Mechanical damage mechanism of frozen coal subjected to liquid nitrogen freezing

Liquid nitrogen (LN 2 ) fracturing is an anhydrous fracturing technology that enhances coal permeability and supports unconventional oil and gas exploitation. In this Review, we provide a systematic review of five aspects of LN 2 fracturing. They are the history of the technology's development, research topics, factors influencing fracturing efficiency, fracturing mechanism, and engineering processes and systems. Liquid nitrogen fracturing transforms coal and rock pore structure through mechanisms such as low temperature, freeze−thaw damage, and gas expansion. It changes coal and rock mechanical properties and improves the pore penetration and efficiency of unconventional oil and gas extraction. However, in-depth studies are still required in many areas. They include theoretical studies of twophase nitrogen flow in coal and rock, development of technical equipment to support field operations, and plans to monitor and evaluate fracturing efficiency. On the basis of the advances in LN 2 fracturing research and the challenges, we conclude that future research should focus on multiphase flow and field equipment and technology.

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Section: Ln2 Fracturing Coal Rock Mass In the Field Of Oil And Gas Ex...mentioning

confidence: 99%

Section: Ln2 Fracturing Coal Rock Mass In the Field Of Oil And Gas Ex...mentioning

confidence: 99%

Advances in Liquid Nitrogen Fracturing for Unconventional Oil and Gas Development: A Review

et al. 2022

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“…As a result, gas dynamic disasters in coal mines are triggered more easily with higher intensity, making it more difficult to prevent and control gas disasters (Wang et al, 2019). Some anhydrous measures are used to increase the permeability of the coal body and improve the coal seam's drainage method (Qin et al, 2021(Qin et al, , 2022. Borehole gas extraction is one of the most important measures to prevent and control mine gas disasters and accidents.…”

Section: Introductionmentioning

confidence: 99%

Study on the influence mechanism of air leakage on gas extraction in extraction boreholes

Xue-bo

Gao

Jia

et al. 2022

Energy Exploration & Exploitation

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Borehole leakage is an important cause of gas extraction failure. In order to study the influence mechanism of borehole leakage on gas extraction, the borehole air leakage mode was studied, and a mathematical model was established to describe the borehole air leakage of the gas extraction. In addition, this paper also analyzed the change rules of borehole air leakage and gas extraction effect at different borehole sealing depth, negative extraction pressure, degree of fracture development and borehole sealing quality. Research shows that: (1) The hole sealing depth has a certain influence on the borehole air leakage and the gas extraction effect. As the hole sealing depth increased, the borehole air leakage gradually decreased. Moreover, the net amount of gas extraction gradually decreased, but the gas extraction concentration increased to some extent, and the increasing range gradually decreased. The reasonable sealing depth of this coal seam was 9∼10 m. (2) The negative pressure of borehole extraction has little influence on borehole air leakage and gas extraction. With the increase of the negative extraction pressure, the gas extraction net amount and borehole air leakage both increased, but the gas extraction concentration decreased. In the later stage of the gas extraction, the negative pressure can be properly reduced to improve the gas extraction effect. (3) The borehole sealing quality has a great influence on the borehole air leakage and gas extraction effect. With the improvement of the sealing quality, the coal-rock permeability gradually decreased. Moreover, the borehole air leakage significantly reduced, and the gas extraction concentration increased significantly. Therefore, attention should be paid to the selection and improvement of sealing materials and sealing techniques in the actual production so that the airtightness and sealing quality of the hole sealing section can be improved.

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“…In recent years, some researchers have also started to study the mechanical properties and microstructure of coal subjected to F-T cycles and made some achievements. Qin et al (2017aQin et al ( , 2017bQin et al ( , 2022 found that different freezing times, coal moisture contents and anhydrous liquid nitrogen F-T cycles had significant influences on the mechanical properties of coal, and a freeze-thaw method using liquid nitrogen (LN2) was proposed to improve coal permeability for the production of coal bed methane. Zhai et al (2017) studied the impact of consecutive freeze-thaw cycles on the coal pore structure deterioration by NMR and scanning electron microscope.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation on mechanical properties of coal samples under different freeze–thaw cycles

Zhou

Hou

Cai

et al. 2022

Energy Exploration & Exploitation

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Due to the extensive excavation of open-pit coal mines in northwest of China, the rock slopes formed by special environments are subjected to freeze-thaw (F-T) action, which has a certain impact on their stabilities. In order to evaluate the mechanical properties and micro damage characteristics of coal under different freeze-thaw cycles, uniaxial compression experiments combining acoustic emission tests were conducted. The results suggest that as the number of freeze-thaw cycles increased, elastic modulus of coal samples decreased, the samples showed ductile damage characteristics and initial compaction stage gradually increased. Compared with unfrozen-thawed coal sample, the compressive strength of the coal samples decreased by 23.27% after 10 F-T cycles, 31.06% after 15 F-T cycles, and 36.01% after 20 F-T cycles. The internal fissures in the coal samples transitioned from tensile fissures to shearing fissures, and the samples gradually showed tensile-shear combined failure. The final cumulative energy of the coal sample became lower, the cumulative energy duration increased and the time point of the energy surge was delayed with the increase of cyclic freeze-thaw times. A damage model based on the evolution law of the cumulative energy was established to bridge the gap between macro-micro damage mechanics.

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Mechanical damage mechanism of frozen coal subjected to liquid nitrogen freezing

Cited by 79 publications

References 24 publications

Advances in Liquid Nitrogen Fracturing for Unconventional Oil and Gas Development: A Review

Advances in Liquid Nitrogen Fracturing for Unconventional Oil and Gas Development: A Review

Study on the influence mechanism of air leakage on gas extraction in extraction boreholes

Experimental investigation on mechanical properties of coal samples under different freeze–thaw cycles

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