Experimental Study on Identification Diffusion Pores, Permeation Pores and Cleats of Coal Samples

Zou, Mingjun; Wei, Chongtao; Huang, Zhiquan; Zhang, Miao; Lv, Xiaochun

doi:10.1115/1.4031610

Cited by 20 publications

(15 citation statements)

References 24 publications

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“…In general, many factors are affecting the T 2 cutoff value, such as coal rank, pore structure, and so forth . The T 2 cutoff value determined by the saturation–centrifugation method may be more suitable for coal reservoirs with better pore connectivity. , In this paper, the immovable water peak and the movable water peak of the sample have obvious trough (Figure ), and each peak represents a kind of pore system. Therefore, C f determined by the spectral morphology method (0.050 MPa –1 ) can express the dynamic process of permeability and improve the calculation accuracy of numerical simulation of different depressurization schemes.…”

Section: Resultsmentioning

confidence: 90%

“…T 2 cutoff values are most commonly determined by saturation–centrifugation and curve distribution morphology. , The first method is obtained from saturation and centrifugal experiments (see Subsection for details). The obtained T 2 spectrum distribution of saturated and immovable water is transformed into cumulative T 2 spectral integration.…”

Section: Theory and Calculationmentioning

confidence: 99%

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Physical Experiment and Numerical Simulation of the Depressurization Rate for Coalbed Methane Production

et al. 2020

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The influence of the depressurization rate on coalbed methane desorption and percolation was studied using physical experiment and numerical simulation. First, low-field nuclear magnetic resonance technology provided a new approach to conduct desorption experiments with different depressurization schemes and obtain the compressibility ( C f ) of coal samples. Then, the productivity calculation of different depressurization schemes was carried out via numerical simulation. The results showed that the first-slow-then-fast (FSTF) depressurization scheme had the highest desorption efficiency (94%), followed by one-stop desorption (85%), first-fast-then-slow desorption (79%), and uniform depressurization desorption (61%). T 2 cutoff values and the corresponding compressibility were obtained by the saturation–centrifugation method and spectral morphology method, and a high-precision permeability expression for dynamic evaluation of numerical simulation was established by the historical production data fitting approach. Through numerical simulation, high production efficiency can be achieved using depressurization rates of medium (15 kPa/d) and FSTF schemes (8 & 50 kPa/d), and depressurization funnel expansion in the single-phase water flow stage plays a decisive role in stable and high-yield production in the later stage. Thus, the FSTF pressure reduction strategy could be advocated to promote gas production. Slow depressurization should be applied in ineffective desorption and the slow desorption stage for saturated coal seam or single-phase flow stage for undersaturated coal seam, given the higher single-phase water permeability. During the rapid and sensitive desorption stage, rapid depressurization is recommended because of large desorption capacity and low water phase permeability. This paper provides a possibility for the optimization of coalbed methane field production management.

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Section: Resultsmentioning

confidence: 90%

Section: Theory and Calculationmentioning

confidence: 99%

Physical Experiment and Numerical Simulation of the Depressurization Rate for Coalbed Methane Production

et al. 2020

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“…The measurements run up to a pressure of 6 × 10 4 Psia, indicating that pore diameters as small as 3 nm are penetrated. MIP aims to obtain the pore size, pore connectivity, and sorting characteristic of the coal samples. , T 2 spectra obtained by NMR measurements in the fully water-saturated condition are obtained in this paper, which aims to classify the coal pore system and calculate the volumetric proportion of each pore system, as described in detail in ref .…”

Section: Experimental Sectionmentioning

confidence: 99%

Geological Control of Irreducible Water Within the Coal Matrix and Its Quantified Evaluation Model

et al. 2020

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This paper adopts the measurement of mercury intrusion porosimetry and nuclear magnetic resonance (NMR) to analyze the pore system and the pore structure of coal samples, and the measurement of maceral group composition, scanning electron microscopy, and energy dispersive X-ray spectroscopy to obtain the organic/inorganic composition of coal samples. Gravimetric and NMR methods are both used to calculate irreducible water saturation of the samples, and qualitative and quantitative research studies are therefore conducted. The following knowledge is obtained. Coal samples can be classified as micro-trans-pore-dominated samples, meso-macro-pore-dominated samples, cleat-dominated samples, and even development samples. The main composition of the samples is organic, and a little kaolinite and pyrite can be observed. Irreducible water saturation obtained by the gravimetric method is almost close to that gained by the NMR method. The influencing parameters can be divided into two categories. The first category contains the maximum vitrinite reflectance, volumetric factor, fixed carbon yield, volatile yield, vitrinite percentage, and inertinite percentage, which have a strong correlation with irreducible water saturation. The second category includes the buried depth and median radius, and they have a weak correlation with irreducible water saturation. Multivariate regression shows that there is a linear quaternion equation between irreducible water saturation and independent variables such as maximum vitrinite reflectance, volumetric factor, volatile yield, and vitrinite percentage.

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“…Notably, coal is a porous medium whose internal pore morphology is diverse and complex. When studying the complexity of coal’s internal structure, it is necessary to analyze the adsorption pore structure that, in turn, reveals the occurrence law and transmission characteristics of CH 4 . − At present, the pore size classification standard of the International Union of Pure and Applied Chemistry (IUPAC) is mostly used in the research field of coal adsorption/diffusion performance, namely the micropore (pore size < 2 nm), mesopore (pore size between 2 and 50 nm), and macropore (pore size > 50 nm) . The research shows that the pore structure of coal has fractal characteristics in a certain range.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Methane Adsorption and Diffusion and its Influencing Factors Based on the Fractal Structure of Coal-based Porous Media

Liu

Yang

et al. 2022

Energy Fuels

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The adsorption–diffusion process of methane (CH4) in coal seams directly affects the amount of extractable gas (i.e., the free gas content). To clarify the relationship between the CH4 multiscale migration process and complex pore structure characteristics, the adsorption and diffusion characteristics of coal samples with different metamorphic degrees were taken as the research object, subdivided the gas adsorption structure scale, and quantitatively characterized the adsorption capacity of coal under different adsorption modes. Then, combined with the fractal characteristics of the coal adsorption pore complex structure, the evolution law of methane nonsteady-state diffusion was introduced to calculate the effective diffusion coefficient of methane under the unsteady state, elucidated the mathematical quantitative relationship between diffusion characteristics and structure characteristics, and explored the influence mechanism of coal structural parameters on the methane diffusion law. The results verified that the specific surface area was the dominant factor in the case of monolayer adsorption, while the complexity of the microporous structure was the most important factor in the case of microporous filling. Based on the calculation results of the fractal capillary bundle diffusion model, it was found that the specific surface area indirectly affects the diffusion movement by affecting the gas adsorption process, thus playing a leading role in the influence of fractal diffusion capacity of methane in coal. Overall, our research results provide a theoretical reference for the efficient mining of coalbed methane and mine gas disaster prevention.

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Experimental Study on Identification Diffusion Pores, Permeation Pores and Cleats of Coal Samples

Cited by 20 publications

References 24 publications

Physical Experiment and Numerical Simulation of the Depressurization Rate for Coalbed Methane Production

Physical Experiment and Numerical Simulation of the Depressurization Rate for Coalbed Methane Production

Geological Control of Irreducible Water Within the Coal Matrix and Its Quantified Evaluation Model

Mechanism of Methane Adsorption and Diffusion and its Influencing Factors Based on the Fractal Structure of Coal-based Porous Media

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