Abstract: Apparatus and methods to image pipes of a multi-pipe structure can be implemented in a variety of applications. The multi-pipe structure may be associated with a well site, such as a multi-casing structure for a production well. Individual pipes of the multi-pipe structure may be investigated in a multi-stage process using delta-like responses, where previous stages provide inputs to subsequent stages. The results of multi-stage processing can be used to image defects in the multi-pipe structure.

Abstract: In some embodiments, an apparatus and a system, as well as methods, include operating to estimate a range of true resistivity in a geological formation, based on measurements made over multiple frequencies. Further activity may comprise selecting a subset of the measurements associated with at least one measurement frequency included in the multiple frequencies, based on the range of the true resistivity, to determine a value of a property of the geological formation. Additional methods, apparatus, and systems are disclosed.

Abstract: A method of real-time impedance matching includes conveying a tool through a borehole where the tool includes a transmit cavity antenna and receive cavity antenna for transmitting and receiving signals through a subsurface formation. The tool also includes a cable for routing signals within the tool and at least one variable inductor or variable capacitor in an impedance-matching circuit. The method further includes measuring a reflection of a signal transmitted through the formation and determining a target impedance based on the impedance of the cable and the reflection. The method further includes adjusting the at least one variable inductor or variable capacitor such that the impedance of the matching circuit substantially equals the target impedance and receiving a signal from the formation via the adjusted impedance of the matching circuit.

Abstract: A dielectric logging tool for use in a borehole that penetrates a subsurface formation, includes: at least one wall-contacting face with one or more embedded microstrip antennas including a transmit antenna; an oscillator that supplies a transmit signal; a coherent receiver that measures the one or more scattering coefficients; and a processor that derives a formation property from the one or more scattering coefficients. The tool may be conveyed along a borehole, with the scattering coefficients and derived formation property values associated with tool position and orientation to provide a permittivity log.

Abstract: Disclosed embodiments include various borehole imaging tools and methods to provide sensing surface configurations for improving the assessment of anisotropy in layered formations. In at least some embodiments, the borehole imaging tools employ a unitary conductive body to provide a wall-contacting face with grooves that define multiple elongated sensing surfaces. This wall-contacting face can be provided on an extendable sensor pad of a wireline logging tool or embedded on the outer surface of a LWD stabilizer fin. Toroids may be seated in the grooves around each elongated sensing surface for measuring the current flow through each sensing surface. The elongated sensing surfaces can be configured in arranged in pairs as a series of rectangular-shaped grooves that are aligned perpendicularly to each other within each of the pairs to improve detection of anisotropy in thin layered formations and improves the sensitivity to dipping in anisotropic formations.

Abstract: A method for determining tubing permeability includes conveying a tool through a tubular string in a borehole. The tool includes a transmitter that transmits a primary electromagnetic field and a receiver that receives at least one collar response. The collar response includes a secondary electromagnetic field produced in response to the primary field by a collar in the tubular string. The method further includes determining a permeability of at least one portion of the tubular string based on a magnitude of the at least one collar response. The method further includes displaying a representation of the at least one portion of the tubular string based on the permeability.

Abstract: A method, apparatus and system for defect evaluation of downhole pipes are disclosed. One such method includes transmitting an electromagnetic wave into a pipe. A first electromagnetic field response for a delta-like defect is measured from the pipe. A second electromagnetic field response for an arbitrary defect is measured from the pipe. The first and second electromagnetic field responses are calibrated and a holographic inversion is applied to the first and second calibrated electromagnetic field responses to obtain an image of the pipe along an axial and an azimuthal direction.

Abstract: An example system includes an electrode-based tool for deployment in a downhole environment. The electrode-based tool has a plurality of current electrodes, at least one voltage monitoring electrode, at least one return electrode, and electronics to collect one or more voltage measurements from the at least one voltage monitoring 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 to estimate leakage current between at least one of the plurality of current electrodes and the at least one return electrode based on the collected one or more voltage measurements and a predetermined internal impedance model or table. The at least one processor is configured to derive a corrected downhole environment parameter based at least in part on the estimated leakage current.

Abstract: Method and articles for evaluating mud effect in imaging tool measurements are described. In an example, the method includes taking a plurality of measurements with a sensor positioned down a borehole, the sensor offset from a wall of the formation by a layer of mud, each measurement having an associated azimuth angle and depth. The plurality of measurements are related into a measurement set with each of the plurality of measurements having the same azimuth angle and depth within a designated depth range. The method includes determining, with a motion sensor, a relative position change of the sensor of each of the measurements within the measurement set and determining the offset of the sensor, one or more formation property, and one or more mud property.

Abstract: Calibration tools and procedures that provide calibration to galvanic tools can include use of measurement tools to measure resistivity of a calibration box. The resistivity of the calibration box can also be measured by a galvanic tool of interest. The two sets of measurements can be used to calibrate the galvanic tool. Additional apparatus, systems, and methods are disclosed.

