Gamma Ray Cement Evaluation Tool
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Solution Overview
Problem
Interpreting the quality of cement bonds between wellbore casing and formation is challenging, especially in cases of partial cement bonds, mixed cement, and drilling fluids, due to the ambiguity in sonic waveform signatures and the need for extensive knowledge in ultrasonic waveform analysis.
Innovation Solution
A logging tool equipped with a rotatable collimated gamma ray source and detector, capable of emitting and detecting collimated gamma rays at adjustable elevation and azimuthal angles, is used to evaluate cement quality by measuring backscattered gamma rays and comparing them to calibration data, providing a method to identify discontinuities and inhomogeneities in the cement layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If sonic and ultrasonic waveforms are used to evaluate cement quality, then the basic understanding of cement sheath composition is provided, but the interpretation becomes ambiguous in cases of partial cement bonds and mixed materials
Solution Approach 1:
The patent introduces gamma ray measurements as an intermediary method to detect cement density and composition. The gamma ray source and detector system serves as a mediator that provides additional information about cement properties without being affected by the limitations of sonic wave interpretation, thereby resolving the ambiguity in partial cement bond detection
Solution Approach 2:
The patent changes the measurement parameter from acoustic properties (sonic wave velocity and amplitude) to nuclear properties (gamma ray attenuation and density). This parameter change allows for more reliable detection of cement quality, especially in cases where sonic waveforms are ambiguous, by measuring the density and composition of the cement sheath directly
2Measurement precision
If ultrasonic measurements are used to determine impedance and attenuation, then cement sheath evaluation is possible, but extensive knowledge and complicated calculation methods are required
Solution Approach 1:
The gamma ray measurement system is self-sufficient in providing cement evaluation data. The method uses direct gamma ray attenuation measurements that inherently provide density and composition information without requiring complex mathematical models or extensive operator knowledge to interpret, making the system more self-service oriented
Solution Approach 2:
The patent replaces the mechanical/acoustic measurement system (ultrasonic transmitters and receivers) with a nuclear measurement system (gamma ray source and detector). This substitution eliminates the need for complicated impedance and attenuation calculations by directly measuring cement density and composition through gamma ray attenuation, thereby reducing operational complexity
3Ease of operation
If visual interpretation of cement bond log data is used, then basic cement sheath composition is understood, but reliable identification of partial bonds relies on operator experience
Solution Approach 1:
The patent introduces gamma ray density measurements as an intermediary that provides objective quantitative data about cement quality. This additional measurement layer serves as a mediator between the visual interpretation of sonic logs and the actual cement properties, enabling more reliable identification of partial bonds without requiring extensive operator experience
Solution Approach 2:
The patent implements a feedback mechanism by comparing gamma ray measured density values against known good cement density ranges. This feedback allows for automated or semi-automated identification of cement quality issues, reducing dependence on operator experience while maintaining ease of operation through clear quantitative criteria
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 accurate evaluation of cement bonds by comparing backscattered gamma ray ratios, enabling the identification of homogeneous and inhomogeneous cement layers, thus improving the assessment of cement quality and reducing reliance on operator experience.
Implementation Method 1
EP3201434 A1 discloses a tomographic imaging apparatus which utilises Compton backscattering to evaluate cement behind the casing. The imaging apparatus includes a slant-hole or pin-hole collimator coupled to a series of detectors in order to count the number of photons that backscatter off from the cement.
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A method and logging tool for evaluating the cement behind casing. In an embodiment, a collimated source emits gamma rays at selectable elevation angles. A fixed collimated detector received reflected gamma rays. Reflected calibration gamma rays are measured in a wellbore section having a cement layer of known condition. Backscattered evaluation gamma rays are measured in a section of wellbore to be analyzed and are compared with the backscattered calibration gamma rays to provide an indication of the quality of the cement layer at that location.