Lost circulation detection method through transient pressure wave based on STA/LTA analysis

Abstract

Effective management of lost circulation is essential for the development of oilfields, directly impacting the safety and operational efficiency of oil wells. In response to the problem that it is difficult to locate the leakage of open hole wells during the drilling process, this paper proposes the use of transient pressure wave method for the precise positioning of leakage location, which mainly uses the short-term averaging/long-term averaging(STA/LTA)method to accurately capture the characteristic waveforms of the leakage signals, extract the leakage characteristic information, and then determine the location of the leakage layer, but the accuracy is affected by multiple factors such as the length of the time window, the triggering threshold, and the selection of the characteristic function, and so on. In order to solve the problem that the pressure wave signals collected in the experiments contain more noise, a signal denoising method based on VMD-WTD-CCF is proposed, which employs variational mode decomposition (VMD), wavelet thresholding denoising (WTD) and cross-correlation function (CCF) together to extract effective intrinsic mode functions (IMFs), and reconstruct the signals in order to achieve the purpose of signal denoising. The experimental results verify that: the signal denoising method based on VMD-WTD-CCF can effectively remove the noise interference in the pressure wave, and can maximally retain the morphological characteristics of the original signal and eliminate the noise component, and the root mean square error and the smoothness of the denoised signal are reduced by 36% and 50.4%, respectively, and the signal-to-noise ratio is improved by 13.2%; STA/LTA is effective in identifying sudden pressure wave signals, and when lost circulation occur, the STA/LTA ratio produces a significant plunge at the moment of the lost circulation; the STA/LTA method can be used to effectively locate the first plunge point of the transient pressure wave signal, so as to obtain the time difference Δt of the reflection of the pressure wave, which can be combined with the wave speed to achieve the location of the leakage point; in the same condition experiments, the STA/LTA method is superior to similar lost circulation localisation methods including the wavelet mode maxima method and the frequency domain method, with an error rate as low as 1.38%. In this paper, several sets of experiments were carried out for different leakage locations and leakage amounts, and the experimental error was controlled at 0.08–6.00%, which is in line with the reasonable range of experimental error. The results of this study have certain guiding significance in the detection of leakage in open hole wells during the drilling process.