The evolution process of fractures and their modification effects on the liquid–solid interface during liquid nitrogen cyclic freeze–thaw of coal and shale

Li, Yunbo; Wang, Haifeng; Song, Dangyu; Pan, Jienan; Wang, Zhenzhi; Guo, Xingxin

doi:10.1016/j.fuel.2024.130877

Cited by 4 publications

(4 citation statements)

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“…Liu [103] emphasized that the shape factor of coal plays a decisive role in fluid migration under in situ conditions, while the fracture type resulting from LNF impacts the reservoir permeability. Our research group investigated changes in the coal permeability before and after LNF [37]. It was observed that the water-bearing samples exhibited significantly higher permeability growth rates following cyclic LNF than the dry samples, which were similar to the fracture development rates (Figure 6).…”

Section: Effect On Gas Migration Efficiencymentioning

confidence: 58%

Section: The Intermediate Freeze-thaw Fracturing Processmentioning

confidence: 99%

“…Numerous experiments have demonstrated that saturated coal samples exhibit significantly higher susceptibilities to low-temperature fracturing than dry samples [36]. Moreover, an increase in the water content leads to longer and denser coal fractures (Figure 3d-f), with saturated coal samples exhibiting much greater increases in new fractures compared to dry samples (by 10-20 times) (Figure 3a-c) [37]. At present, most of the conclusions suggest that the low temperature of LN2 causes water in the coal and rock pores and volume expansion (a volume increase of approximately 9%), which produce a substantial frost heaving force (more than 207 MPa) at the tip of the pore fracture, leading to fracture expansion [38].…”

Section: The Intermediate Freeze-thaw Fracturing Processmentioning

confidence: 99%

“…Previous studies have indicated that significant temperature differences cause stress concentration in rocks, whereas repeated cold-hot cycles deteriorate the mechanical properties of coal. This leads to differential shrinkage among the minerals and structures within coal, resulting in the expansion and extension of the primary coal fractures, the surface shedding of coal particles, and the initiation and development of new fractures [37]. Following LN 2 transformation, coal fractures can be categorized into three types: extended fractures, intersecting fractures, and new fractures.…”

Section: Fracture Propagation Process and Fracturing Effect 41 Fractu...mentioning

confidence: 99%

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Mechanism and Model Analysis of Ultralow-Temperature Fluid Fracturing in Low-Permeability Reservoir: Insights from Liquid Nitrogen Fracturing

Wang,

Li,

Song

et al. 2024

Processes

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Ultralow-temperature fluids (such as liquid nitrogen, liquid CO2) are novel waterless fracturing technologies designed for dry, water-sensitive reservoirs. Due to their ultralow temperatures, high compression ratios, strong frost heaving forces, and low viscosities, they offer a solution for enhancing the fracturing and permeability of low-permeability reservoirs. In this study, we focus on the combined effects of high-pressure fluid rock breaking, low-temperature freeze-thaw fracturing, and liquid-gas phase transformation expansion on coal-rock in low-permeability reservoirs during liquid nitrogen fracturing (LNF). We systematically analyze the factors that limit the LNF effectiveness, and we discuss the pore fracture process induced by low-temperature fracturing in coal-rock and its impact on the permeability. Based on this analysis, we propose a model and flow for fracturing low-permeability reservoirs with low-temperature fluids. The analysis suggests that the Leidenfrost effect and phase change after ultralow-temperature fluids enter the coal support the theoretical feasibility of high-pressure fluid rock breaking. The thermal impact and temperature exchange rate between the fluid and coal determine the temperature difference gradient, which directly affects the mismatch deformation and fracture development scale of different coal-rock structures. The low-temperature phase change coupling fracturing of ultralow-temperature fluids is the key to the formation of reservoir fracture networks. The coal-rock components, natural fissures, temperature difference gradients, and number of cycles are the key factors in low-temperature fracturing. In contrast to those in conventional hydraulic fracturing, the propagation and interaction of fractures under low-temperature conditions involve multifield coupling and synergistic temperature, fluid flow, fracture development, and stress distribution processes. The key factors determining the feasibility of the large-scale application of ultralow-temperature fluid fracturing in the future are the reconstruction of fracture networks and the enhancement of the permeability response in low-permeability reservoirs. Based on these considerations, we propose a model and process for LNF in low-permeability reservoirs. The research findings presented herein provide theoretical insights and practical guidance for understanding waterless fracturing mechanisms in deep reservoirs.

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Section: Effect On Gas Migration Efficiencymentioning

confidence: 58%

Section: The Intermediate Freeze-thaw Fracturing Processmentioning

confidence: 99%