Electrochemical sensor system

Patent metadata

Field	Value
Publication number	US-9523667-B2
Application number	US-201213584587-A
Country	US
Kind code	B2
Filing date	Aug 13, 2012
Priority date	Aug 15, 2011
Publication date	Dec 20, 2016
Grant date	Dec 20, 2016

Abstract

An electrochemical sensor measuring concentration of an analyte in a test fluid at 50° C. or above by voltammetry uses electrodes in contact with an electrolyte containing the analyte and a redox-active species electrochemically convertible between reduced and oxidised forms. At least one form of the redox active species is present within surfactant micelles. The surfactant micelles enhance thermal stability of the redox active species and may also solubilise a species with poor water solubility, such as t-butylferrocene. A downhole tool incorporating such a sensor comprises a barrier, permeable to the analyte, to separate the electrolyte from subterranean reservoir fluid, so that the sensor directly measures analyte which has passed through the barrier and thereby indirectly measures analyte in the test fluid.

First claim

The invention claimed is:

1. A method of measuring concentration of hydrogen sulfide or thiol analyte in a subterranean test fluid at a temperature of 50° to 125° C. in a well comprising:
providing a plurality of electrodes in contact with an electrolyte solution containing a redox-active species electrochemically convertible between reduced and oxidized forms, wherein the electrolyte solution contains surfactant and at least one said form of the redox active species is present within surfactant micelles; and
bringing the electrolyte and a test fluid containing the analyte into contact with opposite sides of a membrane, which is permeable to the hydrogen sulfide or thiol analyte so that analyte can migrate through the membrane into the electrolyte solution; and
applying potential to the electrodes and observing current flow as voltage is varied;
wherein the redox-active species comprises ferrocene which is substituted with at least one substituent group which is an alkyl group of 1 to 6 carbon atoms or an alkenyl group of 2 to 6 carbon atoms such that the water solubility of the substituted ferrocene is less than the water solubility of unsubstituted ferrocene; and
wherein the substituted ferrocene is solubilized by the surfactant micelles.

2. A method according to claim 1 wherein application of potential and observation of current obtains a voltammetric response.

3. A method according to claim 1 which comprises bringing the test fluid into contact with a barrier which separates the test fluid from said electrolyte but which is permeable to the hydrogen sulfide or thiol so that hydrogen sulfide or thiol can migrate into said electrolyte through the barrier.

4. A method according to claim 1 wherein the surfactant is cationic.

5. A method according to claim 1 wherein the surfactant is anionic.

6. A method according to claim 1 wherein the redox-active species is 1,1-diethyl ferrocene.

7. A method according to claim 1 wherein the redox-active species is t-butyl ferrocene.

8. A method according to claim 1 wherein the redox-active species is vinyl ferrocene.

Assignees

• Lafitte Valerie
• Tustin Gary John
• Schlumberger Technology Corp

Inventors

• Lafitte Valerie
• Tustin Gary John

Classifications

• G01N33/2823 Primary

  Raw oil, drilling fluid or polyphasic mixtures · CPC title

• G01N27/48

  using polarography, i.e. measuring changes in current under a slowly-varying voltage · CPC title

• E21B49/0875

  determining specific fluid parameters · CPC title

• E21B49/087

  Well testing, e.g. testing for reservoir productivity or formation parameters · CPC title

• E21B47/01

  Devices for supporting measuring instruments on drill bits, pipes, rods or wirelines; Protecting measuring instruments in boreholes against heat, shock, pressure or the like · CPC title