基于能量范数成像条件的一阶方程弹性波逆时偏移

Reverse time migration using energy norm imaging condition based on first-order elastic wave equation

弹性波逆时偏移能够充分利用地震记录数据,更接近于波传播规律,得到的多分量偏移成像结果能提供更准确、丰富的地下地质信息,但由于偏移过程中正反传波场各种分量混杂,基于逆时偏移框架直接采用常规互相关成像条件会造成偏移结果中干扰噪声较多。为此,提出了用一阶速度应力弹性波方程能量范数成像条件逆时偏移方法压制成像噪声。分析了能量范数成像条件噪声压制原理。数值求解时,方程其它变量求解过程不变,引入中间应变分量,构造应变时间偏导项,应变分量与其它分量同步更新,实现能量范数成像条件偏移。多个模型数据测试结果验证了该方法压制背向散射噪声的有效性。复杂模型试算结果表明:本文方法对比垂直、水平分量互相关成像条件偏移低频噪声得到压制,对比纵横波波场分离偏移则无需考虑转换波极性反转问题。

The elastic reverse time migration(RTM)can make full use of seismic data and produce multi-component migration imaging results,thereby producing more geological information.However,conventional cross-correlation imaging conditions in the inverse time migration framework can cause more noise interferences to the migration results,due to the complex components in both forward and reverse wavefields.This study developed an RTM using the norm-imaging condition based on the first-order velocity-stress elastic wave equation.We first analyzed the principle of noise suppression based on the energy norm imaging condition and then derived the form of the imaging condition applied to the first-order velocity stress equation.During wave propagation,the strain component was introduced to construct the strain time partial derivative,and the strain component was updated synchronously with other components to realize the migration based on the energy norm imaging condition.The results showed that the proposed RTM can suppress backscattering noise compared with the method based on cross-correlation imaging condition,and there is no need to consider the polarity reversal of conversion wave,compared with the method based on wavefield separation.