A state-of-the-art time-domain electromagnetic tool is presented that is capable of quantifying four barriers individually, and inspecting a fifth barrier qualitatively. The working physics and salient features of the tool and its underlying technology are described. The new tool uses time-domain electromagnetic (TEM) or pulsed eddy current (PEC) technology, which has set the benchmark for individual quantitative tubular corrosion evaluation in multi-annular well systems (multiple concentric tubulars) in recent years. Time-domain electromagnetic tools widely used in the industry are currently capable of quantifying the individual metal thickness/loss in up to three barriers. The new tool employs three highly sensitive sensors to provide high-resolution analysis of the inner barrier, while providing sufficient radial depth of investigation for up to five barriers. The above features and advantages of the new tool are supported by modeling and fixture test results. Additional modeling is shown to compare and contrast the resolution and radial depth of investigation of the three sensors. Case studies from actual wells are also presented that illustrate how three sensors enhance the performance of this technology. Corrosion evaluation of multi-barrier systems is a major component of well integrity management because it can provide timely and cost-effective information for planning well repairs if needed. The ability of the new tool to inspect more barriers is important because it gives the operator better information for more proactive well integrity management. The novelty of the tool is in its ability to exploit the information-rich wideband pulsed excitation using three sensors that enhance the sensitivity to multiple barriers.

A novel electromagnetic instrument is presented that uses transient or pulsed eddy current measurements to perform quantitative evaluation of downhole corrosion in four concentric tubulars individually, and to inspect a fifth tubular qualitatively. Case studies are presented that compare results from this instrument with industry-standard single-string evaluation tools such as multi-finger calipers and high-resolution magnetic flux leakage tools. The new instrument is based on transient or pulse eddy current technology and comprises three highly sensitive sensors that simultaneously achieve high-resolution of the inner barrier and high radial depth of investigation for up to five barriers. Each sensor induces coaxial rings of eddy currents in multiple concentric tubulars and measures a time-varying response from the outward-diffusing eddy currents. The full transient responses from multiple sensors are then interpreted to obtain individual tubular thickness profiles. Case studies are presented where the thickness profiles of outer barriers are obtained with the new instrument and are compared with high-resolution benchmark logs of multi-finger calipers and magnetic flux leakage tool. The benchmark logs were measured when the outer barrier was directly accessible because, either the inner barriers were not yet present, or the inner barriers were removed. These comparisons show that the new electromagnetic instrument is able to provide accurate individual tubular corrosion evaluation while logging through tubing. This ability is invaluable for proactive well integrity management because electrochemical corrosion, which is the primary corrosion mechanism in these wells, causes the outermost casing to fail first and then continues to penetrate inwards. Therefore, the new electromagnetic instrument enables early diagnosis of the outer tubulars to identify potential weak zones in the completion string while logging through tubing and eliminating the cost of pulling completions for this purpose. This paper describes the advantages and limitations of state-of-the-art multi-sensor pulsed eddy current measurements for individual barrier thicknesses of four or five strings. New case studies with high-resolution magnetic flux leakage tools and multi-finger calipers support these conclusions.

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Reliable evaluation of the cement-bonding quality and identification of isolation zones of a cased-hole well are challenging problems, particularly for a plugged and abandoned (P&A) well. Ultrasonic tools have been developed to conduct pitch-catch and/or pulse-echo measurements for cement evaluation at high spatial resolutions. Recently, extended data processing of pitch-catch measurements has been developed to identify third-interface echoes (TIE) from flexural mode waveforms. The derived information of TIEs can be integrated with flexural attenuation rates of casing and acoustic impedances of annulus materials to enhance the accuracy and confidence of evaluations of cement quality and zone isolation. However, there are limitations in conventional pitch-catch measurements. The conventual pitch-catch measurements are longitude measurements. Their vertical resolution is limited by the spacing between transducers. A utilized piezoelectric transducer used by such measurements needs a liquid couplant. The received signals of this kind of sensor are sensitive to the mud density. The heavy mud may cause strong attenuations of intensities of received flexural mode waveforms. Additionally, a piezoelectric sensor is sensitive to the direction of wave propagation. Therefore, a TIE can be missed if two walls of the annulus of a well are not parallel, such as a deviated well. This paper introduces a new compensated pitch-catch measurement method for reliably detecting the eccentricity of the inner pipe and annulus material in a cased-hole environment. The electromagnetic acoustic transducers (EMATs) are utilized to excite and acquire Lamb and shear horizontal waves, respectively, which propagate circumferentially. The operation parameters of this new measurement method are optimized to excite and acquire waves for more reliably extracting TIEs from received waveforms. Compared with piezoelectric sensors, EMAT sensors do not require couplants and are not sensitive to the wave propagation angle, the mud density, and the rugosity of the pipe surface. The vertical resolution of the Lamb wave measurements is controlled by the vertical sampling rate of the tool and the sensor size. This new measurement method has been validated with Lab measurements. The test fixtures with varied annulus spacings were designed, constructed, and cemented. Multiple tests were designed and conducted to verify the modes of Lamb and shear horizontal waves, existences of TIEs with different operation parameters of measurements, and the relations between arrival times of TIE and annulus spacing, as well as filled in materials of annulus. The visibility of TIE for a deviated inner pipe has also been confirmed. The tests results confirmed the optimal operation parameters of this new measurement method. The detected arrival times of TIEs are consistent with their predicted values. This new measurement method has some key technical advantages. The tool measurements do not require a liquid-filled inner casing for acoustic coupling. The arrangement of the transducers in the tool enables fully compensated measurements. Furthermore, the vertical resolution of detected tubing eccentricity is governed by the vertical sampling rate of the tool rather than the physical transmitter-receiver spacing. The long length of received waveforms can provide the time window to exposure the trainlet of TIE for revealing the types of filled-in materials of annulus and acoustic impedance contrast of filled materials and well barriers.