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我们提出了一种适于不规则层状介质的偏移方法,这种介质中,一阶速度不连续将速度恒定或缓慢变化的区域分开。该方法利用逆时方法由表层向下逐层地偏移地震资料。作为特定层偏移的一部分,其底部边界依据偏移信号的能量确定,并沿它采集地震剖面。这个新的地震剖面作为下一层偏移时的边界条件。对每层重复这一过程,最后由各层的图象组成最终剖面。层剥离偏移分为三步:(1)层定义;(2)波场外推和成象;(3)确定边界。当采用逆时外推时,这种偏移方法类似于根据成象条件确定基准面。这种逆时偏移方法采用了标量波动方程的显式4阶时间、10阶空间有限差分近似。层剥离逆时偏移的优点有:(1)保留了逆时方法处理地层间的剧烈速度差和陡倾构造的特点;(2)占用更少的计算机内存,且节省高速层内计算时间;(3)可对图象进行解释性控制。通过合成CMP资料实例对叠后层剥离逆时偏移进行了说明。叠前偏移则用合成数据集和实际资料加以阐述,实际资料为横穿加利福尼亚中部Santa Maria盆地和Hosgri断裂的海上地震反射剖面。
We propose a migration method suitable for irregularly layered media in which first-order velocity discontinuities separate areas of constant velocity or slowly varying velocity. The method uses the inverse time method to offset the seismic data layer by layer downward from the surface layer. As part of a particular layer offset, the bottom boundary is determined by the energy of the offset signal and the seismic profile is acquired along it. This new seismic section serves as the boundary condition for the next layer of offset. This process is repeated for each layer, and finally the final section is composed of the images of the layers. The layer exfoliation offset is divided into three steps: (1) layer definition; (2) wavefield extrapolation and imaging; (3) boundary determination. When using inverse time extrapolation, this offset method is similar to determining a datum based on imaging conditions. This inverse time migration method uses the explicit fourth-order time of the scalar wave equation and the finite-difference approximation of the tenth-order space. The advantages of layer delamination reverse time migration are: (1) preserving the reverse velocity method to deal with the characteristics of the intense velocity difference and steep structure between strata; (2) taking up less computer memory and saving high-speed intra-layer computing time ; (3) The image can be interpreted control. The anti-time migration of post-stack peel has been demonstrated by the synthesis of CMP data examples. The prestack migration is illustrated by the synthetic dataset and actual data, the actual data being the seismic reflection profile across the sea from the Santa Maria Basin and the Hosgri Fault in central California.