论文部分内容阅读
地下纵波和横波速度测井曲线,通常是通过在井中获取声波波形而产生的。为此,现代声波测井仪都装有不同类型的声波源:单极声源和偶极声源。偶极声源是专门为横波速度测量而研制的,可是后来发现,在由孔隙度约为35%、横渡速度约为465m/s的未固结的砂岩组成的甚低速层中,在确定纵波速度方面,偶极声源较单极声源优越。在甚低速层中,被记录的折射纵波与其他波场分量(等同于耗散纵波)相干涉,从而影响对砂岩层纵波速度的确定。当用偶极声源时,借助于带通滤波技术实现折射纵波从记录的波形中的分离,这时波场分量显示为两个明显分离的频谱成分:一个以6.5kHz频率为中心的折射纵波;一个以1.3kHz频率为中心的耗散纵波。当用单极声源时,各种波形分量的频谱相当一致,因此不知如何选择通频带,以便将折射纵波从单极波形中分离出来。从偶极折射纵波中求得的砂岩层纵波速度为2150m/s。由偶极声源激发产生的耗散纵波的相速度介乎1800m/s(当频率为1.0kHz时)与1630m/s(当频率为1.6kHz时)之间。可见,在这种甚低速层中记录数据时,为了确定地层纵波速度,需将折射纵波从记录的波形中分离出来,在这个意义上,偶极声源比单极声源优越。
Underground P-wave and S-wave velocity logs are usually generated by acquiring acoustic waveforms in a well. To this end, modern acoustic logging tools are equipped with different types of acoustic sources: unipolar and dipole sources. Dipole sources have been developed specifically for the measurement of shear wave velocities, but later it was found that in very low velocities consisting of unconsolidated sandstone with a porosity of about 35% and a transversal velocity of about 465 m / s, Dipole sources are superior to monopole sources in terms of speed. In very low velocities, the recorded refracted longitudinal waves interfere with other wavefield components (equivalent to dissipative longitudinal waves), thus affecting the determination of the longitudinal wave velocity of the sandstone bed. When dipole sources are used, the separation of the refracted longitudinal waves from the recorded waveforms is achieved by means of band-pass filtering where the wavefield components appear as two distinct spectral components: a refracted longitudinal wave centered at a frequency of 6.5 kHz A dissipative longitudinal wave centered at 1.3 kHz. When using a monopole source, the spectrum of the various waveform components is fairly consistent, so it is not known how to select the passband to separate the refracted longitudinal wave from the monopole waveform. The longitudinal wave velocity of the sandstone layer obtained from the dipole-refraction longitudinal wave is 2150m / s. The phase velocity of the dissipative longitudinal waves generated by the dipole excitation is between 1800 m / s (when the frequency is 1.0 kHz) and 1630 m / s (when the frequency is 1.6 kHz). It can be seen that when data is recorded in such a very low velocity layer, the dipole sound source is superior to the monopole sound source in this sense in order to determine the longitudinal compressional wave velocity of the formation by separating the longitudinal wave from the recorded waveform.