Methods and apparatus for measuring hydrogen sulfide in downhole fluids
A method of determining a concentration of hydrogen sulfide in a fluid comprises exposing a sensor to the fluid, the sensor comprising a pair of electrodes defining a gap therebetween and a sensing material bridging the gap between the electrodes, measuring a value of an electrical parameter of the sensor at an applied frequency of greater than about 10 kHz and a voltage of less than about 1.0 volt when the sensor is exposed to the fluid, and determining the concentration of hydrogen sulfide in the fluid based at least in part on the measured value of the electrical parameter. Related apparatuses and methods are also disclosed.
1. A method of determining a concentration of hydrogen sulfide in a liquid, the method comprising:
exposing a sensor to a liquid within a wellbore, the sensor comprising a pair of electrodes, major surfaces of the electrodes of the pair of electrodes opposing each other and defining a gap therebetween and a sensing material bridging the gap between the major surfaces of the electrodes;
applying, to the sensor, a voltage of less than about 1.0 volt at a frequency greater than about 10kHz;
while applying the voltage, measuring a value of an electrical parameter of the sensor while the sensor is exposed to the liquid; and
determining the concentration of hydrogen sulfide in the liquid based at least in part on the measured value of the electrical parameter.
2. The method of claim 1 , wherein determining the concentration of hydrogen sulfide in the liquid comprises comparing the measured value of the electrical parameter to a previously determined calibration curve or set of values of the electrical parameter of the sensor and correlating the measured value to the previously determined calibration curve or set of values.
3. The method of claim 1 , further comprising selecting the electrical parameter to comprise electrical resistance.
4. The method of claim 1 , further comprising:
selecting the frequency to be greater than about 100 kHz; and
selecting the voltage to be between about 5 millivolts and about 1 volt.
5. The method of claim 1 , further comprising:
selecting the frequency to be between about 100 kHz and about 300 kHz; and
selecting the voltage to be between about 100 millivolts and about 1 volt.
6. The method of claim 1 , further comprising selecting the sensing material to comprise metallic nanoparticles that reversibly adsorb or absorb hydrogen sulfide in the liquid.
7. The method of claim 6 , further comprising selecting the metallic nanoparticles to comprise gold, silver, copper, a gold alloy, a silver alloy, a copper alloy, or combinations thereof.
8. The method of claim 1 , further comprising selecting the sensing material to comprise metallic nanoparticles interdispersed in a conductive carbon network, a conductive polymer matrix, or a combination thereof.
9. The method of claim 8 , further comprising infiltrating the metallic nanoparticles by chemical vapor infiltration, thermal evaporation, dielectrophoretic deposition, plating, or combinations thereof.
10. The method of claim 8 , further comprising selecting the conductive polymer matrix to comprise polyaniline, poly(fluorene), polyphenylene, polypyrene, polyazulene, polynaphthalene, poly(pyrrole), polycarbazole, polyindole, polyazepine, poly(thiophene), poly(3,4-ethylenedioxythiophene), poly(p-phenylene sulfide), poly(acetylene), poly(p-phenylene vinylene), or combinations thereof.
11. The method in claim 1 , further comprising selecting the sensing material to comprise a metallic film having a thickness below about 100 nm.
12. The method of claim 1 , further comprising selecting the electrical parameter to comprise electrical impedance.
13. The method of claim 1 , further comprising disposing the sensor in the wellbore penetrating an earth formation comprising a source of the liquid.
14. The method of claim 1 , wherein exposing a sensor to a liquid within a wellbore comprises advancing a carrier including the sensor to a downhole location within the wellbore, wherein the carrier comprises a wireline, a slickline, a drill string, or coiled tubing.
15. A method of determining a concentration of hydrogen sulfide in a liquid within a wellbore, the method comprising:
operably coupling, to at least a component of a downhole component, a sensor comprising a pair of electrodes and a sensing material electrically coupled to each electrode of the pair of electrodes, major surfaces of the electrodes of the pair of electrodes opposing each other by a gap within which the sensing material is located;
advancing the downhole component to a downhole location within a wellbore;
applying, to the sensor, a voltage of less than about 500 millivolts at a frequency greater than about 10 kHz;
measuring an electrical resistance across the sensing material responsive to exposure of the sensing material to a liquid within the wellbore; and
determining a concentration of hydrogen sulfide in the liquid based on measured electrical resistance.
16. The method of claim 15 , further comprising selecting the sensing material to comprise gold nanoparticles interdispersed in a network of carbon nanotubes.
17. The method of claim 15 , further comprising measuring the electrical resistance while applying a voltage less than about 1.0 V across the pair of electrodes.
18. The method of claim 15 , further comprising selecting the sensing material to comprise a carbon network.
19. The method of claim 15 , further comprising selecting the sensing material to comprise metallic nanorods bridging a gap between the electrodes of the pair of electrodes, the metallic nanorods comprising metallic nanoparticles selected from the group consisting of gold, nickel, platinum, palladium, and combinations thereof.