用VSP数据中下行P-SV转换横波求取横波速度

探讨了用零偏移距三分量VSP数据中的下行P－SV转换横波,求取厚度相当于VSP采集点距的地层横波速度。从井下检波器方位校正得到横向垂直分量,对其二维谱中各类波的能量和特点进行分析,通过二维滤波得到信噪比较高的下行转换横波,选取振幅较强的同相轴提取波至时间,获取了横波速率及泊松比。结果表明,即使是零偏移距VSP数据,只要其上有明显可见的转换横波,也能以采集点距的量级计算横波层速度。

Estimation of velocities of shear-waves using downward converted P-SV waves in VSP data

This paper discusses how to estimate velocities of shear waves traveled in strata using downward converted P-SV waves in VSP data. The thickness of the strata approximately equals to the distance between two adjacent receivers. After adjustment of azimuths for borehole receivers, the TV components of shear waves were determined. The energy and characteristics of different kinds of waves in the 2-D spectra of the resulting components were inferred. Downward converted P-SV waves of high S/N ratio are determined through 2-D filtering. By picking up the travel times for events of strong amplitudes, we computed velocities of shear waves and poissons' ratio. The results indicate that even if the VSP data is zero offset, it is still possible to estimate velocities of shear waves in strata with thickness approximately equaling to the distance between two adjacent receivers as long as the converted P-SV waves is observable.