Dynamic liquid level detection method based on resonant frequency difference for oil wells

The dynamic liquid level of an oil well can be used to determine the oil production strategies and analyze thereservoir performance. Therefore, it is important to measure the dynamic liquid level in an oil field. This paper proposesa novel dynamic liquid level measurement method for oil wells, where the resonant frequency difference (RFD) of theresonant acoustic signal in annular is used to calculate the dynamic liquid level. To solve the noise interference problem inthe resonant acoustic signal, a spectral fast Fourier transform (FFT) method based on Welch power spectrum is proposedto obtain the RFD. First, the Welch power spectrum approach is employed to process the resonant acoustic signal, anda high-pass filter is designed to filter the inherent envelope of low frequency in the power spectrum. In particular, a clearand smooth power spectrum can be obtained by choosing a suitable window and a sectional length. Furthermore, theshort-time Fourier transform method is used to extract the strongest energy spectrum of the power spectrum. Finally,the RFD of two adjacent resonant harmonics can be accurately obtained by using FFT for the strongest energy spectrum.Experimental results show the effectiveness of the proposed approach

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