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Review
Energy & Fuels
Chenghao Wang et al.
Summary: This paper systematically reviews the importance of coal deformation energy and gas expansion energy in coal and gas outbursts. It highlights that most literature related to outburst energy overlooks the contribution of coal deformation energy. Experimental results show that the deformation energy of high outburst risk tectonic coal has a power function relationship with stress, and its releasing mode differs from intact coal. The coal deformation energy is proved to have the same order of magnitude with gas expansion energy.
Article
Energy & Fuels
Xianqi Peng et al.
Summary: This study explores the control mechanism of small organic molecules on the methane adsorption capacity of coal. The results show that small organic molecules increase the methane adsorption capacity of low-rank coal by separating and creating more micropores, while they reduce the methane adsorption capacity of middle-rank coal by closing micropores. In high-rank coal, the presence of small organic molecules has no significant effect on methane adsorption capacity.
Article
Energy & Fuels
Haifei Lin et al.
Summary: The CH4 adsorption-desorption-seepage characteristics of coal are important indicators for measuring the gas extraction capacity of coal seam. The deformation of coal caused by CH4 adsorption-desorption-seepage is a significant factor affecting the CH4 extraction ability. This study conducted synchronous test experiments on CH4 adsorption-desorption-seepage and coal deformation under different gas pressures. It analyzed the timely characteristics of CH4 adsorption-desorption-seepage and coal deformation, clarified the influence of gas pressure, and discussed the quantitative relationship between CH4 adsorption-desorption-seepage and coal deformation. A whole-process strain model of coal for CH4 adsorption-desorption-seepage was established. The research findings showed that increasing gas pressure can promote the CH4 adsorption-desorption-seepage and deformation of coal, and the deformation is affected by coal bedding structure and external stress. The strain caused by CH4 adsorption-desorption-seepage in coal has different growth relationships with the adsorption capacity, desorption capacity, and seepage capacity of CH4. The study provides theoretical support for the efficient extraction of coal seam gas.
Article
Construction & Building Technology
Mao Jing et al.
Summary: In this study, fly ash, nano-silica, and triethanolamine were used to optimize the pore structure of sealing materials for efficient coal mine gas extraction. The analysis showed that common sealing materials mainly contained mesopores (52.19%) and had the smallest volume of micropores (9.88%). Single doping of fly ash reduced the pore volume by 9.5%, but increased the percentage of mesopores by 1.3% and decreased the percentage of micropores by 0.9%. Co-doping with nano-silica and fly ash increased the microporous percentage by 0.77% and the peak stress by 17.43%. The synergistic effect of fly ash, nano-silica, and triethanolamine was the most effective in optimizing the pore structure. The pore volume was reduced to 0.08198 cm(3)/g, and the fractal dimensions D-1 and D-2 increased by 2.88% and 2.48%, respectively. The microscopic morphology of the material became flatter and denser, and the hydration of fly ash was more complete.
CONSTRUCTION AND BUILDING MATERIALS
(2023)
Article
Thermodynamics
Haihui Xin et al.
Summary: This study investigated the changes in pore structure and oxidation properties of coal treated with liquid carbon dioxide and liquid nitrogen. The results showed that the matrix of coal shrank and the pore and crack increased after being soaked in liquid CO2 and liquid N2. The oxygen absorption capacity of the coal also increased, especially when soaked in liquid N2. The changes in pore structure promoted oxygen absorption and led to an increase in spontaneous combustion and reignition tendency. The study provides valuable information for controlling coal spontaneous combustion when using liquid CO2 and liquid N2.
Article
Energy & Fuels
Lei Qin et al.
Summary: This paper characterizes the porosity and pore throat structure of different coal grades (lignite, bituminous coal and anthracite) under liquid nitrogen fracturing cycles by testing the T2 and T1-T2 sequences. The results show that the total pore space of A, L and B is arranged in descending order according to the initial state. The internal porous throat distribution of lignite and anthracite coal samples is wider. With the increase of the number of fracturing cycles, the internal pore space of the three coal grade coal samples has been improved, of which lignite has the largest lifting rate; The internal porous throat distribution of L coal samples was reduced by 0.97%. The internal pore space of B and A coal samples increased by 34.62% and 6.33%, respectively, the pore-throat distribution increased by 28.96% and 16.98%, respectively.
Article
Energy & Fuels
Yanan Miao et al.
Summary: A novel lattice Boltzmann (LBM) - based methodology was developed to estimate methane seepage capacity in coal seams after reagent modification. The addition of oxidizing acid and ionic liquid enhanced pore structure and maximum seepage velocity, but decreased average flow velocity and shifted higher cross-sectional velocity closer to the inlet of seepage channel. The presence of small cracks or pores adsorbed by ionic liquid deteriorated channel connectivity and slowed down gas flow. The study can provide theoretical guidance for acidizing and infiltration enhancement technologies in coal seams.
