富有机质页岩微裂缝地震响应特征——以长宁示范区宁201井为例

Characteristic analysis of seismic response of micro-fractures in organic-rich shale: A case study of Well Ning201 in the Changning demonstration zone

高博乐 潘仁芳 金吉能 张鉴 赵圣贤 鄢杰

Bole Gao Renfang Pan Jineng Jin Jian Zhang Shengxian Zhao Jie Yan

为明确四川盆地长宁示范区龙马溪组-五峰组所发育的构造微裂缝密度和走向对富有机质页岩地震响应特征的影响，基于长宁示范区宁201井富有机质页岩钻井岩心资料建立地质模型，利用各向异性HTI介质计算地层反射系数，开展地震AVAZ正演模拟，结合研究区地震勘探资料对比验证，分析该井富有机质页岩微裂缝地震响应特征。研究表明：①富有机质页岩微裂缝的地震识别受到地震资料的入射角、方位角以及主频控制。地震资料入射角控制不同微裂缝密度对振幅造成的差异性，方位角控制微裂缝走向的识别能力，主频保证振幅不会受到地震波调谐效应的影响；②随着地震波传播方向与裂缝面法向的夹角增大，振幅值逐渐降低，在夹角为90°时达到最低。平行于微裂缝走向的方位角振幅不受微裂缝密度变化的影响，垂直于裂缝面方位角振幅随着微裂缝密度增大而增大。从富有机质页岩微裂缝识别的角度来看，研究结果可以为长宁示范区后期富有机质页岩微裂缝地震解释工作提供依据。

In order to make it clear how the density and strike of structural micro-fractures affect the seismic response features of organic-rich shale in Longmaxi-Wufeng Formations distributed in Changning demonstration zone, Sichuan Basin, we carried out the AVAZ forward modelling based on the geologic model built by the coring data obtained from the dril-ling of organic-rich shale in Well Ning201 and the reflection coefficients calculated by HTI anisotropy media.Meanwhile, the seismic response characteristics of the micro-fractures in organic-rich shales from the well were analyzed combined with the contrast and verification of seismic exploration data in the research area.The results show that:on the one hand, the seismic identification of micro-fractures in organic-rich shale is controlled by incident angle, azimuth and dominant frequency of the seismic data.The incident angles determine the amplitude difference caused by micro-fracture densities, the azimuth affects the identification of micro-fracture strikes, while the dominant frequency ensures that the tuning effect of seismic waves makes no difference to amplitude.On the other hand, the amplitude decreases as the included angle between propagation direction of the seismic wave and the normal direction of the fracture surface increases, and reaches the minimum when the included angle is 90°.The amplitude of azimuth parallel to the micro-fracture strike shall not be affected by the variation of micro-fracture density, while the amplitude of azimuth perpendicular to the fracture surface increases with the increase of micro-fracture density.Overall, the research results may serve as a basis for seismic interpretation later of micro-fractures in the organic-rich shale of Changning demonstration area.

10.11743/ogg20200216