Characterization of porous rocks embedded with aligned fractures from shear wave responses

2020 ◽  
Vol 222 (3) ◽  
pp. 2172-2188
Author(s):  
Ding Wang ◽  
Bo Li
Keyword(s):  
Shear Wave ◽  
Dynamic Properties ◽  
Rock Fracture ◽  
Shear Waves ◽  
Symmetry Plane ◽  
Fast Wave ◽  
Porous Rocks ◽  
Anisotropic Rock ◽  
Vibration Direction ◽  
Wave Source

SUMMARY A single shear wave passing through an elastic anisotropic rock can split into two quasi-shear waves (noted by S1 and S2) with different polarization forms if the particle vibration direction of the wave source does not lie in the symmetry plane of the rock. This study focuses on the properties of shear waves penetrating a porous rock containing a set of aligned permeable fractures. The polarization characteristics of shear waves were selected to describe the dynamic properties of the rock as they are sensitive to the parameters of fractures and saturating fluids. From a physics viewpoint, in addition to the compressional wave, the shear wave (splitting) is governed by a wave-induced fluid flow (WIFF) process due to the specific shear stress decomposition happening on the fractures. The polarization formulas of S1 and S2 were derived based on the frequency-dependent Christoffel equation, which are related to the properties of fractures, fluids and wave frequency. The influence of the properties of fractures and fluids on the velocity and attenuation anisotropies of shear waves were analysed. The results showed that the particle oscillations of two shear waves are not completely mutually orthogonal, and are affected by the pressure equilibrium magnitude between the fractures and the corresponding interconnected pores. The S2 (slow) wave (i.e. particle polarized on the plane approximately perpendicular to the fractures) is more sensitive to the saturated fluids and the WIFF process than that of the S1 (fast) wave (i.e. wave polarized on the plane approximately parallel to the fractures). A frequency factor was proposed for quantifying the effects of WIFF on shear wave polarization and attenuation. Measurements on the unique polarization and the anisotropy of shear waves can provide a generalized indicator to predict the properties of fractures and the migration of infilling fluids in the rock fracture systems.

scholarly journals Lorentz force induced shear waves for magnetic resonance elastography applications

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Guillaume Flé ◽  
Guillaume Gilbert ◽  
Pol Grasland-Mongrain ◽  
Guy Cloutier
Keyword(s):  
Magnetic Resonance ◽  
Shear Wave ◽  
Lorentz Force ◽  
Wave Attenuation ◽  
Shear Waves ◽  
Estimation Method ◽  
Biological Tissues ◽  
Magnetic Resonance Elastography ◽  
Motion Generation ◽  
Wave Source

AbstractQuantitative mechanical properties of biological tissues can be mapped using the shear wave elastography technique. This technology has demonstrated a great potential in various organs but shows a limit due to wave attenuation in biological tissues. An option to overcome the inherent loss in shear wave magnitude along the propagation pathway may be to stimulate tissues closer to regions of interest using alternative motion generation techniques. The present study investigated the feasibility of generating shear waves by applying a Lorentz force directly to tissue mimicking samples for magnetic resonance elastography applications. This was done by combining an electrical current with the strong magnetic field of a clinical MRI scanner. The Local Frequency Estimation method was used to assess the real value of the shear modulus of tested phantoms from Lorentz force induced motion. Finite elements modeling of reported experiments showed a consistent behavior but featured wavelengths larger than measured ones. Results suggest the feasibility of a magnetic resonance elastography technique based on the Lorentz force to produce an shear wave source.

scholarly journals Shear Wave Elastography Based on Noise Correlation and Time Reversal

2021 ◽  
Vol 9 ◽  
Author(s):  
Javier Brum ◽  
Nicolás Benech ◽  
Thomas Gallot ◽  
Carlos Negreira
Keyword(s):  
Shear Wave ◽  
Time Reversal ◽  
Shear Waves ◽  
Shear Wave Elastography ◽  
Noise Correlation ◽  
Elasticity Imaging ◽  
Physiological Noise ◽  
Wave Source ◽  
Imaging Device ◽  
Shear Elasticity

Shear wave elastography (SWE) relies on the generation and tracking of coherent shear waves to image the tissue's shear elasticity. Recent technological developments have allowed SWE to be implemented in commercial ultrasound and magnetic resonance imaging systems, quickly becoming a new imaging modality in medicine and biology. However, coherent shear wave tracking sets a limitation to SWE because it either requires ultrafast frame rates (of up to 20 kHz), or alternatively, a phase-lock synchronization between shear wave-source and imaging device. Moreover, there are many applications where coherent shear wave tracking is not possible because scattered waves from tissue’s inhomogeneities, waves coming from muscular activity, heart beating or external vibrations interfere with the coherent shear wave. To overcome these limitations, several authors developed an alternative approach to extract the shear elasticity of tissues from a complex elastic wavefield. To control the wavefield, this approach relies on the analogy between time reversal and seismic noise cross-correlation. By cross-correlating the elastic field at different positions, which can be interpreted as a time reversal experiment performed in the computer, shear waves are virtually focused on any point of the imaging plane. Then, different independent methods can be used to image the shear elasticity, for example, tracking the coherent shear wave as it focuses, measuring the focus size or simply evaluating the amplitude at the focusing point. The main advantage of this approach is its compatibility with low imaging rates modalities, which has led to innovative developments and new challenges in the field of multi-modality elastography. The goal of this short review is to cover the major developments in wave-physics involving shear elasticity imaging using a complex elastic wavefield and its latest applications including slow imaging rate modalities and passive shear elasticity imaging based on physiological noise correlation.

