Research On The Non-Destructive Inspection Of Multi-Pipe Strings Using The Array Transient Electromagnetic Method

With the development of oil and gas exploration,most of oilfields in China are in the middle and late stage of production.The problem of casing damage is becoming more and more complicate,where the high-precision casing inspection has become one of the key technologies to improve oil and gas recovery.Based on the pulsed eddy current testing,this paper mainly investigates the noise cancellation,the nondestructive inspection(NDI)of multi-pipe strings and the multi-coil array signal processing of the borehole transient electromagnetic(TEM)system.The principle of TEM logging is presented firstly.Aiming at the downhole inhomogeneous multi-cylindrical model,the noise cancellation method in TEM system is studied,where the adaptive coherent integration based signal detection is also presented by employing the correlation of TEM response of adjacent periods.Using the time domain eddy current diffusion property,the principle of the NDI of multi-pipe strings is analyzed.Besides,a high resolution inversion algorithm based on the auxiliary sensor is proposed to improve the NDI resolution.Moreover,the array detection system is studied,and the uniform linear array TEM detection method is analyzed and presented.It is found that the transmitting-receiving distance to the array response of TEM linear array plays the similar role as the array manifold of a phased array in radar signal processing.Using the linear constrained minimum variance criterion,the signal-to-noise ratio of the downhole TEM detection can be effectively improved through applying the optimal weight to the linear array.Finally,both simulation and field experiments were conducted for the NDI of multi-pipe strings,and the results demonstrate that the proposed method can effectively increase the accuracy of the NDI of multi-pipe strings and improve the inspection performance of the downhole TEM system.