不同裂缝密度的物理模型研究

A physicalmodel study of different crack densities

1. 石油大学物探重点实验室,北京100083;2. 国家地震局地球物理研究所,北京100081

1. The University of Petroleum, Beijing l00083,China;2. Institute of Geophysics, China Seismological Bureau, Beijing l00083, China

在实验室内利用人工灌注控制裂缝密度的方法,研究了裂缝密度和形态对地震波的影响。裂缝模型是用环氧树脂作基质,用面积相同的硅橡胶薄片模拟裂缝。结果表明,在不同密度定向排列裂缝介质中,不同程度地观测到了横波分裂现象,在这种裂缝介质中,快横波速度不变,慢横波速度随着裂缝密度的增加而减小,横波分裂的时差主要取决于慢横波的时间。在低裂缝密度(小于6%)时,裂缝密度和横波快慢波速度的关系与理论预测相符。仔细分析慢横波波场时可发现当裂缝形态变化和密度变大时会引起极性相反现象,而裂缝形态对速度的影响小于对衰减的影响,这就提供又一种描述裂缝结构和性质的手段。

The effect of crack density and structure on the propagation of seismic shear wave is studied through laboratory experiments with instillation controlled crack densities.The physicalmodels that are used in the experiments aremade of epoxy resin with silicon rubber slims embedded in them to simulate the cracks.The experiments show that shear waves are split in some degree in the oriented crackmodels of different crack densities.In thesemodels, fast shear wave velocity is stable, whereas slow shear wave velocity decreases with the crack density increases.The time difference of shear wave splitting is dependent on velocity of the slow shear wave. In case of low crack density (less than 6%), the relationship between crack densities and velocities of the fast and slow shear waves agrees well with theoretical prediction.The analysis of the slow shear wave field reveals that the polarization is reversed when the crack shape varies and the density is high, but the effect of the crack structure on velocity is less than that on attenuation.Thus provides another kind ofmethod to describe the crack structure and its characteristics.