基于改进的时移成像条件的保幅叠前深度偏移研究

Amplitude-preserved prestack depth migration based on modified time-lapse imaging condition

(1.同济大学海洋与地球科学学院,上海200092;2.中国石油化工股份有限公司胜利油田分公司物探研究院,山东东营257022；3.中国石油化工股份有限公司石油物探技术研究院，江苏南京210014)

^{School of Ocean and Earth Sciences,Tongji University,Shanghai 200092,China}

为了实现保幅叠前深度偏移,在波动方程保幅偏移方程的基础上详细推导了傅里叶有限差分波动方程延拓算子。由于波动方程叠前深度偏移技术的应用受计算效率的制约，因而,提出了利用大延拓步长进行波场延拓,在延拓层位,利用相关成像条件进行成像。对延拓步长层间的层位,结合含有绕射聚焦项的时移映射函数,对延拓层位上未基于频率叠加的上、下波场的互相关值进行傅里叶逆变换,并结合零时刻成像原理求出延拓层间的成像值。脉冲响应测试和Marmousi模型试算表明该方法可以实现保幅叠前深度偏移,并可以大幅度提高偏移成像效率。

The amplitude-preserved Fourier finite-difference wave equation operator is derived in detail for amplitude-preserved prestack depth migration.Prestack depth migration based on wave equation is restrained for its poor computation efficiency.So,wavefield extrapolation based on coarse-step was proposed,by this method,imaging on the extrapolation layer is calculated based on correlation imaging condition,imaging between the extrapolation layers is based on modified time-lapse imaging interpolation.That is by using time lag mapping function considering diffraction focusing function,inverse Fourier transform is done to the cross-correlation of upgoing and downgoing wavefield of extrapolation layer without frequency stack,and imaging is obtained based on zero time imging principle.The impulse response and numerical Marmousi model test show that the method can realize amplitude-preserved prestack depth migration and largely improve the computational efficiency