声体波与井眼周围in situ应力的关系
Relationship between acoustic body waves and in situ stresses around a borehole
摘要：
本文证明了在井眼穿透的均匀地层中传播的声体波有三种形态：简单波、双重波和共振波。这一事实与钻井后位于井周围的区域相对于原地应力状态所经历的修改有关。有过应力和欠应力的垂直圆柱形区域与“气泡形”的横截面，其中声体波被认为是反射。应力修正区的水平大小和形状取决于（K1+K2）/2 -（其中K1=SH/Sv（上覆压力）和K2=Sh/Sv -）的值，即取决于原地水平应力和该应力的各向异性。P和S双波速度的计算使我们能够评估这些应力修改区域的径向厚度。由于它们的值根据它们是由P波还是S波产生而不同，因此我们提出了基于它们的波长的解释。与其他工作的研究钻孔的原地应力的比较，使我们能够提出一种方法来评估水平应力及其各向异性，由于值（K1+K2）/2的估计。
英文摘要：
This paper shows that there are three types of shape of acoustic body waves propagating inside competent and homogeneous formations penetrated by a borehole : simple, double, and resonant. This fact is connected to the modifications undergone by the area located around a well after drilling in relation to in situ state of stress. There are overstressed and understressed vertical cylindrical zones with "bubble-shaped" cross-sections, in which acoustic body waves are supposed to reflect. The horizontal size and the shape of the stress modified areas depend on the values of (K1+K2)/2 - with K1=SH/Sv (the overburden pressure) and K2=Sh/Sv -, that is to say on the in situ horizontal stress and the anisotropy of this stress. The calculation of the velocities of the P and S double waves allows us to evaluate the radial thicknesses of these stress modified areas. As their values are different according to whether they result from P or S waves, we propose an explanation based on their wavelengths. The comparisons with other works on the in situ stress of the studied boreholes allow us to propose a method for evaluating the horizontal stress and its anisotropy, thanks to the estimation of the value (K1+K2)/2.
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