scholarly journals Studies on a Piezoelectric Cylindrical Transducer for Borehole Dipole Acoustic Measurements

2021 ◽  
Vol 11 (3) ◽  
pp. 1036
Author(s):  
Yinqiu Zhou ◽  
Xiuming Wang ◽  
Yuyu Dai
Keyword(s):  
Numerical Simulation ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Low Frequency ◽  
Compressional Wave ◽  
Wave Measurements ◽  
New Development ◽  
Cylindrical Transducer ◽  
Simulation Results

In this article, a novel design of a piezoelectric dipole transducer is proposed for formation acoustic velocity measurement in the vicinity of a borehole with a frequency range of 0.4–6 kHz. The transducer which actuates a cylindrical shell to generate a pure dipole mode wave by using multiple piezoelectric bender bars is analyzed theoretically and simulated numerically by using the finite element method (FEM). Moreover, the transducer is fabricated and tested to compare with the numerical simulation results, which shows that the test and simulation results are in good agreement. Finally, compared with numerical simulation results of the traditional dipole transducer, it is shown that the proposed dipole transducer has higher transmitting sensitivities than commonly used ones, especially in low frequency responses. This work lays a foundation for the new development of the transducer in borehole dipole acoustic shear wave measurements. Especially, in a slow formation where the shear wave velocity is lower than that of compressional wave in the borehole fluid, the transducer could be used for highly efficient shear wave velocity measurements.

Deep Shear Wave Velocity Profiles from Surface Wave Measurements in the Mississippi Embayment

2007 ◽  
Vol 23 (4) ◽  
pp. 791-808 ◽  
Author(s):  
Brent L. Rosenblad ◽  
Jianhua Li ◽  
Farn-Yuh Menq ◽  
Kenneth H. Stokoe
Keyword(s):  
Surface Wave ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Site Response ◽  
Source Surface ◽  
Mississippi Embayment ◽  
Near Surface ◽  
Wave Measurements ◽  
Central United States

Shear wave velocity ( VS) profiles to depths of approximately 200 m were developed from active-source surface wave velocity measurements in the Mississippi Embayment region of the Central United States. Soil deposits in this region are hundreds of meters thick, but are poorly characterized at depths below 60 m. Measurements were performed at five locations in Arkansas and Tennessee with a maximum distance between sites of approximately 130 km. The median VS profile calculated from the five profiles is in good agreement with a generic reference VS profile for the Mississippi Embayment that has been used in recent site response studies. The near-surface VS profiles at the five sites were remarkably consistent with average shear wave velocities in the top 30 m ( VS30), varying by less than 10%. Increasing variability between the VS profiles was observed at greater depths. The variability between VS profiles was shown to be correlated with changes in lithology at two of the sites where nearby lithologic information was available.

The Finite Element Model Determination in the Loess Regions under Subway Vibration Loads

2011 ◽  
Vol 368-373 ◽  
pp. 2586-2590
Author(s):  
Zhao Bo Meng ◽  
Shi Cai Cui ◽  
Teng Fei Zhao ◽  
Liu Qin Jin
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Low Frequency ◽  
Time History ◽  
Ground Vibration ◽  
Element Model ◽  
Vibration Velocity

According to measured shear wave velocity of Xi’an Bell Tower area (Loess Area), the dynamic parameters of site soil are determined by using the relationship between shear wave velocity and compression wave velocity. Using Matlab program, the finite element size for low frequency subway vibration is obtained by analyzing soil dispersion phenomenon. On this basis, two-dimensional model with viscous - elastic boundaries is established by using the ANSYS program. The load-time history of the train is applied to the right tunnel, and the effects of the depth and breadth of the different models on the ground vibration velocity are discussed. Finally, the dimensions and element sizes of finite element model are obtained for the Xi'an No. 2 Metro Line with 15m depth in the loess regions.

scholarly journals Prediction of the Shear Wave Velocity from Compressional Wave Velocity for Gachsaran Formation

2015 ◽  
Vol 63 (5) ◽  
pp. 1231-1243 ◽  
Author(s):  
Saeed Parvizi ◽  
Riyaz Kharrat ◽  
Mohammad R. Asef ◽  
Bijan Jahangiry ◽  
Abdolnabi Hashemi
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Compressional Wave ◽  
Compressional Wave Velocity ◽  
Gachsaran Formation

Shear‐wave logging to enhance seismic modeling

Geophysics ◽  
1991 ◽  
Vol 56 (12) ◽  
pp. 2129-2138 ◽  
Author(s):  
M. A. Payne
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Field Data ◽  
Compressional Wave ◽  
Oil Sand ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Amplitude Versus Offset ◽  
Amplitude Versus

In an effort to understand better the amplitude variation with offset for reflections from an oil sand and the sensitivity of the AVO response to shear‐wave velocity variations, I studied synthetic and field gathers collected from an onshore field in the Gulf of Mexico basin. A wave‐equation‐based modeling program generated the synthetic seismic gathers using both measured and estimated shear‐wave velocities. The measured shear‐wave velocities came from a quadrupole sonic tool. The estimated shear‐wave velocities were obtained by applying published empirical and theoretical equations which relate shear‐wave velocities to measured compressional‐wave velocities. I carefully processed the recorded seismic data with a controlled‐amplitude processing stream. Comparison of the synthetic gathers with the processed field data leads to the conclusion that the model containing the measured shear‐wave velocities matches the field data much better than the model containing the estimated shear‐wave velocities. Therefore, existing equations which relate shear‐wave velocities to compressional‐wave velocities yield estimates which are not sufficiently accurate for making quantitative comparisons of synthetic and field gathers. Even small errors in the shear‐wave velocities can have a large impact on the output. Such errors can lead to an incomplete and perhaps inaccurate understanding of the amplitude‐versus‐offset response. This situation can be remedied by collecting shear‐wave data for use in amplitude‐versus‐offset modeling, and for building databases to generate better shear‐wave velocity estimator equations.

