适合起伏地表的炮点波场延拓正演模拟

Forward simulation of wavefield continuation at shot point appropriate for fluctuate surface

本文提出一种波形相对保真、运算效率更高的适合起伏地表的炮点波场延拓正演模拟方法,炮点波场按波的传播方向延拓,运算中使用了适合起伏地表的波场延拓起始面技术,波形相对保真,无需做横向叠加。其基本思路是:①根据惠更斯原理,按地震波的传播方向,将炮点波场从起伏地表炮点深度处开始逐层向下延拓,与界面反射系数相关,直至最深处;②逐层向上延拓,并加上向下延拓时产生的新反射波炮点波场,直至起伏地表排列处,将炮点波场逐个与其检波点波场相关,经反傅里叶变换后可以获得一个排列的地震合成记录;③重复上述步骤,得到整个工区的所有炮记录。用文中方法对山峰体模型和高速透镜体模型的理论试算表明,地震合成记录的反射波和绕射波十分清晰,没有多次波、直达波和其他干扰波,信噪比高,所有炮记录的叠前深度偏移成像结果与地质模型完全吻合。

The paper presented a forward simulation method for wavefield continuation at shot point,which is characteristics of relative hi-fi waveform,high computational efficiency and appropriate for fluctuate surface:the wavefield at shot point makes continuation along the wave propagating direction;the technique of initial plane of wavefield continuation appropriate for fluctuate surface is used in computation,which is characterized by relative hi-fi waveform and without lateral stack.The basic ideas are as follows:①based on Huygen's principle,the downward continuation of wavefiled at shot point is started from the shot-point depth on fluctuate surface along the propagating direction of seismic wave layer by layer,the continued wavefield correlates with coefficient of interface and until to the deepest position;②upward continuation is carried out layer by layer,adds new wavefield of reflection at shot point produced at stage of downward continuation,and until to the position of spread on fluctuate surface,then correlation of wavefield at shot point with that at receiver point is carried out one by one,in which the synthetic seismogram of a spread is got after inverse Fourier Transform;③repeating abovementioned steps,the all shot record in the whole work area is got.The theoretical model test of steep mountain body and high-velocity lenticular body by using the method showed that the reflections and diffractions on the synthetic seismogram are very clear and without multiple,direct wave and other interference waves,the S/N is higher and prestack depth migration imaging of all shot records completely coincides with geologic model.