页岩气地震勘探中页岩各向异性的地震模拟研究

A study on anisotropy of shale using seismic forward modeling in shale gas exploration

页岩的强各向异性特征挑战地震波传播数值模拟方法的精度极限,特别是易引起频散的高频波(>100Hz)传播的数值模拟.鉴于目前我国页岩气地震勘探主要以常规地震声波资料为主,本文首先介绍了一种VTI介质声波方程的任意偶数阶有限差分数值模拟方法,并讨论其稳定性条件和吸收边界条件.任意偶数阶的差分解可有效提高计算精度,压制数值频散噪声.针对页岩较强的各向异性特征,本文比较了不同模型的声波方程和VTI介质声波方程计算得到的地震响应.数值结果表明,各向异性对地震波的运动学(相位)和动力学(振幅)特性影响作用明显.因此,在页岩气地震勘探资料处理的各个环节必须充分考虑各向异性的影响,采取有别于常规油气勘探的处理流程和技术.

The accuracy of numerical methods is challenged by strong anisotropies shown by shale, especially for high-frequency components （〉100 H z）. Since the shale gas exploration still employs the acoustic seismic data, we first introduce an artificial even-order differential solution to VTI acoustic wave equation in the paper. The high-order solution can improve the computational accuracy and suppress numerical dispersion effectively. To show the effect of strong anisotropy of shale, we compare the seismic response of VTI acoustic wave equation with that of acoustic wave equation for different models. Numerical results show that anisotropy has large influences on the kinetics （phases） and the dynamics （amplitudes） of seismic waves. We conclude that the anisotropy must be considered when processing seismic data.