Study on fracture characteristics in coal and shale for coal-measure gas reservoir based on 3D CT reconstruction and fractal features

Wang, Huijun; Chen, Shangbin; Zhang, Shaojie; Zhang, Chengxing; Wang, Yan; Yi, Guang-Yu; Peng, Yang

doi:10.1007/s11707-022-1027-9

Cited by 4 publications

(5 citation statements)

References 37 publications

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“…The innovation of this research is mainly reflected in the following aspects: (1) pore structure, connected pore structure, and isolated pore structure of the coal reservoir are visually reconstructed to build the equivalent pore network model. (2) The pore structure analysis from a multidimensional perspective was completed by using a variety of algorithms and combining representative elementary volume (REV). (3) The pore connectivity analysis of the coal samples was completed by using coordination parameters with the constructed equivalent pore network model.…”

Section: Introductionmentioning

confidence: 99%

“…Coal is a complex porous medium, that not only contains solid components, but also a large number of pores and fractures. , The distribution of the pore and fracture structure of coal stores coalbed methane and allows for its migration. It also directly affects the accumulation and migration of fluids and plays a very important role in the exploration and development of coalbed methane. , The pores and fractures not only restrict the gas content of the coal seam but also affect the economic viability of the coal seam .…”

Section: Introductionmentioning

confidence: 99%

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Comprehensive Analysis of Connectivity and Permeability of a Pore-Fracture Structure in Low Permeability Seam of Huainan–Huaibei Coalfield

Wang,

Fang,

Sang

et al. 2024

ACS Omega

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The connectivity and permeability of the coal seam pore structures control the occurrence and migration of coalbed methane. Coal samples were used from Huainan−Huaibei to reconstruct three-dimensional models of the pores and an equivalent pore network model, Statistical pore structure characteristic parameters. The pore structure of the coal reservoir was analyzed from the direction of multidimensional and multiangle. It shows that based on quantitative analysis, the representative Elementary volume of 500 × 500 × 500 was the most suitable experimental volume. The Y-axis direction of the Renlou sample had poor pore connectivity compared to that of other samples. Large volume connected pores dominated their pore systems. In terms of coal sample pore connectivity, the coal samples from the Liuzhuang and Qidong regions had pore connectivity better than those from the other regions. The pore connectivity of the Liuzhuang coal samples was the best. In terms of coal permeability, the Liuzhuang sample had better permeability than the other three samples, and the permeability was the best in the Y-axis direction. For all the combinations of the different types of throats, the shorter the throat, the greater the equivalent radius and the better the permeability. Conversely, the worse the permeability. During gas injection production, the closer the gas injection area was to the gas injection well, the poorer the connectivity and the lower the permeability over time. Near the production area, where the CO 2 did not reach the production area, the fracture porosity and effective connected porosity of the coal reservoir increased over time. When CO 2 reached the production area, the change in its connected pore structure was consistent with the change in the connected pores in the gas injection area. With this study, the coal seam pore structure on a microscale was characterized. A comprehensive analysis of the coal reservoir pore connectivity and permeability was completed. The study results are significant for the exploration and development of coalbed methane in the Huainan−Huaibei coalfield.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Comprehensive Analysis of Connectivity and Permeability of a Pore-Fracture Structure in Low Permeability Seam of Huainan–Huaibei Coalfield

Wang,

Fang,

Sang

et al. 2024

ACS Omega

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Section: Introductionmentioning

confidence: 99%

“…Focused ion beam scanning electron microscopy (FIB-SEM) and X-ray computed tomography (X-ray μ-CT) are the current technologies capable of providing high-resolution three-dimensional parameters of unconventional reservoirs. , The shale microstructure and porosity can be imaged at resolutions of a few to several hundred nanometers using high-resolution scanning electron microscopy imaging techniques, such as two-dimensional broad ion beam scanning electron microscopy (BIB-SEM) and nanoscale three-dimensional focused ion beam scanning electron microscopy (FIB-SEM). Using X-ray computed tomography, the distribution of shale components such as organic matter, macromineral grains, and clay minerals can be imaged in three dimensions from millimeter to micrometer scales, and the micrometer-scale pore and fracture systems can be characterized qualitatively and quantitatively. , X-ray μ-CT can effectively and nondestructively obtain parameters such as pore density, specific surface area, and volume, as well as its surface morphology and spatial distribution characteristics. , However, the maximum resolution is usually 1 μm due to limitations in resolution caused by the instrumentation, and X-ray μ-CT cannot display nanoscale pores and gas adsorption space and can only show the three-dimensional structural features of micrometer-scale pores.…”

