Article
Geochemistry & Geophysics
K. Sawayama, T. Ikeda, T. Tsuji, F. Jiang, O. Nishizawa, Y. Fujimitsu
Summary: This study developed a numerical approach to calculate changes in elastic wave velocity with fracture aperture opening and revealed that the velocity can be accounted for by the superposition of a linear function of fracture density and quadratic function of aperture. The relationship between fracture permeability and elastic wave velocity was found to depend on fracture density, but the offset-normalized relationship showed clear linearity with fracture density. The findings suggest that laboratory-scale properties of a single fracture can be applied to multiple fractures on a larger scale.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2022)
Article
Engineering, Geological
K. Sawayama, T. Ishibashi, F. Jiang, T. Tsuji, Y. Fujimitsu
Summary: This study investigates simultaneous changes in hydraulic and geophysical properties of natural rock fractures under increasing normal stress, and correlates the property changes through coupling experiments and digital fracture simulations. It is found that electrical resistivity is linked with permeability and flow area, while elastic wave velocity is roughness-dependent.
ROCK MECHANICS AND ROCK ENGINEERING
(2021)
Article
Geosciences, Multidisciplinary
Yongjiang Yu, Jingjing Liu, Yuntao Yang, Di Wu, Wenbo Zhai, Feng Miao
Summary: This paper conducted experimental studies on the percolation, permeability, and adsorption of supercritical CO2 in coal seams, and analyzed the effects of injection pressure and temperature. The results showed that the permeability of supercritical CO2 in coal increased by 93% compared to CO2. The excess adsorption capacity of supercritical CO2 by coal decreased with increased pressure, and the adsorption capacity decreased by 8.3% on average with a temperature increase of 10 degrees C. The propagation velocity of the longitudinal wave in the sample decreased significantly after the action of supercritical CO2, indicating its effective promotion of pore and fracture development in coal.
FRONTIERS IN EARTH SCIENCE
(2023)
Article
Mining & Mineral Processing
Shuangjiang Zhu, Jianhong Kang, Youpai Wang, Fubao Zhou
Summary: This study investigates the effects of different boundary conditions and gases on the P-wave velocity after the interaction of coal with CO2. The results show that pore pressure and matrix swelling are important factors affecting the P-wave velocity. CO2 causes more severe damage to the coal matrix, resulting in a significant decrease in P-wave velocity, with the decline increasing with vitrinite content.
INTERNATIONAL JOURNAL OF MINING SCIENCE AND TECHNOLOGY
(2022)
Article
Energy & Fuels
Kun Xiao, Zetian Zhang, Ru Zhang, Mingzhong Gao, Jing Xie, Anlin Zhang, Yang Liu
Summary: The distribution of natural fractures in coal seams plays a crucial role in the anisotropy of coal permeability and stress sensitivity. A modified permeability model and anisotropic evaluation index were established to analyze the anisotropic evolution law of stress sensitivity. Results showed significant anisotropic permeability and stress sensitivity due to the complex heterogeneity of natural fractures in coal.
Article
Energy & Fuels
Li Huanran, Tang Xiaoming, Li Shengqing, Su Yuanda
Summary: This paper proposes a novel method for evaluating the fluid transport properties of hydraulic fractures by studying the dynamic fluid flow through fractures and its effect on borehole acoustic waves. The method takes into account the fractal characteristics of fractures observed in hydraulic fracturing experiments and combines them with the Biot-Rosenbaum theory to calculate and analyze the influence of hydraulic fractures on the velocity dispersion of borehole Stoneley-wave. The field application shows that this method is practical and effective in assessing the permeability and connectivity of hydraulic fractures.
PETROLEUM EXPLORATION AND DEVELOPMENT
(2022)
Article
Multidisciplinary Sciences
Xiang Ji, Tianjun Zhang, Lei Zhang, Wen Yang, Hang Zhang
Summary: This study investigated the ultrasonic characteristics and crack propagation law of coal and rock bodies around boreholes. Different grouting samples with boreholes were tested, and the ultrasonic parameters of the samples were analyzed. The influence of grouting material on the crack propagation law was quantitatively analyzed.
