Sonic Logging Cement Quality Analysis in Multi-String Wells
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Solution Overview
Problem
Current methods lack reliable and commercially available measurements to detect and assess the quality of cement in the second annulus of a doubly cased wellbore, which is crucial for hydraulic isolation between hydrocarbon-bearing and adjacent earth layers, as existing ultrasonic measurements only diagnose imperfect cement in the first annulus effectively.
Innovation Solution
The method involves using sonic tools with monopole and dipole transmitters to generate and record waveforms within the wellbore, processing the data to obtain slowness dispersion curves, and comparing them to model curves to determine the shear modulus and quality of cement in the outer annulus, thereby assessing the cement quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing ultrasonic measurements (50 to 500 kHz) are used, then cement quality in the first annulus can be diagnosed reliably, but cement quality in the second annulus cannot be detected
Solution Approach 1:
The patent changes the frequency parameter of the ultrasonic measurements from the conventional 50-500 kHz range to a higher frequency range (1-10 MHz), enabling the measurements to penetrate through the first cement annulus and detect the second cement annulus. This parameter change allows the same measurement technique to be applied to a previously inaccessible target.
2Measurement precision
If higher frequency sonic measurements (1-10 MHz) are used, then cement quality in the outer annulus can be detected, but the measurements become more complex and require advanced processing
Solution Approach 1:
The patent introduces an intermediary layer of wavefield decomposition that separates the complex high-frequency sonic measurements into distinct wave modes (Stoneley waves, flexural waves, and compressional waves). This intermediary processing step makes the complex data interpretable by attributing specific features to specific physical phenomena, thereby reducing the overall complexity of the measurement system.
3Measurement precision
If wavefield decomposition into Stoneley and flexural waves is performed, then cement quality can be determined through slowness dispersion analysis, but data processing complexity increases
Solution Approach 1:
The patent performs preliminary wavefield decomposition and slowness dispersion calculation during the initial data processing stage, before the actual cement quality interpretation. By pre-computing the dispersion curves and comparing them against a library of theoretical curves corresponding to different cement qualities, the method reduces the time required for final interpretation and decision-making.
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 allows for the reliable determination of cement quality in the outer annulus, enhancing hydraulic isolation and ensuring the integrity of the wellbore by providing accurate measurements of cement quality in the second annulus, which was previously unattainable with existing technologies.
Implementation Method 1
analyzing a Stoneley wave slowness dispersion curve resulting from processing of waveforms detected after the firing of a monopole source
Implementation Method 2
analyzing a flexural wave slowness dispersion curve resulting from processing of waveforms detected after the firing of a dipole source
Data Source
AI summary
Methods and systems are provided for determining cement quality in an outer annulus of a multi-string cased wellbore having an inner annulus of mud. Data from a sonic logging tool is processed to obtain a slowness dispersion. The slowness dispersion is compared to a plurality of model slowness dispersions generated for a plurality of different values for cement quality in the outer annulus. The cement quality in the outer annulus is determined based on the comparison.