Role of natural fractures characteristics on the performance of hydraulic fracturing for deep energy extraction using discrete fracture network (DFN)

Yao, Wenli; Sharifzadeh, Mostafa; Yang, Zhaozhong; Xu, Guang

doi:10.1016/j.engfracmech.2020.106962

Cited by 28 publications

(8 citation statements)

References 32 publications

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“…To avoid coal disintegration and damage in the immersion process, the samples were put into a self-made nondestructive water-immersion device specially designed for coal rock. According to previous experience of the author (Yao et al., 2020), the coal sample has been completely saturated with water after being kept in this device for 48 h. After the coal sample is kept in the device for 48 h, it is weighed on the electronic balance every 1 h, and it is considered to have become completely saturated with water if the difference between two measurements is within 0.5 g. Since a standard coal sample is hundreds of grams in weight, an error of less than 0.5 g is acceptable for the two sizes of saturated coal samples. The geometric size and basic physical properties of coal samples are listed in Table 1.…”

Section: Experimental Materials and Methodsmentioning

confidence: 99%

“…Considering the necessity to improve the fragmentation degree of coal and rock mass, some hydraulic measures have been taken in coal mines, e.g. hydraulic fracturing and high-pressure water jet (De Silva et al., 2018; Li et al., 2019; Liu et al., 2020; Yao et al., 2020). Although traditional hydraulic fracturing can strengthen the fracture network and enhance the permeability of reservoir, it is inferior in coal breakage.…”

Section: Introductionmentioning

confidence: 99%

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Effects of cyclic freeze-thaw by liquid nitrogen on the coal breakage properties and fragment size distribution

Chong

Yao

et al. 2022

International Journal of Damage Mechanics

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Transforming intact coal seams into broken coals that are convenient to transport is one of the technical problems of fluidized coal mining. In this paper, cyclic freeze-thaw by liquid nitrogen (CFT-LN2) was adopted to improve the fragmentation degree of coal seams. The coal pore structure evolutions and coal breakage properties were explored using the acoustic emission (AE) parameter method (the kernel density estimation method), the fractal theory, and the nuclear magnetic resonance spectra. The main factors discussed include the number of freeze-thaw cycles, the LN2 freezing time and the moisture content of the coal sample. Variations of these factors alter the mechanical and physical characteristics and pore structures of coal samples treated with CFT-LN2. The results reveal that the kernel density estimation method can distinguish the density region determined based on the rise angle (RA) and average frequency (AF) values and visualize the rupture modes of coal samples formed after CFT-LN2. As the number of freeze-thaw cycles grows, the tensile rupture mode gradually transits to shear rupture mode; the fractal dimension gradually increases; the equivalent average size gradually decreases; and the mass of different fragment sizes tend to be more uniform. Only freezing in LN2 without CFT-LN2 cannot notably change the rupture mode or fragmentation degree of a coal sample. During CFT-LN2, the coal matrix is subjected to repeated action of contraction in LN2 and expansion at room temperature. As a result, new micro-pores are formed easily in the matrix, and micro-pores incline to connect into larger pores. Meanwhile, increasing the moisture content is conducive to coal fracturing through CFT-LN2.

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Section: Experimental Materials and Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of cyclic freeze-thaw by liquid nitrogen on the coal breakage properties and fragment size distribution

Chong

Yao

et al. 2022

International Journal of Damage Mechanics

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“…However, it is difficult to achieve this goal in single, low-permeability, and high-gas coal seams. At present, some technologies, such as deep hole presplitting blasting [13,14], hydraulic fracturing [15][16][17], hydraulic slotting [18,19], and gas injection displacement [20][21][22], have been used in single coal seams and have achieved good results. However, these methods are difficult to popularize due to the resulting workplace pollution caused by water contamination issues, missfire problems, and the difficulty associated with approving explosives.…”

Section: Introductionmentioning

confidence: 99%

Pressure Relief and Permeability Enhancement with Carbon Dioxide Phase Transition Blasting: Fracture, Seepage, and Practice

Chen¹,

Yuan²,

Wang³

et al. 2021

Lithosphere

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Coal seams are generally characterized by high pressure, low permeability, and strong adsorption in China. Moreover, carbon dioxide phase transition blasting (CDPTB) is an effective way to achieve pressure relief and permeability enhancement in high-gas pressure coal seams. Multiple fractures can be created in the coal body by CDPTB due to its characteristics of having a great impact stress and high energy efficiency. To determine the dual characteristics of coal fracturing and seepage after CDPTB, this paper developed a fluid solid coupling programme based on CDPTB cracking and permeability enhancement, which unifies the fracture and seepage of CDPTB. FLAC was used to determine the distribution characteristics of the stresses and fractures caused by CDPTB. The results showed fracture propagation from the initial fracture to multiple additional fractures or the main fractures over time. Then, the fractures were introduced into COMSOL software to simulate the characteristics of the gas flow field. The main fracture forms an effective channel for gas flow, which greatly reduces the gas pressure in coal. The successful application of CDPTB in the field induced the increase in the gas drainage effect by 10-20 times.

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“…In recent years, many scholars have studied and developed numerical simulation of fractured porous media, and the most widely used models are equivalent continuum models and discrete fracture model (DFM) [7]. However, considering that the equivalent continuum model is unable to characterize the differential flows in fractures, the DFM is deficient in the mesh generation of complex fractures [8][9][10]. Lee et al [11] and Moinfar et al [12] proposed the embedded discrete fracture method (EDFM).…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Numerical Simulation of Multiscale Fractures and Multiphase Flow in Heterogeneous Unconventional Reservoirs with Coupled Fractal Characteristics

Hong

Cao

et al. 2021

Geofluids

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A simulated reservoir model, based on the permeability fractal model and three-dimensional (3D) Gaussian filter, was established to account for in-layer and interlayer heterogeneity so that the result conforms to the law of geological statistics. Combined with an embedded discrete fracture method (EDFM), a multiscale fracture system was established, forming the numerical simulation method of multiphase flow in horizontal wells in heterogeneous reservoirs with complex fractures. The heterogeneity and saturation of the reservoir mixed five-point pattern of vertical and horizontal wells and the injection and production of horizontal wells were discussed. The results show that it is difficult to characterize complex reservoirs using a homogeneous permeability model. Thus, it is best to use a heterogeneous model that considers permeability differences in tight reservoirs. Formation fluids coexist in multiple phases, and water saturation has a direct effect on the production. Thus, a multiphase flow model is needed and can play a greater role in injection and production technology. The mixed five-point pattern of vertical and horizontal wells can improve productivity to a certain extent, but the dual effects of heterogeneity and fracturing will cause a decline in production by accelerating the communication of injected fluid. The reservoir is heterogeneous between wells, and there are differing effects on adjacent wells. Therefore, near-well natural microfractures are opened because of fracturing in horizontal wells, and the heterogeneity cannot be ignored, especially when multiple wells are simultaneously injected and produced.

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Role of natural fractures characteristics on the performance of hydraulic fracturing for deep energy extraction using discrete fracture network (DFN)

Cited by 28 publications

References 32 publications

Effects of cyclic freeze-thaw by liquid nitrogen on the coal breakage properties and fragment size distribution

Effects of cyclic freeze-thaw by liquid nitrogen on the coal breakage properties and fragment size distribution

Pressure Relief and Permeability Enhancement with Carbon Dioxide Phase Transition Blasting: Fracture, Seepage, and Practice

Three-Dimensional Numerical Simulation of Multiscale Fractures and Multiphase Flow in Heterogeneous Unconventional Reservoirs with Coupled Fractal Characteristics

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