structural order of CM within authigenic minerals is significantly enhanced. Thus, geothermometers based on RSCM must be used carefully with a thorough awareness of the petrographic context.
{"title":"Authigenic mineral growth in sedimentary and metasedimentary rocks enhances the degree of structural order of carbonaceous material","authors":"Sami Nabhan , Christoph Heubeck , Don E. Canfield","doi":"10.1016/j.coal.2026.104966","DOIUrl":"10.1016/j.coal.2026.104966","url":null,"abstract":"<div><div>The degree of structural order of carbonaceous matter (CM) in metasedimentary rocks is thought to largely depend on the maximum temperature the host rock experienced. This led to the widespread use of Raman spectroscopy of carbonaceous matter (RSCM) as geothermometer to determine maximum burial or metamorphic temperatures. The analytical certainty of most geothermometers based on RSCM is given as ±30–50 °C and the structural order of CM is often shown to be heterogeneous within individual samples, geological beds and units. To better understand the influence of authigenic mineral growth on CM maturation and heterogeneity we analyzed samples from three Precambrian CM-bearing stratigraphic units. Raman spectroscopic results indicate large heterogeneities in the degree of structural order of CM, resulting in ranges of up to 190 °C in calculated temperature within individual samples. Generally, within each sample, CM within authigenic minerals shows a significantly higher degree of structural order than CM in areas devoid of authigenic minerals. This results in calculated average temperatures from CM within authigenic minerals that are 27–94 °C higher than temperatures calculated from CM in neighboring areas devoid of authigenic minerals. Our results indicate that the structural order of CM within authigenic minerals is significantly enhanced. Thus, geothermometers based on RSCM must be used carefully with a thorough awareness of the petrographic context.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"316 ","pages":"Article 104966"},"PeriodicalIF":5.7,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146160596","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}
Pub Date : 2026-02-28Epub Date: 2026-01-31DOI: 10.1016/j.coal.2026.104952
Lin Wei , Maria Mastalerz , Jingwen Wang , Yanan Wang , Xiaomiao Li , Xiong Cheng
Vitrinite reflectance is a key parameter for thermal maturity assessment in sedimentary basins; however, its application in high-maturity marine shales is complicated by optical convergence between vitrinite and solid bitumen and strong reflectance anisotropy. These factors lead to substantial data dispersion, as highlighted by interlaboratory studies defining the empirical bounds of analytical reproducibility. This study aims to evaluate the internal reliability of reflectance datasets and quantify uncertainty in maturity interpretations.
We present an integrated statistical framework combining the analytical hierarchy process (AHP) and bootstrap resampling to assess data reliability and quantify uncertainty in thermal maturity assessments. This approach is demonstrated with three high-maturity shale samples (Barnett, Haynesville, and Eagle Ford), analyzed by two petrographers with contrasting experience levels.
The AHP model incorporates three evaluation indices-interval coverage probability, confidence interval width, and mean absolute percentage error-to generate composite reliability scores for each dataset. Results show that AHP assigns higher credibility to measurements from the more experienced analyst, effectively distinguishing data quality within the same environment, highlighting the model's ability to capture systematic biases. Bootstrap resampling generates robust confidence intervals for mean reflectance values, establishing probabilistic maturity ranges that better capture uncertainty than conventional single-point estimates. Our findings show that maceral identification and particle selection at high maturity levels introduce variations in reflectance measurements, ranging from 0.01% to 0.29% Ro (%Ro = mean random vitrinite reflectance). These variations arise from sample heterogeneity and subjective selection, rather than analytical error alone.
The integrated framework shifts from deterministic maturity reporting to probabilistic, credibility-weighted maturity assessment, providing a practical tool for uncertainty-aware maturity interpretation in high-maturity shale systems.
