Start Date

2016 12:00 AM

Description

Modeling and understanding the complex elastic-wave physics prevalent in fluid-elastic cylindrically-layered structures is of importance in many NDE fields, and most pertinently in the domain of well integrity evaluation in the oil and gas industry. It is believed that acoustical measurements provide one of the effective means to provide a diagnosis. Historically, the problem has been researched and addressed to a good extent for well intervals with a single steel string. For these cases, high-frequency ultrasonic imaging has been optimized and demonstrated to yield acceptable diagnosis of the annulus properties behind the first string the signal encounters. However, they fail to provide information about the outer annulus in a double or triple string geometry. To probe with more effective radial depth, lower-frequency signals are used. In a typical double-string configuration, the inner casing is eccentered with respect to the outer string which itself is also eccentered within the cylindrical hole. The annuli may or may not be filled with solid cement, and the cement may have liquid-filled channels or be disbonded over localized azimuthal ranges. The complexity of wave propagation along axial intervals is significant in that multiple modes can be excited and detected with characteristics that are affected by the various parameters in a non-linear fashion.


To gain understanding of the complex wave physics and leverage it to design effective diagnosis means, we have developed modeling capabilities that address the configurations of interest. In this talk, we first establish a mathematical framework to analyze the guided wave fields in a multi-string system embedded in infinite media. We then develop and implement a Chirp Sweeping Finite Element Modeling (CSFEM) method to investigate the dispersions and modal characteristics of the complex propagating signals synthesized over an axial array of receivers. The CSFEM provides for a flexible framework to study the modal sensitivities in a multi-string system with arbitrary eccentricity, azimuthal heterogeneities, and partial bonded interfaces. We have also conducted scaled laboratory experiments to acquire reference data used to verify the range of validity of the modeling approach in predicting the guided modal characteristics of axially-propagating waves in concentric and non-concentric cylindrical structures immersed in fluid. An acoustic transmitter having four selectable, active elements at 90 degrees apart allows sourcing of all guided modes of interest and is located at one end of the string length. Received waveforms are acquired from a single receiver which is scanned axially and circumferentially inside the inner string. The acquired data set is then analyzed for spectral modal content using both Slowness-Time-Coherence and Matrix Pencil methods and compared to theoretical predictions. The comparisons indicate good agreement and provide confidence in the CSFEM capability to accurately predict the complex wave field dispersion characteristics estimated from the experimentally acquired signals in the fluid-filled double string geometries.

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Guided Waves in Fluid-Elastic Concentric and Non-Concentric Cylindrical Structures: Theoretical and Experimental Investigations

Modeling and understanding the complex elastic-wave physics prevalent in fluid-elastic cylindrically-layered structures is of importance in many NDE fields, and most pertinently in the domain of well integrity evaluation in the oil and gas industry. It is believed that acoustical measurements provide one of the effective means to provide a diagnosis. Historically, the problem has been researched and addressed to a good extent for well intervals with a single steel string. For these cases, high-frequency ultrasonic imaging has been optimized and demonstrated to yield acceptable diagnosis of the annulus properties behind the first string the signal encounters. However, they fail to provide information about the outer annulus in a double or triple string geometry. To probe with more effective radial depth, lower-frequency signals are used. In a typical double-string configuration, the inner casing is eccentered with respect to the outer string which itself is also eccentered within the cylindrical hole. The annuli may or may not be filled with solid cement, and the cement may have liquid-filled channels or be disbonded over localized azimuthal ranges. The complexity of wave propagation along axial intervals is significant in that multiple modes can be excited and detected with characteristics that are affected by the various parameters in a non-linear fashion.


To gain understanding of the complex wave physics and leverage it to design effective diagnosis means, we have developed modeling capabilities that address the configurations of interest. In this talk, we first establish a mathematical framework to analyze the guided wave fields in a multi-string system embedded in infinite media. We then develop and implement a Chirp Sweeping Finite Element Modeling (CSFEM) method to investigate the dispersions and modal characteristics of the complex propagating signals synthesized over an axial array of receivers. The CSFEM provides for a flexible framework to study the modal sensitivities in a multi-string system with arbitrary eccentricity, azimuthal heterogeneities, and partial bonded interfaces. We have also conducted scaled laboratory experiments to acquire reference data used to verify the range of validity of the modeling approach in predicting the guided modal characteristics of axially-propagating waves in concentric and non-concentric cylindrical structures immersed in fluid. An acoustic transmitter having four selectable, active elements at 90 degrees apart allows sourcing of all guided modes of interest and is located at one end of the string length. Received waveforms are acquired from a single receiver which is scanned axially and circumferentially inside the inner string. The acquired data set is then analyzed for spectral modal content using both Slowness-Time-Coherence and Matrix Pencil methods and compared to theoretical predictions. The comparisons indicate good agreement and provide confidence in the CSFEM capability to accurately predict the complex wave field dispersion characteristics estimated from the experimentally acquired signals in the fluid-filled double string geometries.