Leaky Flexural Wave Semblance for Annular Velocity Determination
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Solution Overview
Problem
Current methods for evaluating cement integrity behind casing strings in well drilling and completions lack effectiveness in determining the thickness of the cement and its bond with the formation and casing, which is crucial for preventing fluid migration and ensuring zonal isolation.
Innovation Solution
The use of acoustic logging tools to emit and measure acoustic signals that traverse through the casing, cement, and formation, allowing for the analysis of reflected signals to determine cement bonding integrity and thickness, as well as the creation of semblance maps to estimate annular compression wave velocities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If acoustic bond logs are used to evaluate cement integrity, then cement bonding assessment is provided, but the method lacks precision in determining cement thickness and annular velocity
Solution Approach 1:
The patent uses feedback by iteratively adjusting velocity models and comparing predicted travel times with observed acoustic data. The semblance calculation provides feedback on how well the current velocity model fits the data, allowing continuous refinement of both velocity and thickness measurements until optimal agreement is achieved.
Solution Approach 2:
The patent applies preliminary action by first establishing a velocity model before attempting to measure cement thickness. The semblance method pre-determines annular velocity values, which are then used as input for subsequent thickness calculations, ensuring that thickness measurements are based on accurate velocity information.
2Reliability
If acoustic signals are transmitted through casing to evaluate cement, then cement integrity assessment is enabled, but the method cannot accurately determine annular compression wave velocities
Solution Approach 1:
The patent segments the acoustic signal analysis into distinct components: casing waves, cement annular waves, and formation waves. By separating these signals and analyzing their individual travel times and characteristics, the method can accurately determine annular compression wave velocities without interference from other wave types.
Solution Approach 2:
The patent uses excessive action by transmitting acoustic signals at multiple frequencies and analyzing a broad spectrum of wave modes. This over-determines the system, providing redundant information that improves the precision of velocity measurements while maintaining reliable cement integrity assessment.
3Ease of operation
If conventional acoustic logging is used, then basic cement bonding evaluation is provided, but the method lacks the capability to create accurate velocity models for time-to-depth conversion
Solution Approach 1:
The patent applies dynamics by using adaptive, depth-dependent velocity models that change continuously with depth rather than using static, uniform velocity assumptions. The semblance method dynamically adjusts velocity parameters at each depth interval, allowing accurate time-to-depth conversion while maintaining ease of operation through automated processing.
Solution Approach 2:
The patent changes parameters by allowing velocity and thickness to vary as independent parameters that are simultaneously optimized. Rather than fixing velocity and calculating thickness, or vice versa, the method treats both as variable parameters that can be adjusted to best fit the acoustic data, improving both operational simplicity and conversion 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 enables accurate evaluation of cement integrity, thickness, and bonding conditions, thereby enhancing the hydraulic seal and zonal isolation in wellbore completions, reducing the risk of fluid migration and improving well performance.
Implementation Method 1
transmitting an acoustic signal into at least part of a conduit string... computing travel times for leaked and reflected waves
Implementation Method 2
measuring a return signal from at least part of the conduit string... analysis of reflected signals to determine cement bonding integrity
Implementation Method 3
computing travel times for leaked and reflected waves... The leaked portion that gets reflected back is called the secondary flexural mode
Implementation Method 4
The interface between cement and formation affects the leaked and subsequently reflected energy that escapes out of the flexural mode traveling through the casing
Data Source
AI summary
Disclosed herein are systems and methods of determining cement integrity behind a casing string using acoustic signals in the field of well drilling and completions. Specifically, the systems and methods evaluate the interface between cement and formation and/or cement-second casing and determine the thickness of the cement. Data are processed to determine annular compression wave velocities in a cased well using a semblance method or by stacking the amplitude of the leaked A0 mode energy that has reflected from the cement-formation or cement-second casing interface. The annular compression wave velocity is necessary to convert time domain images of the annulus into radial distance domain images for better interpretation of annular conditions. A semblance method is used to determine a velocity estimate for the annulus and annular thickness. The semblance method is used for all depths and azimuths to create detailed radial distance domain images of the annulus in cased wells.