井壁边界条件和泥饼对声波全波波形的影响

针对测井中的泥饼问题,按修改的Biot孔隙地层的波动理论,计算了声波全波波形。通过分析讨论,指出井壁上的边界条件对声波影响很大,它引起的斯通利波幅度衰减变化,不代表地层渗透率的变化。当泥饼层薄时,仍可用斯通利波幅度衰减估算地层渗透率,但要作一些必要的校正;当泥饼层较厚时,用斯通利波幅度衰减估算的地层渗透率及提取的横波时差是错误的结果。高频伪瑞利波艾雷相(低速)也是地层渗透率很好的指示器,但要考虑环境条件的影响。利用低频伪瑞利波(高速),能很好地估算原状地层的横波衰减。

Effects of Condition in the Vicinity of the Borehole and Mud Cakes on Full-Wave Acoustic Log.

In view of mud cakes problem in well logging acoustic full waveform is computed in light of the updated Biot theory. It is pointed out in this paper that condition in the vicinity of the borehole has a great effect on acoustic wave. The attenuation of the amplitude of Stoneley wave caused by the boundary condition doesn't represent the variation of formation permeability. When mud cake is thin, formation permeability can be evaluated with the attenuation of the amplitude of Stonely wave. But certain correction must be made. When mud cake is thick, formation permeability and shear wave slowness evaluated from the attenuation of the amplitude of Stoneley wave are wrong. Airy-phase of pseudo-Rayleigh wave at high frequency (low velocity)is also a good indicator for formation permeability. But environmental effect must be taken into account. Pseudo-Rayleigh wave at low frequency (high velocity)can be used for the computation of shear wave attenuation in virgin zone.