Wave Propagation in Isotropic Media with Two Orthogonal Fracture Sets

Shao, Siyi; Pyrak‐Nolte, L. J.

doi:10.1007/s00603-016-1084-z

Cited by 14 publications

(11 citation statements)

References 46 publications

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“…Intersection waves are key to understanding the complex partitioning of energy into scattered waves and guided modes near fracture intersections. At the very least, intersections are features that affect the propagation velocity and attenuation of through‐going waves (Shao & Pyrak‐Nolte, ). This work is the first step toward understanding the effect of any geometric intersection (i.e., nonorthogonal) and indicates the possible applications of this work to seismically interogate the subsurface.…”

Section: Resultsmentioning

confidence: 99%

Intersection Waves

2017

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Intersections in a fracture network control the connectivity of the flow paths through rock. The long near‐linear geometric nature of fractures makes them difficult to identify and characterize. We present a new type of elastic wave, an intersection wave, which travels along an intersection and is sensitive to the coupling between two orthogonal fractures that define the intersection. Group theory for C2v and C4v point groups predicts sets of propagating elastic waves confined to the fracture intersection. Along with the use of the wave equation and displacement discontinuity boundary conditions, the dispersion relationships for intersection waves are predicted. Experimental ultrasonic measurements on a nonwelded linear intersection between two orthogonal, synthetic fractures in aluminum confirm the existence of multiple modes that travel between the speed of wedge waves (sub‐Rayleigh waves) when the intersection is completely, and bulk shear waves, when the intersection is closed, as predicted by theory. Between these two limits, the intersection behaves as a nonwelded contact and yields these new intersection waves that are dispersive and sensitive to the coupling along the intersection. Intersection waves provide the foundation for new geophysical approaches for characterizing the hydraulic connectivity of fracture networks.

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Section: Resultsmentioning

confidence: 99%

Intersection Waves

2017

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“…While the focus of this review is on fracture pattern formation, fundamental questions exist on the role of fracture array patterns, mineral bridges, and mineral rinds on elastic wave propagation and scattering in systems. Fracture‐specific stiffness is commonly used in theoretical and numerical studies of wave propagation in fractured media to determine the effect of fractures and fracture sets on seismic wave attenuation and velocity (Bakulin et al, ; Choi et al, ; De Basabe et al, ; Nakagawa & Schoenberg, ; Pyrak‐Nolte et al, , ; Schoenberg & Douma, ; Shao et al, ; Shao & Pyrak‐Nolte, ). Fracture stiffness as currently conceptualized captures the complex topology of a surface in contact with voids of variable shape and aperture and is fundamentally related to fluid flow and seismic wave attenuation and velocity for fractured media (Petrovitch et al, ; Pyrak‐Nolte, ; Pyrak‐Nolte & Nolte, ).…”

Section: Questions For Future Researchmentioning

confidence: 99%

The Role of Chemistry in Fracture Pattern Development and Opportunities to Advance Interpretations of Geological Materials

Laubach

Lander²,

Criscenti

et al. 2019

Reviews of Geophysics

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Fracture pattern development has been a challenging area of research in the Earth sciences for more than 100 years. Much has been learned about the spatial and temporal complexity inherent to these systems, but severe challenges remain. Future advances will require new approaches. Chemical processes play a larger role in opening‐mode fracture pattern development than has hitherto been appreciated. This review examines relationships between mechanical and geochemical processes that influence the fracture patterns recorded in natural settings. For fractures formed in diagenetic settings (~50 to 200 °C), we review evidence of chemical reactions in fractures and show how a chemical perspective helps solve problems in fracture analysis. We also outline impediments to subsurface pattern measurement and interpretation, assess implications of discoveries in fracture history reconstruction for process‐based models, review models of fracture cementation and chemically assisted fracture growth, and discuss promising paths for future work. To accurately predict the mechanical and fluid flow properties of fracture systems, a processes‐based approach is needed. Progress is possible using observational, experimental, and modeling approaches that view fracture patterns and properties as the result of coupled mechanical and chemical processes. A critical area is reconstructing patterns through time. Such data sets are essential for developing and testing predictive models. Other topics that need work include models of crystal growth and dissolution rates under geological conditions, cement mechanical effects, and subcritical crack propagation. Advances in machine learning and 3‐D imaging present opportunities for a mechanistic understanding of fracture formation and development, enabling prediction of spatial and temporal complexity over geologic timescales. Geophysical research with a chemical perspective is needed to correctly identify and interpret fractures from geophysical measurements during site characterization and monitoring of subsurface engineering activities.

