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叠前偏移结果的质量,对于速度场的误差是非常敏感的。但是,如果去进行偏移处理的仅仅是炮检距接近的那些道(共炮检距道),情形就不是这样。在这种情况下,速度的偏离在被偏移界面的传播时间中只引起很少的移动,而且不会影响偏移质量。这种时移与速度误差和炮检距的平方成正比。针对以上情况,建议执行下述偏移方案:对不同的共炮检距平面道或相邻共炮检距组分别进行偏移;对每个共中心点平面作为传播时间的函数进行剩余正常时差寻优,以确定偏移同相轴沿着它校准的最大相干轨迹t=t_0+Px~2;对剩余正常时差进行校正,叠加各种炮检距平面的偏移结果,从而得到最终的偏移结果。本偏移处理方案不仅注意到了偏移速度中的误差,而且还部分地校正了折射的影响。本文用实例表明,甚至在速度场存在着相当大的偏差情况下也能获得良好的偏移结果。
The quality of the prestack offset results is very sensitive to errors in the velocity field. However, this is not the case if the only ones that are offset are those that are close to the offset (total offset). In this case, the deviation in speed causes only a small amount of movement in the propagation time of the shifted interface without affecting the offset quality. This time-shift is proportional to the square of the velocity error and offset. In view of the above, it is suggested that the following offsetting schemes be implemented: offsetting different common offset planes or adjacent common offset sets individually; performing residual normal time differences as a function of propagation time for each common-center plane To find out the maximum coherence trajectory along which the offset-phase axis is calibrated t = t_0 + Px ~ 2; to correct the remaining normal time difference, and to add the offset results of various offset planes to get the final offset result. The offset processing scheme not only noticed the error in the offset velocity but also partially corrected the effect of refraction. In this paper, an example is given to show that good offset results can be obtained even with considerable deviations in the velocity field.