A dynamic evolution model of coal permeability during enhanced coalbed methane recovery by N<sub>2</sub> injection: experimental observations and numerical simulation

Li, Bo; Zhang, Junxiang; Ding, Zhiben; Wang, Bo

doi:10.1039/d1ra02605d

Cited by 22 publications

(15 citation statements)

References 34 publications

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“… 2 , 3 CBM extraction can not only reduce the risk of gas outburst but also yield clean energy and improve the efficiency of energy utilization. 4 , 5 The average CBM extraction concentration in China is lower than 20 and 80% of the air entering the drainage system under a low negative pressure. 6 , 7 There are two ways to increase the CBM extraction concentration: (1) to address problems, such as small pore size and massive adsorption in low-permeability coal seams, by means of hydraulic fracturing, hydraulic cutting, and coal seam water injection 8 − 11 and (2) to improve the sealing effect through narrowing down the gas leakage channels of boreholes.…”

Section: Introductionmentioning

confidence: 99%

“…Coalbed methane (CBM) is a kind of unconventional natural gas mainly adsorbed to coal seams and their surrounding rock . As its pressure and concentration increase considerably, CBM has become one of the main hazards in coal mines. , CBM extraction can not only reduce the risk of gas outburst but also yield clean energy and improve the efficiency of energy utilization. , The average CBM extraction concentration in China is lower than 20 and 80% of the air entering the drainage system under a low negative pressure. , There are two ways to increase the CBM extraction concentration: (1) to address problems, such as small pore size and massive adsorption in low-permeability coal seams, by means of hydraulic fracturing, hydraulic cutting, and coal seam water injection − and (2) to improve the sealing effect through narrowing down the gas leakage channels of boreholes. − The former has been widely used, whereas the latter still has a long way to go with respect to the sealing material. Both sides of the roadway undergo yield deformation due to concentrated stress.…”

Section: Introductionmentioning

confidence: 99%

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Preparation and Performance Investigation of Optimized Cement-Based Sealing Materials Based on the Response Surface Methodology

Zhang

Wang

et al. 2022

ACS Omega

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A new cement-based sealing material, which used Portland cement (PC) as a raw material and supplemented several gel components, such as accelerant, alkali activator, suspension agent, expansion agent, reinforcing agent, was prepared in this work. The effects of these components on the fluidity, setting time, and expansion rate of these sealing materials were investigated by an orthogonal test. The results show that the water–cement ratio and the reinforcing agent content, the accelerant content and the water–cement ratio, and the expansion agent content and the accelerant content are the most important influencing factors on fluidity, setting time, and expansion rate, respectively. In addition, the regression models and response surfaces of the factors were established using a multiple linear regression method. By this means, the influences of the two main factors on each performance of this sealing material were accurately and intuitively reflected for obtaining the optimal value in the optimization area. The results indicate that the sealing materials possess the best performances when the water–cement ratio is 1.1, the accelerant content is 50%, the expansion agent content is 0.1%, and the reinforcing agent content is 3%, which is corresponding to a fluidity of 360–380 mm, an initial (final) setting time of 60 (80)–80 (100) min, and an expansion rate of 2–12%. Furthermore, the microstructures of the optimized sealing material also reveal that the main hydration products of PC are transformed from layered Ca(OH) 2 crystals into fine needle-like AFt crystals and C–S–H gels by the promotion effect of the optimizing ratio, thus leading to a more compact structure of optimized cement-based sealing materials.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Preparation and Performance Investigation of Optimized Cement-Based Sealing Materials Based on the Response Surface Methodology

Zhang

Wang

et al. 2022

ACS Omega

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“…), low permeability is one of the main characteristics of coal seams in China. − To rely on the original permeability of coal seams for gas extraction is far from solving the problem of coal-mine gas-disaster prevention and best utilization of energy resources. In order to improve the efficiency of gas extraction, measures for transforming the structure of coal deposits by boosting cracks that penetrate the coal seam are the most commonly used means to increase the permeability. , To this end, a variety of technologies for enhancing the permeability of low-permeability coal seams have been carried out by many researchers, including hydraulic techniques, deep-hole explosive blasting, dense drilling, liquid nitrogen freeze-thaw, fluidized mining, protective-layer mining, and the acidification technique. − These methods have had some success in increasing the permeability of low-permeability coal seams but have limitations. , In order to realize an efficient extraction of CBM, it is still necessary to actively explore and put forward new technology for improving the permeability of low-permeability coal deposits.…”

Section: Introductionmentioning

confidence: 99%

“…In order to improve the efficiency of gas extraction, measures for transforming the structure of coal deposits by boosting cracks that penetrate the coal seam are the most commonly used means to increase the permeability. 8,9 To this end, a variety of technologies for enhancing the permeability of lowpermeability coal seams have been carried out by many researchers, including hydraulic techniques, deep-hole explosive blasting, dense drilling, liquid nitrogen freeze-thaw, fluidized mining, protective-layer mining, and the acidification technique. 10−16 These methods have had some success in increasing the permeability of low-permeability coal seams but have limitations.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of the Structural Damage to Coal Treated by a High-Voltage Electric Pulse Discharge in Water

