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Leaky modes and the first arrivals in cased boreholes with poorly bonded conditions

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Science China(Physics,Mechanics & Astronomy) 2016年第2期59卷 49-56页

作者： XiuMei Zhang XiuMing Wang HaiLan Zhang State Key Laboratory of Acoustics Institute of Acoustics Chinese Academy of Sciences

The generation mechanism of the first arrivals in the cased boreholes for the poorly bonded conditions is investigated. Based on the analyses of the Riemann surface structure of the characteristic function, the dispersion features, excitation spectra and contributions of modes excited in the cased boreholes with different cementing types are studied. The phase velocity dispersion studies of leaky modes show that high-order modes form "plateau" regions with one approximate velocity denoted by v separated by their cutoff frequencies, in which the phase velocity changes little with a considerable frequency range, while the group velocity keeps a relatively constant high value. Usually, the operation frequency range of a specific cementing evaluation acoustic logging tool is covered by such a "plateau" region. Mode excitation and contribution analyses show that the first arrivals in the cased boreholes for the poorly bonded conditions are the contributions from leaky modes, where the traveling velocity of the first arrivals processed by slowness time coherence(STC) method is equal to the approximated velocity v. Analyses on generation of leaky modes in the cased boreholes supplement the understanding of the generation mechanism of the first arrivals.

关键词： leaky modes cased borehole dispersion curves cement bonding conditions

An acoustic-wave theory for casing bond evaluation using viscoelastic slip boundary modeling

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Science China Earth Sciences 2018年第8期61卷 1057-1064页

作者： Xiaoming TANG Can JIANG YuANDa SU Xuelian CHEN School of Geosciences China University of Petroleum

Slip boundary condition is commonly utilized to model elastic wave propagation through layered earth media. The same approach is used here to characterize acoustic wave propagation along a cased borehole with various cement bond conditions. By modeling the cement layer between casing and formation as a viscoelastic slip interface with complex coupling rigidity parameters, one can not only reduce the complexity in the classical elastic wave modeling of the problem, but also efficiently model various complicated wave phenomena that are difficult for the existing modeling. More specifically, the new theory can well describe the effect of the cement bond condition change and the location of the change(i.e., whether it is in the first interface between casing and cement, or the second interface between cement and formation) on the acoustic waves,demonstrating the good modeling capability and predicting power. Application of the theory to field data shows that the theory can correctly model the acoustic wave characteristics and interpret the cement bond condition, thus providing a useful fundament theory for casing bond evaluation using acoustic logging.

关键词： cased borehole Acoustic logging Cement evaluation Viscoelastic slip boundary Cement bond quality

Numerical study of dispersion characteristics of dipole flexural waves in a cased hole with different cement conditions

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Applied Geophysics 2022年第1期19卷 29-40,143,144页

作者： Yang Meng-En Lv Wei-Guo Wu Yang Cui Zhi-Wen Liu Jin-Xia College of Physics Jilin UniversityChangchun 130021China

Crossed-dipole acoustic logging technology is mainly used to measure shear wave and determine the anisotropy or fractures of formation in the fi eld of acoustic *** on the propagation characteristics of dipole flexural waves in cased holes,and the wavefi eld of fundamental flexural mode at three bonding conditions:good cement bonding,poorly bonded interface I,and poorly bonded interface *** dispersion curves of flexural waves are calculated,and the eff ects of cement parameters(elastic parameters and geometric dimensions)on dispersion curves are *** RAI method is used to calculate the dipole full waveforms in a cased hole with conventional or ultralight cement surrounded by a soft ***,the weighted spectral semblance is used to conduct the dispersion analysis of the full *** numerical results show that the cutoff frequency of flexural waves exceeds the frequency band of the current dipole logging tools in the well-bonded cased hole with conventional cement in soft ***,when ultralight cement is used,the cutoff frequency shifts toward low values,and the ultralight cement bonding is conducive to measuring flexural waves in soft *** interface I is poorly bonded,the cutoff frequency shifts toward low values,and the change is evident in soft *** cutoff frequency in the case of ultralight cement bonding is more evident than that of conventional cement *** only interface II is poorly bonded,regardless of the cement used,the cutoff frequencies are all below 2 *** dipole full-wave analysis of diff erent bonding conditions further illustrates that the dispersion characteristics of flexural waves are sensitive to the cement bonding quality of cased holes.

关键词： Soft formation cased borehole flexural wave ultralight cement dispersion analysis cement bonding