地震资料中的多尺度断裂与流体响应特征:数值模拟分析

Multi-scale fracture and fluid response characteristic in seismic data: Numerical simulation analysis

流体在断裂和岩石骨架间的交换被认为是影响岩石弹性参数各向异性的主要原因,理论研究表明断裂尺度同样对弹性参数的各向异性也有影响.为了说明两者对各向异性影响以实现多尺度断裂裂隙的识别,本文在等效介质模型的基础上,应用数值分析的方法研究速度和衰减(1/Q)随多尺度断裂、频率和流体因子变化规律.结果表明介质弹性参数是频率依赖的,并且参数中存在衰减项,而这种频率依赖性与介质物性参数中的断裂尺度及流体性质存在一定的联系;当断裂定向分布时,参数结果显示为各向异性;不同断裂尺度具有不同的波速频散特性,剪切波分裂程度依赖于频率,断裂尺度起着控制作用,高频时对小尺度的敏感,低频段对大尺度敏感.在地震频段Thomsen参数随着频率的增大而减小,随着断裂尺寸的增大而减小.因此地震数据可能区分断裂和微裂隙引起各向异性,从而可测量断裂尺度.

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.