Borehole electromagnetic induction system with noise cancelation for casing inspection

Abstract

A borehole electromagnetic induction (EMI) system with noise cancelation for casing inspection is presented. Based on the analysis of the model for received signal in multi-cylindrical borehole structures, we choose to utilize a receive-only channel as the reference to cancel the effect of the background noise, where a registration matrix is used to compensate for the correlation of the non-isolated reference channel. Moreover, the performance of noise cancelation is verified by applying it to an oil borehole EMI system for the inspection of oil-well casings. Field experiments are conducted and the results demonstrate the effectiveness of the proposed method.

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

“…In Ref. [ 22 ], even though the correlation between two channels with different TRDs is employed for noise cancellation with a registration matrix, this correlation was not thoroughly investigated because the two parts with respect to the TRD and geometrical–electrical parameters are still coupled to each other. In this section, we decouple the TRD and the other two variables in Equation (7) using a Gauss–Legendre quadrature-based [ 26 ] numerical approximation for the borehole TEM signal model.…”

“…Notably, if the signals obtained from the first case were averaged, although there will be no phase shift and the averaging can increase the SNR substantially, repeated measurements are needed to achieve the same SNR as the proposed method, which will be quite a time-consuming procedure since the motion velocity should be slowed down compared to that of the multi-coil array-based borehole TEM system. It has also to be mentioned that since the two experimental casing structures have only one pipe per case, the amplitude of the late time data usually monotonically increases with the thickness of the metal pipe [ 22 ], and the shape of late time data will be more similar to that of the real casing thickness, as shown in Figure 3 . Furthermore, comparing the experimental results for the two types of casing structures at 40 ms, the TRD will have a stronger influence on the NDE performance of Casing B than that of Casing A, which reveals that the TRD will also influence the longitudinal resolution of the NDE of downhole casings.…”

“…In Ref. [ 22 ], a two-coil structure was proposed in the case of motion measurements, where a reference multi-turn receiver was used to cancel the effect of the magnetic background noise in the main channel by employing the correlation of the two receivers with different TRDs. Although the relationship between the two receivers was not investigated thoroughly enough to be extended to a multi-coil array sensor, the use of multiple receivers would offer a new way for solving the problem caused by TRD.…”

Auxiliary Sensor-Based Borehole Transient Electromagnetic System for the Nondestructive Inspection of Multipipe Strings

“…The tool housing is fixed, and the conductivities of the cement ring, formation, and fluids are much smaller than that of the metal pipes, whose thickness can be estimated from U(t) by ignoring the effect of the other layers. Moreover, if only one pipe string exists, a single time slice of the induced EMF, whose amplitude monotonically increases with the thickness of the metal pipe, can be used to describe the relationship between U ( t ) and thickness [ 5 , 16 ]. However, when more than one string of metal pipes is present in oil and gas wells, the coupling of the response from the additional pipe strings will strongly influence the interpretation of the NDI, where additional time slices of the induced EMF in the receiving coils must be used to interpret the logging data.…”

“…The transient electromagnetic (TEM) technique has gained much attention over the past several decades owing to its wide range of applications, such as mineral and petroleum geophysical exploration [ 1 ], hydrogeophysical surveys [ 2 ], and geotechnical and environmental investigation [ 3 , 4 ]. In the field of borehole detection, TEM systems enable the rapid acquisition of broad-frequency-range data related to the electrical and geometrical parameters of each borehole’s cylindrical layer [ 5 , 6 , 7 ]. This technique, which is also known as transient (pulsed) eddy-current testing [ 8 , 9 , 10 , 11 ], enables the highly effective nondestructive inspection (NDI) of downhole casings [ 12 ].…”