含倾斜裂隙页岩介质地震波场传播特征研究

Research on seismic wavefield propagation characteristics in shale medium containing tilt fracture

研究裂隙页岩介质地震波场传播特征对于页岩气的勘探开发有重要意义。基于Hudson理论,Bond变换和Backus加权平均法,从介质参数和裂隙参数出发,推导了含倾斜裂隙页岩介质长波长等效弹性系数的计算公式,进而用高阶旋转网格有限差分法模拟了该介质的地震波场响应。数值模拟结果证明了该弹性系数计算方法的正确性和Backus加权平均法在计算薄互层介质等效弹性系数时的有效性,同时也证明了含倾斜裂隙页岩介质具有和TTI介质类似的倾角各向异性和方位各向异性特征。另外,对比裂隙饱含水和裂隙干燥(含气)时的模拟结果可知,裂隙含气时倾斜裂隙页岩介质具有更强的各向异性特征。

Based on the Hudson theory, Bond transfom and Backus-weighted average method, starting from medi um parameters and fracture parameters we derive a formula for calculating the long wavelength equivalent elastic coefficients of shale medium containing tilt fracture. We use highe-order rotated staggered grid finite difference method to simulate the seismic wave field response of this medium. The results prove that algorithm is accurate and the Backus weighted average method used in the calculating the eguivalent elastic coefficients of thin interbed medium is effective. At the same time,it proves that the shale medium containing tilt fracture has the same incli nation anisotropy and azimuthal anisotropy with the TTI media. Moreover, compared with the fluid filled fracture, the medium containing dry gas filled fracture has stronger anisotropy.