海水速度差异对中深层偏移成像的影响分析

本文针对深水环境下中深层偏移成像质量差的问题,考虑海水速度变化对中深层偏移成像质量的影响,从在大水深中加入深海声道模型入手,分析在偏移成像当中海水速度的不同选取对水平层状介质、倾斜层介质以及较复杂介质模型偏移成像质量的影响,通过在同一模型上改变海水速度进行成像,分析中深层成像效果可以得出:在大水深反射资料数据处理当中应该考虑真实的海水速度进行成像处理,否则会由于海水速度的选取不当而造成偏移成像层位的空间位置和中深层层位几何形态的变化.

Analysis of the influence of sea velocity difference on migration imaging in middle and deep layers

In view of the problem of the poor quality of migration imaging in deep water environments, by analyzing the influence of water velocity change on wave propagation and migration imaging results, this work attempted to explain the effect of water velocity change on the geometry change of spatial location of migration imaging in middle and deep layers. We established a horizontal layered model, tilt-layer dielectric as well as more complex medium models. We added the deep channel model in the large-depth water (water depth 3800 m), and obtained the wave field recorded in the deep channel model by using wave field numerical simulation. We used the seismic records obtained as the input of the wave field, selected the seawater speeds as constant v=1450 m·s^-1, v=1480 m·s^-1, v=1500 m·s^-1, v=1520 m·s^-1, v=1580 m·s^-1 in migration imaging separately. Then we compared the imaging results with the migration results adding deep-sea channel to explain the effect of different sea water velocities on deep migration imaging quality. By comparing migration results from the combination of the deep channel model, the horizontally layered model, tilt-layer dielectric as well as more complex medium model, we found when the migration velocity is taken as v=1450 m·s^-1, the offset profile obviously moves up compared with the true velocity model, the medium is vague beneath the ocean, and the imaging layer is distorted compared with the original velocity model, implying the smaller migration velocity can lead to imaging distortion. With the increasing of migration velocity, the phenomenon of moving up reduces gradually, and the imaging quality is improved. When the migration velocity is v=1520 m·s^-1, the migration results are in best agreement with the original model. When selected larger migration velocity is v=1580 m·s^-1, the offset profile obviously moves downward compared with the true velocity model, and migration imaging horizon is seriously distorted, not consistent with the actual one. Analysis also shows that the change of water speed not only influences the imaging layer in dislocation, but also influences spatial variation of the layer in the tilt-layer dielectric or more complex medium models. And smaller or larger migration velocity has a great impact on the bottom of the migration imaging. Seawater velocity change will affect the spatial location and geometry in the deep water environment, so the real velocity of sea water should be considered in a large depth of reflection seismic data processing, instead simply to select seawater velocity as a constant. Otherwise the improper selected sea water velocity will cause the geometry to change in spatial location of migration imaging layers and the middle and deep layers.