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声波测井中的滑行纵波与地层内部的纵波不同。纵波不能在固体表面存在,在固体表面存在的是相应的滑行集散波。滑行集散波有两种,一种是负指数滑行集散波,另一种是正指数滑行集散波。两种滑行集散波有相同的声速,此声速略低于纵波声速。两种滑行集散波必须并存,才能满足边界条件,单独一种滑行集散波是不能存在的。离开固体表面稍远的区域,可以有平行于表面传播的纵波声束存在,但是需要与相应的滑行集散波相互衔接。滑行纵波系由纵波声束、负指数滑行集散波和正指数滑行集散波三种成份所组成。滑行集散波传播略慢,被纵波声束抛落在后。但前进中的纵波声束不断向表面扩散而产生出新生的滑行集散波。因此,实测所得的滑行纵波声速等于或非常接近纵波声速。这种分析对于井下情况也能近似适用。激发出泥浆纵波而使接收器获得讯号的是滑行集散波,纵波声束并不直接激发泥浆纵波。滑行集散波由于激发泥浆纵波而受到的损耗,要由纵波声束给以补充。滑行集散波的振幅,由于服从指数规律,因而数值上小于纵波声束的振幅,这是滑行纵波讯号并不很强的原因之一。
The gliding longitudinal waves in sonic logging are different from the longitudinal waves in the strata. Longitudinal waves can not exist on the solid surface, there is a corresponding coasting scattered wave on the solid surface. There are two kinds of slip-set scattered wave, one is the negative exponential sliding set of scattered waves, the other is the positive exponential sliding set of scattered waves. The two slippage sets have the same sound velocity, which is slightly lower than the longitudinal wave velocity. The two types of taxiing waves must coexist in order to meet the boundary conditions. A single kind of taxiing wave can not exist. The region far away from the solid surface may have a longitudinal wave beam propagating parallel to the surface, but needs to interface with the corresponding coasting wave. Sliding longitudinal wave system by the longitudinal wave beam, negative exponential sliding setter and positive exponential sliding set composed of three components. Slippery set of scattered wave propagation slightly slower, was longitudinal wave beam fell behind. However, the progressing longitudinal wave beam continuously diffuses to the surface to generate a nascent gliding wave. Therefore, the measured SLWP sound velocity is equal to or very close to the SLW sound velocity. This analysis can also be applied to the downhole situation. Stimulation of the longitudinal wave of the mud and the receiver to obtain the signal is a sliding set of scattered waves, longitudinal wave beam does not directly stimulate the longitudinal waves of mud. Taxi set-slip due to stimulate the longitudinal wave of mud and suffered losses, to be supplemented by the longitudinal wave beam. The amplitude of the coasting scattered wave is smaller than the amplitude of the longitudinal wave beam due to the exponential law, which is one of the reasons why the gliding longitudinal wave signal is not very strong.