Ultrasonic Casing Thickness Estimation Using Complex Group Delay
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing wellbore logging systems face challenges in accurately determining casing thickness due to the complex 2D/3D nature of ultrasonic pulse-echo measurements, which are influenced by the mechanical properties of borehole fluids and casings, leading to computational complexity and inaccurate thickness estimation.
Innovation Solution
A method using complex group delay (CGD) analysis is employed to determine casing thickness by processing the first reflection and reverberations, involving windowing the signal to isolate the relevant acoustic data, calculating CGD components, and identifying the resonant frequency to derive casing thickness using the formula fr=βc²h, where β is a correction factor related to the Poisson ratio of the casing material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex 2D/3D ultrasonic pulse-echo measurements are used to determine casing thickness, then measurement completeness is improved, but computational complexity increases and measurement precision deteriorates
Solution Approach 1:
The patent segments the complex 2D/3D ultrasonic measurement problem into a simplified 1D model by focusing only on the relevant acoustic phenomena (longitudinal wave propagation and reflection) while eliminating unnecessary computational dimensions. This segmentation maintains measurement precision by concentrating on the essential physics of casing thickness determination without the computational burden of full 2D/3D modeling.
Solution Approach 2:
The patent extracts and isolates the first reflection and reverberations from the complete ultrasonic signal, separating the useful information for thickness measurement from other signal components. By taking out only the relevant reflection events and applying CGD analysis specifically to these extracted components, the method achieves accurate thickness determination with reduced computational complexity.
2Loss of information
If the complete ultrasonic signal including all reflections is processed, then information completeness is improved, but measurement precision deteriorates due to transducer noise and interference
Solution Approach 1:
The patent extracts specifically the first reflection and reverberations from the complete ultrasonic signal, isolating the useful information needed for thickness measurement. By taking out only these relevant signal components and excluding later reflections contaminated by transducer noise and interference, the method maintains information completeness for thickness determination while improving measurement precision.
Solution Approach 2:
The patent applies preliminary windowing and signal processing to isolate the first reflection and reverberations before performing CGD analysis. This preliminary action of separating the useful signal components from noise-contaminated portions occurs before the main thickness calculation, preventing noise propagation and improving final measurement accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides accurate and computationally efficient casing thickness determination by isolating the first reflection and reverberations, reducing interference from transducer noise, and utilizing CGD properties to precisely estimate casing thickness.
Implementation Method 1
ultrasonic pulse-echo measurements may be used to characterize material attached to the back of borehole casing
Implementation Method 2
a portion of the incident energy signal is transmitted via the casing into the surrounding medium and further dissipated. As a result of the relatively high contrast in mechanical properties of borehole fluid and a steel casing, a significant part of the incident energy is reflected back toward the transducer
Implementation Method 3
The transducer records the acoustic pulse and converts it into an electric signal
Implementation Method 4
identifying the resonant frequency from the complex group delay, and determining the casing thickness based on the resonant frequency
Implementation Method 5
determining a complex group delay (CGD) in the processing window, the complex group delay having a real component and an imaginary component
Data Source
AI summary
A casing thickness determination based on complex group delay (CGD) properties calculated for the part of the reflected signal from pulse-echo ultrasonic measurements from a downhole tool. A processing window is selected that includes the first reflection followed by reverberations but excludes other reflections to provide the most accurate casing thickness determination. The real and imaginary parts of the CGD, the deflection point and local extremum respectively, indicate the resonant frequency present in the windowed signal. The casing thickness is then determined from the resonant frequency.