近地表层地震层析成像

Seismic tomography for near surface formation

在石油地震勘探中，由于近地表层速度和厚度的变化，使常规叠加剖面的同相轴受到破坏，常导致假构造现象。为此，本文提出一种近地表层地震层析成像法。该法利用地震勘探中单炮记录的初至波，求取连续变化的近地表层速度分布结构。计算中采用打靶法的两点射线追踪完成地面炮点与接收点间回折波的射线追踪，以形成迭代反演时用的线性方程组和相应的雅可比矩阵。然后，用收敛速度较快的最小二乘共轭梯度法（LSCG）求线性方程组的解。对理论模型的计算结果表明，该方法是可行的，是消除近地表层异常对地震资料影响的有效手段。

Variations in velocity and thickness of near surface formation distort the seismicevents of common stack section,resulting in false structures in oil exploration jthere fore,the seismic tomography for near surface formation is introduced to cope withthis problem. Continuous velocity variation in the near surface formation is known byusing first break of single-shot seismic records. The linear equations and the corre sponding Jacobi matrix which will be applied to iterative inversion are formed byrnaking the ray tracing of echo waves from the s0urce to receiver with the use of 'tar get method'. Then the linear equations are solved by using least-squared conjugategradient method that causes fast convergence. Theoretical computation shows thatthis feasible technique is an effectual means for removing the influence of near sur face abnorrnality on seismic data.