Metal Oxide Coated Fiber Optic pH Sensor for High Temperature Subsurface Monitoring
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Solution Overview
Problem
Current pH sensing technologies are inadequate for monitoring pH levels in high temperature and pressure subsurface environments, such as wellbores, due to instability, drifting, and limited temperature stability, which can lead to inaccurate readings and wellbore integrity failures.
Innovation Solution
Development of optical fiber pH sensors coated with metal oxides, such as TiO2 and ZrO2, which provide a stable and reversible optical response to pH changes, enabling continuous and in-situ monitoring of pH levels in harsh conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pH sensors are used in subsurface environments, then pH measurement is possible, but the sensors suffer from instability, drifting, and limited temperature stability at high temperatures
Solution Approach 1:
The patent replaces conventional electrical/electronic pH sensing mechanisms with an optical fiber-based sensing system. The optical fiber sensor uses light transmission properties rather than electrical signals to detect pH changes, eliminating the instability and drifting issues associated with conventional electrical sensors in high-temperature subsurface environments. The optical system remains stable at temperatures up to 300°C where electrical components fail.
Solution Approach 2:
The patent employs a composite sensing structure consisting of an optical fiber core coated with a pH-sensitive metal oxide layer (such as TiO2, ZnO, or ZrO2). This composite material combination provides both the optical transmission capability of the fiber and the pH sensitivity of the metal oxide, while maintaining stability at high temperatures. The metal oxide coating undergoes reversible pH-dependent refractive index changes that are detected by the optical fiber.
2Ease of operation
If electrical components are used in sensor applications, then sensing function is achieved, but packaging, wires, and interconnects become unstable in harsh environments
Solution Approach 1:
The patent completely eliminates electrical components, wires, and interconnects by substituting them with an all-optical sensing system. The optical fiber sensor transmits signals through light rather than electrical currents, removing the packaging and connection issues that plague electrical sensors in harsh subsurface environments. The sensor can be deployed without complex electrical packaging or wiring infrastructure.
3Adaptability or versatility
If fiber optic sensors are used for distributed sensing, then remote and continuous monitoring is enabled, but useful reversible robust sensing materials are lacking for demanding subsurface conditions
Solution Approach 1:
The patent solves the material robustness problem by developing a composite structure where pH-sensitive metal oxide coatings (TiO2, ZnO, ZrO2) are deposited on optical fiber surfaces. These metal oxide layers maintain their sensing functionality and reversibility at high temperatures and pressures, enabling distributed sensing along the entire length of the optical fiber in demanding subsurface conditions where conventional sensing materials fail.
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 metal oxide-coated optical fiber sensors offer improved chemical and temperature stability, allowing for accurate and long-term pH monitoring in high-pressure and high-temperature environments, reducing the risk of wellbore integrity failures and enabling real-time, spatially distributed pH measurements.
Implementation Method 1
metal oxides (MeOx), that present a good optical response to pH with reversibility and repeatability in the conditions of elevated temperature and pressure
Data Source
AI summary
A system for determining pH of a fluid and a method to determine the pH of a fluid contacting a sensor, the method having the steps of: providing the sensor to an environment such that the sensor is in contact with the fluid, wherein the sensor features a fiber extending between a first end and a second end along a longitudinal axis, wherein the fiber further features a medial portion positioned between the first and second ends, wherein the sensor further features a pH sensitive coating on the medial portion of the fiber, and wherein the pH sensitive material features a metal oxide including but not limited to SiO2, TiO2, ZrO2, Ta2O5, A2O3, and combinations thereof; interrogating the sensor with an optical signal; collecting a modified optical signal after the sensor has been interrogated; and determining the pH of the fluid contacting the pH sensor using the modified optical signal.