Abstract
Transient electromagnetic (TEM) techniques have been proven to be efficient for nondestructive testing (NDT) operations due to their pulsed eddy-current properties. However, in the field of downhole measurements, harsh environments may significantly influence the NDT performance in downhole casings. In this paper, an empirical mode decomposition (EMD) method based on borehole TEM array signal denoising and baseline wander (BW) correction is proposed to compensate for the bad measurement conditions that affect downhole NDT. Based on the borehole TEM signal model, we investigated the principle of the EMD approach for the borehole TEM response, where the background magnetic noise and temperature drift effects were analyzed by considering the motion measurement and effective permeability. It was found out that although the BW can be effectively removed with the EMD approach, the performance of the signal denoising is closely related to the measurement speed of the downhole NDT sensors. To solve this problem, we proposed an array-based ensemble EMD method to improve the denoising performance of the borehole TEM signals by formulating a three-dimensional borehole TEM data structure, where the generation of the noise-aided data can be more efficient by employing the borehole TEM array. The performance of the proposed method was verified by applying it to a borehole TEM system for the NDTs of oil-well casings. In addition, field experiments were conducted, and the results demonstrated the effectiveness of the proposed method.
Highlights
Borehole transient electromagnetic (TEM) [1] techniques are widely used in the field of the nondestructive testing (NDT) of downhole metal casings [2], [3] due to their rapid and accurate acquisition of broad-frequency-range data [4], [5], pulsed eddy-current properties [6], [7], and accessibility to targets [8]
We present an empirical mode decomposition (EMD) method based on borehole TEM array signal denoising and baseline wander (BW) correction to compensate the variation in the temperature and motion measurement of downhole NDTs
THE EMD OF THE BOREHOLE TEM SIGNAL In Section II, we describe the effect of the temperature drifts and the motion-induced electromotive forces (EMFs) on the measurement curves of the borehole TEM array, which appear as the BW and undesired noise that influence the NDT performance in downhole casings
Summary
Borehole transient electromagnetic (TEM) [1] techniques are widely used in the field of the nondestructive testing (NDT) of downhole metal casings [2], [3] due to their rapid and accurate acquisition of broad-frequency-range data [4], [5], pulsed eddy-current properties [6], [7], and accessibility to targets [8]. The above methods are based on calibration coefficients to reduce the influence of the nonconstant parameters on borehole measurements They are quite inefficient for borehole TEM systems, as too many measurement data that corresponds to a broad frequency range from early to late sampling times are involved in each signal period of the TEM signal because of the eddy-current diffusion properties in the time domain [3], [13]. We present an EMD method based on borehole TEM array signal denoising and BW correction to compensate the variation in the temperature and motion measurement of downhole NDTs. Using the EMD algorithms, we analyzed the motion measurement and temperature drift effects on the performance of the borehole TEM system with respect to the MBN and effective permeability.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
