Abstract: Methods and systems pertaining to a processing system and a downhole logging tool for investigating nested tubulars in a borehole. The downhole logging tool includes a transmitter coil for emitting a broadband excitation signal including one or more step excitations. The downhole logging tool also includes receiver coils including at least two receiver coils spaced apart from the transmitter coil at respective first and second distances from the transmitter, the first and second distances being distinct from each other, and each receiver coil being able to receive a response signal resulting from the excitation signal. The downhole logging tool also includes an acquisition system for recording the excitation signal and the response signal of each receiver coil over time. The processing system derives information indicative of variations in individual thicknesses of the nested casing tubulars based on variations of the response signals over time.

Abstract: A method includes emitting, with one or more sensors of a downhole tool disposed in a borehole, an excitation signal. The method also includes detecting, with the one or more sensors, a returned signal resulting from an interaction of the excitation signal with the borehole. The method further includes estimating a noise of the returned signal. The method also includes quantifying a probability that the estimated noise is not a white noise of the borehole. The method further includes identifying drill cuttings in a predetermined location of the borehole based on said quantification.

Abstract: Apparatus and methods operable to determine between a wall of a wellbore penetrating in a subterranean formation and a resistivity tool disposed in the 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 standoff distance based on an expression that includes at least one of the unknown parameters.

Abstract: Systems and methods are provided for estimating the tool center position of a downhole tool, the geometry of the borehole, and/or a mud parameter based on sensor measurements from the downhole tool, even when the downhole tool center is moving over time. At least one sensor may obtain a set of measurements that relates to distance-to-borehole in a borehole at a number of azimuths. A processor may estimate a set of values defining borehole boundary and a set of positions of a center of the downhole tool in the borehole, at least in part by estimating the borehole boundary based on the set of measurements assuming a previously estimated position of the center of the downhole tool is true and estimating the position of the center of the downhole tool based on the set of measurements assuming a previously estimated borehole boundary is true, and iterating at least until convergence.

Abstract: 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.

Abstract: Systems and methods for estimating standoff and/or caliper in a wellbore for oil-based mud drilling are provided. The systems include a sensor having a primary electrode and at least two secondary electrodes, and an electronics subsystem having a controller and a processor for driving the system and correlating current measurements with standoff and/or caliper. The electrodes are positioned relative to one another such that there is a distinct flow of current between the primary electrode and each secondary electrode. In operation, a single excitation frequency is applied to the primary electrode and a simultaneous measurement of current flowing between the primary electrode and each secondary electrode is obtained. Standoff is estimated from the measurements. The estimations can be independent of formation properties when an appropriate excitation frequency is used.

Abstract: The present disclosure introduces an apparatus for downhole measurement of a formation resistivity. The apparatus includes a probe having a button electrode, a first guard electrode insulated from the button electrode, a second guard electrode insulated from the first guard electrode, and a return electrode positioned external to the second guard electrode. The apparatus also includes an electrical source for setting a voltage drop between the second guard electrode and the return electrode, a first impedance (RBOG) electrically coupled between the button electrode and the second guard electrode, and a second impedance (RIGOG) electrically coupled between the first guard electrode and the second guard electrode.

Abstract: A method to obtain gain-corrected measurements. A measurement tool having one or more arrays is provided, wherein the arrays include two co-located triaxial transmitters and two co-located triaxial receivers. Measurements are obtained using the transmitters and the receivers. Impedance matrices are formed from the obtained measurements and the impedance matrices are combined to provide gain-corrected measurements. The apparatus may alternatively be a while-drilling logging tool having one or more arrays, wherein each array comprises a transmitter, a receiver, and a buck, and wherein the signal received by the receiver is subtracted from the signal received by the buck or vice versa. A slotted shield may be incorporated into either embodiment of the tool. The slots may form one or more island elements. A material is disposed in the slots. The islands and shield body have complementary tapered sides that confine the islands within the shield body.

Abstract: A method includes emitting, with one or more sensors of a downhole tool disposed in a borehole, an excitation signal. The method also includes detecting, with the one or more sensors, a returned signal resulting from an interaction of the excitation signal with the borehole. The method further includes estimating a noise of the returned signal. The method also includes quantifying a probability that the estimated noise is not a white noise of the borehole. The method further includes identifying drill cuttings in a predetermined location of the borehole based on said quantification.

