套管中模式波的响应特征*

在固井质量评价中主要利用套管中模式波的幅度或衰减变化反映水泥的胶结状况,不同测井仪器在套管中激发的模式波的类型不同,研究套管中各模式波的传播特征和影响因素可充分挖掘测量数据的潜在应用价值。CBL和SBT等测井仪器在套管中主要激发拉伸波,类同于平板中的零阶对称Lamb波,水泥环封隔测井仪器的斜入射模式在套管中主要激发套管弯曲波,类同于平板中的零阶反对称Lamb波,垂直入射模式激发套管共振波,类同于平板中的高阶对称Lamb波。该文重点分析了这些模式波的衰减特征及其对微环的响应,套管弯曲波在套后耦合轻质水泥时对微环不敏感,但在套后耦合常规水泥或重水泥时,其衰减明显高于胶结良好的状况;拉伸波对微环的存在最为敏感;套管共振波对微环不敏感。

Response characteristics of the model waves in the casing

The amplitude or attenuation variation of the guided waves in the casing is mainly used to evaluate the cement bonding quality. The types of the guided waves excited by different logging tools may be different. Studying the propagation characteristics and influencing factors of the guided waves in the casing can fully explore the potential applications of measurement data. CBL and SBT logging instrument can generate the longitudinal wave in the casing, which is analogous to the zero order symmetric Lamb waves in the plate. The pitch-catch pattern of IBC tool with oblique incidence can stimulate flexural wave in the casing, which is analogous to the zero order anti-symmetric Lamb wave in the plate. The ultrasonic reflection pattern with vertical incidence can excite the casing resonance waves, which is analogous to the high order symmetric Lamb waves in the plate. This paper focuses on analyzing the attenuation characteristics of these mode waves and their response characteristics with micro-annulus model. The flexural wave is not sensitive to micro-annulus when the light cement is bonded behind casing. On the contrary, the flexural wave is sensitive to micro-annulus when the regular cement is bonded behind casing. The longitudinal wave is very sensitive to the presence of micro-annulus. Casing resonance waves are insensitive to micro-annulus.