复杂断块地震绕射波分离及其影响因素

Separation of seismic diffraction wave and its influencing factors in complex fault blocks

地震绕射波是地下小尺度不连续构造体(如裂缝、断层、溶洞和地层尖灭等)的地震响应,绕射波的正确识别对复杂断块油气田勘探具有重要意义。平面波预测法通过倾角估计预测连续性较好的反射波同相轴而保留弯曲程度较大的不连续绕射波同相轴,从而分离地震反射和绕射波。在分析绕射波与反射波信号特征差异的基础上,研究了基于平面波预测的绕射波分离方法,分析了噪声和平面波预测滤波器参数对地震绕射波分离结果的影响。模拟数据和实际数据分析结果表明,噪声水平严重影响绕射波分离效果,噪音过大分离结果会不准确;平面波预测滤波器光滑半径偏小会引入噪音和假象,光滑半径偏大会导致绕射波分离不彻底,小断块地震绕射波响应难以分离。

The seismic diffraction wave is the seismic responses of subsurface small-scale discontinuous structures,such as fractures,faults,karst caves and pinching-out strata.Correct recognition of diffraction wave is of great significance for exploration of complex fault block oil and gas fields.Based on the characteristics of diffracted and reflected wave signals,a method for separation of diffracted wave is developed in this paper on the basis of plane wave prediction and the analysis of the influences of noise and plane wave prediction filter parameters.The plane wave prediction method can separate seismic reflections and diffraction waves by predicting the event of reflection wave with better continuity and retain the event of discontinuous diffraction wave with greater bending degree through dip estimation.The comparison of simulation data and actual data shows that noise seriously affects the separation of diffracted wave,and the separation result will be inaccurate if the noise is too large;the noise and false image will be introduced if the smooth radius of plane wave prediction filter is too small,and the separation of diffracted wave will not be complete if the smooth radius is too large,and the diffracted wave response of small fault block is difficult to be separated.