Downhole Gas Breakout Sensor Using Total Internal Reflection
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Solution Overview
Problem
Downhole fluid analysis tools face challenges in accurately detecting gas breakout in formation fluids, leading to inaccurate measurements and potential underestimation of gas presence, which affects the determination of reservoir reserves.
Innovation Solution
A downhole fluid analysis tool with a gas breakout assembly that uses a sensing optic with a known refractive index higher than the downhole fluid, employing total internal reflection to detect changes in refractive index and indicate gas breakout, along with a bubble director to ensure gas bubbles are directed to sensors for accurate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional refractometers and optical cavity systems are used for refractive index measurement, then measurement precision is improved, but the systems become unsuitable for harsh downhole environments due to thermal issues and fouling
Solution Approach 1:
The patent replaces conventional mechanical/optical refractometers and electronic optical cavity systems with a simplified optical fiber-based TIR sensor system. This substitution eliminates the need for complex electronics and mechanical components that are sensitive to thermal and fouling issues in harsh downhole environments, while maintaining measurement capability through pure optical sensing.
Solution Approach 2:
The patent changes the operating principle from conventional refraction measurement to Total Internal Reflection (TIR) measurement. By monitoring the transition from TIR to partial transmission when gas bubbles are present, the system achieves reliable detection in harsh environments. The sensing optic material is selected with refractive index higher than the downhole fluid to enable TIR operation under downhole conditions.
2Device complexity
If gas breakout detection is not implemented, then device complexity is reduced, but measurement precision deteriorates due to inaccurate fluid analysis and reservoir reserve assessment
Solution Approach 1:
The patent uses optical sensing instead of complex mechanical or electronic gas detection systems. The TIR-based optical sensor provides simple yet effective gas breakout detection by monitoring changes in light transmission through the sensing optic, eliminating the need for complex multi-component detection systems.
Solution Approach 2:
The patent detects gas breakout by monitoring the phase transition indicator - the formation of gas bubbles in the liquid phase fluid. When gas bubbles form and contact the sensing optic, they change the optical properties at the interface, transitioning the measurement from TIR to partial transmission, providing a clear signal for gas breakout detection.
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 tool effectively detects gas breakout and maintains fluid pressure above the bubble point, ensuring accurate gas flag measurements and preventing contamination, thereby improving the reliability of fluid analysis and reservoir reserve assessments.
Implementation Method 1
A source generates an input signal that passes to a sensing surface of the sensing optic. The sensing surface interfaces with the downhole fluid... employing total internal reflection to detect changes in refractive index and indicate gas breakout
Implementation Method 2
A first light ray R1 passing through the first medium M1 at some angle of incidence (i.e., θi) toward the interface will have a portion that passes through the interface and refracts in the second medium M2... Snell's Law: n1 sin θ1 = n2 sin θ2
Data Source
Figure 1
Figure 2
Figure 3~4C
AI summary
A downhole fluid analysis tool has a housing and a flow passage for downhole fluid. A device disposed in the tool housing relative to the flow passage has a one or more sources, one or more sensing optics, one or more detectors, and control circuitry. The source generates an input signal. The sensing optic has a refractive index (RI) higher than crude oil and other expected constituents. A sensing surface of the optic optically coupled to the source interfaces with a downhole fluid. When the variable RI of the downhole fluid reaches a defined relationship to the optic's RI, the input signal interacting with the sensing surface experiences total internal reflection, and the reflected signal from the sensing surface remains in the sensing optic and reflects to a detector. The control circuitry monitors the detector's response and indicates gas break out if the response is above a threshold.