基于小振幅波方程的起伏海面构建及其对地震波场传播特性的影响

海面起伏状态对波场传播以及模型空间成像有着非常重要的影响, 在常规海洋地震数据采集和处理中, 都是将海面作为水平界面处理, 实际海洋地震数据采集中, 由于海水受风浪、洋流等的影响, 海面呈现高低起伏状态, 这样来自底层反射界面的反射波经过海水起伏界面反射后会引起波场的强烈散射, 从而造成地震记录反射波同相轴抖动和畸变, 最终影响成像效果.为了更加深入了解起伏海面存在对波场传播以及偏移成像的影响, 本文首先基于流体力学小振幅波方程, 从边界条件出发, 给出包含海浪谱信息的动态边界条件, 并在此基础上构建起伏海面速度模型; 然后在构建的起伏海面速度模型上通过冻结不同时刻海面开展波场传播特征分析, 研究起伏海面在不同冻结时刻下波场传播规律以及对反射地震记录和偏移成像的影响.研究结果表明, 不管是对于简单的层状介质模型还是海底较为复杂的大水深模型, 海面不同形态的起伏变化直接影响着波场记录以及波场快照形态, 同时会对偏移成像结果造成较大影响, 随着海水深度的增加, 该影响对于简单模型影响逐渐变小, 但对于复杂模型, 影响依然很严重.

Construction of undulating sea surface based on small amplitude wave equation and its impact on seismic wave field propagation characteristics

The state of sea surface fluctuation has a very important influence on wave field propagation and model space imaging. In conventional marine seismic data acquisition and processing, the sea surface is treated as a horizontal interface. In the actual acquisition of marine seismic data, due to the influence of wind, waves, ocean currents, etc., the sea surface presents a state of high and low fluctuations, so that the reflected waves from the bottom reflection interface will cause strong scattering of the wave field after being reflected by the seawater fluctuation interface, resulting in the reflection of seismic records. The jitter and distortion of the wave event axis will ultimately affect the imaging effect. In order to have a deeper understanding of the influence of the existence of undulating sea surface on wave field propagation and migration imaging, this paper firstly gives dynamic boundary conditions including wave spectrum information based on the small amplitude wave equation of hydrodynamics, starting from the boundary conditions, and then on this basis constructs the undulating sea surface velocity model. On the constructed model, the wave field propagation characteristics were analyzed by freezing the sea surface at different times, and the wave field propagation law of the undulating sea surface at different freezing times and the impact on reflection seismic records and migration imaging were studied. The research results show that, whether it is a simple layered medium model or a complex seabed model with a large water depth, the fluctuations of different sea surface shapes directly affect the wave field record and the wave field snapshot shape, and at the same time have a large impact on the migration imaging results. As the depth of seawater increases. The impact on the simple model gradually becomes smaller, but for the complex model, the effect is still very serious.