Piezoelectric Sensor Unit for Downhole Pressure Logging
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Solution Overview
Problem
Existing downhole acoustic transducers face challenges in maintaining high sensitivity under high static pressure conditions while accurately recording dynamic pressure fluctuations and directional sound propagation, as they are often affected by static pressure and heat expansion, leading to signal interference and reduced accuracy.
Innovation Solution
A dynamic pressure sensor unit with a ring-shaped piezoelectric sensor housed in a cylindrical sleeve, utilizing a pressure control system with O-rings and a compressible fluid to isolate the piezoelectric element from static pressure and temperature variations, combined with a noise transmitting liquid like silicone oil to maintain signal integrity and directional sound analysis with multiple sensor units positioned at a distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the piezoelectric sensor is directly exposed to high static pressure conditions, then the sensor can measure dynamic pressure fluctuations, but the sensor sensitivity is compromised due to static pressure and heat expansion
Solution Approach 1:
A transfer liquid (such as silicone oil) is introduced as an intermediary medium between the housing and the piezoelectric sensor. This liquid transmits dynamic pressure fluctuations to the sensor while being contained within a sealed chamber that isolates the sensor from static pressure and thermal expansion effects of the external environment
Solution Approach 2:
The sensor unit is divided into functionally separate components: a pressure-sensitive piezoelectric sensor element, a transfer liquid medium, and a sealed housing chamber. This segmentation allows the sensor to measure dynamic pressure while the housing and liquid system together provide isolation from static pressure and temperature effects
2Measurement precision
If a pressure control system with seals and compressible fluid is introduced to isolate the sensor from static pressure, then sensor sensitivity is maintained, but device complexity increases
Solution Approach 1:
Compressible seals (such as O-rings) are used to create a flexible sealed chamber that can accommodate volume changes due to pressure variations. These flexible seals maintain the sealed environment needed to isolate the sensor from static pressure while allowing the system to respond to dynamic pressure fluctuations
Solution Approach 2:
The pressure control system utilizes a compressible fluid (transfer liquid) within a sealed chamber to transmit pressure fluctuations to the sensor. The fluid's compressibility and the sealed chamber configuration work together to isolate the sensor from static pressure while transmitting dynamic pressure signals
3Strength
If the housing is made of high strength steel alloy for downhole operation, then structural strength is improved, but electrical insulation between the housing and sensor becomes more challenging
Solution Approach 1:
The transfer liquid serves as an electrical insulator between the conductive housing and the piezoelectric sensor. Since the liquid is contained within the sealed chamber and does not electrically connect to the housing, it provides the necessary electrical insulation while still transmitting pressure fluctuations to the sensor
Solution Approach 2:
Electrical insulation is achieved through the sealed chamber structure and the transfer liquid, which act as non-conductive barriers between the housing and sensor. The flexible seals and liquid-filled chamber together create an electrically isolated environment that maintains sensor functionality
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 enables high sensitivity measurements of dynamic pressure fluctuations and directional sound analysis, maintaining signal integrity under extreme downhole conditions, with the ability to determine sound propagation direction and spectral distribution, while preventing static pressure interference and thermal expansion effects.
Implementation Method 1
a tubular piezoelectric element with circumferential polarization... pressure fluctuations (noise) or dynamic pressure results in oscillating strain in the housing, and further in the piezoelectric sensor
Implementation Method 2
A transfer liquid in a sealed gap between the sensor housing and the piezoelectric sensor transfers the stress fluctuations from the housing and to the sensor, without transferring static pressure on the housing to the piezoelectric sensor
Implementation Method 3
at least one seal is placed in a circumferential notch in the sensor sleeve. The notch is dimensioned to allow the seal to move in the notch in an axial direction... Pressure is controlled by allowing the seal to adjust the volume of the dynamic pressure transmitting liquid
Data Source
AI summary
The present invention concerns a dynamic pressure sensor unit (5A) for a logging tool for hydrocarbon wells with a piezoelectric element (5) in a sensor sleeve (3). The piezoelectric element (5) is a tubular element with an inner and an outer diameter. The sensor sleeve (3) has an inner cylindrical area with an inner diameter greater than the outer diameter of the tubular piezoelectric element (5). The piezoelectric element is situated in the inner cylindrical area of the sensor sleeve (3). A gap (12) with a gap thickness is formed between the inner cylindrical area of the sensor sleeve (3), defining an annular volume. The gap is filled with a noise transmitting liquid.