井间地震波场数值模拟和弹性波逆时偏移*

该文利用时域有限差分法数值模拟了井间地震波场,探讨了井间地震弹性波逆时偏移成像的若干问题。基于多层地层模型,根据数值模拟的人工合成阵列信号,对比了3种不同成像条件下井间地震逆时偏移的结果,并对不同倾角的狭缝模型进行逆时偏移成像。通过对不同成像条件的对比,发现震源归一化成像条件能够对检波器一端的地质结构成像进行增强。由于纵波和横波在折射过程中的相互转换,利用这种透射转换波和反射波,对于任意倾角的狭缝都可获得清晰的弹性波逆时偏移结果。特别是对于夹角为90°的垂直狭缝模型,如果仅提取反射波只能获得狭缝两端点的成像结果,而保留下纵波和横波在透射狭缝时产生的转换波可应用于高倾角反射体的偏移成像。

Numerical simulation of cross-well seismic wave field and elastic wave reverse time migration

In this paper, the cross-well seismic wave fields are simulated by the finite-difference time-domain method. And some problems in the imaging of cross-well seismic wave reverse time migration are discussed. Based on the multi-layer formation model and the synthetic array signals, the results of cross-well seismic reverse time migration under three different imaging conditions are compared. Reverse time migration imaging is carried out for fracture models with different dip angles. From the comparison between different imaging conditions, it is found that the source normalized imaging conditions can enhance the geological structure imaging at one end of the geophone. Due to the mutual conversion of P-wave and S-wave in the process of refraction, clear reverse time migration results of elastic wave can be obtained for any inclined slit by using the transmitted converted waves and reflected waves. Especially for the vertical fracture model with an angle of 90 degrees, if the reflected waves are extracted, only the imaging results of the two ends of the can be obtained, while the converted P and S waves generated during the transmission through the fracture can be applied to the migration imaging of high dip reflector.