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Comprehensive Evaluation and Utilization of Coal Measure Mineral Resources

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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Chemical Processes and Systems".

Deadline for manuscript submissions: 30 June 2025 | Viewed by 3595

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Dr. Junjian Zhang

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College of Earth Sciences & Engineering, Shandong University of Science and Technology, Qingdao 266590, China
Interests: unconventional resource; methane adsorption; molecular structure
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Dr. Yang Wang

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School of Resources and Geoscience, China University of Mining and Technology, Xuzhou 221116, China
Interests: shale gas; coalbed methane; pore structure; adsorption mechanism; fractal characterization
Special Issues, Collections and Topics in MDPI journals

Dr. Junqiang Kang

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School of Resources and Earth Science, China University of Mining and Technology, Xuzhou 221008, China
Interests: coalbed methane; gas production; numerical simulation

Special Issue Information

Dear Colleagues,

It is of great practical significance to study the comprehensive evaluation and utilization of coal measure mineral resources. With the continuous growth of the global energy demand and an increase in the tension between resources and the environment, as an important source of traditional energy supplies, the efficient and sustainable development and utilization of coal has become crucial. The various metals and minerals associated with coal measures, such as coalbed methane, may have significant economic value and environmental benefits. Through a comprehensive and systematic assessment of the types, reserves, quality and environmental impact of these resources, resource development strategies can be formulated scientifically, resource allocation can be optimized, and the efficiency of resource utilization can be enhanced. At the same time, in-depth research and the promotion of advanced comprehensive utilization technology can not only enhance the added value of coal resources and reduce environmental pollution, but also promote the transformation and upgrade of related industries and facilitate the sustainable development of regional economy. Therefore, the comprehensive evaluation and utilization of coal mineral resources is crucial in achieving the goals of energy security, environmental protection and economic development.

Dr. Junjian Zhang
Dr. Yang Wang
Dr. Junqiang Kang
Guest Editors

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Keywords

coalbed methane
coal measure minerals
critical elements
resource evaluation

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Published Papers (7 papers)

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Research

21 pages, 10018 KiB

Open AccessArticle

Evaluation of Pore-Fracture Structures and Gas Content in Deep Coal Reservoir of Yan’an Gas Field, Ordos Basin

by Zhenchuan Wang, Yongping Wan, Hongtao Gao, Jinlan Fan, Shan Li and Liang Qiao

Processes 2025, 13(4), 1177; https://doi.org/10.3390/pr13041177 - 13 Apr 2025

Viewed by 233

Abstract

Research has delved into the main controlling factors for the evolution of the pore-fracture structure in deep coal samples. The gas content is influenced by multiple factors, among which the pore-fracture structure in deep coal samples stands as one of the key determinants. To ascertain the evolution of the pore-fracture structure and the main controlling factors of the gas content in deep coal samples of the Yan’an Gas Field, 16 coal samples were collected from the Yan’an Gas Field in the Ordos Basin in this study. A series of laboratory tests and analyses were then carried out. According to the test results, the major controlling factors for the evolution of the pore-fracture structure of the samples were analyzed in accordance with the proximate analysis components, maceral components, mineral composition of the coal samples, and R_o,max, in conjunction with the pore volume and specific surface area of nanopores. Meanwhile, based on the in situ desorption experiment, the major controlling factors of the gas content in coal were explored. First, based on the SEM and hand specimen identification, the pore-fracture structure of the samples is relatively well developed. Calcite filling the fractures of samples can be seen in the hand specimens of samples. This indicates that the mineral composition has a very important influence on the evolution of the pore-fracture structure of samples. Secondly, this study indicates that pore-fracture structure evolution is influenced by multiple factors, primarily ash content and fixed carbon. As ash content increased, the mesopore surface area and volume rose across all sample types, with Type C showing the highest increase (78.1% in surface area and 12.4% in volume compared to Type A). Conversely, micropore characteristics declined, with Type C exhibiting a 4.8% drop in surface area and a 4.7% reduction in volume. The R_o,max of the samples is generally higher than 2.8%, which has a multifaceted impact on pore-fracture structure evolution. Finally, the gas content is mainly controlled by pore volume and the specific surface area of nanopores, with industrial components and maceral compositions showing minimal direct influence. This suggests that gas content results from the combined effects of material composition and pore-fracture structure evolution. Inorganic minerals like quartz and calcite indirectly affect gas content by influencing pore structure development—occupying spaces while also creating new pores, especially through calcite dissolution. Conversely, clay minerals generally hinder pore development by filling spaces with limited fracture-forming capacity. The main purpose of this study is to evaluate the gas content of coal samples in Yan‘an Gas Field. There are few studies on this area by previous scholars. Full article

