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为了研究在不同储层厚度、储层下部地层反射界面不同深度情况下低频阴影的出现规律及特征,推导了一种三维弥散黏滞型波动方程的频率波数域波场延拓算法,设计了5个不同的含油气地质模型,对各个模型的地震响应进行了数值模拟,再利用广义S变换对模拟的剖面进行瞬时谱分解,分析了各模型的地震响应以及反射能量随频率的变化等.结果表明:储层低Q时、孔隙介质中流体的黏滞性和弥散性等物理性质明显,且油气层达到一定厚度时低频阴影更明显,它可出现在油气层下部的不同深度位置.在8~12 Hz时,油气层为强能量亮点,其下部显示有强能量的低频阴影,即“上强下强”特征,随着频率增高至16~60 Hz时,低频阴影逐渐减弱直至消失,而油气层的谱能量仍相对较强,即表现为“上强下弱”特征.
In order to study the rules and characteristics of low-frequency shadows at different reservoir depths and reflection depths of lower reservoir strata, a three-dimensional dispersive viscous wave equation wavefield continuation algorithm was derived. Different geologic models of oil and gas, numerical simulating the seismic response of each model, and then using the generalized S transform to transiently decompose the simulated profiles, analyzing the seismic response of each model and the change of the reflected energy with the frequency, etc. Results The results show that when the reservoir is low Q, the physical properties of the fluid such as viscosity and dispersion of the fluid in the pore medium are obvious, and the low frequency shadow is more obvious when the reservoir reaches a certain thickness, which may appear at different depth positions in the lower part of the reservoir. At ~ 12 Hz, the hydrocarbon zone is a bright spot of strong energy, with a low-frequency shadow of strong energy at the lower part of it, which is characterized by a “strong upper / lower” feature. As the frequency increases to 16-60 Hz, the low frequency shadow diminishes until disappears , While the spectral energy of the hydrocarbon layer is still relatively strong, that is, the performance of “strong and weak” feature.