{"title":"Application of statistical methods to evaluate identification credibility of macerals in high-maturity marine shales","authors":"Lin Wei , Maria Mastalerz , Jingwen Wang , Yanan Wang , Xiaomiao Li , Xiong Cheng","doi":"10.1016/j.coal.2026.104952","DOIUrl":"10.1016/j.coal.2026.104952","url":null,"abstract":"<div><div>Vitrinite reflectance is a key parameter for thermal maturity assessment in sedimentary basins; however, its application in high-maturity marine shales is complicated by optical convergence between vitrinite and solid bitumen and strong reflectance anisotropy. These factors lead to substantial data dispersion, as highlighted by interlaboratory studies defining the empirical bounds of analytical reproducibility. This study aims to evaluate the internal reliability of reflectance datasets and quantify uncertainty in maturity interpretations.</div><div>We present an integrated statistical framework combining the analytical hierarchy process (AHP) and bootstrap resampling to assess data reliability and quantify uncertainty in thermal maturity assessments. This approach is demonstrated with three high-maturity shale samples (Barnett, Haynesville, and Eagle Ford), analyzed by two petrographers with contrasting experience levels.</div><div>The AHP model incorporates three evaluation indices-interval coverage probability, confidence interval width, and mean absolute percentage error-to generate composite reliability scores for each dataset. Results show that AHP assigns higher credibility to measurements from the more experienced analyst, effectively distinguishing data quality within the same environment, highlighting the model's ability to capture systematic biases. Bootstrap resampling generates robust confidence intervals for mean reflectance values, establishing probabilistic maturity ranges that better capture uncertainty than conventional single-point estimates. Our findings show that maceral identification and particle selection at high maturity levels introduce variations in reflectance measurements, ranging from 0.01% to 0.29% R<sub>o</sub> (%R<sub>o</sub> = mean random vitrinite reflectance). These variations arise from sample heterogeneity and subjective selection, rather than analytical error alone.</div><div>The integrated framework shifts from deterministic maturity reporting to probabilistic, credibility-weighted maturity assessment, providing a practical tool for uncertainty-aware maturity interpretation in high-maturity shale systems.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"316 ","pages":"Article 104952"},"PeriodicalIF":5.7,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146095634","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}
Unconventional geologic sources of rare earth elements, such as those preserved within coal-bearing strata, represent a potential domestic supply of critical minerals. Here we present major and trace element geochemical data from both the coal bed and stratabounding sediments. Representative samples were collected from the Wyodak-Anderson Coal Zone in U.S. Powder River Basin (WY, MT) and then analyzed using inductively coupled plasma mass spectroscopy and optical emission spectroscopy. These chemical analyses show that coal samples collected from multiple locations across the basin host concentrations of rare earth elements plus yttrium above average coal values for the United States. Additionally, these subbituminous coals are anomalously concentrated in CaO relative to coals from other U.S. basins. Total concentrations of rare earth elements and yttrium are highly variable when sampled at different depths within coal beds but show consistent relative enrichment at their margins. Sample locations within the basin and their proximity to bounding highlands appear to show predictable trends in rare earth element variability indicative of geochemical sorting mechanisms through geologic time. This contribution not only indicates an unconventional source of rare earth elements plus yttrium for active coal mines in the Powder River Basin, but also presents pathways for future work to grow our current understanding of this potential resource.
{"title":"Rare earth element occurrence and distribution within the largest U.S. coal resource: Geochemical variability of powder river Basin Coals, Wyoming and Montana","authors":"D.A. Bagdonas , R.W. Gregory , C.M. Messa , E.H. Phillips , T.C. Brown","doi":"10.1016/j.coal.2026.104964","DOIUrl":"10.1016/j.coal.2026.104964","url":null,"abstract":"<div><div>Unconventional geologic sources of rare earth elements, such as those preserved within coal-bearing strata, represent a potential domestic supply of critical minerals. Here we present major and trace element geochemical data from both the coal bed and stratabounding sediments. Representative samples were collected from the Wyodak-Anderson Coal Zone in U.S. Powder River Basin (WY, MT) and then analyzed using inductively coupled plasma mass spectroscopy and optical emission spectroscopy. These chemical analyses show that coal samples collected from multiple locations across the basin host concentrations of rare earth elements plus yttrium above average coal values for the United States. Additionally, these subbituminous coals are anomalously concentrated in CaO relative to coals from other U.S. basins. Total concentrations of rare earth elements and yttrium are highly variable when sampled at different depths within coal beds but show consistent relative enrichment at their margins. Sample locations within the basin and their proximity to bounding highlands appear to show predictable trends in rare earth element variability indicative of geochemical sorting mechanisms through geologic time. This contribution not only indicates an unconventional source of rare earth elements plus yttrium for active coal mines in the Powder River Basin, but also presents pathways for future work to grow our current understanding of this potential resource.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"316 ","pages":"Article 104964"},"PeriodicalIF":5.7,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146146705","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}
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