Schlumberger-Doll Research, One Hampshire Street, Cambridge, Massachusetts 02139, USA.
J Acoust Soc Am. 2011 Oct;130(4):1799-809. doi: 10.1121/1.3624819.
In the laboratory setup, a borehole traverses a dry sandstone formation, which is subjected to a controlled uniaxial stress in the direction perpendicular to the borehole axis. Measurements are made in a single loading-unloading stress cycle from zero to 10 MPa and then back down to zero stress. The applied stress and the presence of the borehole induce anisotropy in the bulk of the material and stress concentration around the borehole, both azimuthally and radially. Acoustic waves are generated and detected in the water-filled borehole, including compressional and shear headwaves, as well as modes of monopole, dipole, quadrupole, and higher order azimuthal symmetries. The linear and non-linear elastic parameters of the formation material are independently quantified, and utilized in conjunction with elastic theories to predict the characteristics of various borehole waves at zero and finite stress conditions. For example, an analytic theory is developed which is successfully used to estimate the changes of monopole tube mode at low frequency resulted from uniaxial stress, utilizing the measured material third order elasticity parameters. Comparisons between various measurements as well as that between experiments and theories are also presented.
在实验室设置中，一个钻孔穿过一个干燥的砂岩地层，该地层受到垂直于钻孔轴的单向应力的控制。在从 0 到 10 MPa 的单次加卸载应力循环中进行测量，然后再降至零应力。施加的应力和钻孔的存在会导致材料主体的各向异性和钻孔周围的应力集中，既有方位角的也有径向的。在充满水的钻孔中产生并检测到声波，包括压缩和剪切首波，以及单极、偶极、四极和更高阶方位对称性的模式。地层材料的线性和非线性弹性参数被独立地量化，并与弹性理论结合使用，以预测在零应力和有限应力条件下各种钻孔波的特征。例如，开发了一种解析理论，成功地利用测量的材料三阶弹性参数来估计单极管模式在单向应力下低频的变化。还展示了各种测量之间的比较以及实验和理论之间的比较。
