单极源钻铤波传播机制的实验研究

In this paper, the acoustic logging while drilling(LWD) measurements are conducted with a scaled LWD detector in the laboratory, in order to analyze the properties of monopole collar wave. We first build a high resolution data acquisition system (24 bit resolution and 1.25 MS/s sampling rate) and a high precision motorial system with the minimum movement of 0.5 mm. The detector and test system are validated by measuring acoustic signals propagated in the water. After that, the measurements with four different LWD models are conducted in a water pool. The time domain waveforms of the collar waves (direct collar wave in the collar and leaked collar wave out of the collar) in these models are recorded and analyzed. The properties of leaked collar wave,such as the amplitude differences and the attenuation along the axial direction and the radial direction,are further studied based on the experimental data. The results show that the collar wave can be excited even if the source and the collar are separated. However, when the collar is cut off, the collar wave disappears and transfers to liquid wave at the truncated section. In addition, we make a quantitative analysis on the amplitudes of the direct collar wave and leaked collar wave. Since the amplitude of the leaked collar wave is about a quarter of that of the direct collar wave, it is confirmed that the influence of leaked collar wave on the measurements of formation P and S waves can not be ignored in the acoustic LWD. Our experimental results are helpful for understanding the mechanism of the excitation and propagation of the monopole collar waves.