绕射波与一次波联合黏声最小二乘逆时偏移
Joint Q-compensated least-squares reverse time migration using primary and diffracted waves
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摘要: 由于照明不足,小尺度断层和孔洞的成像是一个难题,地下衰减导致地震波振幅损失和相位畸变,在成像过程中忽略这种衰减会造成偏移振幅模糊。基于黏声最小二乘逆时偏移(QLSRTM)能够优化小尺度构造的成像,但这需要大量的迭代和计算成本。为了提高小尺度构造的成像效果,提出了一种充分使用绕射波的面向地质目标的的黏声LSRTM(J-QLSRTM)。在该方法中,构建了新的目标函数和梯度公式,并基于反演理论和伴随理论,推导了一次波和绕射波的Q补偿波场传播算子、Q补偿伴随算子和Q衰减反偏移算子。数值实例证明了J-QLSRTM比传统QLSRTM和声波J-LSRTM更有优势。Abstract: Poor illumination poses great challenges to the imaging of small-scale faults and pores.Subsurface attenuation leads to amplitude loss and phase distortion of seismic waves,and ignoring such attenuation during imaging will blur migration amplitudes.The Q-compensated least-squares reverse time migration (QLSRTM) can improve the imaging of these small-scale structures,but it requires a huge amount of iterations and computational cost.To improve the imaging effect of these small-scale structures,this study proposed a geological-target-oriented joint QLSRTM (J-QLSRTM) that fully utilizes diffracted waves.In this method,a new objective function and gradient formula was constructed.Moreover,the Q-compensated wavefield propagation operators,Q-compensated adjoint operators,and Q-attenuated demigration operators were derived for both primary and diffracted waves based on the inversion and adjoint theories.The numerical examples verified that the proposed J-QLSRTM is superior to the conventional QLSRTM and the acoustic J-LSRTM.
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