混合法VSP共炮记录叠前深度偏移

VSP处理方法反演地下结构直接、精确，是寻找复杂构造的、隐蔽的油气藏的最重要的方法系列之一。文章提出的混合波场延拓法VSP共炮记录单程波动方程叠前深度偏移，就是一种VSP对复杂构造精确成像的方法。首先把波动方程分解为上行和下行单程波，把波动方程解析解法(傅氏变换法)和数值解法(有限差分法)相结合，提出VSP偏移的混合波场延拓法，以使波场延拓适应速度的纵横向变化；再结合VSP的特点，在波场外推过程中，当在某深度处继续下延波场时，把从上部延拓至此的波场加上此处埋置的检波器的记录结果作为此处的波场；借鉴地面地震叠前深度偏移原理，提出了可适应速度纵横向变化的、可对复杂构造精确成像的单程波动方程混合波场延拓VSP共炮记录叠前深度偏移方法。纵、横向变速介质的数值模拟结果显示，该方法精确、有效。

VSP Common Shot Pre-stack Depth Migration with Hybrid Method

As a direct and accurate inversion method of subsurface structures, VSP processing is one of the most important approaches to identify complex subtle oil and gas reservoirs. In order to accurately image complex subsurface structures, one-way-wave-equation-based hybrid wave field extrapolation method is used to perform VSP common shot pre-stack depth migration. The wave equation is decomposed into upgoing and downgoing one-way waves, and the hybrid wave field extrapolation method of VSP migration is presented based on the combination of the analytical solution (Fourier transform method) and numerical solution (finite difference approach) of wave equation, so as to make the wave field extrapolation adapting to the arbitrary vertical and lateral variations of velocity. In combination with the characteristics of VSP, when the wave field needs to be further extended downward from a certain depth in the process of wave field extrapolation, the wave field at this depth is the sum of the waves that have been extrapolated from the above and the records of geophones that are positioned at this depth. Based on the surface seismic pre-stack depth migration theories, the one-way-wave-equation-based hybrid wave field extrapolation method is presented for VSP common shot pre-stack depth migration. This method can adapt to the arbitrary vertical and lateral variations of velocity and can accurately image complex structures. This method is proved to be accurate and effective by Numerical simulation displays of media with variable vertical and lateral velocities.