A Uniform Linear Multi-Coil Array-Based Borehole Transient Electromagnetic System for Non-Destructive Evaluations of Downhole Casings

Abstract

Borehole transient electromagnetic (TEM) techniques have been proven to be efficient for nondestructive evaluations (NDEs) of metal casings using eddy-current properties. However, physical limitations and bad borehole conditions restrict the use of eddy-current sensors, which makes downhole casing inspections very different from those of conventional NDE systems. In this paper, we present a uniform linear multi-coil array-based borehole TEM system for NDEs of downhole casings. On the basis of the borehole TEM signal model, a numerical multi-coil array approach using the Gauss–Legendre quadrature is derived. The TEM response can be divided into two independent parts related to the transmitting-receiving distance (TRD) and the observation time and casing thickness. Using this property, the signal received by the multi-coil array is weighted to cancel the influence of the TRDs of the different array elements to obtain the optimal response according to the linearly constrained minimum variance criterion, which can be shown to be identical to that of achieving the maximum signal-to-noise ratio. The effectiveness of the proposed method was verified by applying the uniform linear multi-coil array to a borehole TEM system for NDEs of oil-well casings. Field experiments were conducted, and the results demonstrate the effectiveness of the proposed method.

EMD-Based Borehole TEM Array Signal Denoising and Baseline Wander Correction for NDT of Downhole Casings

“…To overcome the impacts of the bad borehole conditions, a lot of research works have been conducted with respect to the design and use of eddy-current sensors for improving the performance of downhole NDTs. Aimed at improving the signal-to-noise ratio (SNR) of borehole TEM systems, multi-turn approaches [13]- [16] that are composed of coaxial multi-turn transmitting and receiving coils wound around magnetic or air cores were proposed to enhance the eddycurrent response in high-temperature applications. Based on the correlation of the multiple receivers with the different distances between the transmitting and receiving (TRD) coils [13], [14], a multi-receive single transmit TEM array was proposed to improve the SNR of borehole TEM systems for NDTs in downhole casings, and the multi-receive array was weighted according to the array signal processing in order to improve the detection performance [13].…”

“…Aimed at improving the signal-to-noise ratio (SNR) of borehole TEM systems, multi-turn approaches [13]- [16] that are composed of coaxial multi-turn transmitting and receiving coils wound around magnetic or air cores were proposed to enhance the eddycurrent response in high-temperature applications. Based on the correlation of the multiple receivers with the different distances between the transmitting and receiving (TRD) coils [13], [14], a multi-receive single transmit TEM array was proposed to improve the SNR of borehole TEM systems for NDTs in downhole casings, and the multi-receive array was weighted according to the array signal processing in order to improve the detection performance [13]. Also, aimed at improving the spatial resolution of the NDT of metal pipes, a combination of transverse and longitudinal sensors was utilized to inspect different crack shapes of metal casings [15].…”

“…The above methods are based on calibration coefficients to reduce the influence of the nonconstant parameters on borehole measurements. However, 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]. Similar to the TEM denoising method in [21] and [22], [23] presented a discrete wavelet transform-based denoising method for borehole TEM data by employing a curve fitting technique.…”

Non-Contact Geomagnetic Detection Using Improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise and Teager Energy Operator

“…Nevertheless, their practicality is restricted by the limitations of inspection robotics. External inspection techniques represented by the transient electromagnetic method (TEM) [10] and Nopig [11] can be applied for the inspection of buried steel pipelines where the use of ILI is challenging. However, these techniques have low detection efficiencies and are influenced by the excitation source.…”

Modeling and Solution of Signal Oscillation Mechanism of the Multi-Coil Sensor

“…Multi-coil is an effective tool for detecting electromagnetic fields. Magnetic sensors based on air-core coils are widely used as a transducer in transient electromagnetic (TEM) exploration [1,2,3,4,5,6] and metallic crack detection [7,8,9,10], and coil sensors with integrated excitation module are commonly used in aeronautical transient electromagnetic detection [11], mine transient electromagnetic detection, and small loop towed systems [12].…”