(This article belongs to the Special Issue Comprehensive Evaluation and Utilization of Coal Measure Mineral Resources)

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24 pages, 2685 KiB

Open AccessArticle

Characteristics of Pyrolysis Products of Tar-Rich Coal Under Cryogenic Pretreatment with Liquid Nitrogen

by Tao Xu, Lingyun Chen, Jie Chen, Yurui Lei, Xinxin Wang, Xinyu Yang and Zhifu Yang

Processes 2025, 13(4), 1064; https://doi.org/10.3390/pr13041064 - 2 Apr 2025

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Abstract

The conventional pyrolysis of tar-rich coals faces limitations in maximizing tar yield and optimizing tar composition, often resulting in inefficient resource utilization and elevated emissions of CO₂. This study investigates a novel cryogenic pretreatment method using liquid nitrogen to enhance pyrolysis efficiency, aiming to improve tar yield and transform tar quality for sustainable coal utilization. Three tar-rich coals underwent cryogenic pretreatment at varying temperatures (0 to −90 °C) via liquid nitrogen, followed by pyrolysis. The product distribution (tar, gas) and quality were analyzed and compared to conventional pyrolysis and the Gray–King assay. The cryogenic pretreatment increased the tar yield by 25.8–44.6% compared to conventional methods, achieving a maximum yield of 7.8–16.0 wt% at −90 °C. The emissions of CO₂ decreased by 12.7–27.4%, while CH₄ and H₂ proportions rose by 15.1–60.2%, enhancing gas energy content. The pretreatment reduced benzene compounds by 4.4–13.9 wt% and increased aromatic derivatives by 13.9–20.5 wt%, indicating a shift toward higher-value chemicals. The cryogenic approach demonstrates the dual benefits of boosting tar productivity while reducing carbon emissions, offering a promising path for cleaner and more efficient coal pyrolysis. Full article

(This article belongs to the Special Issue Comprehensive Evaluation and Utilization of Coal Measure Mineral Resources)

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18 pages, 9930 KiB

Open AccessArticle

Effects of Thermal Evolution Degree and Industrial Components on Pore Fracture Distribution Heterogeneity in Deep Coal Reservoirs

by Yufei He, Jinbin Wan, Renjie Yang, Shuangbiao Han, Xiaoming Yang, Jingbo Zeng and Hongtao Gao

Processes 2025, 13(3), 710; https://doi.org/10.3390/pr13030710 - 28 Feb 2025

Viewed by 436

Abstract

Many studies have shown that the thermal evolution degree is the main factor affecting the micropore structure of coal reservoirs. However, within the same thick coal seam, the R_o,max of the entire coal seam is not much different, which affects the determination of the main controlling factors of pore structure heterogeneity. Therefore, No. 8 coal collected from Benxi Formation in the eastern margin of Ordos was taken as an example, and 16 samples were selected for low-temperature liquid nitrogen, carbon dioxide adsorption, and industrial component tests. Based on heterogeneity differences of R_o,max, industrial components and pore volume distribution of adsorption pores (pore diameter is less than 100 nm), the main controlling factors affecting the micropore structure of ultra-thick coal seams, were discussed. Then, the surface free energy theory was used to study the influencing factors affecting surface free energy variations during coal adsorption. First of all, R_o,max is not the main controlling factor affecting the micropore-fracture structure, as the effects of industrial components on the micropore structure are obvious, which indicates that industrial components are the main factors affecting vertical differences in the micropore structure within the same thick coal seam. Second of all, R_o,max and industrial components affect the adsorption process. When the adsorption pressure is lower, the adsorption volume and adsorption potential increase rapidly. When the adsorption pressure is higher (pressure is larger than 15 Mpa), the adsorption capacity and potential tend to be stable. Moreover, the maximum surface free energy increases with the increase in coal rank, which indicates that the degree of thermal evolution is the core factor affecting the adsorption free energy, but it is also controlled by the influence of industrial components (ash content). Lastly, micropores affect the adsorption capacity, and mesopores have little effect on the adsorption capacity, since micropores restrict the adsorption capacity and change the adsorption process by affecting surface free energy variations. The refined characterization of pore-fracture structures in deep coal reservoirs plays a crucial role in the occurrence and seepage of coalbed gas. This research can provide a theoretical basis for the efficient development of deep coalbed gas in the target area. This study aims to identify the primary factors controlling micropore structures in No. 8 coal from the Benxi Formation and to analyze the role of industrial components, which has been overlooked in previous research. Full article

