Steeply dipping structural target-oriented viscoacoustic least-squares reverse time migration and its application

陡倾角地质目标导向的黏声最小二乘逆时偏移方法与应用

Steeply dipping structural imaging is a significant challenge because surface geophones cannot obtain seismic primary reflection wave information from steeply dipping structures.Prismatic waves with a significant amount of steeply dipping information can be used to improve the imaging eff ect on steeply dipping structures.Subsurface attenuation leads to amplitude loss and phase distortion of seismic waves,and ignoring this attenuation during imaging can cause blurring of migration amplitudes.In this study,we proposed a steeply dipping structural target-oriented viscoacoustic least-squares reverse time migration(LSRTM)method with prismatic and primary waves as an objective function based on the viscous wave equation,while deriving Q-compensated wavefield propagation and joint operators of prismatic and primary waves and the Q-compensated demigration operator.Numerical examples on synthetic and field data verified the advantages of the proposed viscoacoustic LSRTM method of joint primary and prismatic waves over conventional viscoacoustic LSRTM and non-compensated LSRTM when using attenuating observed data.

因地表检波器难以接受到来自高陡构造的地震一次反射波信息,导致高陡构造地震成像极为困难,而棱柱波包含了大量的高陡构造信息,可以被用来改善高陡构造的成像效果。地下介质的黏弹性引起地震波的振幅衰减和相位频散,忽略其衰减的影响会导致地震成像振幅的模糊与深部能量的不足。提出了一种陡倾角地质目标导向的黏声最小二乘逆时偏移方法,该方法构建了一种新的一次波和棱柱波目标函数,并引入黏声波动方程,推导了一次波与棱柱波联合黏声最小二乘逆时偏移的波场延拓算子、伴随算子与梯度公式。通过典型洼陷模型与实际资料的数值试算证明了本文提出的陡倾角地质目标导向的黏声最小二乘逆时偏移方法相比于传统最小二乘逆时偏移方法,补偿了深部能量,能明显改善高陡构造的成像精度。