An apparatus and method for making resistivity measurements of an underground formation surrounding a borehole is disclosed. The apparatus includes a conductive tool body section. The apparatus includes an electrically decoupling insulated tool body section mechanically coupled to the conductive tool body section. The apparatus includes a conductive current return (CR) tool body section mechanically coupled to the electrically decoupling insulated tool body section. The apparatus includes a pad mounted on the conductive tool body section that injects current into the formation at a frequency in a range above 100 kHz and below 10 MHz. The pad includes at least one button electrode that measures current injected into the formation. The pad also includes a standoff spacer affixed to the conductive plate configured for direct contact with the formation. The apparatus includes extendable suspension means affixed to the conductive plate, that, when extended, cause direct contact between the standoff spacer and the formation.

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.

Apparatus, systems, and methods may operate to correct measured voltage data for selected weak differential measurements to provide corrected voltage data. Additional activity may include adjusting the corrected voltage data to remove level shifts in the measured voltage data caused by downhole tool impedance to provide adjusted voltage data, converting the adjusted voltage data into apparent resistivity data, inverting the apparent resistivity data to determine true resistivity values for a geological formation, and operating a controlled device according to the true resistivity values for the geological formation. Additional apparatus, systems, and methods are disclosed.

An example system includes an electrode-based tool for deployment in a downhole environment, where the electrode-based tool having a plurality of current electrodes, at least one voltage monitoring electrode, at least one return electrode. The electrode-based tool also includes electronics to measure leakage current between at least one of the plurality of current electrodes and the at least one return electrode as current from at least one of the plurality of current electrodes is injected into the downhole environment and flows to the at least one return electrode. The system also includes at least one processor configured to derive a corrected downhole environment parameter based at least in part on the measured leakage current.

An example system includes an electrode-based tool for deployment in a downhole environment, where the electrode-based tool having a plurality of current electrodes, at least one voltage monitoring electrode, at least one return electrode. The electrode-based tool also includes electronics to measure leakage current between at least one of the plurality of current electrodes and the at least one return electrode as current from at least one of the plurality of current electrodes is injected into the downhole environment and flows to the at least one return electrode. The system also includes at least one processor configured to derive a corrected downhole environment parameter based at least in part on the measured leakage current.

A variety of methods and systems are disclosed, including, a method for improving resistivity imaging, comprising: disposing a downhole tool into a borehole, wherein the downhole tool comprises a pad and a button array disposed on the pad; taking a measurement with the button array at a location in the borehole; selecting a projection angle; obtaining a corrected measurement from the projection angle and the measurement; and constructing an image using the corrected measurement. A system for improving resistivity imaging, comprising: a downhole tool, wherein the downhole tool comprises: an arm, and a pad; a conveyance; and an information handling system, wherein the information handling system is configured to take a measurement with the button array at a location in the borehole; select a projection angle; obtain a corrected measurement from the projection angle and the measurement; and construct an image using the corrected measurement.

A variety of methods and systems are disclosed, including, a method for improving resistivity imaging, comprising: disposing a downhole tool into a borehole, wherein the downhole tool comprises a pad and a button array disposed on the pad; taking a measurement with the button array at a location in the borehole; selecting a projection angle; obtaining a corrected measurement from the projection angle and the measurement; and constructing an image using the corrected measurement. A system for improving resistivity imaging, comprising: a downhole tool, wherein the downhole tool comprises: an arm, and a pad; a conveyance; and an information handling system, wherein the information handling system is configured to take a measurement with the button array at a location in the borehole; select a projection angle; obtain a corrected measurement from the projection angle and the measurement; and construct an image using the corrected measurement.

Apparatus and methods operable to determine a resistivity of a subterranean formation surrounding a wellbore. One such method includes using an apparent impedance function depending on a frequency variable and a plurality of unknown parameters, at least one of the unknown parameters depending on a formation impedance of the subterranean formation. The method also includes applying a voltage, at each of a plurality of frequency values, between electrodes of a resistivity tool that is disposed in the wellbore. The method also includes measuring, across the electrodes, a plurality of apparent impedance values, each corresponding to a different one of the frequency values. The method still further includes determining the unknown parameters based on the frequency values and the apparent impedance values, and estimating the formation resistivity based on an expression that includes at least one of the unknown parameters.

An example calibration method for a galvanic tool may include determining an internal coupling impedance between at least two electrodes of the galvanic tool, and inputting the determined internal coupling impedances into an equation used to evaluate the response of the tool. Voltage and current measurements may be generated from the galvanic tool using a calibration device. A leakage current value through at least one of the two electrodes may be determined based, at least in part, on the voltage and current measurements and the equation. The leakage current may be stored.

An example calibration method for a galvanic tool may include determining an internal coupling impedance between at least two electrodes of the galvanic tool, and inputting the determined internal coupling impedances into an equation used to evaluate the response of the tool. Voltage and current measurements may be generated from the galvanic tool using a calibration device. A leakage current value through at least one of the two electrodes may be determined based, at least in part, on the voltage and current measurements and the equation. The leakage current may be stored.