Simulation and inversion of ultrasonic pitch-catch through-tubing well logging with an array of receivers

Current methods for ultrasonic pitch-catch well logging use two receivers to log the bonded material outside a single casing. For two casings separated by a fluid, we find by simulation that increasing the number of receivers provides a better picture of the effect of the bonded material outside the second casing. Inverting simulated measurements with five receivers, using a simulated annealing algorithm and a simple forward model, we find for a subset of simulations that we can estimate the impedance of the material outside the outer casing

Analysis of outer-casing echoes in simulations of ultrasonic pulse-echo through-tubing logging

-Cased petroleum wells must be logged to determine the bonding and hydraulic isolation properties of the cement. Ultrasonic logging of single casings has been widely studied and is commercially available. However, ultrasonic logging in multiple-casing geometries is an unexplored topic despite its importance in plug and abandonment operations. Therefore, current logging technologies should be studied to evaluate whether they indicate the potential for multiple-casing logging. In this study, we used two finite-element models of pulse-echo logging. The first model represents logging in the transverse cross section of a double-casing well. The second model is a copy of the first, but with the outer casing and formation removed so that the pulse-echo transducer receives only a resonant first interface echo from the inner casing. By subtracting the received signals of the second model from those of the first, we can recover the third interface echo (TIE) signal representing the resonant reflection from the outer casing. This signal is used to study what information can, in principle, be drawn from TIEs in double-casing geometries, with the caveat that TIEs can only approximately be recovered in practical cases. We simulated variations of the material in the annulus beyond the outer casing, of the thickness of the outer casing, and of the eccentering of the outer casing. We have determined that the first two of these variations have only weak effects on the TIE, but that the eccentering of the outer casing can, in principle, be found using the TIE arrival time

Simulation and modeling of ultrasonic pitch-catch through-tubing logging

-Cased petroleum wells must be logged to determine the bonding and hydraulic isolation properties of the sealing material and to determine the structural integrity status. Although ultrasonic pitch-catch logging in single-casing geometries has been widely studied and is commercially available, this is not the case for logging in double-casing geometries despite its increasing importance in plug and abandonment operations. It is therefore important to investigate whether existing logging tools can be used in such geometries. Using a finite-element model of a double-casing geometry with a two-receiver pitch-catch setup, we have simulated through-tubing logging, with fluid between the two casings. We found that there appears a cascade of leaky Lamb wave packets on both casings, linked by leaked wavefronts. By varying the geometry and materials in the model, we have examined the effect on the pulse received from the second wave packet on the inner casing, sometimes known as the third interface echo. The amplitude of this pulse was found to contain information on the bonded material in the outer annulus. Much stronger amplitude variations were found with two equally thick casings than with a significant thickness difference; relative thickness differences of up to one-third were simulated. Finally, we have developed a simple mathematical model of the wave packets’ time evolution to encapsulate and validate our understanding of the wave packet cascade. This model shows a more complex time evolution in the later wave packets than the exponentially attenuated primary packet, which is currently used for single-casing logging. This indicates that tools with more than two receivers, which could measure wave packets’ amplitude at more than two points along their time evolution, would be able to draw more information from these later packets. The model was validated against simulations, finding good agreement when the underlying assumptions of the model were satisfied

Analysis of acoustic impedance matching in dual-band ultrasound transducers

acceptedVersio

Laboratory experiments on ultrasonic logging through casing for barrier integrity validation

Verification of annular barriers is essential for well integrity, with ultrasonic methods being central in well integrity testing for many decades. By doing ultrasonic pitch-catch measurements on a bench top laboratory setup developed to replicate an oil well casing, we were able to show that the beam width,-6dB, of the leaky Lamb wave propagating in the pipe widens only from 14 to 20.4 mm after 140mm of propagation in the pipe. This indicates that the excited Lamb wave has beam-like features, with litle spreading perpendicular to the propagation direction, hence, can be used to evaluate a limited area of the pipe. When introducing two pipes in the experimental setup, as an extension of a previously conducted simulation study by Viggen et al. [1], we could observe multiple Lamb wave packets being excited in the pipes. By adjusting the setup to replicate casing eccentricity, the effects of this could be observed in the measurement

Laboratory Experiments on Ultrasonic Logging Through Casing for Barrier Integrity Validation

Verification of annular barriers is essential for well integrity, with ultrasonic methods being central in well integrity testing for many decades. By doing ultrasonic pitch-catch measurements on a bench top laboratory setup developed to replicate an oil well casing, we were able to show that the beam width,-6dB, of the leaky Lamb wave propagating in the pipe widens only from 14 to 20.4 mm after 140mm of propagation in the pipe. This indicates that the excited Lamb wave has beam-like features, with litle spreading perpendicular to the propagation direction, hence, can be used to evaluate a limited area of the pipe. When introducing two pipes in the experimental setup, as an extension of a previously conducted simulation study by Viggen et al. [1], we could observe multiple Lamb wave packets being excited in the pipes. By adjusting the setup to replicate casing eccentricity, the effects of this could be observed in the measurement

Analysis of acoustic impedance matching in dual-band ultrasound transducers

Dual-frequency band probes are needed for ultrasound (US) reverberation suppression and are useful for image-guided US therapy. A challenge is to design transducer stacks that achieve high bandwidth and efficiency at both operating frequencies when the frequencies are widely separated with a frequency ratio ∼6:1–20:1. This paper studies the loading and backing conditions of transducers in such stacks. Three stack configurations are presented and analyzed using one-dimensional models. It is shown that a configuration with three layers of material separating the transducers is favorable, as it reduces high frequency ringing by ∼20 dB compared to other designs, and matches the low frequency (LF) transducer to the load at a lower frequency. In some cases, the LF load matching is governed by a simple mass–spring interaction in spite of having a complicated matching structure. The proposed design should yield improved performance of reverberation suppression algorithms. Its suitability for reduction of probe heating, also in single-band probes, should be investigated

Analysis of acoustic impedance matching in dual-band ultrasound transducers

Dual-frequency band probes are needed for ultrasound (US) reverberation suppression and are useful for image-guided US therapy. A challenge is to design transducer stacks that achieve high bandwidth and efficiency at both operating frequencies when the frequencies are widely separated with a frequency ratio ∼6:1–20:1. This paper studies the loading and backing conditions of transducers in such stacks. Three stack configurations are presented and analyzed using one-dimensional models. It is shown that a configuration with three layers of material separating the transducers is favorable, as it reduces high frequency ringing by ∼20 dB compared to other designs, and matches the low frequency (LF) transducer to the load at a lower frequency. In some cases, the LF load matching is governed by a simple mass–spring interaction in spite of having a complicated matching structure. The proposed design should yield improved performance of reverberation suppression algorithms. Its suitability for reduction of probe heating, also in single-band probes, should be investigated

Analysis of acoustic impedance matching in dual-band ultrasound transducers

acceptedVersio