Abstract: A method includes deploying an electromagnetic (EM) defect detection tool in a borehole having one or more tubular strings. The method also includes collecting measurements by the EM defect detection tool as a function of measured depth or position. The method also includes using the measurements and a first inversion process to determine a defect in the one or more tubular strings. The first inversion process involves a cost function having a misfit term and having a stabilizing term with nominal model parameters. The method also includes performing an operation in response to the determined defect.

Abstract: Apparatus, systems, and methods may operate to detect rugosity in a borehole. Additional activity may include generating a rugosity correction, responsive to detecting rugosity in the borehole, by finding an effective borehole diameter, consistent with the presence of rugosity, for which a simulation of a model of the borehole using the effective borehole diameter generates simulation resistivity measurements that match, within a tolerance, resistivity measurements before execution of a borehole correction algorithm. Additional activity may include applying rugosity correction by generating resistivity logs, using the effective borehole diameter, that are corrected for rugosity and borehole effect. Additional apparatus, systems, and methods are disclosed.

Abstract: A calibration system for an electromagnetic (EM) tool includes a processor. The processor employs the EM tool to measure responses at each of a plurality of channels. The processor records the measured responses at each of the channels in an EM data log for the channel. The processor determines a nominal value of each of the channels, as being equal to a histogram peak of the EM data log. The processor selects one or more calibration points from the EM data log for a particular channel, based on a difference between the nominal value of the particular channel and the measured response at the calibration point being greater than a particular threshold. The processor determines a plurality of parameters by reducing a misfit between synthetic data and both the nominal values of the channels and the measured responses of the channels at the selected one or more calibration points.

Abstract: A calibration system for an electromagnetic (EM) tool includes a processor. The processor employs the EM tool to measure responses at each of a plurality of channels. The processor records the measured responses at each of the channels in an EM data log for the channel. The processor determines a nominal value of each of the channels, as being equal to a histogram peak of the EM data log. The processor selects one or more calibration points from the EM data log for a particular channel, based on a difference between the nominal value of the particular channel and the measured response at the calibration point being greater than a particular threshold. The processor determines a plurality of parameters by reducing a misfit between synthetic data and both the nominal values of the channels and the measured responses of the channels at the selected one or more calibration points.

Abstract: A method includes deploying an electromagnetic (EM) defect detection tool in a downhole environment having a plurality of tubular strings with different diameters. The method also includes receiving raw measurements collected by the EM defect detection tool. The method also includes deconvolving the raw measurements with another input to obtain deconvolved raw measurements. The method also includes using the deconvolved raw measurements to determine a defect in at least one of the plurality of tubular strings. The method also includes performing, by a device, an operation in response to the determined defect.

Abstract: In some embodiments, an apparatus and a system, as well as methods, may include operating a transmitting antenna and a receiving antenna as equivalent tilted dipoles, wherein the tilted dipoles provide a selection of equivalent tilt angles for at least one of the transmitting antenna or the receiving antenna. Further activity may comprise receiving signals by the receiving antenna disposed in a geological formation, the signals to be inverted to obtain at least one of resistivity or dielectric constant properties of the geological formation at a selected depth of investigation, the depth determined by the selection of the equivalent tilt angles and weighting with pre-computed integrated radial sensitivity signal data. Additional methods, apparatus, and systems are disclosed.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may operate to obtain a plurality of measurements of a formation parameter, each measurement obtained in response to energy propagated into the formation at a plurality of frequencies of propagated energy; to process the measurements over each of the plurality of frequencies to obtain estimated values of the formation parameter; to select an estimated value from the obtained estimated values for each logging depth as a true measurement value for the logging depth based on one or more of the plurality of frequencies and a resistivity range; to generate a combination log that combines a plurality of the true measurement values for each logging depth; and to control a drilling operation based on the combination log. Additional apparatus, systems, and methods are disclosed.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may operate to estimate a value for a mud cake parameter to provide an estimated mud cake parameter value; to generate, in a solution operation, a formation parameter value and an adjusted mud cake parameter value using the estimated mud cake parameter value; and to provide corrected galvanic tool resistivity measurements based on at least the adjusted mud cake parameter value. Additional apparatus, systems, and methods are disclosed.

Abstract: Apparatus, systems, and methods may operate to detect rugosity in a borehole. Additional activity may include generating a rugosity correction, responsive to detecting rugosity in the borehole, by finding an effective borehole diameter, consistent with the presence of rugosity, for which a simulation of a model of the borehole using the effective borehole diameter generates simulation resistivity measurements that match, within a tolerance, resistivity measurements before execution of a borehole correction algorithm. Additional activity may include applying rugosity correction by generating resistivity logs, using the effective borehole diameter, that are corrected for rugosity and borehole effect. Additional apparatus, systems, and methods are disclosed.

Abstract: A method, apparatus, and system operate to include transmitting a plurality of electromagnetic waves, over a range of frequencies, into a plurality of pipes. The secondary electromagnetic field responses, associated with the electromagnetic waves, from the plurality of pipes are measured. Selective ones of the secondary electromagnetic field responses are canceled or reduced based on a selected pipe for inspection of the plurality of pipes.