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23 pages, 5894 KiB

Open AccessArticle

Characteristics of Deep Coal Reservoirs Based on Logging Parameter Responses and Laboratory Data: A Case Study of the Logging Response Analysis of Reservoir Parameters Is Carried Out in Ordos Basin, China

by Xiaoming Yang, Jingbo Zeng, Die Liu, Yunhe Shi, Hongtao Gao, Lili Tian, Yufei He, Fengsheng Zhang and Jitong Su

Processes 2025, 13(7), 2062; https://doi.org/10.3390/pr13072062 - 29 Jun 2025

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Abstract

The coal reservoir in the Ordos Mizhi block is buried at a depth of over 2000 m. This study aims to obtain the characteristics of the coal reservoir in the Mizhi block through various experimental methods and combine the gas-bearing characteristics obtained from [...] Read more.

The coal reservoir in the Ordos Mizhi block is buried at a depth of over 2000 m. This study aims to obtain the characteristics of the coal reservoir in the Mizhi block through various experimental methods and combine the gas-bearing characteristics obtained from on-site desorption experiments to analyze the gas content and logging response characteristics of the study area. On this basis, a reservoir parameter interpretation model for the study area is established. This provides a reference for the exploration and development of coal-rock gas in the Mizhi block. The research results show that: (1) The study area is characterized by the development of the No. 8 coal reservoirs of the Benxi Formation, with a thickness ranging from 2 to 11.6 m, averaging 7.2 m. The thicker coal reservoirs provide favorable conditions for the formation and storage of coal-rock gas. The lithotypes are mainly semi-bright and semi-dark. The coal maceral is dominated by the content of the vitrinite, followed by the inertinite, and the exinite is the least. The degree of metamorphism is high, making it a high-grade coal. In the proximate analysis, the moisture ranges from 0.36 to 1.09%, averaging 0.65%. The ash ranges from 2.34 to 42.17%, averaging 16.57%. The volatile ranges from 9.18 to 15.7%, averaging 11.50%. The fixed carbon ranges from 45.24 to 87.51%, averaging 71.28%. (2) According to the results of scanning electron microscopy (SEM), the coal samples in the Mizhi block have developed fractures and pores. Based on the results of the carbon dioxide adsorption experiment, the micropore adsorption capacity is 7.8728–20.3395 cm³/g, with an average of 15.2621 cm³/g. The pore volume is 0.02492–0.063 cm³/g, with an average of 0.04799 cm³/g. The specific surface area of micropores is 79.514–202.3744 m²/g, with an average of 153.5118 m²/g. The micropore parameters are of great significance for the occurrence of coal-rock gas. Based on the results of the desorption experiment, the gas content of the coal rock samples in the study area is 12.97–33.96 m³/t, with an average of 21.8229 m³/t, which is relatively high. (3) Through the correlation analysis of the logging parameters of the coal reservoir, the main logging response parameters of the reservoir are obtained. Based on the results of the logging sensitivity analysis of the coal reservoir, the interpretation model of the reservoir parameters is constructed and verified. Logging interpretation models for parameters such as industrial components, microscopic components, micropore pore parameters, and gas content are obtained. The interpretation models have interpretation effects on the reservoir parameters in the study area. Full article

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

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23 pages, 3609 KiB

Open AccessArticle

Structural Characterization of Low-Rank Coals in the Ningdong Coalfield Under the Control of the First Coalification Jump

by Xiaoyan Ji, Caifang Wu, Bin Gao, Xuezhong Lu, Bei Wang, Yongping Liang, Xiaowu Zhang and Zhifeng Zhang

Processes 2025, 13(7), 1996; https://doi.org/10.3390/pr13071996 - 24 Jun 2025

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Abstract

The first coalification jump (FCJ) has a significant effect on changes in the microstructural properties of coal and plays a crucial role in understanding the efficient utilization of low-rank coal. One lignite (QSY-2), two subbituminous (MHJ-10 and YCW-2), and three high-volatile A-grade bituminous [...] Read more.