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“…Many methods such as hydraulic fracturing, high-pressure water jet and blasting vibration (Li et al, 2009;Shen et al, 2012;Li and Xing, 2015;Shao and Pyrak-Nolte, 2016), have been tested and applied to achieve these goals. The desorption rate and permeability of CSG can also be significantly increased by physical stimulation through changing the thermal field (Azmi et al, 2006;Charrié re and Pokryszka, 2010;Pan et al, 2012), stress field (Hol et al, 2011), electrical and magnetic field (Liu et al, 2006) and their coupling effects.…”

Section: Backgroundsmentioning

confidence: 99%

“…There are many studies that indicate wave propagation could be highly affected by the structure and distribution of fractures in geomaterials (Korneev, 1993;Amalokwu et al, 2014). Especially, Shao and Pyrak-Nolte (2016) studied the acoustic wave propagation in isotropic media with orthogonal fracture sets. The research indicates that the fracture intersections have stronger effects for wave front propagation than merely the superposition of two independent fractures; intersections could also highly delay and attenuate acoustic wave (Amalokwu, 2014;Shao and Pyrak-Nolte, 2016).…”

Section: Overviewmentioning

confidence: 99%

“…Especially, Shao and Pyrak-Nolte (2016) studied the acoustic wave propagation in isotropic media with orthogonal fracture sets. The research indicates that the fracture intersections have stronger effects for wave front propagation than merely the superposition of two independent fractures; intersections could also highly delay and attenuate acoustic wave (Amalokwu, 2014;Shao and Pyrak-Nolte, 2016). This effect is drawing more and more attentions; however, currently, there is no analytical solution available for this phenomenon.…”

Section: Overviewmentioning

confidence: 99%

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Numerical simulation of acoustic stimulation for enhancing coal seam gas reservoir permeability

Jiang¹

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Acoustic stimulation method has been recognized as one of the most effective methods for enhancing coal permeability and improving the production amount of gas. Laboratory data has proved that the geometrical parameters (width and length) of coal cleats, which are the crucial pathway for gas migration, could be highly increased by acoustic field stimulation. The main reason for this positive effect is that acoustic energy could induce the mechanical vibration effect around coal cleats. However, the basic mechanism of this effect is still poorly understood due to the limitation of experimental facilities; the progress and details about this effect cannot be directly observed. It is imperative to conduct proper numerical simulation for the technology to improve the understanding of mechanical vibration. And only based on the conclusion of simulation results, the engineering parameters for optimal stimulation effect could be found. This thesis addresses this key issue and demonstrates how exactly the mechanical vibration is induced and affect the original coal cleat system. This thesis focuses on conducting numerical simulation for acoustic wave induced mechanical vibration around the coal cleats. The primary contributions are summarized as follows:(1) The numerical simulation based on the staggered-grid finite differential method (FDM) is applied to simulate 3D wave propagation in a single coal cleat model. Two parameters, shear wave energy (SE) and variable width of cleat (DW), are introduced and implemented in the numerical model to explicitly evaluate the acoustic stimulation effects. The results indicate that these parameters could accurately represent the variations of acoustic energy and geometrical parameters of the coal cleat model.(2) The polarized wave induced wave dynamics in a coal sample with a single cleat model is numerically simulated and analyzed; the energy trapping and dynamic variation of fracture width in coal for the cleat model with three different filled media (i.e. air, water and weak mineral) are numerically analyzed and compared with each other subjected to different incident wave angles, and the optimal stimulation parameters are obtained through such sensitivity analysis. Simulation results show that the mechanical vibration is induced by the energy trapping effect; coal property (i.e. cleat and its filled media) and incident wave angles are crucial for acoustic stimulation to produce physical damages around coal cleats and enhance the permeability of fractured coal samples. II (3)The numerical simulation is further applied to simulate the viscoelastic wave propagation in 3D coal sample with a coal cleat system. Two kinds of coal cleat system model, orthogonal cleat sets (OCS) and T-junction cleat sets (TCS), are adopted to investigate the influence of coal cleats special structure for mechanical vibration. A stochastic model building process, which includes Monte Carlo method and von-Ká rmá n function, is proposed to better represent the structure of coal cleat system and hete...

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Wave Propagation in Isotropic Media with Two Orthogonal Fracture Sets

Cited by 14 publications

References 46 publications

Intersection Waves

Intersection Waves

The Role of Chemistry in Fracture Pattern Development and Opportunities to Advance Interpretations of Geological Materials

Numerical simulation of acoustic stimulation for enhancing coal seam gas reservoir permeability

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