摘要
The exchange of fluid between fractures and rock matrix is considered to be a main factor influencing the calculated anisotropic elastic properties. Theoretical study shows that the fracture scales also have the same impact on it. To identify the multi-scale fracture, numerical analysis was introduced to analyze the variation of velocity and attenuation with the changes of the multi-scale fracture, frequency and fluid factor based on the equivalent medium model. The results show that the elastic parameters are frequency dependent, including the attenuation. This frequency dependence is related to the fracture scale and fluid properties of rocks. Within the various fracture scales with different velocity dispersion, the shear wave splitting depends on the frequency, and the scale of fracture is the leading factor, small scale is sensitive to high frequency, while low frequency to large scale. In the seismic frequency band, Thomsen parameters decreased with increasing frequency as well as the increasing of the fracture scale. Thus, seismic data may be an indication to distinguish the anisotropy caused by the fracture or micro-crack and also used to distinguish fracture scale.
