Mechanism of Increasing the Permeability of Water-Bearing Coal Rock by Microwave Steam Explosion

Qi, Qi; Guan, Weiming; Li, Xin; Ge, Yingzi; Nan, Senlin; Liu, Huabin

doi:10.1155/2021/6661867

Cited by 5 publications

(4 citation statements)

References 42 publications

(42 reference statements)

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“…Local tensile stress was formed by the expanding volume in the pores and cracks of the coal, which promoted the formation and propagation of cracks. , Some cracks were interconnected to form a crack network leading to contact with the external environment. Hence, the water vapor in the coal was ejected along the crack, resulting in a microwave heating effect that was similar to a “steam explosion” (see Figure b). This led to the exponential change of the coal sample mass with increased microwave intensity (see Figure ).…”

Section: Discussionmentioning

confidence: 99%

Effects of Microwave Heating Paths on Pores and Cracks in Bituminous Coal

et al. 2021

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To follow the effect of the microwave heating path on the structure of coal, eight 50 mm diameter, 30 mm long dry coal cores from the same coal seam with similar pore structure characteristics were microwave-treated using 4 pathways. The T 2 spectrum, pore-volume, temperature, mass, and visual changes of coal samples were analyzed before and after microwave heating. The microwave heating path affected the macropores and microcracks and the crack development mode. When the same microwave energy was applied, microwave heating on the coal was mainly manifested by the opening of closed pores, before the pyrolysis temperature of the coal was reached. Increasing the energy density caused the water vapor to move from constant pressure expansion to constant volume expansion. This resulted in an exponential growth of the mesopore and macropore volumes. Meanwhile, the micropore volume increased due to the collapse of pore structures. As a result, high-power microwave heating could accelerate the vaporization rate of water. The rapid expansion of water vapor volume brought about a microwave heating effect similar to the “steam explosion”. The resulting local tensile stress enabled the cracks to develop, expand, and connect to others continuously. Thus, it formed a complex crack network leading to the outside of the coal sample.

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Section: Discussionmentioning

confidence: 99%

Effects of Microwave Heating Paths on Pores and Cracks in Bituminous Coal

et al. 2021

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“…We have also previously shown that the water contained in coal rocks can be quickly heated under microwave irradiation. The water vapor that is formed in this process exerts a high pressure on the inner wall of the pores, eventually destroying the pore structure and increasing the connectivity [25]. Figure 1 displays the macro-and microprocesses of explosion caused by water vapor contained in the coal; of course, in the process of microwave heating, the cracks in the coal are not only caused by steam pressure but also caused by the imbalance of the thermal stress, the thermal decomposition of natural filler, and so on.…”

Section: Introductionmentioning

confidence: 99%

Enhancement of Coal Permeability Using Aqueous NaCl with Microwave Irradiation

Guan

Nan

et al. 2022

Geofluids

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Water in coal pores can generate strong steam explosions when treated with microwave irradiation. In order to improve the sensitivity of coal reservoirs to microwaves, we used varying concentrations of NaCl on the pore solution, which further increased the effect of microwaves on permeability enhancement. In our experiments, we selected 3 ratios of water content and 5 different concentrations of NaCl. The changes of coal water content and permeability before and after irradiation were compared. In addition, changes in coal surface temperature and internal thermal power were analyzed through thermal imaging and random sphere numerical modeling. Results showed that the increase of the proportion of solution mass and the ion concentration in the solution improved the overall dielectric properties of coal rock samples. After microwave irradiation, the average reduction rate of water content in coal rock samples increased with the increase of ion concentration in the solution. Both the average surface temperature of the coal rock samples and the average electromagnetic heating power gradually increased; this increases the temperature rise rate and maximum temperature of coal rock samples under the same irradiation time, which is conducive to better rapid accumulation of steam pressure, thereby improving the pore structure more effectively. Finally, the maximum growth rate of permeability reached 466.18%. This work provides a novel train of thought to enhance coal permeability by using microwave irradiation.

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“…The fundamental measure to improve the gas extraction rate is to create a large-scale fracture network in the coal seam to provide pressure relief space for the coal seam and gas drainage and migration channels, subsequently increasing the permeability of the coal seam (Bai et al, 2017;Qi et al, 2021). In recent years, relevant experts and scholars at home and abroad have carried out a large number of theoretical analyses, laboratory experiments, numerical simulations, similar simulations, and engineering experiments to improve coal seam permeability.…”

Section: Introductionmentioning

confidence: 99%

Study on improving the gas extraction efficiency by deep-hole pre-split blasting in Wulunshan Coal Mine, Guizhou

Yang

Zheng²,

Li³

et al. 2022

Front. Earth Sci.

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Due to the low permeability of the coal seam and the low gas extraction rate in conventional boreholes in the Wulunshan Coal Mine in Guizhou, in this study, the deep-hole pre-split blasting method is applied to study the improvement of the gas extraction efficiency by increasing the permeability of the coal seam. The study comprehensively expounds the process in which the deep-hole pre-split blasting method is applied to improve the gas extraction efficiency and proposes a numerical simulation method that combines ANSYS/LS-DYNA and COMSOL Multiphysics. Using the method, the initiation of blasting fracture channels and the subsequent influence on the gas extraction range have been comprehensively and directly researched and analyzed. Finally, some theoretical research has been verified by field experiments. According to the recorded simulation of the Wulunshan Coal Mine, the exposed area of the blasting borehole was 42 times the size of the conventional drilling borehole, and the pressure relief space was 1,050 times that of the conventional drilling borehole, which can connect about 32 m3 of coal. Compared with conventional drilling boreholes, in the process of gas extraction, the control range of the controlled pressure reduction was 4–7 times, the range of gas pressure reaching the standard was 25 times, and the peak pressure was reduced by 3–5 times. The average gas concentration was 1.85 times that of conventional boreholes, and the cumulative gas extraction volume of blasting boreholes was 4.48 times that of conventional boreholes. The research results prove that the application of blasting and permeability enhancement in the coal seam with a high gas content and low permeability can effectively improve the gas extraction efficiency in the Wulunshan Coal Mine in Guizhou.

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Mechanism of Increasing the Permeability of Water-Bearing Coal Rock by Microwave Steam Explosion

Cited by 5 publications

References 42 publications

Effects of Microwave Heating Paths on Pores and Cracks in Bituminous Coal

Effects of Microwave Heating Paths on Pores and Cracks in Bituminous Coal

Enhancement of Coal Permeability Using Aqueous NaCl with Microwave Irradiation

Study on improving the gas extraction efficiency by deep-hole pre-split blasting in Wulunshan Coal Mine, Guizhou

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