Downhole electrochemical sensor and method of using same

A method of determining downhole parameters of a downhole fluid about a wellbore penetrating a subterranean formation, the method comprising:

• deploying a downhole tool into the wellbore, the downhole tool having a flowline therein to receive downhole fluid and an electrochemical sensor, the electrochemical sensor comprising a bulkhead carried by the downhole tool, a membrane exposed to the downhole fluid in the flowline, and an electrochemical cell supported by the bulkhead adjacent the membrane, the electrochemical cell comprising a plurality of cell sensors, at least one cell electrode, and a sensing solution, the plurality of cell sensors comprising an analyte sensor, a temperature sensor, and a pH sensor;
• exposing the membrane to the downhole fluid in the flowline;
• measuring parameters of the downhole fluid by measuring electrical signals generated by reaction of the sensing solution with certain analytes in the downhole fluid with the plurality of cell sensors, wherein the measuring parameters comprises measuring square wave voltammetry with the analyte sensor, cyclic voltammetry with the analyte sensor, and square wave voltammetry with the pH sensor;
• comprising determining a mediator concentration from the square wave voltammetry, the current-voltage relationship, and the pH;
• determining a concentration of the analyte of the downhole fluid in the flowline by combining the mediator concentration, the current-voltage relationship, and the pH with temperature measured by the temperature sensor using a calibration model;
• comprising measuring pressure of the downhole fluid in the flowline and determining a partial pressure of the analyte within the flowline by combining the concentrate of the analyte with the measured pressure using a gas solubility model.

A method of determining downhole parameters of a downhole fluid about a wellbore penetrating a subterranean formation, the method comprising:

• deploying an electrochemical sensor into the wellbore;
• obtaining square wave and cyclic voltammetries measurements of the electrochemical sensor exposed to the downhole fluid;
• generating electrode parameters of the electrochemical sensor based on the square wave and cyclic voltammetries, the electrode parameters comprising mediator concentration, current-volt relations, and pH;
• obtaining temperature and pressure measurements of the downhole fluid;
• generating a concentration of an analyte of the downhole fluid by combining the generated electrode parameters with the temperature measurement using a calibration model;
• and
• generating pressure of the analyte by combining the concentration of the analyte with the pressure measurement using a gas solubility model.