Article
Energy & Fuels
Chaoping Xu et al.
Summary: This paper presents a comprehensive analysis of the evolutionary characteristics of the macromolecular structure of coal using X-ray diffraction and Raman spectroscopy. The results show that microwave irradiation triggers the conversion of ordered graphitic carbon to amorphous carbon, as well as the condensation and spatial arrangement of aromatic clusters. Microwave-assisted oxidation facilitates the directional growth of aromatic rings and the cross-linking of aliphatic chains, and induces the rotation, displacement, stacking, and gradual parallel alignment of aromatic lamellae, thereby improving the integrity of the graphite structure and the orderliness of the macromolecular structure.
Article
Energy & Fuels
Jiexin Lu et al.
Summary: This study investigates the effects of microwave heating on the methane adsorption capacity of Pingdingshan bituminous coal. The results show that microwave irradiation can promote methane diffusion from the coal matrix.
Article
Thermodynamics
Yuzhou Cong et al.
Summary: Liquid Nitrogen (LN2) cold shock is a promising technology for coal reservoir, and the fracture networks in coal are influenced by temperature changes of different components. The effects of temperature include differential expansion of mineral particles, evaporation of pore water, gas volume expansion, and water-to-ice phase transition. This study investigates the relationship between minerals, moisture, and porosity of six coal types and the overall thermal expansion coefficient of coal samples using various testing and analysis methods. The results show that the thermal expansion coefficient of major minerals in coal is generally lower than the overall coefficient. Moisture and porosity of coal samples are proportional to the overall thermal expansion coefficient, with the porosity of small pores having the highest influence, indicating that the temperature effect of pore water evaporation and gas volume expansion plays a crucial role in coal temperature change.
CASE STUDIES IN THERMAL ENGINEERING
(2023)
Article
Thermodynamics
Yujie Li et al.
Summary: Steam has great potential in the recovery of coalbed methane due to its advantages in coal gasification, drying of low-rank coals, and heavy oil recovery. This study characterizes the changes in coal's surface morphology, internal moisture, pore-fissure structure, and molecular structure caused by steam treatment, and investigates its effects on CBM recovery. The findings indicate that steam treatment can expand coal cracks and enhance pore-fissure connectivity, providing more channels for CBM flow.
Article
Thermodynamics
Lei Qin et al.
Summary: Liquid nitrogen fracturing technology is crucial for improving the permeability of coal seams and enhancing unconventional natural gas extraction. Research has shown that freezing coal with liquid nitrogen can effectively expand the coal pores, thereby promoting the migration and drainage of coalbed methane. These findings have significant implications for further research on liquid nitrogen fracturing technology.
Article
Energy & Fuels
Chunshan Zheng et al.
Summary: Enhancing coal permeability by adopting chemical solvents treatment is an effective method to improve coalbed methane production efficiency. This study investigated the changes in coal ultrasonic characteristics, pore structure, and permeability after treatment with different chemical solvents. Results showed that ultrasonic velocity in coal reduces while ultrasonic attenuation coefficient increases after treatment, indicating good development of coal fractures. The porosity and permeability of CS2-treated coal experienced the maximum increase, and the permeability changes obtained from the NMP calculation model were consistent with lab measurements. The results demonstrate that chemical solvents can dissolve molecular substances in coal and improve pore connectivity.
GEOENERGY SCIENCE AND ENGINEERING
(2023)
Article
Energy & Fuels
Zheng Wang et al.
Summary: "Organic solvent erosion is an efficient method to promote fracture and pore development in coal. The effects of different solvents vary depending on their extraction rates on coal."
Article
Energy & Fuels
Lei Qin et al.
Summary: Cracking low-permeability coal seams with anhydrous liquid nitrogen can enhance coalbed methane extraction efficiency, but freezing variables significantly affect the mechanical properties of coal, with an increase in freezing cycles leading to a decrease in mechanical strength.
Article
Energy & Fuels
He Li et al.
Summary: This paper introduces the concept of using microwave-assisted oxidation to enhance the permeability of coalbed methane (CBM) reservoirs. The study shows that microwave-assisted oxidation can change the physicochemical structure of coal and improve its permeability.
Review
Energy & Fuels
He Li et al.
Summary: Chemical stimulation is a potential technology for enhancing coal permeability. Current research focuses on developing efficient chemical stimulation techniques and understanding the mechanisms of permeability enhancement. Laboratory studies have shown that acidising, oxidizing, organic solvent extraction, and electrochemistry stimulation techniques can improve coal permeability. Factors such as coal composition, pore-fracture structure, chemical reagent type, precipitation formation, in-situ stress, and water blocking influence the efficiency of permeability enhancement. The field application of chemical stimulation techniques is still limited, and future research should investigate their feasibility and consider the synergistic effects of chemical and physical stimulation techniques.