Article
Engineering, Civil
Shaoyang Geng, Xing He, Runhua Zhu, Chengyong Li
Summary: This study investigates the permeability modeling of filled fractures and proposes a new permeability prediction model that can more accurately predict the permeability of fractures filled with spherical proppants. Moreover, a prediction model for effective permeability under non-Darcy flow is also proposed.
JOURNAL OF HYDROLOGY
(2023)
Article
Energy & Fuels
Baiquan Lin, Zheng Wang, Wei Yang, He Li, Yidu Hong
Summary: The low permeability of coalbed methane (CBM) reservoirs can be improved by organic solvent erosion, and ultrasonic testing is an effective method for identifying the erosion effects on coal. The effects of organic solvent erosion on coal can be divided into three grades and are influenced by the extraction rate of the solvent. N-Methylpyrrolidone (NMP) and tetrahydrofuran (THF) have high extraction rates for coal and are suitable for solvent treatment.
Article
Engineering, Chemical
Qingao Zhu, Liming Yin, Qiming Huang, Enmao Wang, Zhiguo Hou
Summary: In this study, the pressure changes and pulverized coal blocking characteristics were experimentally studied using deionized water and three surfactant solutions (1227, SDS, and TX-100). A device capable of visualizing propped fractures was established, and simulation experiments were conducted. The results showed that surfactant solutions can lower the injection pressure, and different surfactants have different effects at different injection flow rates. This study provides theoretical support for improving coal seam permeability and dust prevention effect of coal seam water injection.
Article
Mechanics
Swapnil Kar, Abhijit Chaudhuri, Avtar Singh, Siladitya Pal
Summary: In this study, a phase field model was used to simulate hydraulic fracturing in a porous reservoir with poorly connected natural fractures. The finite element method (FEM) was used to solve the poro-elastic deformation and phase field equation, while the finite volume method (FVM) was used to solve the flow field. The numerical model was validated using existing analytical and numerical solutions, and the simulation results showed that the phase field method could accurately capture complex fracture propagation patterns. The results also indicated that high injection pressure could lead to crack branching, which is desirable for creating multiple high-permeable flow paths and improving connectivity among natural fractures.
ENGINEERING FRACTURE MECHANICS
(2023)
Article
Geochemistry & Geophysics
Sam S. Hashemi, Mark D. Zoback
Summary: The experimental study found that supercritical carbon dioxide (scCO(2)) has an impact on fracture permeability and surface characteristics in shales of various compositions, especially in samples with high carbonate content. Permeability may increase and fracture surface may degrade with longer exposure time. The sensitivity of permeability to effective normal stress also increases as the fracture surface becomes more compliant after exposure to scCO(2).
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2021)
Article
Energy & Fuels
Mingyao Wei, Jishan Liu, Derek Elsworth, Yingke Liu, Jie Zeng, Zhihong He
Summary: The study extends the conventional dual porosity model to account for equilibration time lag between matrix and fractures, dividing the matrix REV into two sub-REVs using the MINC concept. The model is verified against experimental observations of coal permeability evolution under constant effective stress for over 80 days, showing significant impact of matrix strain variations on coal permeability evolution.
Article
Energy & Fuels
Adelina Lv, Mohammad Ali Aghighi, Hossein Masoumi, Hamid Roshan
Summary: The study investigates the mechanisms influencing wave propagation in fractured coals through a combination of ultrasonic transmission and XRCT imaging. The results show that the closure of fractures by matrix swelling predominantly controls the change in wave velocities, while the effect of gas adsorption on matrix properties on wave propagation is trivial. Further numerical simulations confirm the insignificant impact of changes in coal matrix properties by gas adsorption on wave velocity. The findings have implications for characterizing and monitoring coal seam gas production and gas drainage.
INTERNATIONAL JOURNAL OF COAL GEOLOGY
(2022)
Article
Energy & Fuels
Jiang Liu, Yili Kang, Mingjun Chen, Lijun You, Tingshan Zhang, Xinping Gao, Zhangxing Chen
Summary: Enhancing coal permeability through formation heat treatment is an effective method for coalbed methane exploitation. The process involves removing residual water and inducing cracks in the coal structure, significantly increasing permeability. Additionally, the stimulation mechanisms consist of alleviating aqueous phase trapping, weakening coal mechanical properties, and inducing coal fracture to produce more gas flow channels.
