Pressure-Compensated CMUTs for Downhole Acoustic Arrays
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Solution Overview
Problem
Piezoelectric transducers used in downhole acoustic tools are limited by their large size and degradation at high temperatures, restricting the number of transducers that can be used and reducing accuracy, as well as performing poorly in high-temperature environments.
Innovation Solution
The use of pressure-compensated capacitive micromachined ultrasound transducers (CMUTs) with a substrate, electrodes, insulation, and pressure-compensating fluid, allowing for a dense array of transducers that can operate effectively in high-pressure and high-temperature conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If piezoelectric transducers are used in downhole acoustic tools, then acoustic signal transmission and reception can be achieved, but the transducer size becomes large which restricts the number of transducers that can be used in the tool
Solution Approach 1:
The patent replaces piezoelectric transducers with capacitive micromachined ultrasound transducers (CMUTs). CMUTs use a capacitive mechanism with a flexible membrane and electrode structure instead of piezoelectric materials, enabling miniaturization while maintaining acoustic transduction functionality. This substitution allows for smaller transducer footprint and higher density arrays in downhole tools.
Solution Approach 2:
The patent divides the acoustic transducer into multiple smaller functional elements within the CMUT structure, including segmented electrodes and membrane regions. This segmentation enables compact design and allows multiple transducers to be packed into a smaller overall volume, increasing the number of elements that can fit in the downhole tool.
2Reliability
If piezoelectric transducers are used in downhole applications, then acoustic measurements can be performed, but the transducer performance degrades significantly at high temperatures above 150° C. due to depoling
Solution Approach 1:
The patent changes the material parameters and operating characteristics by using CMUT technology instead of piezoelectric materials. CMUTs operate based on capacitive principles that are not subject to depoling effects, allowing reliable operation at high downhole temperatures exceeding 150° C. The flexible membrane and electrode structure maintain their functional properties across a wide temperature range.
Solution Approach 2:
The patent employs composite material structures in the CMUT design, including the flexible membrane material combined with electrode layers and support structures. These composite materials are selected to maintain mechanical and electrical properties at high temperatures, ensuring reliable transducer performance in extreme downhole environments.
3Measurement precision
If more piezoelectric transducers are used to increase accuracy, then measurement resolution improves, but the tool size increases which exceeds the available space in borehole-sized tools
Solution Approach 1:
The patent replaces bulk piezoelectric transducers with miniaturized CMUTs, dramatically reducing the length and volume of each transducer element. This size reduction enables the inclusion of many more transducer elements within the constrained length of downhole tools, achieving high-resolution measurements without exceeding tool size limitations.
Solution Approach 2:
The patent transitions from one-dimensional or two-dimensional arrangements of large transducers to three-dimensional dense arrays of miniaturized CMUTs. This dimensional optimization allows maximum utilization of available tool volume, packing numerous transducer elements in a compact configuration that achieves high resolution while maintaining acceptable tool dimensions.
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 solution enables a higher number of transducers to be packed into a downhole tool, increasing accuracy and resolution while maintaining operation at extreme temperatures, and providing improved bandwidth compared to traditional piezoelectric transducers.
Implementation Method 1
a pressure compensating fluid disposed in the cavity and in pressure communication with ambient borehole pressure at the array
Implementation Method 2
each acoustic transducer in the array comprises: a substrate; a bottom electrode disposed on the substrate; a top electrode disposed above the bottom electrode
Implementation Method 3
An acoustic tool includes one or more acoustic transducers that convert electrical energy into sound wave energy to transmit an acoustic signal or convert sound wave energy into electrical energy to receive an acoustic signal
Data Source
AI summary
An apparatus for interrogating a subsurface material includes a carrier configured to be conveyed through a borehole penetrating the earth, an array of acoustic transducers disposed on the carrier and configured to be compensated for ambient pressure in the borehole, and electronics coupled to the array and configured to operate the array to interrogate the subsurface material. Each acoustic transducer in the array includes a substrate, a bottom electrode disposed on the substrate, a top electrode disposed above the bottom electrode, an insulation layer disposed between the bottom electrode and the top electrode and defining a cavity into which the top electrode may deflect, and a pressure compensating fluid disposed in the cavity and in pressure communication with ambient pressure of the array.