The first coalification jump (FCJ) has a significant effect on changes in the microstructural properties of coal and plays a crucial role in understanding the efficient utilization of low-rank coal. One lignite (QSY-2), two subbituminous (MHJ-10 and YCW-2), and three high-volatile A-grade bituminous coals (YX-12, JF-18, and HY-5) from the Ningdong coalfield were selected for research, avoiding the influence of regional geology. The evolution characteristics of the microstructures before and after the FCJ were investigated via spectroscopic experiments. The complex and unstable molecular structure of low-rank coal gradually decomposes and polymerizes at 350 °C. The aliphatic structure shows a V-shaped change trend as metamorphism increases. The inflection point is around an R_o of 0.6%. Demethylation and polymerization occur simultaneously during the FCJ. The reconnection of benzene substances with the aromatic ring increases the density of aromatic rings in the YCW-2 sample, significantly enhancing its aromaticity. The removal of oxygen-containing functional groups, especially methoxy and carbonyl groups, provides the possibility for the formation of CH₄ and CO₂ during the metamorphosis of lignite to subbituminous coal. Furthermore, high temperatures result in a loss of moisture content during the FCJ, which is the primary factor leading to a reduction in the hydroxyl content in coal. The selected samples are primarily composed of organic matter, with low levels of heteroatoms in the coal. It is preliminarily determined that coalification is not significantly affected. This study provides a theoretical foundation for investigating the molecular structure evolution of low-rank coal during the FCJ. Full article

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

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17 pages, 6931 KiB

Open AccessArticle

Stress Sensitivity of Tight Sandstone Reservoirs Under the Effect of Pore Structure Heterogeneity

by Haiyang Pan, Yun Du, Qingling Zuo, Zhiqing Xie, Yao Zhou, Anan Xu, Junjian Zhang and Yuqiang Guo

Processes 2025, 13(7), 1960; https://doi.org/10.3390/pr13071960 - 20 Jun 2025

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Abstract

The effect of the pore–fracture structure on the porosity and permeability affects the production process of tight sandstone gas. In this paper, 12 groups of tight sandstone samples are selected as the object, and the pore–fracture volume of a tight reservoir is quantitatively [...] Read more.

The effect of the pore–fracture structure on the porosity and permeability affects the production process of tight sandstone gas. In this paper, 12 groups of tight sandstone samples are selected as the object, and the pore–fracture volume of a tight reservoir is quantitatively characterized by a high-pressure mercury injection test. The multifractal and single fractal characteristics of different types of samples are calculated by fractal theory. On this basis, the pore volume variation under stress is discussed through the overlying pressure pore permeability test, and the pore–fracture compressibility is calculated. Finally, the main factors affecting the stress sensitivity of tight sandstone are summarized from the two aspects of the pore structure and mineral composition. The results are as follows. (1) The samples could be divided into types A and B by using the mercury-in and mercury-out curves. There is a significant hysteresis loop in the mercury inlet and outlet curves of type A, and the efficiency of the mercury inlet and outlet in the pores is relatively higher. The mercury removal curve of type B is almost parallel, and its mercury removal efficiency is relatively lower. (2) The applicability of singlet fractals in characterizing the heterogeneity of micropores is higher than that of multifractals. This is because the single fractal characteristics of the two types of samples have significant differences, while the differences in the multifractals are relatively weak. (3) A pore diameter of 100–1000 nm provides the main compression space for the type A samples. A pore distribution heterogeneity of 100–1000 nm affects the compression effect and stress sensitivity of this type B sample. Full article

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

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21 pages, 2249 KiB

Open AccessArticle

Multifractal Characterization of Full-Scale Pore Structure in Middle-High-Rank Coal Reservoirs: Implications for Permeability Modeling in Western Guizhou–Eastern Yunnan Basin

by Fangkai Quan, Yanhui Zhang, Wei Lu, Chongtao Wei, Xuguang Dai and Zhengyuan Qin

Processes 2025, 13(6), 1927; https://doi.org/10.3390/pr13061927 - 18 Jun 2025

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Abstract

This study presents a comprehensive multifractal characterization of full-scale pore structures in middle- to high-rank coal reservoirs from the Western Guizhou–Eastern Yunnan Basin and establishes a permeability prediction model integrating fractal heterogeneity and pore throat parameters. Eight coal samples were analyzed using mercury [...] Read more.

