Acoustic LWD Tool Blade Transducer Standoff Reduction
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Solution Overview
Problem
Existing acoustic logging while drilling tools face challenges in accurately determining shear wave slowness in acoustically slow formations due to poor transmission of shear wave energy, aliasing of compressional wave signals, and dispersive guided wave propagation, which complicates the measurement and increases tool complexity and expense.
Innovation Solution
Deploying an acoustic transmitter and a linear array of receivers on a blade with non-uniform spacing, reducing the standoff distance to the borehole wall, allowing for improved signal strength and detection of leaky shear wave arrivals, and centralizing the tool in the borehole to reduce azimuthal dependence and enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transmitter power and receiver sensitivity are increased to improve signal strength, then detection capability improves, but tool noise increases due to acoustic energy transmission through the tool body
Solution Approach 1:
The patent transitions from deploying transducers on the cylindrical tool body to deploying them on radially extending blades. This dimensional change in transducer placement creates a geometric configuration where the blades extend outward to contact the borehole wall, fundamentally altering the acoustic path and reducing tool noise transmission to the receivers.
Solution Approach 2:
The patent applies different structural properties to different parts of the tool by extending blades radially outward from the tool body. The blades have different acoustic coupling characteristics compared to the tool body, creating localized zones of improved acoustic contact with the borehole wall while isolating the receiver array from tool noise.
2Measurement precision
If the tool is decentralized in a large borehole to improve guided wave excitation, then signal strength improves, but the solution becomes complex and expensive
Solution Approach 1:
The patent divides the tool structure into distinct functional segments: a central tool body housing the receiver array and a separate radial blade structure carrying the transmitter. This segmentation allows the transmitter to be positioned at the blade tip for optimal acoustic contact with the borehole wall, while the receiver array remains protected on the tool body, simplifying the overall design compared to complex decentralized configurations.
3Ease of manufacture
If uniform spacing of receivers is used, then manufacturing is simplified, but aliasing of compressional wave signals occurs in acoustically slow formations
Solution Approach 1:
The patent introduces asymmetric, non-uniform spacing between receivers in the array. Specifically, the spacing between adjacent receivers varies, with at least one spacing being different from others. This asymmetric configuration disrupts the periodic patterns that cause aliasing of compressional waves while maintaining the ability to accurately measure shear wave arrivals in acoustically slow formations.
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 configuration enhances the accuracy of shear slowness measurements, improves signal strength, and reduces the complexity and cost of the tool by enabling direct determination of shear wave slowness in acoustically slow formations and reducing the impact of tool azimuth on measurements.
Implementation Method 1
an acoustic transmitter configured to generate an acoustic waveform
Implementation Method 2
a linear array of acoustic receivers including a plurality of acoustic receivers spaced apart from one another in a longitudinal direction configured to receive the transmitted acoustic waveform
Data Source
AI summary
An acoustic logging while drilling tool includes an acoustic transmitter and a linear array of acoustic receivers. At least one of the transmitter and the linear array of receivers is deployed on a blade having an outer diameter greater than that of the tool body. In preferred embodiments the transmitter and linear array are each deployed on a distinct blade. Deployment of the transmitter and/or the receivers on a blade reduces the standoff distance to the borehole wall which tends to improve the signal strength of received guided waves without an increase in transmitter power or receiver sensitivity.