黏弹TTI介质旋转交错网格微地震波场模拟

Micro-seismic forward modeling in visco-elastic TTI media based on rotated staggered grid finite-difference method

基于Carcione提出的黏弹各向异性一阶速度—应力方程,采用旋转交错网格有限差分正演模拟方法,利用地震矩张量分解方法,将力源转化为速度源,并将其加载到旋转交错网格点上,实现了ISO、DC、CLVD等3种基础震源机制的旋转交错网格微地震震源加载,得到了微地震波场、微地震记录以及震源照明图,并分析了微地震信号的波场特征。结果表明:(1)微地震波场qP波和qSV波的能量相对关系以及qP波初动极性都仅仅受制于震源类型,与储层类型无关,可据此考察震源机制以及反演水力压裂裂缝参数;(2)微地震波场qP波旅行时仅仅受制于储层类型,与震源机制无关,可根据其同相轴曲率预测储层类型及性质;(3)微地震波场能量辐射方式受震源机制及储层类型等因素的影响,且存在较大差异,因此在实际观测系统布设时,要综合多方面先验信息,优选出主能量方位和有效辐射强度,从而设计出合理、高效的观测系统。

Based on visco-elastic anisotropic first-order velocity-stress wave equations presented by Carcione, micro-seismic wave fields, records, and illumination maps are acquired by the rotated staggered grid finite-difference forward modeling. With seismic moment tensor decomposition, the force source is turned into velocity source and then loaded on the rotated staggered grids for ISO, DC and CLVD three kinds of basis sources. Micro-seismic wave field characteristics are analyzed at the same time and the following observation are obtained: (1) The relative strength between qP-wave and qSV-wave, and the qP-wave first-motion focal mechanism solutions are only restricted to focal mechanism; this can be used to investigate different focal mechanism and inverse fracture parameters. (2) qP-wave arrival time is only subjected to reservoir property, so qP-wave event curvature can be set as prior information for reservoir prediction. (3) Both focal mechanisms and medium types will affect the micro-seismic event radiation pattern and there are many differences among different cases. So different prior information should be considered for energy orientation optimization in the geometry design process. © 2017, Editorial Department OIL GEOPHYSICAL PROSPECTING. All right reserved.