Numerical evaluation of the transient acoustic waveform due to a point source in a fluid‐filled borehole

Tsang, Leung; Rader, Dennis

doi:10.1190/1.1440932

Cited by 212 publications

(107 citation statements)

References 9 publications

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“…We use the modeling technique described by Tsang and Rader [1979], Cheng and Toksöz [1981] and Kurkjian and Chang [1986]. Assuming that the borehole is an infinite fluid-filled cylinder in an infinite elastic medium, the excitation of a receiver located at a distance z from the transmitter is the sum of a direct pulse through the borehole fluid p i and of a formation response pulse p r given by…”

Section: Waveform Modelingmentioning

confidence: 99%

“…where X(w) is the Fourier transform of the source pulse x(t), V f is the sonic velocity in the fluid, k z is the along-axis wave number, and A(k z ,w) a function describing the response of the formation [Tsang and Rader, 1979;Kurkjian, 1985;Kurkjian and Chang, 1986]. The attenuation is introduced by using complex velocities:…”

Section: Waveform Modelingmentioning

confidence: 99%

“…The source function is simplified by an exponentially decaying sinusoid. Tsang and Rader [1979] and Kurkjian and Chang [1986] use Hankel functions to give the expressions for A in the case of monopole and dipole source, respectively, and the branch cut integration is detailed by Tsang and Rader [1979] and Kurkjian [1985].…”

Section: Waveform Modelingmentioning

confidence: 99%

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Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

2002

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[1] The Mallik 2L-38 research well was drilled to 1150 m under the Mackenzie Delta, Canada, and penetrated a subpermafrost interval where methane hydrate occupies up to 80% of the pore space. A suite of high-quality downhole logs was acquired to measure in situ the physical properties of these hydrate-bearing sediments. Similar to other hydrate deposits, resistivity and compressional and shear sonic velocity data increase with higher hydrate saturation owing to electrical insulation of the pore space and stiffening of the sediment framework. In addition, sonic waveforms show strong amplitude losses of both compressional and shear waves in intervals where methane hydrate is observed. We use monopole and dipole waveforms to estimate compressional and shear attenuation. Comparing with hydrate saturation values derived from the resistivity log, we observe a linear increase in both attenuation measurements with increasing hydrate saturation, which is not intuitive for stiffening sediments. Numerical modeling of the waveforms allows us to reproduce the recorded waveforms and illustrate these results. We also use a model for wave propagation in frozen porous media to explain qualitatively the loss of sonic waveform amplitude in hydratebearing sediments. We suggest that this model can be improved and extended, allowing hydrate saturation to be quantified from attenuation measurements in similar environments and providing new insight into how hydrate and its sediment host interact.

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Section: Waveform Modelingmentioning

confidence: 99%

Section: Waveform Modelingmentioning

confidence: 99%

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Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

2002

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“…Because of the complexity of the wave equations involved, models of the acoustic logging problem almost always assume radial symmetry and depth independent elastic properties (e.g .. Biot, 1952; White and Zechman,196B; Tsang and Rader, 1979;Cheng and Toksoz, 19B1). This type of analysis is certainly acceptable for identifying the major "permanent address: P.O.Boz 567, West Falmouth.…”

Section: Introductionmentioning

confidence: 99%

Finite-difference synthetic acoustic logs

1986

International Journal of Rock Mechanics and Mining Sciences &am

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Synthetic seismograms of elastic wave propagation in a fluid-filled borehole were generated using both the finite difference technique and the discrete wavenumber summation technique. The latter is known to be accurate for both body and surface (gUided) waves. The finite difference grid has absorbing boundaries on two sides and axes of symmetry on the remaining two sides. A grid size no less than 10 points per wavelength was used. The far absorbing boundary was located at a distance of five to 10 radii from the borehole. Two types of solid-liquid interfaces were investigated: 1) a velocity gradient using the heterogeneous formulation, and 2) a sharp boundary using a second order Taylor expansion of the displacements. The results from the finite difference modeling were compared with the synthetic seismograms generated by the discrete wavenumber summation method. No comparison the heterogeneous formulation and the discrete wavenumber method has been made. The second order approximation to the solid-liquid interface produced seismograms that compared 'well with the discrete wavenumber seismograms. A detailed comparison between the seismograms generated by the two methods showed that the body waves (refracted P and S waves) are identical. while the gUided waves showed a slight difference in both phase and amplitude. These differences are believed to be due to the approximations introduced in the fluid-solid interface, the absorbing boundary at the edge of the grid, and the grid and time step sizes involved. Owing. to the fact that they are interface waves, the gulded waves, especially the higher modes, are much more sensitive to the above mentioned approximations.

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“…In this paper, on the basis of published work by various researchers [4][5][6][7][8][9][10], we use an acoustic logging transmission network model [11,12] to perform calculations and discuss the effects of the acoustic-electric conversion of the transducer on the acoustic logging signals.…”

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confidence: 99%

Effects of electric-acoustic and acoustic-electric conversions of transducers on acoustic logging signal

Xie

Tian

et al. 2012

Chin. Sci. Bull.

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Based on an acoustic logging transmission network and the engineering pattern of a sliding wave in acoustic logging, analysis and calculations have been performed in a study of the effects of the electric-acoustic and acoustic-electric conversions of the transducers on the acoustic logging signal. The results show that acoustic-electric conversion through the transducer can cause not only a serious disturbance in the signal amplitude, but also an apparent transmission delay. For engineering applications, the amplitude variation and transmission delay must be accounted for in a practical analysis of the acoustic logging signal in rocks. The results also show that with enhanced understanding and proper justification, the error caused by the acoustic-electric conversion can be significantly reduced in evaluation of the cement bond quality of a cased well, and the accuracy of rock porosity calculated using the measured acoustic velocity can be increased. The amplitude information of an acoustic signal and its propagation speed in rocks has been widely used in the petroleum industry. For example, in acoustic logging, the applications and developments include: (1) use of the amplitudes of the head wave and the later arrivals of the acoustic logging signal to evaluate the cement bond quality of cased wells; (2) use of the P-wave velocity of the acoustic signal to calculate rock porosity by the Wyllie formula [1] and to calibrate seismic data; (3) use of the P-and S-wave velocities to calculate the mechanical parameters of rock (such as Young's modulus and the Poisson ratio); (4) use of the acoustic logging data to construct the atoms in a seismic wavelet dictionary. In seismic exploration, the applications and developments include: (1) use of the P-wave amplitude information to perform amplitude variation with offset (AVO) analysis to search for oil reservoirs; and (2) use of the P-wave speed of a seismic wavelet to perform timedepth conversion for inversion of the rock structure in the Earth's interior. Accurate measurements of both the amplitude and the propagation speed of the acoustic signal in rocks are therefore very important for correct inversions and interpretations of acoustic logging and seismic data. In the research conducted by many geophysicists to accurately obtain the amplitude, propagation speed, phase and frequency spectrum of an acoustic signal propagating in rock, considerable attention has been paid to the effects of the rock properties on the measured acoustic signals. Cong et al.[2] performed experimental studies on the effects of the rock porosity on acoustic resonance spectroscopy. Fa et al. [3,4] calculated the effects of rock anisotropy on the propagation speed and reflection amplitude of a seismic wavelet. The purpose of these studies is to obtain accurate infor-

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Numerical evaluation of the transient acoustic waveform due to a point source in a fluid‐filled borehole

Cited by 212 publications

References 9 publications

Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

Finite-difference synthetic acoustic logs

Effects of electric-acoustic and acoustic-electric conversions of transducers on acoustic logging signal

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