Acoustic waves from an impulsive source in a fluid-filled borehole

Roever, W. L.; Rosenbaum, J. H.; Vining, T. F.

doi:10.1121/1.1914679

Cited by 71 publications

(47 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Studies by Forristall and Ingram (1969) show that an off-centered condition for a fiuid cylinder yields two types of refiected arrivals: one associated with the source waveform, and the other with its derivative. Roever et al (1974) conclude that when the source and detector are displaced off-center on the same side, P waves constructively interfere, and S waves destructively interfere, and that when source and detector are on opposite sides of the center, P waves destructively interfere while S waves constructively ,interfere. Approximations for P and S waves for an off-center source in terms of a sum of an infinite number of potentials have been derived by Winbow (1980).…”

Section: Introductionmentioning

confidence: 99%

Approximate effects of off‐center acoustic sondes and elliptic boreholes upon full waveform logs

Willis¹,

Toksöz²,

Cheng³

1982

SEG Technical Program Expanded Abstracts 1982

View full text Add to dashboard Cite

Full waveform acoustic well logging has become instrumental to hydrocarbon exploration because of its ability to determine in situ velocity information for P and S waves as well as the attenuation (or absorption) of seismic energy. It is therefore important that the factors infiuencing these logs be understood. In addition to formation properities, Poisson's ratio, the borehole environment, and tool centering can affect the full waveform acoustic logs. These latter factors are evaluated through modeling of elliptic boreholes and de-centralized tools in the borehole. INTRODUCTIONA number of factors affect the observed full waveform acoustic log amplitudes. Formation properities play an important role. In addition the borehole environment can cause variations. For example, borehole rugosity impedes the propagation of head waves (Morris et aI., 1964). In areas of' cavitation and washouts, critical refraction may be prevented, resulting in low amplitude waveforms. Lebreton et al. (1978) report a strong reduction in waveform amplitude proportional to an increase in mud cake thickness.Centering of the sonde and a cylindrical borehole are crucial to waveform amplitudes and arrival times. In most full waveform logging systems the tool is held centralized in the borehole by several bow type springs which press against the formation. In other systems, rubber "fingers" keep the tool centralized. The reliability of these methods in keeping the tool centralized in holes with a true circular cross section as well as in irregular holes has not been well documented. The actual amount of "rattle" that the tool experiences is not generally known.Morris estimates that moving the source one quarter of an inch (0.64 cm) off-center decreases the P wave amplitude by one half (Morris et al., 1964). This is a significant effect for such a small displacement. In experiments with a tool placed in a trough to simulate a cased borehole it was determined that moving the centralized source completely against the casing not only decreases the amplitude of the recorded waveform but also increases its complexity and reverses the apparent polarity of the first motion (Riddle, 1962). Studies by Forristall and Ingram (1969) show that an off-centered condition for a fiuid cylinder yields two types of refiected arrivals: one associated with the source waveform, and the other with its derivative.

show abstract

Section: Introductionmentioning

confidence: 99%

Approximate effects of off‐center acoustic sondes and elliptic boreholes upon full waveform logs

Willis¹,

Toksöz²,

Cheng³

1982

SEG Technical Program Expanded Abstracts 1982

View full text Add to dashboard Cite

show abstract

“…Usually it is believed that the full wave field is represented as a sum of the contributions of poles and branch cuts on the complex wavenumber (k) plane [10][11][12] .P Tsang and RaderP [11] presented a numerical method, called the vertical branch cut integration (VBCI), and evaluated the first few cycles of the compressional (p-) and shear (s-) head wave arrivals. Kurkjian and Chang [13] P applied the VBCI to study the acoustic wave field excited by multipole sources, and pointed out that the pole contributions corresponded to the mode arrivals while the branch cuts were associated with the body waves (i.e., head waves).…”

mentioning

confidence: 99%

Acoustic mode waves and individual arrivals excited by a dipole source in fluid-filled boreholes

Zhang

Wang

2009

Sci. China Ser. G-Phys. Mech. Astron.

