Based on the wave equations in cylindrically layered structures and boundary conditions, the frequency equation for axisymmetric guided waves and the expression for sound fields in a cased borehole excited by a monop...Based on the wave equations in cylindrically layered structures and boundary conditions, the frequency equation for axisymmetric guided waves and the expression for sound fields in a cased borehole excited by a monopole or multipole source have been derived. The synthetic full waveforms excited by the monopole and dipole source are simulated using a real axis integration and FFT method. According to the axisymmetric guided wave modes, the synthetic full waveforms and the effects of the interface conditions on the sound field in a cased borehole have been analyzed and studied respectively. Numerical results indicate that it may be difficult to distinguish well bonded, poorly bonded or unbonded intermediate layer between the steel pipe and formation if only using a monopole source or dipole source. To properly estimate the case boundary conditions, a combination of monopole source logging with dipole source logging is suggested.展开更多
High cement bond quality is required to keep an oil well from hydraulic commu- nication between zones. In the cement bond evaluation, the ultrasonic echo method is widely used for its capability of channeling azimuth ...High cement bond quality is required to keep an oil well from hydraulic commu- nication between zones. In the cement bond evaluation, the ultrasonic echo method is widely used for its capability of channeling azimuth detection. Full waveforms reflected from the cased hole are simulated for different bonding conditions by the generalized transfer matrix method. Because of the high acoustic impedance of casing, the amplitudes of the reflected waves from the cement and the formation are small and cannot easily be used to evaluate the cementing condition. The wave that can propagate into the cement and the formation through the casing concentrates closely on the casing resonant frequency. To reduce the amplitude of the reflected wave from the casing inner surface and highlight the part of the reflected wave which carries the cementing quality information, the reflected full wave is filtered according to the casing resonant frequency. There are several wave packets in the filtered waveform. When the amplitude of the second wave packet is low, the cement bonds well with the casing, otherwise poorly. A low amplitude third wave packet is an indication of a good bond of the cement with the formation, otherwise poor. To reveal the sensitivity of the reflection wave amplitudes to the incident angle, reflected full waveform is modeled when an acoustic beam with finite width is incident on the casing. It is shown that the bond evaluation method based on filtered wave packets is valid for incident angle less than 5 degrees.展开更多
The displacement and stress as well as the dispersion equation for the guided waves of antiplane shear (SH) modes in a bonded plate are presented explicitly. The spring model is used to account for the interface rigid...The displacement and stress as well as the dispersion equation for the guided waves of antiplane shear (SH) modes in a bonded plate are presented explicitly. The spring model is used to account for the interface rigidity between the layers of the bonded plate. It is found that the dispersion equation is composed of the terms pertinent with the welded and the cracked or slip boundary conditions with the compliance sT of the spring model as the sum-coefficients. Numerical results for an adhesive plate of aluminum and steel whose wave velocities are very close to each other of equal thickness indicate that the modes of odd order are more sensitive than the even ones to the variations of the bond quality, and so are the higher modes than the lower ones for this special layered plate. The phenomena of the cut-off frequency-shift and the phase velocity decrease resulting from the degradation of the bond quality are found to the modes of odd order, which may be used to evaluate the bond states of the adhesive plate. Numerical results for an adhesive plate of rubber and steel whose wave velocities are very different to each other of equal thickness are presented and discussed as well.展开更多
基金The project is supported by the National Natural Science Foundation of China and Natural ScienceFoundation of Jiangsu Province
文摘Based on the wave equations in cylindrically layered structures and boundary conditions, the frequency equation for axisymmetric guided waves and the expression for sound fields in a cased borehole excited by a monopole or multipole source have been derived. The synthetic full waveforms excited by the monopole and dipole source are simulated using a real axis integration and FFT method. According to the axisymmetric guided wave modes, the synthetic full waveforms and the effects of the interface conditions on the sound field in a cased borehole have been analyzed and studied respectively. Numerical results indicate that it may be difficult to distinguish well bonded, poorly bonded or unbonded intermediate layer between the steel pipe and formation if only using a monopole source or dipole source. To properly estimate the case boundary conditions, a combination of monopole source logging with dipole source logging is suggested.
基金supported by the National Natural Science Foundation of China(41174110,41204092)
文摘High cement bond quality is required to keep an oil well from hydraulic commu- nication between zones. In the cement bond evaluation, the ultrasonic echo method is widely used for its capability of channeling azimuth detection. Full waveforms reflected from the cased hole are simulated for different bonding conditions by the generalized transfer matrix method. Because of the high acoustic impedance of casing, the amplitudes of the reflected waves from the cement and the formation are small and cannot easily be used to evaluate the cementing condition. The wave that can propagate into the cement and the formation through the casing concentrates closely on the casing resonant frequency. To reduce the amplitude of the reflected wave from the casing inner surface and highlight the part of the reflected wave which carries the cementing quality information, the reflected full wave is filtered according to the casing resonant frequency. There are several wave packets in the filtered waveform. When the amplitude of the second wave packet is low, the cement bonds well with the casing, otherwise poorly. A low amplitude third wave packet is an indication of a good bond of the cement with the formation, otherwise poor. To reveal the sensitivity of the reflection wave amplitudes to the incident angle, reflected full waveform is modeled when an acoustic beam with finite width is incident on the casing. It is shown that the bond evaluation method based on filtered wave packets is valid for incident angle less than 5 degrees.
基金National Natural Science Foundation of China! (No. 19974063).
文摘The displacement and stress as well as the dispersion equation for the guided waves of antiplane shear (SH) modes in a bonded plate are presented explicitly. The spring model is used to account for the interface rigidity between the layers of the bonded plate. It is found that the dispersion equation is composed of the terms pertinent with the welded and the cracked or slip boundary conditions with the compliance sT of the spring model as the sum-coefficients. Numerical results for an adhesive plate of aluminum and steel whose wave velocities are very close to each other of equal thickness indicate that the modes of odd order are more sensitive than the even ones to the variations of the bond quality, and so are the higher modes than the lower ones for this special layered plate. The phenomena of the cut-off frequency-shift and the phase velocity decrease resulting from the degradation of the bond quality are found to the modes of odd order, which may be used to evaluate the bond states of the adhesive plate. Numerical results for an adhesive plate of rubber and steel whose wave velocities are very different to each other of equal thickness are presented and discussed as well.
