3D3C陆地反射PS转换波CMP成像影响因素分析

三维三分量(3D3C)陆地反射PS转换波共中心点(CMP)叠加成像方法,虽然抽道集简单,但是对实际资料处理结果往往不理想.尤其当反射界面为三维倾斜界面时,其成像质量较差.本文提出有三个主要因素影响其成像质量:第一,转换点离散.运用实例计算得出,转换点离散度随着纵横波速度比、偏移距和界面倾角的增大而增大.相同界面倾角,不同测线方位的转换点离散度不同,视倾角的绝对值越大离散度也越大;第二,道集内静校正量差异增大.CMP道集中,由于转换点离散使得转换点横向跨度较大,经倾斜界面反射转换的S波出射到近地表地层时的角度差异也较大,导致静校突出;第三,加大动校叠加复杂性.三维倾斜界面PS波CMP道集近炮检距时距方程可表示为双曲形式,但是曲线的顶点位置和动校速度同时随测线方位变化,使得CMP道集同相轴很难校平,动校叠加过程很复杂.

Influencing factors analysis of imaging for 3D3C land reflection by CMP of PS-converted wave

Trace gather sorting is very simple using the imaging method of three-dimensional three-component (3D3C) land reflection by common-midpoint (CMP) of PS-converted wave. But the result of processing actual data is usually very bad with the method. Especially, the quality of the image is poor when the reflection interface is three-dimensional dipping interface. We present three major points for the reason why the image quality is so poor: First, conversion-point is discrete on CMP gathers. We reach a conclusion by calculating some example data. The discreteness of the conversion-point is greater with the increasing of P-S wave velocity ratio, offset and dip angle. And it is different in different survey directions from the same dipping interface. Its value is greater with the increase of the absolute value of apparent angle. Second, the static of PS-converted wave is much greater on CMP gathers. The horizontal span of the receiver is large because of the CMP trace gather sorting. And the difference of the incident angle of the S wave to near surface is also larger when the reflection interface is three-dimensional dipping interface. So, the static is serious with the CMP gather of PS wave. Third, the complexity of NMO stacking is increased. The time-distance curve of PS wave on three dimensional dipping interface can be written as a hyperbolic form when the x is near. But both the vertex position of the hyperbolic and the NMO velocity change with the survey line directions. This makes it difficult to flatten the events of CMP gather and the process of NMO stack very complex.