This study presents a comprehensive multifractal characterization of full-scale pore structures in middle- to high-rank coal reservoirs from the Western Guizhou–Eastern Yunnan Basin and establishes a permeability prediction model integrating fractal heterogeneity and pore throat parameters. Eight coal samples were analyzed using mercury intrusion porosimetry (MIP), low-pressure gas adsorption (N₂/CO₂), and multifractal theory to quantify multiscale pore heterogeneity and its implications for fluid transport. Results reveal weak correlations (R² < 0.39) between conventional petrophysical parameters (ash yield, volatile matter, porosity) and permeability, underscoring the inadequacy of bulk properties in predicting flow behavior. Full-scale pore characterization identified distinct pore architecture regimes: Laochang block coals exhibit microporous dominance (0.45–0.55 nm) with CO₂ adsorption capacities 78% higher than Tucheng samples, while Tucheng coals display enhanced seepage pore development (100–5000 nm), yielding 2.5× greater stage pore volumes. Multifractal analysis demonstrated significant heterogeneity (Δα = 0.98–1.82), with Laochang samples showing superior pore uniformity (D₁ = 0.86 vs. 0.82) but inferior connectivity (D₂ = 0.69 vs. 0.71). A novel permeability model was developed through multivariate regression, integrating the heterogeneity index (Δα) and effective pore throat diameter (D₁₀), achieving exceptional predictive accuracy. The strong negative correlation between Δα and permeability (R = −0.93) highlights how pore complexity governs flow resistance, while D₁₀’s positive influence (R = 0.72) emphasizes throat size control on fluid migration. This work provides a paradigm shift in coal reservoir evaluation, demonstrating that multiscale fractal heterogeneity, rather than conventional bulk properties, dictates permeability in anisotropic coal systems. The model offers critical insights for optimizing hydraulic fracturing and enhanced coalbed methane recovery in structurally heterogeneous basins. Full article

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

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18 pages, 2892 KiB

Open AccessArticle

Study on Smelting Process Parameters of a Blast Furnace with Hydrogen-Rich Gas Injection Using Coalbed Methane

by Huayun Du, Lei Cheng, Zicong Qian, Yan Zhou, Zhiqiang Gao, Lifeng Hou and Yinghui Wei

Processes 2025, 13(6), 1702; https://doi.org/10.3390/pr13061702 - 29 May 2025

Cited by 1 | Viewed by 469

Abstract

The extensive use of coal in the steel metallurgy sector has resulted in significant greenhouse gas emissions. Hydrogen-rich gases have been introduced to partially replace coal in the blast furnace reduction process to mitigate this issue. This research explores using abundant coalbed methane [...] Read more.

The extensive use of coal in the steel metallurgy sector has resulted in significant greenhouse gas emissions. Hydrogen-rich gases have been introduced to partially replace coal in the blast furnace reduction process to mitigate this issue. This research explores using abundant coalbed methane (CBM) resources near steel plants for metallurgical applications. Addressing the challenge of determining optimal process parameters in hydrogen-rich blast furnace smelting, this project first develops an energy and mass balance model for the hydrogen-rich blast furnace, providing a foundation for process analysis. Using this model, the substitution ratio and oxygen enrichment rate of the blast furnace are calculated under varying preheating temperatures of coalbed methane. Additionally, this study assesses carbon dioxide emission patterns based on the elemental balance principle, emphasizing the potential of coalbed methane to reduce carbon emissions and support low-carbon metallurgical development. Full article

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

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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 351

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. [...] Read more.

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

Viewed by 442

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 [...] Read more.

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 576

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 [...] Read more.

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 [...] Read more.

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 [...] Read more.

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

Cited by 1 | Viewed by 612

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 [...] Read more.

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

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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 [...] Read more.

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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27 pages, 2036 KiB

Open AccessReview

Potential, Efficiency, and Leakage Risk of CO₂ Sequestration in Coal: A Review

by Xueliang Liu, Baoxin Zhang, Xuehai Fu, Jielin Lu, Manli Huang and Fanhua (Bill) Zeng

Processes 2025, 13(6), 1680; https://doi.org/10.3390/pr13061680 - 27 May 2025

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Abstract

CO₂ sequestration in coal is effective for reducing carbon emissions, but related projects have encountered challenges in sustained CO₂ injection, highlighting the need for a comprehensive understanding of CO₂ sequestration in coal. This study reviews variations in the properties of [...] Read more.

CO₂ sequestration in coal is effective for reducing carbon emissions, but related projects have encountered challenges in sustained CO₂ injection, highlighting the need for a comprehensive understanding of CO₂ sequestration in coal. This study reviews variations in the properties of coal/rock during/after CO₂ injection, demonstrating the potential and stability of CO₂ sequestration in coal. The coal with a high V_L-CO₂/V_L-CH₄ is accompanied by high CO₂ sequestration capacity. The matrix swelling and acid corrosion restrict CO₂ sequestration efficiency, which can be enhanced by employing coatings and increasing permeability. Long-term CO₂–water–rock interactions weaken the integrity of coal/caprocks and decrease the adsorption capacity of coal, leading to the CO₂ leakage risk. Three issues are critical in future studies: (1) Increasing CO₂ adsorption capacity. (2) Establishing optimal approaches to enhance CO₂ injection efficiency. (3) Accurately predicting variations in the adsorption capacity of deep coal and the integrity of coal/caprocks during long-term CO₂–water–rock interactions. This review provides foundations for formulating CO₂ sequestration strategies in coal. Full article

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

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