Characterization of hydraulic crack initiation of coal seams under the coupling effects of geostress difference and complexity of pre-existing natural fractures

Liu, Peng; Ju, Yang; Feng, Zheng; Mao, Lingtao

doi:10.1007/s40948-021-00288-9

Cited by 11 publications

(4 citation statements)

References 49 publications

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“…Numerous researchers have studied quantitative descriptions. Previous research has verified that rock fracture surfaces satisfy self-affine scaling characteristics (Odling 1994;Mandelbrot 1967;Gao et al 2021;Liu et al 2021;Yang et al 2021). The characterization of surface roughness is thus a basic prerequisite for further analysis.…”

Section: Introductionmentioning

confidence: 99%

Morphology differences between fractional Brownian motion and the Weierstrass-Mandelbrot function and corresponding Hurst evaluation

Dong

Jin

et al. 2023

Geomech. Geophys. Geo-energ. Geo-resour.

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Fractional Brownian motion (FBM) and the Weierstrass-Mandelbrot (W-M) function are two important methods for constructing self-affine objects. Accurately characterizing their features, such as the morphology and fractal geometry, is fundamental for their follow-up applications. However, due to the differences between self-similar and self-affine properties, the fractal dimension evaluation is difficult and sometimes unconvincing. In addition, the sampling length and diversity of calculation methods both lead to the non-uniqueness of the fractal dimension. This study compared the morphology differences between FBM and the W-M function and then analyzed the effects of each parameter on their morphology. Comparisons indicated that FBM has fewer control parameters than the W-M function. Finally, from basic fractal geometric properties, we derived the relationship between the measurement scale r and profile lengths L(r) for self-affine profiles and found that it is a complicated form rather than $$L(r)\sim c r^{H-1}$$ L ( r ) ∼ c r H - 1 , where H is the Hurst exponent. Meanwhile, the equivalent vertical height v(r) has an intuitive and clear power law relationship to the measurement scale $$v(r)\sim \sigma r^H$$ v ( r ) ∼ σ r H , which provides a method to estimate the Hurst exponent.

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Section: Introductionmentioning

confidence: 99%

Morphology differences between fractional Brownian motion and the Weierstrass-Mandelbrot function and corresponding Hurst evaluation

Dong

Jin

et al. 2023

Geomech. Geophys. Geo-energ. Geo-resour.

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“…However, it is also influenced by reservoir heterogeneity, especially when the reservoir has widespread development of micro-fractures. In such cases, the primary factor influencing fracture expansion is the reservoir's heterogeneity rather than the stress state, and strong heterogeneity significantly consumes the energy of hydraulic fracturing construction [19][20][21]. Another impact of heterogeneity arises from its structural characteristics.…”

Section: Introductionmentioning

confidence: 99%

Study on Fracture Propagation Rules of Shale Refracturing Based on CT Technology

Zhang,

Wang,

Xiao

et al. 2024

Processes

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Reactivating oil and gas wells, increasing oil and gas production, and improving recovery provide more opportunities for energy supply especially in the extraction of unconventional oil and gas reservoirs. Due to changes caused by well completion and production in pore pressure around oil and gas wells, subsequently leading to changes in ground stress, and the presence of natural and induced fractures in the reservoir, the process of refracturing is highly complex. This complexity is particularly pronounced in shale oil reservoirs with developed weak layer structures. Through true triaxial hydraulic fracturing experiments on Jimsar shale and utilizing micro-CT to characterize fractures, this study investigates the mechanisms and patterns of refracturing. The research indicates: (1) natural fractures and the stress states in the rock are the primary influencing factors in the fracture propagation. Because natural fractures are widely developed in Jimsar shale, natural fractures are the main influencing factors of hydraulic fracturing, especially in refracturing, the existing fractures have a greater impact on the propagation of secondary fracturing fractures. (2) Successful sealing of existing fractures using temporary blocking agents is crucial for initiating new fractures in refracturing. Traditional methods of plugging the seam at the root of existing fractures are ineffective, whereas extensive injection of blocking agents, forming large “sheet-like” blocking bodies in old fractures, yields better sealing effects, promoting the initiation of new fractures. (3) Moderately increasing the pumping rate and viscosity of fracturing fluid is advantageous in forming “sheet-like” temporary blocking bodies, enhancing the complexity of the network of new fractures in refracturing. (4) When there is a high horizontal stress difference, after sealing old fractures, the secondary hydraulic fractures initiate parallel to and extend from the old fractures. In cases of low horizontal stress difference, the complexity of secondary hydraulic fractures increases. When the horizontal stress changes direction, the secondary hydraulic fractures also change direction. It is recommended to use high-viscosity fracturing fluid and moderately increase the pumping rate, injecting blocking agents to seal old fractures, thereby enhancing the complexity of the network of refracturing. These findings provide important technical guidance for improving the efficiency of shale oil reservoir development.

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“…However, theoretical analysis cannot address the complex conditions encountered in hydraulic fracturing field operation because of the complex stress state and heterogeneity of deep rock masses. Many factors, such as natural fractures (Li et al 2020), in situ stress (Liu et al 2021a) and viscosity of the fluid (Krzaczek et al 2020), can affect the development of hydraulic fractures. Numerous researchers have utilized numerical simulations and laboratory tests to investigate the fracture propagation process to comprehend the impact of these factors.…”

Section: Introductionmentioning

confidence: 99%

“…Cylindrical and cube samples are usually used for hydraulic fracturing laboratory tests. In terms of sample selection, it is divided into natural materials (Lei et al 2021), such as clay (Xu et al 2015) granite, (Li et al 2019), sandstone (Zheng et al 2020b), coal (Liu et al 2021a) and artificial materials such as cement mortar, which can be poured through a certain mix proportion (Shi et al 2021). The researchers studied the effect of stress, type and rate of injected fluid, natural fracture, borehole diameter and perforation azimuth.…”

Section: Introductionmentioning

confidence: 99%

A DEM–CFD coupling method for modelling two-hole synchronous hydraulic fracturing

Yang

Wang

et al. 2023

Geomech. Geophys. Geo-energ. Geo-resour.

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This work introduced a novel numerical approach for modelling hydraulic fracturing processes. The Edinburgh bonded particle model was employed to establish the discrete element model of the rock samples, and it was further coupled with computational fluid dynamics to simulate the hydraulic fracturing. The fracture propagation law was taken into account under various principal stress differences to confirm the viability of the model. In addition, the model was used to investigate the fracture propagation mechanism of two-hole synchronous hydraulic fracturing. The results indicate that the arrangement and spacing of two holes will affect the complexity of hydraulic fractures. The principal stress difference becomes more prominent in the direction of hydraulic fracture propagation with the increase in the principal stress difference.

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Characterization of hydraulic crack initiation of coal seams under the coupling effects of geostress difference and complexity of pre-existing natural fractures

Cited by 11 publications

References 49 publications

Morphology differences between fractional Brownian motion and the Weierstrass-Mandelbrot function and corresponding Hurst evaluation

Morphology differences between fractional Brownian motion and the Weierstrass-Mandelbrot function and corresponding Hurst evaluation

Study on Fracture Propagation Rules of Shale Refracturing Based on CT Technology

A DEM–CFD coupling method for modelling two-hole synchronous hydraulic fracturing

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