基于有效邻域波场近似的起伏地表保幅高斯束偏移

随着我国陆上地震勘探向复杂地表探区的转移,高精度、适应性强的地震成像方法在地震资料的处理、解释及后续属性分析、储层预测中具有重要意义.本文基于有效邻域波场近似理论发展了一种成像精度更高且适用于复杂起伏地表条件的叠前保幅高斯束偏移方法.在传统水平地表高斯束偏移的基础上,本文根据中心射线附近有效邻域内高斯束表征的近似波场,导出了起伏地表条件下具有相对振幅保持的高斯束偏移公式,并给出了一种精度更高的旁轴射线传播角度计算方法.同现有的高斯束偏移方法相比,本文方法不仅考虑了起伏地表对高斯束走时的线性影响,而且首次引入了由地表高程差异和近地表速度变化引起的二次时差校正项和振幅校正项,使得成像结果更加准确可靠.两个典型模型算例验证了本文方法的正确性和有效性.

An amplitude-preserved Gaussian beam migration based on wave field approximation in effective vicinity under irregular topographical conditions

With the transformation of seismic exploration to regions with irregular topography areas in China, it is of vital importance for seismic processing, interpretation and subsequent seismic attribute analysis, reservoir prediction to develop a seismic migration method which is highly accurate and strongly robust. Based on the theory of wave field approximation in effective vicinity, we developed a more accurate method of pre-stack amplitude-preserved Gaussian beam migration, which is adaptable for irregular topographical conditions. On the basis of conventional Gaussian beam migration from horizontal surface and according to the approximate wave field expressed by Gaussian beam in the effective vicinity of central ray, we derived an amplitude-preserved Gaussian beam migration formula under irregular topographical conditions, and proposed a more accurate computation method for propagation angle of paraxial ray. Compared with existing methods for Gaussian beam migration, the proposed method in this paper not only considers the linear effects of irregular topography on travel time, but also first introduces the items of quadratic travel time correction and amplitude correction caused by the irregular topography and the variation in near-surface velocity, leading to more valid and accurate migration results than the previous methods. Two typical numerical examples verify the validity of the proposed method.