双平方根叠前深度偏移的广义高阶屏方法

叠前深度偏移技术既可在炮点-接收点域实现,也可在共中心点一炮检距域实现。前人将裂步延拓算子推广到共中心点一炮检距域相移法双平方根叠前偏移中。在波场向下延拓的每一步长内,仅通过一次时移量来校正常速相移延拓产生的误差,得出了简单、高效的裂步双平方根叠前深度偏移方法,但精度较低。本文基于波场延拓的非稳态相移公式,通过引入参考速度,并对双平方根项中的两个平方根项作泰勒级数展开,经过适当的数学推导,得出了共中心点-炮检距域波场延拓的双平方根非稳态相移新的高阶屏近似公式。该公式可直接在共中心点-炮检距域高效地延拓叠前波场。通过增加屏的阶数,提高了剧烈横向变速条件下叠前深度偏移的精度。它是裂步双平方根叠前深度偏移方法的推广。理论模型和实际资料的试算结果表明,本文方法是有效而实用的。

Generalized high-order screen method for pre-stack depth migration by double-square-root

Pre-stack depth migration technique can be realized either in shotpoint receiver domain or in CMP offs et domain.The predecessors popularized split step extrapolation operator into DSR pre stack migration based on phase shift in CMP offset domain.The simple a nd high efficient split-step DSR pre-stack depth migration has been resulted from correction for errors produced by phase shift extrapolation in constant ve locity using time shift quality only once within each step length of downward c ontinued wave field,but this method has a poor precision. Based on non station ary phase shift formula for wave field extrapolation and through introducing re ference velocity,the paper deduced a new high order screen approximate formula conducted wave field continuation in CMP offset domain,using Taylor's series ex tension for two square roots in DSR and suitable mathematical process.The formul a can directly conducted continuation to pre stack wave field in CMP-offset n high efficiency.Through increasing order of screen,the precision of pre stack depth migration in a condition of strong l ateral changes in velocity has been improved.The method is extension of pre sta ck depth migration by split step DSR.The test results from theoretical model an d real data showed that the method is effective and practical.