Electrochemical sensor

Abstract

An electrochemical sensor for measuring contents of a fluid or gas at high pressure and / or high temperature, for use, for example, in a wellbore for hydrocarbon applications, is provided. The sensor includes: a bulkhead-like electrode assembly including a cylindrical housing and a cylindrical electrode structure. The cylindrical electrode structure includes a cylindrical conductive pin extending from a high pressure region to a low pressure region and an electrode connected to one end of the pin at the high pressure region and having an electrode surface for exposure to a flow path of the fluid or gas in the high pressure region. At least a part of the surface of the pin is protected from direct contact with the fluid or the gas by an insulating coating impermeable to the fluid or gas. The pin may include an alternating pattern of protruding and receded portions.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to an electrochemical sensor operable at high temperature and / or high pressure conditions.[0002]Quantitative measurements and evaluation of wellbore fluids are important aspects of determining the quality and economic value of the well. More recently, studies aiming to characterize contents of corrosion-causing components such as H2S, CO2, pH and scale-forming ion species have been reported. This has been driven largely by the need to come up with effective mitigation of the severe impact of corrosion to both oil field operations and investments.[0003]Among the various techniques identified to measure the corrosion contents of wellbore fluids is electrochemical sensing. However, to date, research on high pressure and high temperature electrochemistry has been limited by factors such as corrosion, thermoelectric effects and the decomposition of most polymeric materials. As a result, there still is a great need for thermod...

AI Technical Summary

Benefits of technology

[0012]Thus, the conductive pin can be protected from direct contact with fluid or gas even if the fluid or the gas penetrates into the cylindrical housing when the electrode faces high pressure and high temperature conditions.

Problems solved by technology

However, to date, research on high pressure and high temperature electrochemistry has been limited by factors such as corrosion, thermoelectric effects and the decomposition of most polymeric materials.

Commercially available press fitted electrodes are limited to use mostly at ambient temperature and pressure conditions due to the eventual penetration of the electrolyte or sensing solution in addition to the wellbore fluids into the small gap found between the electrode materials and the main body.

However, it has recently been confirmed through experimental evaluations that the previously suggested electrode manufacturing methods have problems in applications in extreme wellbore conditions.

Designs that involve press-fitting and / or simple metal mounting procedures on top of electrical pin connectors have failed to obtain the much needed sensor stability and robustness, especially for high temperature and high pressure conditions.

Persistent creeping problems, where the liquid electrolyte penetrates into polymer sealant down to the electrical pin sections, have been consistently encountered.

This mechanical design failure results in increased background response, or unwanted peak signals related to metal stripping, thus rendering the sensing technique useless, especially at high pressure conditions.

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