Seismic detection of a hydraulic fracture from shear‐wave VSP data at Lost Hills Field, California

Geophysics ◽  
1994 ◽  
Vol 59 (1) ◽  
pp. 11-26 ◽  
Author(s):  
Mark A. Meadows ◽  
Don F. Winterstein
Keyword(s):  
Shear Wave ◽  
Numerical Solutions ◽  
Scattered Wave ◽  
Hydraulic Fractures ◽  
Fast Wave ◽  
S Wave ◽  
Wave Source ◽  
Arrival Times ◽  
Fractured Medium ◽  
Fracture Closure

A shear‐wave (S‐wave) VSP experiment was performed at Lost Hills Field, California, in an attempt to detect hydraulic fractures induced in a nearby well. The hydrofrac well was located between an impulsive, S‐wave source on the surface and a receiver well containing a clamped, three‐component geophone. Both direct and scattered waves were detected immediately after shut‐in, when the hydraulic pumps were shut off and recording started. The scattered energy disappeared within about an hour, which is consistent with other measurements that indicate some degree of fracture closure and leak‐off within that period. Although S‐wave splitting was evident, no change was detected in the fast wave (polarized parallel to the fracture). However, the slow wave (polarized perpendicular to the fracture) did change over a period of about an hour, after which the prehydrofrac wavelet shape was recovered. The fact that only the wave polarized perpendicular to the fracture was affected is a dramatic confirmation of both theoretical predictions and laboratory observations of S‐wave behavior in a fractured medium. Subtracting the prehydrofrac wavelet from the wavelets recorded within the first hour after shut‐in revealed scattered wavelets that were diminished and phase‐rotated versions of the incident (prehydrofrac) wavelet. Arrival times of the direct and scattered waves were matched by ray tracing. We accounted for the scattered‐wave amplitudes by using numerical solutions of S‐wave diffractions off of ribbon‐shaped fractures. Amplitudes derived from full‐wavefield Born scattering, however, did not match recorded amplitudes. The phase of the scattered wavelets was matched very well by Born scattering when the incident wavelet was input, but only for fracture lengths no larger than half those predicted from fracture‐simulator models. These results show that a carefully controlled experiment, combined with accurate modeling, can provide important information about the geometry of induced fractures.

Converted waves in a shallow marine environment: Experimental and modeling studies

Geophysics ◽  
2011 ◽  
Vol 76 (1) ◽  
pp. T1-T11 ◽  
Author(s):  
Nihed Allouche ◽  
Guy G. Drijkoningen ◽  
Willem Versteeg ◽  
Ranajit Ghose
Keyword(s):  
Shallow Water ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Shear Waves ◽  
Seismic Survey ◽  
Wave Source ◽  
Shallow Marine ◽  
Modeling Studies ◽  
Water Bottom

Seismic waves converted from compressional to shear mode in the shallow subsurface can be useful not only for obtaining shear-wave velocity information but also for improved processing of deeper reflection data. These waves generated at deep seas have been used successfully in hydrocarbon exploration; however, acquisition of good-quality converted-wave data in shallow marine environments remains challenging. We have looked into this problem through field experiments and synthetic modeling. A high-resolution seismic survey was conducted in a shallow-water canal using different types of seismic sources; data were recorded with a four-component water-bottom cable. Observed events in the field data were validated through modeling studies. Compressional waves converted to shear waves at the water bot-tom and at shallow reflectors were identified. The shear waves showed distinct linear polarization in the horizontal plane and low velocities in the marine sediments. Modeling results indicated the presence of a nongeometric shear-wave arrival excited only when the dominant wavelength exceeded the height of the source with respect to the water/sediment interface, as observed in air-gun data. This type of shear wave has a traveltime that corresponds to the raypath originating not at the source but at the interface directly below the source. Thus, these shear waves, excited by the source/water-bottom coupled system, kinematically behave as if they were generated by an S-wave source placed at the water bottom. In a shallow-water environment, the condition appears to be favorable for exciting such shear waves with nongeometric arrivals. These waves can provide useful information of shear-wave velocity in the sediments.

