基于不同震源机制的黏弹各向异性微地震波场模拟

Micro-seismic forward modeling in viscoelastic anisotropic media based on different focal mechanisms

考虑到介质的复杂性和微地震震源的多样性,基于黏弹各向异性波动方程和地震矩张量,通过交错网格有限差分方法,进行了微地震波场正演模拟,并分析了微地震信号的传播特性和偏振特性。研究表明:1双力偶成分(DC)源产生的能量主要分布在V_y分量的qS波上,而各向同性(ISO)源和补偿线性矢量极偶成分(CLVD)源产生的能量主要分布在V_x和V_z分量的qP和qS波上,且CLVD源相对于ISO源能激发出更强的qS波;2介质的黏弹性会导致振幅和波形改变,对qS波更是如此。对于各向异性介质,在三种基础源的模拟结果中都能观测到剪切波分裂现象,在黏弹性情况下剪切波分裂更为明显;3当存在CLVD源时,在不同的入射角范围内各类介质的偏振角出现突变现象,可以通过引起偏振角突变的入射角范围识别VTI介质。此外,黏弹性对微地震信号的偏振特征影响较小。

In view of complexity of real media and variation of micro-seismic source,micro-seismic wave field is simulated based on seismic moment tensor and viscoelastic anisotropic wave equation by staggered-grid finite difference method,and then micro-seismic signal propagation characteristics and polarization characteristics are studied.The following conclusions are obtained: The energy of DC source simulations mainly focuses on qS-wave in the Vycomponent; on the contrary,the energy of ISO and CLVD source simulations mainly focuses on both qP-wave and qS-wave in Vxand Vzcomponents,and the CLVD source would generate stronger qS-wave than ISO source in Vxcomponent; The viscoelasticity of media would result in amplitude attenuation and waveform characteristics change,especially for qS-wave; shear wave splitting can be observed in three kinds of source simulations especially in viscoelastic media; VTI media can be distinguished from other types of media with CLVD source because its curve sudden change between polarizing angle and incident angle is different.In terms of micro-seismic signal polarization characteristics,the viscoelasticity impact is very small. © 2017, Editorial Department OIL GEOPHYSICAL PROSPECTING. All right reserved.