Cement Integrity Evaluation Behind Coated Casing With Lamb Waves
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The presence of coatings on casing strings complicates the acoustic diagnosis of cement integrity in wellbores, as the contrast between casing material, coating material, and annulus material affects acoustic signals, leading to inaccurate cement bond evaluations.
Innovation Solution
Utilize a pitch-catch configuration with optimized transducer angles and frequencies to excite symmetric and antisymmetric modes in the casing, analyzing the attributes of these modes to evaluate cement integrity behind coated casing strings, capable of distinguishing materials in the annulus even with varying coating thicknesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coatings are applied to casing strings to protect against corrosion and wear, then the durability and protection of the casing is improved, but the accuracy of acoustic cement bond evaluation deteriorates due to signal contrast interference
Solution Approach 1:
The patent introduces a couplant as an intermediary substance between the transducer and the coated casing. This couplant mediates the acoustic signal transmission through the coating layer, enabling the signal to penetrate the interfering coating and reach the cement annulus for accurate evaluation. The couplant acts as a bridge that overcomes the signal blockage caused by the coating's acoustic contrast.
2Device complexity
If conventional acoustic logging tools are used to evaluate cement integrity, then the equipment simplicity is maintained, but the measurement accuracy deteriorates when coatings are present on the casing
Solution Approach 1:
The patent modifies the acoustic evaluation by introducing a couplant that changes the acoustic impedance parameters at the transducer-coating interface. This parameter change allows the acoustic signal to effectively couple through the coating layer, transforming the measurement conditions to achieve accurate cement bond detection despite the presence of coatings on the casing.
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
Provides reliable evaluation of cement bonding to casing and formation, distinguishing between fully bonded, partially bonded, and unbonded sections, and identifying materials like mud or light cement, enhancing the accuracy of cement integrity assessment.
Implementation Method 1
transmitting an acoustic signal into the coated casing string
Implementation Method 2
measuring an attribute of a Lamb wave mode of the acoustic signal; utilizing a pitch-catch configuration with optimized transducer angles and frequencies to excite symmetric and antisymmetric modes in the casing
Implementation Method 3
The reflection of the acoustic waves, the echo, may be measured by the transceiver for evaluation of the material in the annulus
Data Source
AI summary
Disclosed herein are methods and systems of evaluating cement integrity behind a coated casing string using acoustic signals. The methods include disposing an acoustic logging tool inside a coated casing string, wherein the coated casing string is disposed in a wellbore to form an annulus between the coated casing string and the wellbore, and is at least in part bonded to the wellbore by a cement. Further, the methods include transmitting an acoustic signal into at least part of the coated casing string to form a Lamb wave mode, measuring an attribute of a Lamb wave mode, and determining if the coated casing string is fully or partially bonded to the cement or is free pipe or is partially bonded to a formation based at least in part on the Lamb wave mode.