View full text Add to dashboard Cite

An approach of separating individual wave arrivals for a dipole logging is presented. The branch points are treated as a type of logarithm and the Riemann surface structure of the multivalued function is studied, that is, the displacement potential within the borehole. Based on the theoretical analysis, the complex poles contributing to the wave field on various Riemann sheets are investigated in detail for the case of a fast formation. It is shown that poles on Riemann sheet (0,0) are real and form branches of modes with dispersion. Mathematically, it is demonstrated that the flexural mode has no cutoff frequency, which is different from the traditional point of view. Poles on other relevant Riemann sheets are complex and form many branches on the complex frequency-wavenumber plane. Further investigation on the pole and branch cut contributions indicates that the vertical branch cut integration method has limitations in separating wave arrivals. By properly taking into account the complex poles on various Riemann sheets together with branch cut integrations, wave arrivals are separated from the full waveforms effectively for both the fast and slow formation models. Specially, there are complex poles on Riemann sheet (0,−1) in the vicinity of the compressional branch cut for a slow formation with a large Poisson's ratio, which have small imaginary parts and contribute a lot to the p-wave arrival.dipole sources, Riemann sheet, cutoff frequency, individual arrivals Acoustic wave propagation within a borehole excited by multipole sources has attracted intensive attention, and multipole acoustic logging has been widely used in oilfields for measuring the shear wave velocities and anisotropy caused by fractures or residual stress in formation surrounding boreholes [1 -4] . Initially, White [5] brought forward the virtue of a dipole source for generating S-waves. PIn the following years, the physics of dipole source excitation in the borehole has been studied in many papers, either by numerical simulation [6,7] or by laboratory experiments [8,9] . It was realized that the full waveform was a combination of several arrivals of modes and body waves, which are dependent on the parameters of the borehole and the surrounding formation [10] . Therefore, the studies of all these arrivals separately are required although difficult. For example, the popular numerical simulation method, real axis integration (RAI), gives the full waveform only, and it does not show the individuals separately except for the compressional head arrivals with a long source-receiver offset.The individual arrival separation, such as compressional head arrival and shear wave arrival separation from full borehole acoustic waveforms, is interesting to many research scientists [10,11] . Usually it is believed that the full wave field is represented as a sum of the contributions of poles and branch cuts on the complex wavenumber (k) plane [10][11][12] .P Tsang and RaderP [11] presented a numerical method, called the vertical branch cut integration (VBCI),...

show abstract

“…To investigate wavefields varying with the time and space, transforming the acoustic function ϕ(ω, k z ) in the frequency-axial-wavenumber domain into ϕ(t, z) in the time-space domain is required. There are two common ways to implement such a computation process: one is the real axis integration [1] from which we can directly obtain the full waveforms; the other way is to calculate the total wavefield as a sum of contributions from both poles and branch points in the complex axial-wavenumber plane according to Cauchy's theorem [2]. By the latter method, all component waves, including the compressional, shear, and guided waves, can therefore be separated from the full waveform in the simulation.…”

mentioning

confidence: 99%

Single-valued definition of the multivalued function for borehole acoustic waves in transversely isotropic formations

2010

Sci. China Phys. Mech. Astron.

View full text Add to dashboard Cite

It is useful to extract all components, including compressional, shear, and guided waves, from the full waveforms when we investigate the acoustic log data. The component waves can be simulated by calculating the contributions from poles and branch points of the borehole acoustic function according to Cauchy's theorem. For such an algorithm to be implemented, the multivalued function for the borehole wave field in the frequency-axial-wavenumber domain has to be rendered single-valued first. Assuming that the borehole axis is parallel to the symmetry axis of transverse isotropy, this paper derives the branch points of the borehole acoustic function. We discover that the number and the locations of those branch points are determined by the relation among the formation parameters c 33 , c 44 , ε, and δ. Thus the single-valued definitions in the acoustic-wave computation are sorted into two different cases. After building the Riemann surface related to each radial wavenumber, we give the single-valued definition of the borehole acoustic function inside and on the integration contour based on the radiation condition.In a formation with δ > ε + c 44 /2c 33 , if we choose the integration contour and the single-valued definition of the acoustic function in the way used in isotropic cases, the simulation results of component waves will be wrong.anisotropy, acoustic logging, elastic wave, Riemann sheet PACS: 43.20.Fn, 43.40.Ph, 91.30.Fn In the theoretical research on acoustic logging, it is important to simulate and analyze the borehole full wave and the component waves within. To investigate wavefields varying with the time and space, transforming the acoustic function ϕ(ω, k z ) in the frequency-axial-wavenumber domain into ϕ(t, z) in the time-space domain is required. There are two common ways to implement such a computation process: one is the real axis integration [1] from which we can directly obtain the full waveforms; the other way is to calculate the total wavefield as a sum of contributions from both poles and branch points in the complex axial-wavenumber plane according to Cauchy's theorem [2]. By the latter method, all component waves, including the compressional, shear, and guided waves, can therefore be separated from the full waveform in the simulation. The acoustic function ϕ(ω, k z ), however, is a multivalued function which has many values with single k z and ω, so the contour integration on the complex plane cannot be evaluated unless the integrand is single-valued. Kurkjian [3] and Liu et al. [4] have discussed the characteristics of the borehole acoustic functions for wavefields in elastic and quasi-elastic media, respectively. They gave the single-valued choices of the acoustic function on the vertical integration paths related to the branch points. Zhang and Wang [5,6] analyzed the algebraic and logarithm multivalued features of the radial wavenumbers and the modified Bessel functions of the second kind, respectively. They calculated all poles on each sheet of the Riemann surface. In their numeri...

show abstract

Acoustic waves from an impulsive source in a fluid-filled borehole

Cited by 71 publications

References 0 publications

Approximate effects of off‐center acoustic sondes and elliptic boreholes upon full waveform logs

Approximate effects of off‐center acoustic sondes and elliptic boreholes upon full waveform logs

Acoustic mode waves and individual arrivals excited by a dipole source in fluid-filled boreholes

Single-valued definition of the multivalued function for borehole acoustic waves in transversely isotropic formations

Contact Info

Product

Resources

About