Segmented Acoustic Transducer for Cement Bond Logging
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Solution Overview
Problem
Conventional cement bond logging tools face challenges such as limited frequency utility due to resonant frequency constraints, spurious vibrations, slow data processing, and tedious calibration procedures, which hinder efficient data acquisition and analysis in harsh downhole environments.
Innovation Solution
A longitudinally segmented acoustic transducer design using thin-walled piezoelectric cylinders divided into band-like rings separated by resilient spacers, operating in an anti-resonant mode, combined with high-speed digital signal processing and real-time normalization, enables efficient data transmission and improved signal clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional cylindrical piezoelectric crystal is used operating at resonant frequency, then the transducer can generate and detect acoustic signals efficiently, but the crystal produces spurious vibrations and harmonics that interfere with the desired signal
Solution Approach 1:
The transducer crystal is divided into multiple longitudinal segments separated by resilient spacers. This segmentation prevents the generation of spurious vibrations and harmonics by breaking up the continuous crystal structure, while still allowing the segments to work together to transmit and receive acoustic signals at the desired fundamental frequency.
Solution Approach 2:
Resilient spacers are introduced as intermediary elements between adjacent crystal segments. These spacers act as mechanical isolators that prevent direct coupling between segments, thereby eliminating the spurious vibrations and harmonics that would otherwise be generated by the continuous crystal structure.
2Adaptability or versatility
If the piezoelectric crystal is operated at a single resonant frequency, then the transducer functions efficiently at that frequency, but the utility of the transducer is limited to only that one frequency
Solution Approach 1:
The segmented transducer design enables the same crystal structure to efficiently operate at multiple frequencies. By dividing the crystal into segments, the transducer can function at the fundamental frequency and at higher harmonic frequencies, making it a multi-functional device that can be used for various acoustic measurement applications without requiring multiple separate crystals.
3Productivity
If conventional PZT elements are used, then the transducer can operate in harsh downhole environments, but the data processing speed is slow compared to the amount of data that can be provided
Solution Approach 1:
The patent implements digital signal processing to replace conventional mechanical/analog data processing methods. By using digital signal processing circuits, the system can rapidly process the large amounts of data generated by the segmented transducer array in real-time, significantly increasing data acquisition rate and reducing processing time compared to traditional methods.
4Productivity
If conventional cement bond logging tools are used, then basic cement bond logging can be performed, but calibration procedures are tedious and time-consuming
Solution Approach 1:
The segmented transducer array with its standardized resilient spacer construction provides self-consistent acoustic characteristics that reduce the need for extensive manual calibration. The uniform segmentation and spacing create predictable acoustic responses that can be easily characterized, allowing for rapid calibration or even calibration-free operation in many applications.
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
The solution allows for faster data acquisition, higher signal-to-noise ratio, and reduced calibration time, enabling more comprehensive and accurate cement bond logging with improved operational efficiency in extreme conditions.
Implementation Method 1
The use of piezoelectric materials such as a polycrystaline form of lead titanate or lead zirconate titanate, sometimes referred to as 'PZT' material
Implementation Method 2
the crystal may produce an alternating voltage in the presence of sufficient mechanical stress at or near the resonant frequency of the crystal
Implementation Method 3
the plurality of transducer rings are driven synchronously in parallel by one or more pulses provided by the output of a pulse generator and caused to vibrate in an anti-resonant mode, that is, at a frequency substantially below the resonant frequency of an individual transducer ring
Data Source
AI summary
A longitudinally segmented acoustic transducer for a cement bond logging (CBL) tool having a plurality of adjoining PZT ring-like segments driven synchronously in parallel by one or more pulses and caused to vibrate in an anti-resonant mode, substantially below the resonant frequency of an individual segment when used in a transmitting application. When used in a receiving application, each of the plurality of transducer rings are caused to vibrate by acoustic signals detected by the transducer array, also in an anti-resonant mode. High speed digital signal processing enables on-depth, high quality data for all azimuths at each depth to be obtained, processed, normalized and either sent to the surface in real time for each 20 Hz firing cycle, as the CBL tool is pulled toward the surface, or stored in a memory module in digital form for later retrieval. Built-in calibration factors used for normalizing the output signals to the operating conditions of use may be accessed at any time.