Densitometer Piston Pressure Compensation
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Solution Overview
Problem
Existing densitometers used in wireline and logging while drilling operations face challenges in accurately measuring fluid density due to sensitivity to temperature and pressure changes, as well as unpredictable external forces, which affect the accuracy of fluid density measurements.
Innovation Solution
The design incorporates dissimilar materials for the tube and clamp with different coefficients of thermal expansion to reduce temperature sensitivity, uses fluid pressure to convey axial tension and reduce pressure sensitivity, and employs tension measuring devices to account for external forces, thereby improving the accuracy of fluid density measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a standard densitometer design is used, then the device structure is simple, but the measurement precision deteriorates due to sensitivity to temperature and pressure changes
Solution Approach 1:
The patent applies parameter changes by selecting specific material properties (coefficient of thermal expansion, Young's modulus, density) for the tube and clamp materials, and by optimizing geometric parameters (tube diameter, clamp dimensions, tube-clamp fit) to minimize the sensitivity of resonant frequency to temperature and pressure variations, thereby improving measurement accuracy
Solution Approach 2:
The patent employs composite materials by using dissimilar materials for the tube and clamp components. The tube is made of one material (e.g., titanium alloy) and the clamp is made of a different material (e.g., stainless steel or Inconel), selected specifically for their different coefficients of thermal expansion and mechanical properties, which together reduce temperature and pressure sensitivity of the measurement system
2Object-affected harmful factors
If dissimilar materials with different coefficients of thermal expansion are used for tube and clamp, then temperature sensitivity is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent directly applies thermal expansion principles by selecting tube and clamp materials with different coefficients of thermal expansion. The differential expansion between the two materials compensates for thermal effects on the resonant frequency, reducing temperature sensitivity. The patent provides specific guidance on selecting material pairs and their CTE ratios to achieve optimal temperature compensation
3Measurement precision
If fluid pressure is used to convey axial tension, then pressure sensitivity is reduced, but device complexity increases due to additional components
Solution Approach 1:
The patent applies self-service by using the fluid pressure itself to generate the axial tension force needed for compensation. The pressurized fluid acts on the closed-end piston, and this same pressure force is transmitted through the tube to create the compensating axial tension. The system uses the harmful pressure effect to benefit the measurement by automatically generating the compensation force without external intervention
4Measurement precision
If tension measuring devices are added to account for external forces, then measurement accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent applies feedback by using tension measuring devices (strain gauges) to continuously monitor the axial tension in the tube, and by using this measured tension information to correct or compensate for external force effects on the resonant frequency measurement. The system measures the actual tension state and uses this feedback to improve the accuracy of fluid density determination
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 enhances the accuracy of fluid density measurements by minimizing the impact of temperature and pressure changes and external forces, leading to more reliable formation sampling and fluid identification during wireline and LWD operations.
Implementation Method 1
a vibration source that drives a sample fluid cavity to resonance and measures a resonant frequency of the sample fluid
Implementation Method 2
The design incorporates dissimilar materials for the tube and clamp with different coefficients of thermal expansion to reduce temperature sensitivity
Implementation Method 3
uses fluid pressure to convey axial tension and reduce pressure sensitivity
Data Source
AI summary
A densitometer in the present disclosure comprises a piston attached to an end of a tube of the densitometer to reduce pressure dependence of density estimates of a sample fluid. The densitometer measures sample fluid density by vibrating the tube containing sample fluid and measuring the resonant frequency of the tube, then estimating the sample fluid density based on this resonant frequency. The piston is designed with a predetermined diameter that converts pressure inside the tube to tension in the tube. This tension produces an opposite effect on the resonant frequency of the tube to that caused by the fluid pressure itself and thereby reduces pressure dependence of the sample fluid density estimates.