Effects of cyclic saturation of supercritical CO2 on the pore structures and mechanical properties of bituminous coal: An experimental study

Su, Erlei; Liang, Yunpei; Chang, Xianyin; Zou, Quanle; Xu, Minghan; Sasmito, Agus P.

doi:10.1016/j.jcou.2020.101208

Cited by 51 publications

(24 citation statements)

References 56 publications

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“…To ensure uniformity of the analysis, all coal samples were obtained from the same piece of coal, and then crushed and mixed thoroughly to extract coal samples with particle sizes of around 3 mm. 25,26 The samples were processed as follows: First, 100 g of coal sample j was put into high-pressure tank i, and after tightening it, the system was linked and the gas tightness was checked (Figure 2). Computer control system h was turned on, and then vacuum pump g was used to evacuate high-pressure tank i and the temperature of water bath f was set to the predetermined temperature.…”

Section: Methodsmentioning

confidence: 99%

Coupling Effect of Temperature, Gas, and Viscoelastic Surfactant Fracturing Fluid on the Microstructure and its Fractal Characteristics of Deep Coal

Wang

et al. 2021

Energy Fuels

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The study of the microstructure evolution law of coal in a natural reservoir environment for the extraction of coalbed methane mining (ECBM), especially deep ECBM, is of major significance. We treated coal samples from Qinshui Basin under combined temperature–gas–fracturing fluid conditions and analyzed the evolution of the microstructure and its fractal characteristics to study the microstructural evolution of coal under natural hydraulic fracturing conditions. In the temperature range of 303.15 to 343.15 K and the gas-pressure range of 0.5–4.5 MPa, our data demonstrate that the pore structure is more susceptible to the temperature influence, compared with microfracture. The treatment of viscoelastic surfactant fracturing fluid (VES-FF) can effectively increase the permeation pore and fracture ratio by more than 300% and reduce the adsorption pore by more than 200% through dissolution, gas wedge, and other effects, which is favorable to ECBM. At the same temperature, as the gas pressure increases, the pore decreases, whereas the fracture ratio increases. The pore fractal dimension ranges from 2.90 to 2.99, which is significantly higher than that of microfractures. The temperature has a minor effect on the fracture fractal dimension, but it causes a decrease in the pore fractal dimension. The treatment of VES-FF induces an increase in the fracture fractal dimension, implying an increase in the fractal complexity. In contrast, the pore fractal characteristics show a contrary trend. At a gas pressure of 4.5 MPa, the negative effect of VES-FF on the pore structure reaches its maximum, whereas the effect on the fracture drops to its minimum. The results document that high temperature and high gas pressure can severely limit the penetration enhancement effect of VES-FF.

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Section: Methodsmentioning

confidence: 99%

Coupling Effect of Temperature, Gas, and Viscoelastic Surfactant Fracturing Fluid on the Microstructure and its Fractal Characteristics of Deep Coal

Wang

et al. 2021

Energy Fuels

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“…Methods other than CO 2 substitution and N 2 displacement will have a significant effect on reservoir permeability. 8 One approach is fluid injection, which includes hydraulic, 9 high energy gas, 10 , 11 supercritical CO 2 , 12 , 13 liquid nitrogen, 14 − 16 and steam injection fracturing. 17 , 18 Another approach is the application of external acoustic, 19 − 21 electric, 22 electromagnetic, 23 − 26 or electrochemical fields.…”

Section: Introductionmentioning

confidence: 99%

Effect of Cyclical Microwave Modification on the Apparent Permeability of Anthracite: A Case Study of Methane Extraction in Sihe Mine, China

Zhang

Kang

et al. 2021

ACS Omega

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The application of cyclical microwave modification for accelerating the extraction of coalbed methane (CBM) from anthracite is limited. In this study, the apparent permeability of anthracite samples before and after each microwave treatment (three in total) for 120 s was measured by a self-built permeability-testing platform. Microcomputed tomography (micro-CT) technology and image-processing technology were employed to analyze the 3D micron-scale pore structures, especially the quantitative characterization of connected pores and throats. After modification, the average apparent permeability increased from 0.6 to 5.8 × 10 –3 μm 2 . The generation, expansion, and connection of micron-scale pores and fractures became more obvious with each treatment. The total porosity increased from 3.5 to 6.2%, the connected porosity increased from 0.9 to 4.8%, and the porosity of isolated pores decreased from 2.5 to 1.4% after three cycles. The number, volume, and surface area of the connected pores as well as the number, radius, and surface area of the throats were significantly increased. In addition, the release of alkyl side chains from the anthracite surface reduced the capacity of the anthracite to adsorb CH 4 and the decomposition of minerals promoted the development and connectivity of pores. As a result, the gas seepage channels have been greatly improved. This work provides a basis for micron-scale pore characterization after cyclical microwave modification and contributes to CBM extraction.

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“…e pore characteristics of coal are closely related to the adsorption capacity of gas in coal seams and also greatly influence the dynamic characteristics of gas [26][27][28][29]. e effect of cyclic loading may influence the characteristics of micropores in coal matrix in the process of improving permeability of coal seams through pulse hydraulic fracturing.…”

Section: Introductionmentioning

confidence: 99%

Effects of Cyclic Loading on the Pore Structure of Anthracite Coal

Wang

Cheng

2021

Advances in Civil Engineering

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In the process of improving coalbed permeability through pulse hydraulic fracturing, the cyclic loading effect influences the characteristics of micropores in coal matrix, thus affecting the process of gas migration. Therefore, it is essential to investigate the effect of cyclic loading on the pore structure of coal. Seven groups of loading tests at different frequencies and amplitudes were conducted on anthracite coal obtained from Shanxi Province, China, using a fatigue-testing machine. Subsequently, using a PoreMaster GT-60 Mercury-intrusion apparatus, the influence of the frequency and amplitude on the structural characteristics (including mercury-injection and mercury-ejection curves, pore size distribution, porosity, and specific surface area) of pores in coal samples was analyzed. Finally, the law and mechanism of action of the loading frequency and amplitude on pores in coal samples were comprehensively analyzed. The test results showed that, in the case of maintaining the sine-wave amplitude unchanged during loading while altering the loading frequency, the overall porosity and pore volume rise at different degrees. The growth of the loading frequency presents a more significant promotive effect on the initiation and development of pores and fractures. Moreover, it drives the transformation of micropores and transition pores into mesopores and macropores, thus increasing the proportion of seepage pores. Under the condition of large sine-wave amplitude during loading, macropores and mesopores are subjected to the repeated action of the external force, thereby reducing the overall porosity. In addition, the volume of the seepage pores declines, and the number of the coalesced pores decreases. Finally, in light of these results, the implications of frequency and amplitude selection in the process of pulse hydraulic fracturing are discussed. Therefore, the results of this research will provide an important theoretical basis for the field application of pulse hydraulic fracturing technology in coal mines.

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Effects of cyclic saturation of supercritical CO2 on the pore structures and mechanical properties of bituminous coal: An experimental study

Cited by 51 publications

References 56 publications

Coupling Effect of Temperature, Gas, and Viscoelastic Surfactant Fracturing Fluid on the Microstructure and its Fractal Characteristics of Deep Coal

Coupling Effect of Temperature, Gas, and Viscoelastic Surfactant Fracturing Fluid on the Microstructure and its Fractal Characteristics of Deep Coal

Effect of Cyclical Microwave Modification on the Apparent Permeability of Anthracite: A Case Study of Methane Extraction in Sihe Mine, China

Effects of Cyclic Loading on the Pore Structure of Anthracite Coal

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