超声波检测套管井水泥环缺陷仿真模拟

Simulation of cement defect in casing well with ultrasonic

针对固井过程中由于顶替效率过低、气窜等原因造成水泥环局部缺失的现象,基于超声脉冲反射原理,运用有限元方法建立不同大小、不同方位的水泥环缺失模型,数值模拟了超声波在套管井多层介质中的传播规律。通过提取回波首波幅度、首波的接收时间,对回波进行频谱分析,对比了胶结良好和水泥环缺失两种情况下的时域特征和频域特征。在研究不同方位缺失影响时,引入了缺陷敏感频率,发现在一定激发频率下,有缺陷的位置上敏感频率会出现极大值,不同方位的缺陷有不同的敏感频率,而且区别较为显著,以此可以判断缺失方位。

For studying the patial defect phenomenon of cement sheath caused by low displacement efficiency and gas channeling in the cementing process, the finite element method is used to establish different size and different orientation models of cement sheath defect and to simulate the propagation rules of ultrasound in multilayer medium of casing well. By extracting the echo amplitude and the headwave time in different directions and by analyzing ccho frequency spectrum, the time domain and frequency domain characteristics of the models are compared effectively. For determining the cement sheath defect at different orientations, the defect’s sensitive frequency（Dev） is introduced, and it is found that a great value of Dev in the defective position appears under a certain excitation frequency and the defects in different directions show different Devs, which can determine the orientation of the defect.