双层套管井中单极子声波测井的响应特征

目前，在深井中采用多层套管实现层间封隔的方法已非常普遍，对多层套管井固井质量评价的需求越来越迫切，目前还未有针对外层套管与地层之间水泥胶结评价的有效手段.本文利用三维有限差分仿真了单极声波测井在双层套管井中的响应特征，探讨了利用套管波幅度和斯通利波频散特征识别外层套管与地层之间环空是否胶结水泥的可行性.数值计算结果显示在两层套管之间胶结水泥时，套管波的幅度或衰减对外层套管和地层之间是否胶结水泥非常敏感，外层环空若充填水泥则全波中的套管波幅度降低明显；在两层套管之间充填泥浆时，全波波形中首先到达的套管波幅度较大，其对外层套管的胶结状况不再敏感，通过对接收的阵列波形做频率-慢度相关分析发现，在外层套管和地层之间胶结水泥后，井孔内接收到的低于10 kHz的外斯通利波慢度明显增大，仿真波形的处理结果与解析计算的斯通利波的频散曲线吻合较好，进一步验证了可尝试利用内层环空激发的外斯通利波判断外层套管与地层之间是否胶结水泥.

Response characteristics of monopole sonic log in double casing strings

In the well plug-and-abandonment processes, an evaluation of the well's hydraulic barriers is one of the key technologies at the time of operation and the logging data can provide this important information. The existing logging tools for cement bonding quality evaluation are mainly designed for single casing geometries and they may not be able to distinguish the bonding condition between the out casing and formation. In this paper, the response characteristics of monopole array acoustic logging in double casing strings are simulated by three-dimensional finite difference method, and the feasibility of identifying whether the annulus between outer casing and formation is cemented is discussed by using the dispersion characteristics of the casing waves and the Stoneley waves. The numerical results show that while the Annulus between inner and outer casing is filled with cement, the amplitude of the first arriving casing wave is closely associated with the acoustic impedance of the medium filled in the Annulus between the outer casing and formation. If the annulus between inner casing and outer casing is filled with mud, the first arriving casing wave cannot distinguish mud from cement in the Annulus between outer casing and formation. But the amplitude and slowness of the Stoneley waves (denoted by inner Stoneley wave and outer Stoneley wave) show significant difference caused by acoustic impedence contrast of the annulus between outer casing and formation. Compared with mud in the annulus between out casing and formation, both the inner Stoneley-wave amplitude and the outer Stoneley-wave slowness increase substantially with cement in the annulus. The dispersion curves of inner and outer Stoneley waves extracted from simulated waveforms agree with the analytical results. The numerical modeling results provide a theoretical basis for using the casing-mud interaction modes to evaluate the cement bonding in double casing strings and the sonic full-wave logging has great potential in cement bonding evaluation.