Compressibility of Different Pore and Fracture Structures and Its Relationship with Heterogeneity and Minerals in Low-Rank Coal Reservoirs: An Experimental Study Based on Nuclear Magnetic Resonance and Micro-CT

Cheng, Ming; Fu, Xuehai

doi:10.1021/acs.energyfuels.0c02119

Cited by 33 publications

(35 citation statements)

References 42 publications

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“…Direct observation methods mainly include optical microscope observations, scanning electron microscopy (SEM), helium ion microscopy (HIM), atomic force microscopy (AFM), , and transmission electron microscopy (TEM). , Fluid intrusion methods mainly include gas adsorption , and mercury injection methods. The X-ray and spectroscopic methods mainly include X-ray microcomputed tomography (micro-CT), − nuclear magnetic resonance (NMR), , small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) experiments. In addition, the introduction of fractal theory makes it possible to quantitatively characterize the complexity and heterogeneity of pores .…”

Section: Detection Methods For Coal Poresmentioning

confidence: 99%

Coal Pores: Methods, Types, and Characteristics

et al. 2021

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Coal pores are the locations of coalbed methane occurrence and enrichment and the main storage space targeted in CO2 sequestration. The systematic investigation of the coal pore structure and its development is of great significance to provide insights into coalbed methane generation, coal mine gas outburst mechanisms, and coal seam CO2 sequestration. In this study, coal pore testing technologies and methods, pore classification methods, and coal pore structure characteristics and their main control factors were systematically investigated and summarized. The results show that direct test methods, indirect fluid injection test methods, and X-ray and spectroscopic methods have been used for the quantitative characterization of the pore structure. However, each testing method has limitations. Therefore, a comprehensive method for the quantitative characterization of the full-scale pore structure must be developed, especially for the accurate quantitative characterization of closed pores in coal. The in situ measurement of pores in coal is one of the future research trends. Classification methods of pores in coal mainly include the classification of the genetic pore type, pore size, and pore morphology. Metamorphism, tectonic deformation, and macerals are the main internal factors affecting the pore distribution in coal. The effect of tectonic deformation on the macromolecular structure and micro- and ultramicropores of coal must be further studied. In addition, molecular mechanics simulations, molecular dynamics simulations, and quantum chemistry calculations of the dynamic response of the macromolecular structure and micro- and ultramicropores during gas adsorption and desorption must be carried out.

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Section: Detection Methods For Coal Poresmentioning

confidence: 99%

Coal Pores: Methods, Types, and Characteristics

et al. 2021

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“…Abundant discontinuous and significant nonlinear mechanical characteristics of plastic fracture-seepage are the two notable features of fractured low-permeability coal. e material is a typical pore (i.e., coal matrix)-fracture (i.e., coal discontinuities) medium [20]. ere are three mechanical responses in the coal process during hydraulic fracturing [21], which are as follows: plastic damage-seepage of coal matrix, ductile fracture-seepage of coal discontinuities, and the stress-seepage interaction between them.…”

Section: The Fluid-solid Coupling Theory Model Of Pore-fractured Coalmentioning

confidence: 99%

Optimization of Indirect Fracturing Process Parameters Based on Mechanical Properties of Fractured and Low-Permeability Coal

2022

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The coal-bed methane (CBM) resources in soft and low-permeability coals are assumed to be as much as 15 × 1012 m3 in China. Indirect fracturing technology can be an effective method to successfully extract methane within soft coals. The key to the success of this technique is to optimize the parameters, such as water injection flow rate and fracture initiation location, so that the hydraulic fracturing parameters enable the fractures to pass through the interface between coal and rock and propagate sufficiently into the coal. This paper focuses on solving the above problems by focusing on discontinuities and plastic characteristics of soft coals. Voronoi polyhedron was used to simulate the discontinuities of coal, and the constitutive relations of ductile fracture-seepage and elastoplastic damage-seepage are, respectively, given to the discontinuities and coal matrix. A numerical model was established based on the above theory to simulate the effect of stress difference Δσ, coal-rock interface friction coefficient fc,r, water injection flow rate i w , and distance between the well and the interface Dop on indirect fracturing fractures. The results show that the HFs area in the coal is positively correlated with Δσ, fc,r, and i w , and it first increases and then decreases with the decrease of Dop. The above results were applied in the Zhaozhuang mine of Qinshui Basin by optimizing Dop = 1 m and iw = 8 m3/min, so that CBM production has been greatly increased. The results can provide theoretical support for the efficient development of CBM in fractured and low-permeability coal seam areas.

