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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.

Borehole transient electromagnetic (TEM) array has proven to be efficient for the downhole nondestructive testing (NDT) of metal casings through the eddy-current property. However, restricted by bad downhole conditions, the simple increase of the receiving array is not sufficient enough for improving the downhole NDT performance. In this paper, we present a multiple-transmit focusing (MTF)-based borehole TEM system for the NDT of downhole casings. On the basis of the borehole TEM signal model, the response of the multiple-transmit array is derived by employing the matrix form of the borehole TEM response. It was shown that the excited magnetic field by the multiple-transmit array can be focused by weighting the current of each transmitter. Using this property, a modified linear constrained minimum variance-based multiple-transmitting array weighting method was proposed to realize the MTF. Moreover, a subarray partition approach was proposed to simplify the MTF realization, where the subarray weighting and mean square error were also analyzed. The MTF method performance was verified by applying it to a borehole TEM system for the NDTs of downhole casings. Finally, simulations and experiments were conducted, and the results demonstrated the effectiveness of the proposed method.

The target localization of underwater acoustic sensor networks is mainly based on the geometric principle. The uneven underwater sound speed leads to the bending of sound ray propagation. U sing constant sound speed to calculate the distance between the node and the target will produce a large error. At the same time, the complex and variable underwater environment makes it difficult to achieve strict clock synchronization between the underwater nodes and the target. In this paper, a sound ray correction method for deep-sea target localization is proposed for the case of clock asynchronization between nodes and target and sound ray bending. The method can obtain the accurate horizontal distance between the node and the target when the grazing angle of the node is known, and then improve the target localization accuracy. The sound ray correction method is verified by BELLHOP model and MATLAB simulation. Firstly, the correction effect of the traditional sound ray correction method is simulated when there is an error in the propagation time, and the results show that the traditional sound ray correction method is no longer applicable to the situation of clock asynchronization between node and target. Finally, the sound ray correction method proposed in this paper is simulated, and the results show that the method can significantly improve the accuracy of the target localization.

In the process of offshore and land drilling, once the blowout out of accident occurs, oil and gas resources will be seriously damaged, which will be easy to cause catastrophic events such as casualties and environmental pollution. Drilling a relief well beyond a certain distance around the blowout well to achieve connection is an effective way to control blowout. Affected by the error ellipse, it is difficult for the relief well to hit the accident well directly only depending on the trajectory information, where the relative distance and azimuth information of two wells should be measured in real time. In this paper, the borehole transient electromagnetic system is used to measure the resistivity of surrounding medium in relief well, and the relative distance of two wells can be inversed by using the influence of the accident well casing on the resistivity of surrounding formation. On this basis, the relative azimuth can be calculated in real time by using the spatial geometric positioning algorithm. Moreover, the experiments demonstrated that the proposed system can measure and calculate the relative distance and azimuth between the relief well and the blowout well, and finally guide the successful connection between two wells.

Borehole transient electromagnetic (TEM) techniques are widely used for nondestructive evaluation (NDE) of oil & gas well casings with eddy-current diffusion properties. In this paper, we present a multiple-eccentric-sensor-based borehole TEM system for NDE of downhole casings. Using the borehole TEM signal model, the TEM responses of sensors with eccentric transmitting coils are analyzed. The response of the eccentric sensor contains sensitive information in the direction of eccentricity while offering an improved detection performance. Hence, multiple eccentric sensors at different azimuthal angles are used to image casing damage, allowing directional NDE of downhole casings to be realized while improving the inspection resolution of the casing circumference. The effectiveness of the proposed method is verified by applying it to NDE of oil & gas well casings in the Shengli Oilfield. The experimental results demonstrate that the proposed method can effectively realize directional NDEs of downhole casings and improve the detection performance of the borehole TEM system.

Relying on eddy current changes with source distances, borehole transient electromagnetic (TEM) array techniques have achieved good results in nondestructive evaluation (NDE) of oil and gas well casings. However, the existing TEM array techniques cannot achieve sufficient longitudinal resolution of NDE. In this paper, a magnetic field focusing array for NDE of oil and gas well casings is presented. Based on the borehole TEM signal model, the eddy current field distribution is analyzed. The results show that the detection performance of NDE is strongly influenced by eddy current diffusion in the longitudinal direction which will be increased corresponding to the sampling time and transmitting power. To solve this problem, a uniform longitudinal linear transmitting array is adopted, and the transmitting weight of each element is optimized using the linear constraint minimum variance criterion. Thus, longitudinal focusing is achievable to significantly reduce the longitudinal diffusion range but improve the longitudinal resolution. Simulation results demonstrate that the proposed method effectively focuses the transmitting array’s eddy current field, improving the borehole TEM system’s resolution for NDE of oil and gas well casings.

Drilling relief well is one of the most effective way to control blowout well at present. In order to improve the connection rate, the relief well needs to trace a short distance and then gradually approaches the accident well, where the relative space attitude determination of relief well and blowout well is the key to improve the drilling efficiency. In this paper, a symmetry multi-coil array-based borehole transient electromagnetic (TEM) system for relative attitude determination of relief well drilling is presented. On the basis of the borehole TEM theory, the multi-coil array weighting is applied to improve the detection performance in the case that the blowout well is parallel to the relief well. Moreover, in order to determine the relative attitude, a symmetrical borehole TEM array structure is proposed for the short-range detection. Experiments were conducted and the results demonstrate the effectiveness of the proposed method for improving the short-range detection performance, which would offer significant information for the tracing phase of relief well drilling.

Power line communication (PLC) techniques have been proven to be efficient for the intelligent separate layer production (ISLP) system with single-core cables. However, the permanent mode of the ISLP may cause a continuous change of the resistance and capacitance of the single-core cables due to the long-term effect of high temperature, high pressure as well as the vibration of the bad downhole conditions, which will have great influence on the data transmission efficiency. In this paper, we present an adaptive PLC approach for the data transmission of ISLP with single-core cables. Instead of the precise slide rheostat, program-controlled potentiometer is used to achieve an adaptive decoding algorithm for fast initialization of the ISLP transmission. Moreover, a long-term adaptive method is also proposed to adjust the gain and filter coefficients in real time according to the bit error rate of data transmission systems. Finally, experiments were conducted and the results demonstrate the effeciveness of the proposed adaptive PLC data transmission for the improvement of the efficiency and stability of the ISLP system.

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&ndash, 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.

Transient electromagnetic (TEM) techniques are widely used in the field of geophysical prospecting. In borehole detection, the nondestructive inspection (NDI) of a metal pipe can be performed efficiently using the properties of eddy currents. However, with increasing concern for safety in oil and gas production, more than one string of pipe is used to protect wellbores, which complicates data interpretation. In this paper, an auxiliary sensor-based borehole TEM system for the NDI of multipipe strings is presented. On the basis of the characteristics of the borehole TEM model, we investigate the principle behind the NDI of multipipe strings using multiple time slices of induced electromotive force (EMF) in a single sensor. The results show that the detection performance of NDI is strongly influenced by eddy-current diffusion in the longitudinal direction. To solve this problem, we used time slices of the induced EMF in both the main and auxiliary sensors. The performance of the proposed system was verified by applying it to an oil well with a production casing and liner. Moreover, field experiments were conducted, and the results demonstrate the effectiveness of the proposed method.