Dual Redox Electrochemical Sensor for Downhole pH and H2S Monitoring
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Solution Overview
Problem
Existing electrochemical sensors face challenges in maintaining physical stability and reversibility when redox systems are distributed along polymer chains, leading to interference from other anions and instability in pH and H2S measurements, particularly in downhole environments where temperature and pressure changes affect chemical species like H+, CO2, and H2S.
Innovation Solution
A multi-redox compound with a determinate structure, containing two redox systems within a single molecule, is used on a solid conductive substrate, where one system is sensitive and the other is insensitive to the species of interest, allowing for potentiometric sensing and avoiding electron hopping issues that affect signal reversibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If redox systems are distributed along polymer chains, then the sensor can detect multiple species, but electron hopping between redox centers interferes with signal reversibility and measurement stability
Solution Approach 1:
The patent divides the sensor into separate functional components: distinct working electrodes each equipped with specific redox systems (ferrocene for pH, anthraquinone for H2S), rather than distributing all redox systems along a single polymer chain. This segmentation prevents electron hopping interference while maintaining multi-species detection capability through multiple independent measurement sites.
Solution Approach 2:
The invention extracts and removes the problematic polymer chain structure that causes electron hopping. Instead of using a polymer backbone to support multiple redox systems, the patent employs separate molecular redox systems attached to individual electrode surfaces, eliminating the continuous electron pathway that causes signal instability while preserving the ability to detect multiple chemical species.
2Adaptability or versatility
If multiple redox systems are attached to a single substrate, then measurement versatility increases, but physical stability and compositional consistency deteriorate
Solution Approach 1:
The sensor system is segmented into multiple independent working electrodes, each with a defined and stable composition. Rather than attaching multiple redox systems to a single substrate which creates compositional heterogeneity, each electrode maintains a consistent, reproducible structure with specific redox systems attached, ensuring both physical stability and measurement versatility across the sensor array.
3Ease of operation
If redox systems are used in downhole environments, then in-situ measurement capability is achieved, but temperature and pressure changes cause chemical species transformation affecting measurement accuracy
Solution Approach 1:
The patent employs reference electrodes with redox systems that provide stable reference potentials unaffected by downhole temperature and pressure variations. These reference electrodes (using ferrocene and other pH-insensitive redox systems) provide a feedback mechanism that compensates for environmental changes, allowing the measurement system to maintain accuracy despite in-situ conditions that would otherwise cause chemical species transformation and measurement drift.
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 approach enhances the stability and accuracy of pH and other species measurements by maintaining physical stability and reducing interference, enabling reliable downhole monitoring of critical parameters like pH, H2S, and oxygen content in aqueous and non-aqueous fluids.
Implementation Method 1
one redox system displays a reversible oxidation or reduction at a voltage which is sensitive to the concentration of a species to be detected, and another redox system in the same molecule displays a reversible oxidation or reduction at a voltage which is essentially insensitive to the concentration of the species to be detected
Data Source
AI summary
An electrochemical sensor utilizes a chemical compound which is not a macromolecule but rather is a single chemical compound of determinate structure, incorporating two redox systems which differ in their response to a species to be detected. In one form, one redox system displays a voltammetric wave which is pH dependent while another displays a voltammetric wave which is pH independent and acts as an internal reference. The sensor comprises a solid substrate, which may be carbonaceous, on which the compound is immobilized. The sensor may be incorporated into a tool to be suspended in a wellbore.