Section: Introductionmentioning

confidence: 99%

Quality Enhancement of μ-CT Scanned Shale Images and Optimization of Experimental Conditions

Lin,

Chen,

et al. 2024

Energy Fuels

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Micrometer CT scanning (μ-CT) is a crucial technique for three-dimensional characterization of pore structures, but both the scanning resolution and scanning outcomes are constrained by several factors. This paper selects shale samples from a section of the Wufeng−Longmaxi Formation in the Luzhou block in southern Sichuan, prepares samples of different sizes and water-bearing conditions, investigates the characteristics of pore development, connectivity, and structural variability of different samples through μ-CT scanning combined with digital image processing technology, and selects the optimal experimental conditions for μ-CT scanning. The results show that the smaller the shale sample size, the higher the accuracy and resolution of the CT image and the more accurate the identification of pore fractures. Moisture in the sample can make the values obtained from CT scanning higher, affecting the identification of pores. Sporadic water at the edge of the pore space and in the pore space will not change the number of pores but will reduce the pore volume; complete water in the pore space will reduce the number of pores and the pore volume; the pore space is separated by the endowment of water into a number of zones; and when the pore space increases, the number of pore spaces and pore volume decrease. Therefore, the smaller the size of the shale samples after drying, the higher the quality of the CT images and the more accurate the identification of the pores. This result can provide more accurate experimental conditions for μ-CT shale porosity research reference.

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“…Multifractal theory utilizes spectral functions to describe structural behavior caused by different data levels within evolving fractal structures under varying local conditions, providing a more detailed description of rock fracture evolution processes . Applying multifractal theory for analyzing CT scan images , and NMR spectra is an effective means for quantitatively evaluating pore distribution and fracture structure in complex reservoirs. Furthermore, multifractal theory can also be employed for analyzing infrared thermal images to provide quantitative indices for infrared monitoring of rock failure events .…”

Section: Introductionmentioning

confidence: 99%

Multifractal Analysis for the Acoustic Emission Energy Dissipation of Shale after Long-Term Immersion in Fracturing Fluids with Various pH

Xie,

Tan,

Lyu

et al. 2023

Energy Fuels

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The interaction between shale and fracturing fluids will change the internal pore structure and adsorption capacity of shale, which have an important impact on shale gas productivity. This study aims to investigate the variations in acoustic emission (AE) energy and multifractal characteristics of shale under different pH values of fracturing fluids with implications for shale gas productivity. A series of immersion experiments were carried out on shale with fracturing fluids, with pH values of 6, 7, and 8, respectively. The uniaxial compression tests and AE tests were conducted on shale under fracturing fluid immersion with pH values of 6, 7, and 8. The multifractal theory is applied to analyze the evolution of fracture closure and propagation during uniaxial compression based on AE signals. The study also examines the deformation and crack evolution of shale after long-term fracturing fluid immersion, with particular emphasis on fluid−rock reactions. The results show that the maximum cumulative AE energy of shale after immersion is higher than that of intact shale. The focus is on understanding the fracture evolution process of shale during uniaxial compression at different stages. The fluid−rock reactions determine the deformation and crack evolution of shale after longterm fracturing fluid immersion. The increase of shale spectrum width Δα after immersion indicates that the distribution of AE signals is more uneven after immersion. The Δf value of shale after acid fracturing fluid soaking changes more significantly than those of neutral or alkaline fracturing fluids. All the fractal spectra of shale samples generally show a left-skewed distribution. The values of spectrum parameters are affected by soaking fluid, soaking time, and compression stages, resulting in the variation of multifractal characteristics. Hydration expansion of clay minerals is dominant in the middle and late period of immersion. The research results have a certain guidance for understanding the deformation and crack evolution and the influence of rock−fluid reactions on the failure process of shale samples.

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Study on fracture characteristics in coal and shale for coal-measure gas reservoir based on 3D CT reconstruction and fractal features

Cited by 4 publications

References 37 publications

Comprehensive Analysis of Connectivity and Permeability of a Pore-Fracture Structure in Low Permeability Seam of Huainan–Huaibei Coalfield

Comprehensive Analysis of Connectivity and Permeability of a Pore-Fracture Structure in Low Permeability Seam of Huainan–Huaibei Coalfield

Quality Enhancement of μ-CT Scanned Shale Images and Optimization of Experimental Conditions

Multifractal Analysis for the Acoustic Emission Energy Dissipation of Shale after Long-Term Immersion in Fracturing Fluids with Various pH

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