Research On Signal Identification Technology In Liquid Level Detection Of Oil Wells Using Acoustic Method

Liquid level is of great importance in determining reasonable production system of oil wells. The commonly used method in obtaining the liquid level in oilfields is the acoustic method based on the reflection of the acoustic wave. The status of the annulus between tubing and casing is complex and the liquid level reflected wave is difficult to be identified due to the interference of different kinds of noises on the reflection of the acoustic wave. According to the problems in liquid level detection using acoustic method, the acoustic wave signal has been processed through filtering and identification in this paper based on the digital signal processing. The principle of the liquid level detection using acoustic method is studied, the propagation model of acoustic wave in the annulus is established and the causes of the noises are analyzed; the principle of the digital filter is studied and the digital filter is designed for filtering the liquid level reflected wave signal on the basis of the basic methods of the digital signal processing; the wavelet transform is suitable for noise filtering and detection of singularity point due to its characteristics of multi-resolution analysis comparing to the traditional Fourier transform method; Fast Fourier Transform method is used to calculate the periodicity of the collar reflected wave on the fact that the collar reflected wave is periodical, then the velocity of the acoustic wave in the annulus is obtained; the short-time amplitude and zero-crossing method is used in the identification of the liquid level reflected wave according to the characteristics of the liquid level reflected wave, and thus the liquid level is obtained automatically combing the process of the collar reflected wave. The acoustic wave signal which is difficult to be identified can be identified easily after the process of the methods above, and the automatic identification method can help to improve the ability for identification significantly and can be used to realize the automatic identification and calculation of the liquid level.