Monitoring the shear modulus of formations around boreholes is of interest for various applications, ranging from near-surface investigation to reservoir monitoring. Downhole logging tools and borehole seismic are common techniques applied to measure and characterize formation properties. These methods rely on transmitted and reflected waves to retrieve the rock properties. Wave modes traveling along the interface between the well and the formation, such as tube waves, are often considered as noise. However, tube waves are less attenuated than body waves and contain information about the shear modulus of the formation surrounding the well. Hence, a potential use of this interface wave is of interest. Because tube-wave properties depend on several parameters, e.g., well geometry, highly accurate measurements should be performed for use in inferring rock properties. We have studied the feasibility of tube-wave measurements as a monitoring method. Different experiments are conducted using a hydrophone array in two boreholes, with depths of 30 and 95 m. The experiments are used to investigate how accurately the tube-wave velocity can be measured and which parameters have the most impact on the measurements. Our results suggest that it is hard to estimate the absolute shear modulus of the geologic formation using tube-wave velocities only. However, it seems feasible to use them to monitor changes in the shear modulus, depending on the borehole setup and the geologic formation. Tube-wave monitoring can be used as a first step to determine the depth along the well where changes occur before more accurate measurements are performed in a second step.

中文翻译：

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管波监测作为检测井眼周围剪切模量变化的一种方法：一个案例研究

监测钻孔周围地层的剪切模量对于从近地表勘测到储层监测的各种应用都是有意义的。井下测井工具和井下地震是用于测量和表征地层特性的常用技术。这些方法依靠透射波和反射波来检索岩石特性。沿井与地层之间的界面传播的波模式（例如管波）通常被认为是噪声。但是，管波的衰减比体波衰减小，并且包含有关井周围地层剪切模量的信息。因此，该界面波的潜在用途引起了人们的兴趣。由于管波特性取决于几个参数，例如井的几何形状，为了推断岩石的性质，应该进行高精度的测量。我们已经研究了将管波测量作为一种监测方法的可行性。使用水听器阵列在两个钻孔中进行了不同的实验，两个钻孔的深度分别为30 m和95 m。实验用于研究如何精确测量管波速度，以及哪些参数对测量的影响最大。我们的结果表明，仅使用管波速度很难估算地质构造的绝对剪切模量。但是，根据钻孔设置和地质构造，使用它们来监测剪切模量的变化似乎是可行的。