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Estimating annulus sealing properties using the flexural wave spectrum in pitch-catch well-logging
Sander Bøe Thygesen1, Tore Lie Sirevaag2, Sven Peter Näsholm3
1Department of Informatics, University of Oslo, P.O. Box 1080, Oslo, NO-0316, Norway; Equanostic AS, Klaus Torgårds vei 3, Oslo, NO-0372, Norway.
Ultrasonics
|November 8, 2024
Summary
This study introduces a new method using pitch-catch ultrasound logging to distinguish between solid and fluid materials behind oil and gas well casings. The technique analyzes spectral signatures to improve well-barrier inspection and ensure operational safety.
Area of Science:
- Geophysics
- Petroleum Engineering
- Materials Science
Background:
- Effective sealing of the annulus casing is critical for safe oil and gas well operations.
- Pitch-catch ultrasound logging is a key technology for inspecting well barriers.
- Differentiating between cement and mud behind the casing is essential for accurate analysis.
Purpose of the Study:
- To present a novel data processing approach for differentiating fluid and solid materials in the annulus using pitch-catch ultrasound data.
- To develop a method for identifying the presence or absence of a solid annulus based on spectral analysis.
- To estimate the P-wave velocity of annulus materials for improved well diagnostics.
Main Methods:
- Analysis of the spectral signature of the casing flexural wave from pitch-catch datasets.
- Identification of a notch-like dip in the spectrum, indicative of solid annulus materials.
- Exploitation of the notch frequency to estimate the annulus material's P-wave velocity.
- Development of a binary algorithm to detect the dip and classify annulus materials.
Main Results:
- A distinct notch-like dip in the flexural wave's spectral signature is observed in most solid annulus scenarios.
- The frequency of this dip is directly related to the overlap between flexural phase velocity and annulus P-wave velocity.
- The developed algorithm successfully differentiates between solid and fluid materials behind the casing.
- Accurate estimation of annulus material P-wave velocity is achieved, aiding in material differentiation.
Conclusions:
- The proposed data processing approach provides a reliable method for distinguishing solids from fluids behind well casings.
- The algorithm is straightforward to implement in operational settings, enhancing well integrity assessment.
- The study demonstrates the algorithm's performance and accuracy using both simulated and field data, validating its practical applicability.
