面向高陡构造的黏声棱柱波逆时偏移

Viscoacoustic reverse time migration of prismatic wave for steeply dipped structures

由于棱柱波往往包含了很多从一次波中无法获取的高陡构造信息,因此人们利用棱柱波改善高陡构造的照明和成像效果。但地下介质的黏弹性导致地震波能量衰减,引起地下反射界面的弱振幅成像和错位,严重影响棱柱波成像精度。为此,提出了一种面向高陡构造的黏声棱柱波RTM方法,推导了Q补偿的棱柱波正向延拓算子与逆时延拓的伴随算子,并沿着棱柱波的传播方向对Q衰减进行补偿。通过两个典型高陡构造模型试算证明:①黏声棱柱波RTM对高陡构造的成像精度高于黏声RTM、声波棱柱波RTM,成像结果的能量更均衡、分辨率更高,但会牺牲低角度构造的成像分辨率,因此需要联合黏声RTM和声波棱柱波RTM成像结果分析与解释地下构造;②黏声棱柱波RTM的计算时间约为黏声RTM的两倍,且因无法同时重构多个波场值,因此保存波场值需要大量的内存。

Prismatic waves carry more information about steeply dipped structures which primaries can not reflect.Therefore,prismatic waves are separately used in some migration methods to improve the illumination and imaging effect of steeply dipped structures.However,attenuation leads to amplitude loss and phase distortion of seismic waves,which seriously affects the accurate imaging of prismatic waves.A viscoacoustic RTM(reverse time migration)of prismatic waves is proposed for imaging steeply dipped structures.First a Q-compensated forward-propagating operator and a back-propagating adjoint operator are derived,and then Q attenuation is compensated along the propagating path of prismatic waves.Application on two typical steeply dipped structural models has proved that:(1)viscoacoustic RTM of prismatic wave can produce better images of steeply dipped structures with higher signalto-noise ratio,higher resolution and more balanced amplitude than conventional viscoacoustic RTM and acoustic RTM of prismactic wave,but losses some resolution of less dipped structures,therefore underground structures should be interpreted on viscoacoustic RTM and acoustic RTM of prismatic wave;(2)the time used for viscoacoustic RTM of prismatic wave is about 2 times that of viscoacoustic RTM,so the former needs a larger memory to save wavefields because it cannot reconstruct multiple wavefields at the same time.