Attenuation and dispersion phenomena of shear waves in anelastic and elastic porous strips

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Parvez Alam ◽  
Suprava Jena ◽  
Irfan Anjum Badruddin ◽  
Tatagar Mohammad Yunus Khan ◽  
Sarfaraz Kamangar
Keyword(s):  
Shear Wave ◽  
Half Space ◽  
Special Functions ◽  
Shear Waves ◽  
Finite Thickness ◽  
Dissipation Factor ◽  
Initial Stresses ◽  
Whittaker Functions ◽  
Content Type ◽  
Attenuation And Dispersion

Purpose This paper aims to study the attenuation and dispersion phenomena of shear waves in anelastic and elastic porous strips. Numerical investigations are performed for the phase and damped velocity profiles of the wave. For numerical computation purposes, water-saturated limestone and kerosene oil saturated sandstone for the first and second porous strips, respectively. Some other peculiarities have been observed and discussed. Design/methodology/approach Dispersion and attenuation characteristic of the shear wave propagations have been studied in an inhomogeneous poro-anelastic strip of finite thickness, which is clamped between an inhomogeneous poroelastic strip of finite thickness and an elastic half-space. Both the strips are initially stressed and the half-space is self-weighted. Analytical methods are used to calculate the interior deformations of the model with the involvement of special functions. The determination of the frequency equation, which includes the Bessel’s and Whittaker functions, has been obtained using the prescribed boundary conditions. Findings Impacts of attenuation coefficient, dissipation factor, inhomogeneities, initial stresses, Biot’s gravity, porosity and thickness ratio parameters on the velocity profile of the wave have been demonstrated through the graphical visuals. These parameters are playing an important role and working as a catalyst in affecting the propagation behaviour of the wave. Originality/value Inclusion of the concept of doubly layered initially stressed inhomogeneous porous structure of elastic and anelastic medium bedded over a self-weighted half-space medium brings a novelty to the existing literature related to the study of shear wave. It may be helpful to geologists, seismologists and structural engineers in the development of theoretical and practical studies.

Successful Use of a VSP Shear Wave Source

2005 ◽  
Author(s):  
M.A. Ackers ◽  
V.T. Nagassar ◽  
D.J. Klauza ◽  
T. Hilton
Keyword(s):  
Shear Wave ◽  
Wave Source

Effect of Anisotropy on Shear Wave Velocity in Wood

2012 ◽  
Vol 535-537 ◽  
pp. 1923-1926
Author(s):  
Jian Ping Zhou ◽  
Jin Xia Liu ◽  
Wen Yang Gao ◽  
Zhi Wen Cui ◽  
Wei Guo Lv ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Radial Direction ◽  
Rotation Angle ◽  
Wood Specimen ◽  
Shear Waves ◽  
Circular Ring ◽  
The Relationship ◽  
Intrinsic Birefringence

The velocities of shear waves propagating along radial direction of birch and elmwood specimens are measured in order to study the effect of anisotropy on shear wave velocity. The relationship between the shear wave velocity and the oscillation direction is examined by rotating an ultrasonic sensor. The results indicate that the effect of anisotropy on shear wave velocity in birch and elmwood specimens is similar to Japanese magnolia specimen. When the oscillation direction of the shear wave corresponds to the certain anisotropic direction of the wood specimen, the shear wave velocity decreases sharply and the relationship between shear wave velocity and rotation angle tends to become discontinuous. The intrinsic birefringence due to the anisotropy of birch and elmwood woods is observed. Their texture anisotropies are strong. In an isotropic nylon, on the contrary, the value of shear wave velocity was similar to a circular ring. This investigation is significant meanings in architectural and civil engineering field.

scholarly journals Insights Into Traumatic Brain Injury From MRI of Harmonic Brain Motion

2019 ◽  
Vol 13 ◽  
pp. 117906951984044 ◽  
Author(s):  
Ruth J Okamoto ◽  
Anthony J Romano ◽  
Curtis L Johnson ◽  
Philip V Bayly
Keyword(s):  
Traumatic Brain Injury ◽  
Wave Propagation ◽  
Brain Injury ◽  
Shear Wave ◽  
Relative Motion ◽  
Vector Fields ◽  
Shear Waves ◽  
Mechanical Deformation ◽  
Minor Role ◽  
The Brain

Measurements of dynamic deformation of the human brain, induced by external harmonic vibration of the skull, were analyzed to illuminate the mechanics of mild traumatic brain injury (TBI). Shear wave propagation velocity vector fields were obtained to illustrate the role of the skull and stiff internal membranes in transmitting motion to the brain. Relative motion between the cerebrum and cerebellum was quantified to assess the vulnerability of connecting structures. Mechanical deformation was quantified throughout the brain to investigate spatial patterns of strain and axonal stretch. Strain magnitude was generally attenuated as shear waves propagated into interior structures of the brain; this attenuation was greater at higher frequencies. Analysis of shear wave propagation direction indicates that the stiff membranes (falx and tentorium) greatly affect brain deformation during imposed skull motion as they serve as sites for both initiation and reflection of shear waves. Relative motion between the cerebellum and cerebrum was small in comparison with the overall motion of both structures, which suggests that such relative motion might play only a minor role in TBI mechanics. Strain magnitudes and the amount of axonal stretch near the bases of sulci were similar to those in other areas of the cortex, and local strain concentrations at the gray-white matter boundary were not observed. We tentatively conclude that observed differences in neuropathological response in these areas might be due to heterogeneity in the response to mechanical deformation rather than heterogeneity of the deformation itself.

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