南海深水区中尺度现象对多波地震勘探影响之研究

Mesoscale phenomena have been considered to be the main contribution of the temporal and spatial variation in the actual ocean environment. It directly results in the changing of the sound velocity profile structures. Thus the research on the effect of mesoscale phenomena on seismic wave propagation in deep water areas of the South China Sea plays an important role in improving the quality of multi-wave exploration. In this proposal first-order stress-velocity equations are derived for inhomogeneous water, including current effects. The first-order perfectly matched layers (PML) introduced by Kormann is generalize to include shear wave for modeling the propagation of seismic wave in water and elastic layers. The physical model of deep water areas of the South China Sea including mesoscale phenomena is established. The effect of mesoscale phenomena on amplitude and traveltime of P wave and S wave is investigated. Using pre-stack reverse time depth migration, we examine the effect of mesoscale phenomena on seismic imaging. Based on calculation of mesoscale phenomena with different intensity, the internal relation between the perturbation of seismic imaging and key physical parameters of mesoscale phenomena is revealed. Finally, the calibration method for the perturbation of seismic imaging caused by mesoscale phenomena is proposed. This proposal could provide theoretical support for data processing of multi-wave exploration in deep water areas of the South China Sea.

海洋中尺度现象，是引起实际海洋环境空间分布变化的主要因素，它直接影响到声速剖面结构特征。因此，研究中尺度现象对地震波传播的影响对提高南海深水区多波地震勘探精度具有十分重要的意义。本项目拟推导出适用于非均匀运动水体的一阶应力-速度方程组，并将Kormann提出的一阶完全匹配层（PML）算法推广到弹性介质，模拟水层以及海底弹性基底中的地震波传播。建立含中尺度现象的南海深水区物理模型，研究中尺度现象对海底接收的纵波和转换横波走时、振幅的影响。通过弹性波逆时深度偏移，研究海洋中尺度现象对弹性波偏移成像的影响。通过不同强度的内波、中尺度涡和海洋锋的计算，揭示出弹性波偏移成像误差与中尺度现象主要物理参数的内在联系，提出误差校正方法，为深水区多波地震勘探的数据处理提供理论指导。

提高复杂海洋环境下地震成像精度是深水区油气资源勘探的关键问题。本项目首先推导了适用于非均匀运动水体的一阶应力-速度方程组，给出了适用于水体和海底弹性介质的一阶完全匹配层（PML）边界条件，建立了深水区多波地震正演模拟系统。基于实测的南海深水区温盐数据，建立南海深水区物理模型，并在此基础之上，研究中尺度现象对弹性波场、以及海底接收的纵波和转换横波走时、振幅的影响。通过弹性波深度偏移成像，研究海洋中尺度现象对纵横波成像深度的影响，给出了中尺度现象引起的纵横波成像深度误差与传播时间、地层波速的关系式。最后，研究了中尺度涡引起的时间扰动随旋涡表面最大流速和有效半径的变化规律，揭示出弹性波偏移成像误差与中尺度涡有效涡强度的内在联系，提出中尺度涡引起的时间误差和深度误差的校正方法，为深水区多波地震勘探的数据处理提供理论指导。