常规地震解释中波阻抗差异引起的构造假象研究

The Research of Pseudo Structure in Typical Interpretation for Impedance Difference

因埋藏深度、构造复杂、岩性异常体或地层接触关系复杂多变等原因,地层横向速度变化很大,构造形态发生畸变,对地震解释造成一定的影响。为了落实异常体对下伏地层的影响程度,采用波动方程正演模拟技术,设计不同波阻抗组合、岩性组合及异常体大小、形态变化的两类正演模型并模拟其地震响应特征。其波场快照能直观地展现地震波在某种波阻抗组合和岩性组合情况下的传播过程,有利于分析异常体对下伏地层成像的影响。模拟结果表明,利用正演模拟方法能及时发现异常体因其厚度及波阻抗差异引起的假断层和假构造现象,可有效指导解释人员建立正确的解释方案,消除对地震解释的影响。

For burial depth, complex structure, lithological anomalous body or complex formation contact rela- tion, the horizontal velocities change rapidly and the structure g characters deform. They have some effect on the structure interpretation. To study the effects to the underlying formation of local anomalous bodies, the wave equa- tion forward model is used to analyze the seismic response characteristics of different theoretical models according to different impedance association, lithological association and the size and shape of anomalous bodies. The propaga- tion process of seismic wave can be shown illustratively on snapshots, which is beneficial to analyze the effect of anomalous bodies on underlying formation imaging. The forward modeling shows that the unclear reflection of bot- tom boundary in anomalous body is for the small impedance difference between the anomalous body and the under- lying formation. The discontinuity reflectance signature of underlying continuous formation will become more obvi- ous when the anomalous bodies is thick, resulting in forming pseudo structures. The modeling results show that the forward modeling based on wave equation can timely find out the pseudo fault and structures caused by the differ- ence of anomalous bodies thickness and its wave impedances, and effectively guide interpreters building the correct interpretation plan and eliminate the impact on interpretation eventually.