scholarly journals Near-surface characterization using a roadside distributed acoustic sensing array

2020 ◽  
Vol 39 (9) ◽  
pp. 646-653 ◽  
Author(s):  
Siyuan Yuan ◽  
Ariel Lellouch ◽  
Robert G. Clapp ◽  
Biondo Biondi
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Fundamental Mode ◽  
Rayleigh Waves ◽  
Low Frequency ◽  
Frequency Range ◽  
Acoustic Sensing ◽  
Velocity Inversion ◽  
Distributed Acoustic Sensing

Due to the broadband nature of distributed acoustic sensing (DAS) measurement, a roadside section of the Stanford DAS-2 array can record seismic signals from various sources. For example, it measures the earth's quasistatic deformation caused by the weight of cars (less than 0.8 Hz) as well as Rayleigh waves induced by earthquakes (less than 3 Hz) and by dynamic car-road interactions (3–20 Hz). We directly utilize the excited surface waves for shallow shear-wave velocity inversion. Rayleigh waves induced by passing cars have a consistent fundamental mode and a noisier first mode. By stacking dispersion images of 33 passing cars, we obtain stable dispersion images. The frequency range of the fundamental mode can be extended by adding the low-frequency earthquake-induced Rayleigh waves. Due to the extended frequency range, we can achieve better depth coverage and resolution for shear-wave velocity inversion. To assure clear separation from Love waves and to align apparent and true phase velocities, we choose an earthquake that is approximately in line with the array. The inverted models match those obtained by a conventional geophone survey, performed using active sources by a geotechnical service company contracted by Stanford University, from the surface to about 50 m. To automate the VS inversion process, we introduce a new objective function that avoids manual dispersion curve picking. We construct a 2D VS profile by performing independent 1D inversions at multiple locations along the fiber. From the low-frequency quasistatic deformation recordings, we also invert for a single Poisson's ratio at each location along the fiber. We observe spatial heterogeneity of both VS and Poisson's ratio profiles. Our approach is less expensive than ambient field interferometry, and reliable estimates can be obtained more frequently because no lengthy crosscorrelations are required.

Changes in dielectric permittivity and shear wave velocity during concentration diffusion

1995 ◽  
Vol 32 (4) ◽  
pp. 647-659 ◽  
Author(s):  
J.C. Santamarina ◽  
M. Fam
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Electromagnetic Waves ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
High Concentration ◽  
Interparticle Forces ◽  
Wave Measurements ◽  
Concentration Diffusion

This paper documents a study of concentration diffusion with complementary mechanical and electromagnetic wave measurements. The paper starts with a review of the fundamentals of interparticle forces and wave–geomedia interaction. Experimental data were collected during the diffusion of a high-concentration solution of potassium chloride through different soils with different boundary conditions. Bentonite and kaolinite contracted during diffusion. The interaction between the concentration gradient, true interparticle forces, and fabric changes produced a pore-water pressure front that advanced ahead of the concentration front. The complex permittivity changed with the advance of the concentration front, reflecting the decrease in moisture content and the increase in conductivity. Concentration diffusion affected shear wave propagation through changes in true interparticle forces. Bentonite showed a significant increase in shear wave velocity, whereas the velocity of propagation in kaolinite decreased. Published differences in the behavior of bentonite and kaolinite were compiled and hypotheses are proposed to explain observed phenomena. Key words : mechanical waves, electromagnetic waves, clays, diffusion, double layer.

Numerical simulation of seismic cone signals

2005 ◽  
Vol 42 (2) ◽  
pp. 574-586 ◽  
Author(s):  
John A Howie ◽  
Ali Amini
Keyword(s):  
Numerical Simulation ◽  
Wave Propagation ◽  
Finite Difference ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Field Effect ◽  
Near Field ◽  
Ground Conditions ◽  
Near Field Effect

Numerical analysis can provide insight into the effect of ground conditions on seismic signals recorded in downhole seismic testing. As part of a study of the interpretation of seismic cone data in complex ground conditions, this paper deals with the cases of wave propagation in (i) homogeneous soil and (ii) soil of increasing stiffness with depth. The main purpose of this study was to assess the validity of the use of the finite difference program FLAC for the simulation of the downhole seismic test. For realistic assumptions of material stiffness and damping, the main characteristics of field seismic cone penetration test (SCPT) seismic data were reproduced in the simulated data. Both displayed the same general shape of signal, number of oscillations, signal attenuation, frequency content, compression wave component (near-field effect), signal widening, and shift of the peak of the frequency spectrum with depth. Damping was shown to cause signal widening and dispersion, and the shear wave velocity, Vs, interpreted from the simulated wave traces varied with the interval method used to determine it. For a case history of field data, it was found that Vs varied by about 3%, depending on the analysis method used. The results show that finite difference modeling of wave propagation can provide useful insights into the factors affecting the interpretation of downhole seismic tests.Key words: seismic cone testing, shear wave velocity, signal widening, near-field effect, numerical simulation, finite difference.

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