利用零偏VSP资料求取横波速度 ——以七北101井VSP测井为例

:通过分析零偏VSP记录中的一组强波的时距曲线和极化方向，证明这组强波是纵波震源所激发的纵波在地表附近强阻抗差界面上产生的下行直达转换横波。由于这种波具有纯横波的运动学特点，因此可以拾取其初至时间，计算横波的层速度，进一步求取纵横波速度比及泊松比。分析了这些物性参数在判别岩性和气层的应用效果。

Calculation of S-wave velocity from zero-offset VSP data: Taking the VSP data of well 101 in Qibei survey area as an example

This paper discusses how to estimate velocities of S-waves traveled in strata using VSP data.The analysis of the time-distance curve and polarization direction for a group of strong waves on zero-offset VSP data reveals that they are downgoing direct S-waves converted at the strong impedance contrast interface near earth surface from P-waves excited by P-wave source.The S-waves have the kinematics of pure shear waves,thus we can pick their first arrivals,calculate their interval velocities,and further compute the ratio of P-wave velocity to S-wave velocity and poisson's ratio.The applications of these petrophysical properties in identification of lithology and gas-bearing layers were also described.