一种改进的观测系统双聚焦成像分析方法及应用

Improved dual-focus imaging analysis method for seismic geometry and its applications

基于偏移成像分辨率对观测系统进行量化评价,可在地震采集设计阶段为获得最佳成像效果提供保证。目前基于偏移成像分辨率的观测系统评价方法以双聚焦分析为主,其实现过程包含了波场延拓,因而导致双聚焦计算效率低。针对常规双聚焦分析方法效率低的缺点,对其进行如下改进:首先利用基于有限频斯奈尔定律和粘弹介质模型的高斯束正演得到目标点的CFP道集,再根据计算得到的旅行时,将CFP道集在目标点平面内进行检波点和炮点双聚焦,最后以聚焦主能量的宽度作为偏移成像分辨率对观测系统进行评价。改进后的双聚焦分析方法在射线追踪时考虑了菲涅尔带的影响,同时在动力学追踪时考虑了品质因子的影响以及子波主频的变化,因此计算结果更为真实可靠。该方法原理与叠前深度偏移一致,模型应用结果表明,该方法能够高效、可靠地针对地下某一目标点或目标层进行观测系统偏移成像分辨率量化评价,对于复杂地质目标的三维观测系统设计具有较高的应用价值。

Pre-stack depth migration is widely used in seismic data processing,and the result of such pre-stack migration is an important factor in seismic geometry evaluations.Generally,quantitative evaluations of the seismic geometry based on the resolution of migration imaging can guarantee optimal imaging results when designing seismic acquisition.At present,the seismic geometry evaluation method based on migration imaging resolution is primarily based on double-focus analysis,which requires wave field continuation in the realization,resulting in a low calculation efficiency.In this study,an improved Gaussian beam method is used to enhance the calculation efficiency of the conventional double-focus analysis.This method includes the following steps:a.using Gaussian beam propagation based on Snell s law with a limited frequency and a viscoelastic medium model to generate a CFP gather of a target point;b.implementing double-focus calculation in the plane centered on the target point according to the ray tracing result;and c.using the width of the main energy as the migration imaging resolution to evaluate the geometry.In this method,the effect of Fresnel zones is considered during ray tracing,and the effect of the Q factor is included in dynamic tracing,with a consideration of the frequency changing of wavelets;these improvements enhance the reliability of the calculation results.The principle of this method is consistent with pre-stack depth migration.Model application results indicate that this method can efficiently and reliably realize quantitative evaluations of the seismic geometry based on migration imaging resolution for a certain target point or target layer underground.Hence,this method presents high feasibility for the design of 3D seismic surveys of complex geological targets.