【摘要】 本文采用非均匀介质弹性波方程和声波方程的交错网格高阶有限差分法,对盐丘构造的理论模型和实际模型进行了正演模拟。采用单频谐波震源,通过弹性波方程数值模拟获得了弹性波的散度场、旋度场以及动能场和势能能流场,定量刻画了弹性波的能量特征及传播特征。通过弹性波方程和声波方程正演模拟的波场快照、单炮记录和零炮检距剖面记录,详细分析了复杂盐丘构造对地震波响应的影响。理论模型和实际模型数值模拟结果表明:①弹性波散度场、旋度场分别刻画了纵波波场能量特征和转换波波场能量特征,弹性波动能场和势能能流场则刻画了总场能量特征及其传播特征;与声波方程相比,弹性波方程数值模拟能够更加真实地表征复杂盐丘构造的波场特征及其响应。②盐体引起反射波、散射波场的能量聚焦效应明显,对透射波波前面的调制作用很大,且盐体产生的散射波、回转波以及高速盐体的能量屏蔽可形成能量阴影区,均影响了深部反射信号,降低了信噪比。③与基尔霍夫叠前时间偏移相比,基尔霍夫叠前深度偏移对大倾角盐侧和盐下成像较准确,但在盐内左、右侧的散射波成像质量不高,这是由于基尔霍夫积分偏移方法基于射线追踪所致,因此需要引入针对散射波的成像方法。更多还原

【Abstract】 In this paper the forward modeling for theoretical model and field model of the salt dome structure was conducted by using staggered grid high-order finite difference method of the inhomogeneous medium elastic wave equation and acoustic equation,by application of the single-frequency harmonic source and through the elastic wave equation numerical simulation,the divergence field,the vortex field,the kinetic energy field and the potential energy flow field for the elastic wave were acquired,the energy and the propagation characteristics of the elastic wave were quantitatively delineated.Through the wave field snapshot,single shot record and the zero-offset sections,the influence of the complicated salt dome structure to the seismic response were analyzed in detail.The numerical simulation results for the theoretical model and field model show the following conclusions:(1).The elastic wave divergence field and the vortex field respectively described the P-wave wave-field energy characteristics and the converted wave wave-field characteristics,the kinetic energy field and the potential energy flow field then delineated the total field energy characteristics and its propagation characteristics,compared with the acoustic wave equation,the elastic wave numerical simulation could more realistically characterized the total field energy characteristics and its responses,(2).The salt dome caused obvious energy focusing effects for the reflection wave-field and the scattered wave-field,it imposed great modulation on the wavefront of the transmitted wave,the reflection wave-field and the scattered wave-field which were caused by the salt dome,the energy shielding from the high velocity salt dome could form the energy shadow zone,and then the energy shadow zone may affect the deep reflection signal and lowed down the signal to noise ratio.(3).Compared with the Kirchhoff pre-stack time migration,the Kirchhoff pre-stack depth migration could more accurately image for the steep structures beside the salt dome and under the salt dome,however for the scattered wave from the left side and right side within the salt dome,the imaging quality is not great,this is due to the fact that the Kirchhoff integration migration method is based on the ray tracing algorithm,as a result the imaging method for the scattered wave should be developed.更多还原