岩石横波分裂和各向异性的实验室观测

LABORATORY OBSERVATION FOR SHEAR WAVE SPLITTING AND ANISOTROPY IN ROCKS

地矿部石油物探研究所,南京210014

Research Institute of Geophysical Prospecting for Petroleum, MGMR, Nanjing 210014

本文介绍了实验室内观测岩石样品的横波速度各向异性的两种方法.尼科耳棱镜法可以清楚地看到各向异性,岩石中的横波分裂现象;旋转法能较精确地测定出岩样的各向异性程度.通过对干燥与水饱和条件下岩样三个方向上横波速度的测试,得到两个偏振横波的最大速度差为258m/s(灰岩),348m/s(砂岩),376m/s(泥岩).对应的最大各向异性度为11.1％.11.0％,13.9％(均在水饱和条件下).观测结果表明,一些含泥量较高的砂岩样品具有横向各向同性的特性,而砂岩样品则呈现出与层理面有关的速度各向异性.实验还表明微裂隙在液体饱和时对速度各向异性有较大的影响.

This paper recommands two laboratory methods to observe the phenomena of shear wave splitting and anisotropy in rocks. The former is observable with Nicol's sprism method and the measure of anisotropy can be estimated by using the Rotatory method.The S-wave velocties of 7 rock samples in three mutural orthogonal directions are observed in dry and water-saturated conditions. The maximal velocity differences in two polarized S-waves are obtained to 258m/s (limestone), 348m/s(sand) and 376m/s(mudstone) , corresponding to maximal anisotropics 11.1%, 11.0% and 13.9%, in the water-satured condition. As a consequence of the observation, Sand rock samples with higher mud content arc found to behave transversely isotropically and the others exhibit bedding-dependent transversely anisotropy in velocity. Other result shows that minor cracks may have great influence on velocity anisotropy in case of water-saturated samples.