Article
Mining & Mineral Processing
Mingyang Song et al.
Summary: The resistivity testing system for hydraulic fracturing specimens was established to analyze the dynamic response characteristics of resistivity during hydraulic fracture propagation. The water and fracture exert competitive influence on the circuit structure, presenting a double peak resistivity curve with significant points. High resistivity rates lead to rapid release of fracture energy.
INTERNATIONAL JOURNAL OF MINING SCIENCE AND TECHNOLOGY
(2022)
Article
Energy & Fuels
Chaoping Xu et al.
Summary: The study investigates the impact of microwave-assisted oxidation on the pore structure and fractal characteristics of bituminous coal, finding that microwave heating destroys the pore structure and oxidation simplifies it, leading to an increase in total pore volume.
Article
Energy & Fuels
Leilei Si et al.
Summary: An improved model was developed to calculate the effective diffusion coefficient of gas in a water-saturated coal core, providing more accurate results compared to traditional models. Experimental results also showed that as coal rank increases, saturated moisture and equilibrium moisture decrease, along with a shift in pore size dominance from micropore/mesopore-dominated to micropores-dominated.
Article
Energy & Fuels
Jiexin Lu et al.
Summary: The research shows that microwave heating can improve the microstructure of coal, increase the volume and connectivity between mesopores and micropores, and reduce the methane adsorbability of coal.
Article
Energy & Fuels
Leilei Si et al.
Summary: Intrusion of formation water into coal seams reduces gas extraction efficiency. Experiments showed decreased mineral content and changed pore structure in coal due to water intrusion. Factors such as clay mineral collapse, mineral dissolution, and coal swelling play significant roles in influencing the pore structure of coal during water intrusion.
Review
Energy & Fuels
Sheng Xue et al.
Summary: This study explores the benefits of coal seam gas drainage and its relation to coal permeability, categorizing and reviewing coupled permeability models. It identifies current research gaps and future directions in permeability study, aiming to improve accuracy in permeability evaluation and provide better guidance for gas drainage design.
JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING
(2021)
Article
Mining & Mineral Processing
Haijun Guo et al.
Summary: This study investigates the weakening effects of gas on coal strength and deformation properties using reconstituted coal samples. The results show that the degree of weakening of gas on coal strength is influenced by confining stress and gas pressure. Additionally, coal bulk strain decreases with increasing particle sizes and increases with increasing gas pressure, indicating that gas can enhance coal deformation properties.
INTERNATIONAL JOURNAL OF MINING SCIENCE AND TECHNOLOGY
(2021)
Article
Mining & Mineral Processing
Lin Jia et al.
Summary: The paper describes a field test of Gas Wettability Alteration (GWA) technology in Xinjing coal mine, China, showing a significant increase in methane drainage rates and concentrations with GWA treatment, providing valuable insights for application in other coal mines.
INTERNATIONAL JOURNAL OF MINING SCIENCE AND TECHNOLOGY
(2021)
Article
Energy & Fuels
Minghao Yi et al.
Summary: The hydrochloric acid treatment significantly reduced the content of minerals and volatile matter in coal, which increased the porosity and pore connectivity of coal. The role of minerals in pores of different sizes varied, affecting the evolution of coal pore structure.
Article
Energy & Fuels
Li Zhao et al.
Article
Engineering, Chemical
Guanhua Ni et al.
Article
Energy & Fuels
Fazhi Yan et al.
Article
Engineering, Geological
He Li et al.
ROCK MECHANICS AND ROCK ENGINEERING
(2020)
Article
Chemistry, Physical
Remy Guillet-Nicolas et al.
JOURNAL OF COLLOID AND INTERFACE SCIENCE
(2020)
Article
Engineering, Chemical
He Li et al.
Article
Energy & Fuels
Lei Qin et al.
JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING
(2019)
Article
Chemistry, Applied
He Li et al.
FUEL PROCESSING TECHNOLOGY
(2019)
Article
Energy & Fuels
Jizhao Xu et al.
Article
Energy & Fuels
Ruiyue Yang et al.
Article
Energy & Fuels
He Li et al.
Article
Energy & Fuels
Gang Wang et al.
Article
Energy & Fuels
Hongjun Li et al.
Article
Energy & Fuels
Zhenyang Wang et al.
Article
Engineering, Chemical
Lei Qin et al.
Article
Engineering, Chemical
Guangzhi Yin et al.
Article
Energy & Fuels
Lei Qin et al.
Article
Chemistry, Applied
Jie-Feng Zhu et al.
FUEL PROCESSING TECHNOLOGY
(2016)
