Experimental Study on the Damage and Cracking Characteristics of Bedded Coal Subjected to Liquid Nitrogen Cooling

Du, Menglin; Gao, Feng; Cai, Chengzheng; Su, Shanjie; Wang, Zekai

doi:10.1007/s00603-021-02584-y

Cited by 25 publications

(5 citation statements)

References 51 publications

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“…150 For tight rocks such as coal and shale, the longitudinal wave velocity decreases after freezing, and there is a considerable increase in permeability, which is notably affected by the bedding direction. 151 The wave velocity of the shale sample perpendicular to the bedding plane is greater than that of the rock sample parallel to the bedding plane. 152 This is because shale preferentially cracks along the bedding surface under low temperature, hindering sound wave propagation perpendicular to the bedding.…”

Section: Ln 2 Fracturing Coal Rock Mass In the Fieldmentioning

confidence: 96%

“…After freeze–thaw cycles with large temperature differences, the maximum loading force and stiffness of saturated sandstone are reduced, which further reduces the fracture toughness . For tight rocks such as coal and shale, the longitudinal wave velocity decreases after freezing, and there is a considerable increase in permeability, which is notably affected by the bedding direction . The wave velocity of the shale sample perpendicular to the bedding plane is greater than that of the rock sample parallel to the bedding plane .…”

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

confidence: 99%

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

et al. 2022

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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: Ln 2 Fracturing Coal Rock Mass In the Fieldmentioning

confidence: 96%

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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“…After entering the interior of the coal, LN 2 is converted from liquid to gas, and the gas expands in the pore fractures at different scales. Moisture inside the coal mass comes in contact with LN 2 and undergoes expansion in volume as it transforms from water to ice [25][26][27]. Based on this, the coal produces different degrees of deformation, the internal pores are developed, a more complex pore fracture network is formed, its internal gas mobility is increased, and the coalbed methane transport is enhanced; through this, the mechanism of LN 2 action can be explored [28].…”

Section: Introductionmentioning

confidence: 99%

Mechanical Characterization of the Frozen and Thawed States of Coal after the Action of LN2 at In Situ Formation Pressure

Qin,

Liu,

Wang

et al. 2024

Processes

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Coal penetration enhancement technology is the key to increase the production of coalbed methane. Coal bodies are subjected to different peripheral pressures in the in situ strata, and the study of the changes in the mechanical strength of coal bodies under different peripheral pressures after the action of liquid nitrogen is crucial for the penetration enhancement of liquid nitrogen (LN2)-fractured coal. In this paper, an MTS universal testing machine was utilized to carry out experiments to obtain the stress–strain curves of the coal under different freezing times under 1 MPa surrounding pressure and different surrounding pressures after 50 min of LN2 action. The experimental results showed the following: (1) the uniaxial compressive strength and peak strain of coal samples in a frozen state are positively correlated under two conditions. The modulus of elasticity decreased before 100 min at different times of LN2 action, and the modulus of elasticity was maximum at 5 MPa at different peripheral pressure actions; (2) the uniaxial compressive strength and peak strain of the frozen-thawed coal samples decreased before 100 min of LN2 action at different times, and the modulus of elasticity continued to decrease. The uniaxial compressive strength and modulus of elasticity of coal samples in freeze–thaw state under different peripheral pressures were the largest at 5 MPa, and the peak strain was negatively correlated. (3) The elastic strain energy of the frozen coal samples under the action of LN2 at different times was positively correlated with the freezing time before 80 min, and negatively correlated after 80 min. The elastic strain energy of the frozen coal samples was positively correlated with the freezing time. The elastic strain energy and freezing time of the two coal samples under different circumferential pressures were positively correlated before 5 MPa and negatively correlated after 5 MPa, with opposite dissipation energies. (4) The water–ice phase transition and temperature–thermal stresses on the internal structure of the coal in the presence of LN2 cause significant damage. The degradation of coal samples in the freeze–thaw state is even higher under in situ ground pressure.

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“…With low-viscosity slick water, the fracture expands more in length than width, and chemical additives avoid corrosion and bacterial growth. Moreover, water is often the most economical, and furthermore, this water can be recycled [24,25], reducing makeup volume in further stimulation jobs or stages. However, total water consumption is still very high, and low-viscosity water does not transport proppant agents easily.…”

Section: Introductionmentioning

confidence: 99%

Application of Image Processing in Evaluation of Hydraulic Fracturing with Liquid Nitrogen: A Case Study of Coal Samples from Karaganda Basin

et al. 2023

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Research of microstructure and permeability evolution of coal following LN2 treatment elucidate the process of cryogenic fracturing due to environmentally friendly behavior in comparison with conventional hydraulic fracturing. The evolution of the 2D microstructure of bituminous coal before and after LN2 treatment was examined using a high-resolution camera. The image processing was implemented using functions from the OpenCV Python library that are sequentially applied to digital images of original coal samples. The images were converted into binary pixel matrices to identify cracks and to evaluate the number of cracks, crack density, total crack area, and average crack length. Results were visualized using Seaborn and Matplotlib Python libraries. There were calculations of total crack area (TCA), total number of cracks (TNC), crack density (CD), the average length of cracks (Q2), first (Q1) and third (Q3) quartiles in fracture length statistics. Our findings demonstrate a progressive increase in the Total Crack Area (δTCA) with longer freezing times and an increased number of freezing–thawing cycles. In contrast, the change in crack density (δCD) was generally unaffected by freezing time alone but exhibited a significant increase after several freezing–thawing cycles. Among the freezing times investigated, the highest crack density (CD) value of 300 m−1 was achieved in FT60, while the lowest CD value of 31.25 m−1 was observed in FT90 after liquid nitrogen (LN2) treatment. Additionally, the FTC4 process resulted in a 50% augmentation in the number of cracks, whereas the FTC5 process tripled the number of small cracks.

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Experimental Study on the Damage and Cracking Characteristics of Bedded Coal Subjected to Liquid Nitrogen Cooling

Cited by 25 publications

References 51 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

Mechanical Characterization of the Frozen and Thawed States of Coal after the Action of LN2 at In Situ Formation Pressure

Application of Image Processing in Evaluation of Hydraulic Fracturing with Liquid Nitrogen: A Case Study of Coal Samples from Karaganda Basin

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