Abstract: Systems and methods are provided for estimating the tool center position of a down-hole tool, the geometry of the borehole, and/or a mud parameter based on sensor measurements from the downhole tool, even when the downhole tool center is moving over time. At least one sensor may obtain a set of measurements that relates to distance-to-borehole in a borehole at a number of azimuths. A processor may estimate a set of values defining borehole boundary and a set of positions of a center of the downhole tool in the borehole, at least in part by estimating the borehole boundary based on the set of measurements assuming a previously estimated position of the center of the downhole tool is true and estimating the position of the center of the downhole tool based on the set of measurements assuming a previously estimated borehole boundary is true, and iterating at least until convergence.

Abstract: Apparatus and methods operable to determine between a wall of a wellbore penetrating in a subterranean formation and a resistivity tool disposed in the 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 standoff distance based on an expression that includes at least one of the unknown parameters.

Abstract: Systems, methods, and devices for compensating for environmental conditions on electromagnetic measurements are provided. For example, a downhole logging tool may include a first transmitter coil, a second transmitter coil, and a first receiver coil. The first transmitter coil may provide a first magnetic signal in a wellbore having a conductive casing. The second transmitter coil may provide a second magnetic signal in the wellbore. The first receiver may obtain a first measurement relating to the first magnetic signal and a second measurement relating to the second magnetic signal. The first receiver coil may be near enough to the first transmitter coil and the second transmitter coil to obtain measurements predominantly in the near field eddy current regime. A ratio of the first measurement and the second measurement may cancel environmental dependencies of the first receiver coil.

Abstract: A technique facilitates the accumulation and analysis of data related to a subterranean formation. An arrangement of different types of sensors is mounted on a collar utilized in accumulating data on the subterranean formation. The sensors are operable in combination to improve the image quality of data obtained with respect to the subterranean formation. Certain applications utilize an arrangement of sensors comprising at least one of each of an electromagnetic sensor and an ultrasonic pulse-echo transducer. A stabilizer or stabilizers may be used to precisely orient and position the sensors within a wellbore.

Abstract: The present disclosure introduces an apparatus for downhole measurement of a formation resistivity. The apparatus includes a probe having a button electrode, a first guard electrode insulated from the button electrode, a second guard electrode insulated from the first guard electrode, and a return electrode positioned external to the second guard electrode. The apparatus also includes an electrical source for setting a voltage drop between the second guard electrode and the return electrode, a first impedance (RBOG) electrically coupled between the button electrode and the second guard electrode, and a second impedance (RIGOG) electrically coupled between the first guard electrode and the second guard electrode.

Abstract: 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.

Abstract: A disclosed example method involves receiving a first signal transmitted into a reservoir from a production installation in a formation at a wellsite, and determining an apparent resistance of the reservoir based on the first signal. A distance between a fluid extraction tool and a fluid distribution is determined based on the apparent resistance.

Abstract: The apparatus employs the remote field eddy-current (RFEC) inspection technique to electromagnetically measure physical parameters of a metallic pipe. RFEC devices inserted into and displaced along a cylindrical pipes may be used to measure the ratio of pipe thickness to electromagnetic skin-depth and thus allow for the non-invasive detection of flaws or metal loss. Typically these RFEC thickness measurements exhibit a so-called double-indication of flaws, an undesired artifact due to a double-peaked geometrical sensitivity function of the device. The method describes a means by which this double indication artifact may be removed by an appropriate processing of RFEC measurements performed by an apparatus specifically designed for this purpose. The invention is particularly well designed for applications in the oilfield industry.

Abstract: Techniques involve determining the frequency-dependent dielectric permittivity spectrum of a rock sample. Determining the frequency-dependent dielectric permittivity may involve defining a series of electromagnetic measurement data having at least a measurement at a frequency from which a substantially frequency-independent value of dielectric permittivity ?? can be obtained. The electromagnetic measurement data also includes measurements at different frequencies from which values for frequency-dependent dielectric permittivity ?rock (f) can be obtained. Using these measurements, the frequency-dependent spectrum of the sample may be determined.

Abstract: A technique utilizes the acquisition of data from desired subterranean regions via a logging system. The logging system is constructed for use in a wellbore and comprises a transmitter module having a transmitter antenna. Additionally, the logging system utilizes a receiver module spaced from the transmitter module and having a receiver antenna. The transmitter antenna and the receiver antenna are oriented to enable sensitivity in desired directions, such as ahead of the logging system.

Abstract: A technique facilitates the accumulation and analysis of data related to a subterranean formation. An arrangement of different types of sensors is mounted on a collar utilized in accumulating data on the subterranean formation. The sensors are operable in combination to improve the image quality of data obtained with respect to the subterranean formation. Certain applications utilize an arrangement of sensors comprising at least one of each of an electromagnetic sensor and an ultrasonic pulse-echo transducer. A stabilizer or stabilizers may be used to precisely orient and position the sensors within a wellbore.