Nie

Zhang

et al. 2022

Energy Fuels

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High-voltage electric pulse (HVEP) technology has been gradually adopted as an effective method in the drainage and utilization of coalbed methane (CBM) in low-permeability coal reservoirs. An experimental device was established to study the structural variation characteristics of bituminous coal samples treated by an HVEP. The structure parameters of coal samples before and after the HVEP treatment were measured using a scanning electron microscope and low-temperature nitrogen adsorption. Additionally, the current waveforms in the process of HVEP discharge were analyzed by a digital oscilloscope. The results showed that the pressure of the shockwave produced by an HVEP increased with an increase in discharge energy, which intensifies the damage effect on the coal body. Some newly generated pores and cracks appeared in the bituminous coal samples after the HVEP treatment. As the discharge energy increased, the number of pores and fractures increased, and the diameters of the pores and the widths of the fractures also gradually increased. The average pore diameter, specific surface area, and most probable pore diameter of bituminous coal samples treated by an HVEP were greater than those of the untreated coal. Furthermore, after the HVEP treatment, the fractal dimension D 1 was larger than that of raw coal, while the fractal dimension D 2 was smaller than that of raw coal. This indicates that although the pore structure in coal became more complex after an HVEP, the surfaces of the pores became smoother. These changes were unfavorable to the adsorption of gas in the coal but conducive to the diffusion and flow of gas. The combined action of the shockwave cracking effect, the cavitation vibration effect, and the effect of thermal expansion promoted the expansion and connection of micro-and macropores and fractures in the coal, improving the permeability of coal seams. The research results demonstrate that the HVEP technology can significantly alter the structural characteristics of coal deposits in a way favorable for the development of CBM.

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“…Chen et al [12] found that during freezing periods, water in porous media such as rock and concrete tends to form ice or migrate, leading to the redistribution of pore water. Li et al [13][14][15][16] studied the freeze-thaw effect of liquid nitrogen and the pore size, porosity, and permeability of coal rocks; these characteristics were all found to increase with the increase of water saturation. One study analysed the effects of the changes in different conditions on water migration by developing a coupled hydrothermal model for numerical simulation [17].…”

Section: Introductionmentioning

confidence: 99%

The Temperature Field Evolution and Water Migration Law of Coal under Low-Temperature Freezing Conditions

Huang

et al. 2021

IJERPH

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This study examines the evolution law of the coal temperature field under low-temperature freezing conditions. The temperature inside coal samples with different water contents was measured in real-time at several measurement points in different locations inside the sample under the condition of low-temperature medium (liquid nitrogen) freezing. The temperature change curve was then used to analyse the laws of temperature propagation and the movement of the freezing front of the coal, which revealed the mechanism of internal water migration in the coal under low-temperature freezing conditions. The results indicate that the greater the water content of the coal sample, the greater the temperature propagation rate. The reasons for this are the phase change of ice and water inside the coal during the freezing process; the increase in the contact area of the ice and coal matrix caused by the volume expansion; and the joint action of the two. The process of the movement of the freezing front is due to the greater adsorption force of the ice lens than that of the coal matrix. Thus, the water molecules adsorbed in the unfrozen area of the coal matrix migrate towards the freezing front and form a new ice lens. Considering the temperature gradient and water content of the coal samples, Darcy’s permeation equation and water migration equation for the inside of the coal under freezing conditions were derived, and the segregation potential and matrix potential were analysed. The obtained theoretical and experimental results were found to be consistent. The higher the water content of the coal samples, the smaller the matrix potential for the hindrance of water migration. Furthermore, the larger the temperature gradient, the larger the segregation potential, and the faster the water migration rate.

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A dynamic evolution model of coal permeability during enhanced coalbed methane recovery by N₂ injection: experimental observations and numerical simulation

Abstract: A dynamic evolution model of coal permeability during CH4 displacement by N2 injection was proposed, considering the combined effects of matrix swelling/shrinkage and effective stress, for providing a reference on N2-ECBM.

Cited by 22 publications

References 34 publications

Preparation and Performance Investigation of Optimized Cement-Based Sealing Materials Based on the Response Surface Methodology

Preparation and Performance Investigation of Optimized Cement-Based Sealing Materials Based on the Response Surface Methodology

Experimental Study of the Structural Damage to Coal Treated by a High-Voltage Electric Pulse Discharge in Water

The Temperature Field Evolution and Water Migration Law of Coal under Low-Temperature Freezing Conditions

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A dynamic evolution model of coal permeability during enhanced coalbed methane recovery by N2 injection: experimental observations and numerical simulation

Abstract: A dynamic evolution model of coal permeability during CH4 displacement by N2 injection was proposed, considering the combined effects of matrix swelling/shrinkage and effective stress, for providing a reference on N2-ECBM.

Cited by 22 publications

References 34 publications

Preparation and Performance Investigation of Optimized Cement-Based Sealing Materials Based on the Response Surface Methodology

Preparation and Performance Investigation of Optimized Cement-Based Sealing Materials Based on the Response Surface Methodology

Experimental Study of the Structural Damage to Coal Treated by a High-Voltage Electric Pulse Discharge in Water

The Temperature Field Evolution and Water Migration Law of Coal under Low-Temperature Freezing Conditions

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A dynamic evolution model of coal permeability during enhanced coalbed methane recovery by N₂ injection: experimental observations and numerical simulation