(This article belongs to the Special Issue Comprehensive Evaluation and Utilization of Coal Measure Mineral Resources)

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22 pages, 8961 KiB

Open AccessArticle

Heterogeneity of Pore and Fracture Structure in Tight Sandstone Using Different Fractal Models and Its Influence on Porosity–Permeability Variation

by Qinrong Kang, Yongdong Jiang, Jiahui Li, Zhengyuan Qin, Weizhong Zhang, Yuqiang Guo and Junjian Zhang

Processes 2025, 13(3), 679; https://doi.org/10.3390/pr13030679 - 27 Feb 2025

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Abstract

The study of pore structure in low-permeability sandstone uranium deposits has become a key factor in the profitability of uranium mining. In this paper, pore and fracture distribution in the target sandstone were determined by using mercury injection parameters. Single and multi-fractal models are used to calculate the heterogeneity of pore and fracture volume distribution. Moreover, the correlation between compressibility and the heterogeneity of pore distribution has been studied. The results are as follows. (1) All the samples can be divided into three types by using maximum mercury injection volume and mercury withdrawal efficiency. Type A is represented by a lower maximum mercury injection volume (less than 0.5 cm³·g⁻¹) and a higher mercury withdrawal efficiency (larger than 25%). The volume percentage of pores whose diameter is less than 100 nm and 100~1000 nm in type A samples is larger than that of type B and C samples since in this type of sample, micropores are developed. (2) The fractal dimension value assessed using the Menger model has a good linear relationship with the thermodynamic model, which indicates that the abovementioned models have good consistency in characterizing the pore distribution of tight sandstone. Multi-fractal results show that the lower pore volume in the selected samples controls the heterogeneity of pore distribution in the overall sample. (3) As the effective stress increases, the permeability damage rate gradually increases in a power exponential equation. The correlation between porosity and compressibility is weaker, indicating that only a portion of the pore volume in the sample provides compression space. As the pore volume of 100~1000 nm increases, the compressibility decreases linearly, indicating that pore volumes larger than 1000 nm provide compression space for all the selected samples. Full article

(This article belongs to the Special Issue Comprehensive Evaluation and Utilization of Coal Measure Mineral Resources)

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13 pages, 1465 KiB

Open AccessArticle

Pre-Stack Nonlinear Direct Exact Inversion of Fracture Parameters in Deep Shale Reservoirs

by Meng Wang, Liang Yu, Tianchao Guo, Xiuyan Song, Xiaoxin Zhang and Yurun Rui

Processes 2025, 13(2), 426; https://doi.org/10.3390/pr13020426 - 5 Feb 2025

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Abstract

A conventional linear pre-stack inversion method under the conventional stationary convolution model is limited by the assumptions of weak formation contrast change and small angle incidence and fails to take into account the amplitude attenuation of seismic wave propagation. Meanwhile, the resolution and precision of oil and gas evaluation and fracture characterization of shale reservoirs under complex geological conditions are low because the compaction and non-connectivity characteristics of deep shale reservoirs are not fully considered. Therefore, porous rock pores are divided into connected pores and disconnected pores. Combined with the effect of compaction on dry rock skeleton, a petrophysical model considering the compaction and pore dysconnectivity of deep shale reservoir is developed. The quantitative relationship between transverse isotropy with a vertical axis of symmetry (VTI) stiffness matrix, rock physical properties, and fracture parameters is established in this model. It provides a more accurate scheme for the original physical modeling of deep shale. This relationship is incorporated into the exact VTI reflection coefficient equation, and a nonstationary convolution operator is derived by using the attenuation theory of seismic wave propagation. A nonstationary pre-stack nonlinear direct inversion method of fracture parameters of shale reservoirs with horizontal fractures is proposed, which Improves the resolution and accuracy of shale reservoir gas bearing and fracture characteristics prediction. It provides a new way to accurately characterize the fracture development and oil-bearing property of shale reservoirs. A model test and field data test verify the effectiveness of this method. Full article

