Second-Order Approximation of the Seismic Reflection Coefficient in Thin Interbeds
Second-Order Approximation of the Seismic Reflection Coefficient in Thin Interbeds
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DOI：
10.3390/en13061465
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发表时间：
2020-03
期刊：
影响因子：
3.2
通讯作者：
Zhen Yang;Jun Lu
中科院分区：
文献类型：
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作者：
Zhen Yang;Jun Lu
我国岩性地层油气藏多为薄互层，薄互层地震响应研究是岩性油气藏勘探的重要组成部分。但目前勘探地震学对薄互层地震反射系数的研究还比较薄弱，导致后续与薄互层相关的振幅随炮检距变化（AVO）解释缺乏理论依据。针对这一问题，本文提出了薄层和薄互层中地震反射系数的二阶近似方程。在层状介质中阻抗差较小的假设下，对肯内特提出的反射系数计算方法进行了物理意义更为明显的二阶近似。然后，通过对单层理论模型的检验，证实了PP波（反射纵波）的二阶近似方程在小于30°入射角时是准确的，PS波（转换横波）的二阶近似方程在更宽入射角时是准确的。最后，基于单薄层方程，建立了薄互层中地震反射系数的近似方程，并通过理论模型验证了其有效性。我们的方程将适用于PP和PS波反射系数的计算薄夹层的内部多次波是难以抑制和传输损耗是难以精确补偿。这为提高岩性油气藏地震预测精度奠定了理论基础。
As most of the lithostratigraphic reservoirs in China are thin interbeds, the study of seismic responses in thin interbeds is an integral part of lithologic reservoir exploration. However, at present, the research on seismic reflection coefficients of thin interbeds in exploration seismology is still weak, which leads to the lack of theoretical basis for the subsequent interpretation of amplitude variation with offset (AVO) related to thin interbed. To solve this problem, in this paper, we proposed second-order approximate equations of the seismic reflection coefficients in thin-bed and thin-interbed layers. Under the assumption of a small impedance contrast in layered media, we made a second-order approximation with a more evident physical meaning to the reflection coefficient calculation method proposed by Kennett. Then, based on the test of the single thin-layer theoretical model, it was confirmed that the second-order approximation equation of the PP-wave (reflected compressional wave) is accurate at incident angles less than 30°, and that of the PS-wave (converted shear wave) is accurate at wider incident angles. Finally, based on the single-thin-bed equations, the approximate equations of seismic reflection coefficients in thin interbeds were established, the validity of which was verified by the theoretical model. Our equations will be applicable to the calculation of PP- and PS-wave reflection coefficients in thin interbeds where internal multiples are difficult to suppress and transmission loss is hard to accurately compensate. This lays a theoretical foundation for improving the seismic prediction accuracy of lithologic reservoirs.