Huang Xingxing, Di Bangrang, Wei Jianxin, Shuai Da, He Lingyi
IEEE Trans Ultrason Ferroelectr Freq Control. 2021 Mar;68(3):742-752. doi: 10.1109/TUFFC.2020.3011958. Epub 2021 Feb 25.
For oil and gas seismic exploration, rock velocities are essential parameters to tease out reservoir properties from seismic data. The ultrasonic pulse transmission (UPT) method has been a gold standard to estimate reservoir rock velocities in the laboratory. Regarding the UPT method, accurate determination of the travel time of waves plays a significant role in robustly measuring rock velocities. One of the most conventional ways to obtain the travel time is through the arrival picking. However, unclear noise virtually exists preceding the arrival of S-wave interfering with this arrival picking, which, sometimes, can cause enormous errors to measured S-wave velocity. Herein, we develop a 2-D, three-component (2D-3C) finite-element modeling (FEM) algorithm aiming to interpret the noise by combining with UPT measurements. The proposed 2D-3C FEM not only can efficiently compute ultrasonic wavefield radiated by circular P- or S-wave transducers but also able to obtain synthetic waveforms in the testing of S-wave velocity where polarization directions of S-wave transducers are arranged as nonparallel. To analyze the simulated ultrasonic waveforms, we introduce frequently-used concepts of edge and direct plane waves to build elastodynamic models of the ultrasonic wavefield. Then, we compare numerical results with experimental measurements. Our 2D-3C FEM results show good agreement with experimental waveforms both in P- and S-wave velocity testings. Whereafter, we pinpoint constitutions of the noise preceding the arrival of S-wave. Comparison of numerical and experimental waveforms suggests that the edge P-wave with its reflected and converted modes partially contributes to this noise, while the rest part of the noise may stem from the effects of the compressional dipole, the couplant smeared between a transducer and a sample, and inherently parasitic longitudinal vibrations of S-wave transducers. The interpretations on this noise have the potential to benefit future design of more effective S-wave transducers.
对于石油和天然气地震勘探而言，岩石速度是从地震数据中推断储层特性的关键参数。超声脉冲传输（UPT）方法一直是实验室中估算储层岩石速度的黄金标准。关于UPT方法，准确测定波的传播时间对于可靠测量岩石速度起着重要作用。获取传播时间最传统的方法之一是通过波至拾取。然而，在S波到达之前实际上存在不清晰的噪声，干扰了这种波至拾取，有时会给测量的S波速度带来巨大误差。在此，我们开发了一种二维三分量（2D - 3C）有限元建模（FEM）算法，旨在结合UPT测量来解释这种噪声。所提出的2D - 3C FEM不仅能够高效计算圆形P波或S波换能器辐射的超声波场，还能够在S波换能器极化方向非平行排列的S波速度测试中获得合成波形。为了分析模拟的超声波形，我们引入常用的边缘波和直达平面波概念来建立超声波场的弹性动力学模型。然后，我们将数值结果与实验测量结果进行比较。我们的2D - 3C FEM结果在P波和S波速度测试中均与实验波形显示出良好的一致性。此后，我们确定了S波到达之前噪声的组成。数值波形与实验波形的比较表明，边缘P波及其反射和转换模式部分导致了这种噪声，而其余部分的噪声可能源于压缩偶极子的影响、换能器与样品之间涂抹的耦合剂以及S波换能器固有的寄生纵向振动。对这种噪声的解释有可能为未来设计更有效的S波换能器提供帮助。