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“…The pore\fracture based on NMR characterization is divided into adsorption space (T 2 < 2.5 ms) and seepage space (T 2 > 2.5 ms) according to the pore division methods of Li et al (2013) and Cheng et al (2020). To explain the variation of heterogeneity of pore\fracture under different confining pressures, the fractal dimensions of adsorption space and seepage space of different coal rank samples based on NMR test results are calculated by Eq.…”

Section: Pore Heterogeneitymentioning

confidence: 99%

“…In addition, the compressibility of the pore\fracture system is greatly affected by heterogeneity, and the permeability characterized by NMR has an apparent negative correlation with fractal dimension. The occurrence law of minerals (mineral content, mineral morphology, and mineral arrangement) has an evident impact on compressibility, and the coal reservoir with high mineral content has less compressibility (Chen et al, 2019;Cheng et al, 2020). Previous studies mainly focused on the single coal rank, and there was a lack of comparative research of different coal ranks.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Full Pore and Stress Compression Response of Reservoirs With Different Coal Ranks

Kang

et al. 2021

Front. Earth Sci.

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The accurate characterization of coal pore structure is significant for coalbed methane (CBM) development. The splicing of practical pore ranges of multiple test methods can reflect pore structure characteristics. The pore\fracture compressibility is the main parameter affecting the porosity and permeability of coal reservoirs. The difference in compressibility of different coal rank reservoirs and pore\fracture structures with changing stress have not been systematically found. The pore structure characteristics of different rank coal samples were characterized using the optimal pore ranges of high-pressure mercury intrusion (HPMI), low-temperature liquid nitrogen adsorption (LT-N2A), low-pressure carbon dioxide adsorption (LP-CDA), and nuclear magnetic resonance (NMR) based on six groups of different rank coal samples. The compressibility of coal matrix and pore\fracture were studied using HPMI data and NMR T2 spectrum under effective stress. The results show that the more accurate full pore characterization results can be obtained by selecting the optimal pore range measured by HPMI, LT-N2A, and LP-CDA and comparing it with the NMR pore results. The matrix compressibility of different rank coal samples shows that low-rank coal > high-rank coal > medium-rank coal. When the effective stress is less than 6 MPa, the microfractures are compressed rapidly, and the compressibility decreases slowly when the effective stress is more than 6 MPa. Thus, the compressibility of the adsorption pore is weak. Nevertheless, the adsorption pore has the most significant compression space because of the largest proportion in different pore structures. The variation trend of matrix compressibility and pore\fracture compressibility is consistent with the increase of coal rank. The compressibility decreases with the rise of reservoir heterogeneity and mechanical strength. The development of pore volume promotes compressibility. The research results have guiding significance for the exploration and development of CBM in different coal rank reservoirs.

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Compressibility of Different Pore and Fracture Structures and Its Relationship with Heterogeneity and Minerals in Low-Rank Coal Reservoirs: An Experimental Study Based on Nuclear Magnetic Resonance and Micro-CT

Cited by 33 publications

References 42 publications

Coal Pores: Methods, Types, and Characteristics

Coal Pores: Methods, Types, and Characteristics

Optimization of Indirect Fracturing Process Parameters Based on Mechanical Properties of Fractured and Low-Permeability Coal

Characterization of Full Pore and Stress Compression Response of Reservoirs With Different Coal Ranks

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