Borehole seismic-source radiation pattern in transversely isotrophic media

We extend previous discussions on crosswell tomography in anisotropic formations by deriving the radiation patterns of three typical downhole seismic sources (impulsive air gun or dynamite, wall‐clamped vertical vibrators, and cylindrical bender) inside a fluid‐filled borehole embedded in a transversely isotropic (TI) formation. The method of steepest descents, in conjuncture with the low‐frequency and far‐field assumptions, is applied to the exact displacement integrals of these sources to obtain their radiation patterns asymptotically. In spite of complications caused by quasi‐P‐ and quasi‐SV‐wave coupling and wavefront triplication in homogeneous TI media, the final results can still be expressed in slowness components determined by a ray direction, which is desired when source radiation effects are to be accounted for by ray‐based tomography techniques. Tests with the radiation patterns show that while the effect of anisotropy on P‐waves is moderate, its effect on the S‐wave pattern is significant even for slightly anisotropic formations. One can predict the S‐wave pattern from the sign of the Thomsen’s measure δ*.

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Borehole seismic‐source radiation in layered isotropic and anisotropic media: Boundary element modeling

Geophysics ◽

10.1190/1.1443812 ◽

1995 ◽

Vol 60 (3) ◽

pp. 735-747 ◽

Cited By ~ 26

Author(s):

Wenjie Dong ◽

Michel Bouchon ◽

M. Nafi Toksöz

Keyword(s):

Boundary Element ◽

Anisotropic Media ◽

Seismic Source ◽

Borehole Wall ◽

Cement Interface ◽

Secondary Sources ◽

Source Radiation ◽

Guided Modes ◽

Borehole Seismic ◽

Ti Media

In modeling waves radiated from a borehole seismic source in layered isotropic or anisotropic media, the commonly used numerical methods (e.g., finite difference and finite element) encounter difficulties because of the large scale difference between the borehole diameter and the formation extent. To get around this problem, we apply the indirect boundary element method to establish a general algorithm for modeling source radiation from open and cased boreholes in layered transversely isotropic (TI) media. The essence of the algorithm is to use discrete secondary sources (unknowns) on both sides of the borehole wall (formation/cement interface) to represent the influence of the interface on wave scattering, so that wave propagation inside and outside the borehole can be carried out by Green’s functions. The discrete distribution of the secondary sources is determined by matching boundary conditions on the borehole wall. Comparison with the discrete wavenumber method validates the implementation. Applications to fluid‐filled open and cased boreholes in three‐layer media demonstrate the creation of guided modes in low velocity layers. Presence of anisotropy complicates the guided modes as a result of dispersion and P‐ and SV‐waves coupling in homogeneous TI media. Presence of casing and cement enhances the visibility of the guided modes.

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A swept-frequency borehole source for inverse VSP and cross-borehole surveying

Exploration Geophysics ◽

10.1071/eg989133 ◽

1989 ◽

Vol 20 (2) ◽

pp. 133 ◽

Cited By ~ 1

Author(s):

W. Kennedy ◽

W. Wiggins ◽

P. Aronstam ◽

B.A. Hardage

Keyword(s):

Resonant Frequency ◽

Total Energy ◽

Radiation Pattern ◽

Shear Waves ◽

Seismic Source ◽

P Wave ◽

Frequency Range ◽

Pressure Oscillations ◽

Strong Shear ◽

Borehole Seismic

A swept-frequency borehole seismic source has been constructed and tested that consists of a portion of the borehole isolated from the remainder and driven to build up pressure oscillations by resonance.The length of the isolated portion is changed to vary the resonant frequency. The source radiates an approximately isotropic P-wave whose total energy is comparable in magnitude to that created by a surface vibrator truck. Strong shear waves are also generated.The source has been tested over a frequency range of 30 to 120 Hz, but the design can be operated from 15 to 500 Hz. Because the driven section of the borehole is isolated, strong tube waves are not generated. No damage to the casing-cement bond has been observed after prolonged operation of the source at a fixed depth.This source has the strength and uniform radiation pattern to suit it for both inverse VSP and cross-borehole surveying.

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Seismic Source Radiation and Moment Tensor in the Time Domain

Seismic Monitoring in Mines ◽

10.1007/978-94-009-1539-8_7 ◽

1997 ◽

pp. 119-143

Author(s):

A. J. Mendecki

Keyword(s):

Time Domain ◽

Moment Tensor ◽

Seismic Source ◽

Source Radiation ◽

The Time Domain

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Crosswell seismic imaging in a contaminated basalt aquifer

Geophysics ◽

10.1190/1.1649371 ◽

2004 ◽

Vol 69 (1) ◽

pp. 16-24 ◽

Cited By ~ 25

Author(s):

Thomas M. Daley ◽

Ernest L. Majer ◽

John E. Peterson

Keyword(s):

Seismic Source ◽

P Wave ◽

Low Velocity ◽

S Waves ◽

High Attenuation ◽

Well Spacing ◽

Simultaneous Acquisition ◽

Environmental Laboratory ◽

New Type ◽

Borehole Seismic

Multiple seismic crosswell surveys have been acquired and analyzed in a fractured basalt aquifer at Idaho National Engineering and Environmental Laboratory. Most of these surveys used a high‐frequency (1000–10,000 Hz) piezoelectric seismic source to obtain P‐wave velocity tomograms. The P‐wave velocities range from less than 3200 m/s to more than 5000 m/s. Additionally, a new type of borehole seismic source was deployed as part of the subsurface characterization program at this contaminated groundwater site. This source, known as an orbital vibrator, allows simultaneous acquisition of P‐ and S‐waves at frequencies of 100 to 400 Hz, and acquisition over larger distances. The velocity tomograms show a relationship to contaminant transport in the groundwater; zones of high contaminant concentration are coincident with zones of low velocity and high attenuation and are interpreted to be fracture zones at the boundaries between basalt flows. The orbital vibrator data show high Vp/Vs values, from 1.8 to 2.8. In spite of the lower resolution of orbital vibrator data, these data were sufficient for constraining hydrologic models at this site while achieving imaging over large interwell distances. The combination of piezoelectric data for closer well spacing and orbital vibrator data for larger well spacings has provided optimal imaging capability and has been instrumental in our understanding of the site aquifer's hydrologic properties and its scale of heterogeneity.

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