(This article belongs to the Special Issue Comprehensive Evaluation and Utilization of Coal Measure Mineral Resources)

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14 pages, 12055 KiB

Open AccessArticle

Low-Field NMR Investigation of Imbibition in Coalbed Methane Reservoirs: Implications of Gas–Water Coexistence

by Dong Li, Yi Yang, Zekun Yue, Fei Xu, Yanzhi Liu, Yuntian Jiang and Sijian Zheng

Processes 2025, 13(1), 178; https://doi.org/10.3390/pr13010178 - 10 Jan 2025

Viewed by 518

Abstract

Investigating the imbibition characteristics of coals can yield profound insights for advancing coalbed methane extraction and utilization strategies. However, there has been little exploration of the micro-pore imbibition phenomenon during the two-phase flow of gas and water, as research has focused more on the process of static imbibition. In this study, we used an independently developed low-field nuclear magnetic resonance (NMR) displacement experimental device to conduct a systematic study on the dynamic imbibition phenomenon of low-permeability coals under conditions in which gas and water coexist. The experimental results show that the imbibition process under conditions of gas–water coexistence was significantly influenced by the physical properties of the coal samples, such as the wetting contact angle, porosity, and permeability. A smaller wetting contact angle and lower porosity and permeability values were indicative of a stronger imbibition effect. Meanwhile, changes in effective stress and pore pressure had a significant effect on the imbibition process. Changes in effective stress were observed to elastically compress (or expand) the coal pores, leading to intensified (or weakened) imbibition. Greater pore pressure led to a more violent imbibition reaction. These findings provide a new theoretical basis for understanding and predicting imbibition phenomena in the two-phase flow of gas and water in coalbed methane engineering, offering the potential to illuminate the intricate self-absorption phenomena occurring during CO₂ geological sequestration processes. Full article

(This article belongs to the Special Issue Comprehensive Evaluation and Utilization of Coal Measure Mineral Resources)

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23 pages, 11798 KiB

Open AccessArticle

Study on the Influencing Factors of CO₂ Storage in Low Porosity-Low Permeability Heterogeneous Saline Aquifer

by Hongchang Hu, Dongdong Wang, Yujie Diao, Chunyuan Zhang and Ting Wang

Processes 2024, 12(12), 2933; https://doi.org/10.3390/pr12122933 - 22 Dec 2024

Viewed by 755

Abstract

The safety and long-term storage capacity of CO₂ geological storage are necessary factors for project design and engineering development. Evaluating the influencing factors of CO₂ storage and quantitatively analyzing the sensitivity of each parameter have an important guiding role in the design and development of storage projects. In this paper, the Liujiagou Formation in the northeast of the Ordos Basin is taken as an example. Based on the TOUGH/Petrasim simulation tool, the RZ2D geological storage model is established. Seven influencing factors, namely salinity, temperature, horizontal and vertical permeability ratio, pore geometry factor, residual gas saturation, liquid saturation and pore compression coefficient, were compared and analyzed to control the plume migration behavior, interlayer pressure accumulation and storage capacity of low porosity and low permeability heterogeneous reservoirs, and the sensitivity of each parameter to interlayer pressure and storage capacity was quantitatively analyzed. The simulation results show that the uncertain factors affect the safety of CO₂ geological storage to a certain extent by affecting the speed of the residual storage and dissolution storage mechanism. High residual gas saturation and salinity will make CO₂ mostly exist in the form of free state, which will adversely affect the safety and storage capacity of CO₂ saline aquifer storage. High temperature and high vertical permeability ratio will lead to higher interlayer pressure accumulation, which is not conducive to the safety of the storage project but is beneficial to the storage capacity. Temperature, transverse and longitudinal permeability ratio and pore geometry factor control the propagation velocity of plume. The larger these factors are, the faster the plume velocity is. Higher liquid phase saturation is not better; higher liquid phase saturation leads to a large build-up of pressure in the reservoir and can have an adverse effect on the storage volume. The sensitivity analysis of all factors shows that the liquid saturation and temperature have the greatest influence on CO₂ geological storage, and the pore compression coefficient has the least influence. The conclusions of this paper can provide a theoretical reference for the design and development of a CO₂ saline aquifer storage project in a low porosity and low permeability reservoir area. Full article

(This article belongs to the Special Issue Comprehensive Evaluation and Utilization of Coal Measure Mineral Resources)

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