Abstract: Various embodiments include apparatus and methods to inspect casing defects in a pipe such as a casing associated with a drilling operation. Electrical connectors contacting the inside wall of the pipe can be used to generate a current in the pipe. Magnetic fields correlated to an anomaly or anomalies that alter the current can be sensed to identify the presence of the anomaly or anomalies. Additional apparatus, systems, and methods are disclosed.

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 for estimating at least one geophysical property is disclosed. The method includes using a plurality of transmitter electrodes distributed in a conductive medium, periodically passing rectangular current impulses through the media; collecting a sequence of sounding data between each of the impulses with a receiver electrode disposed between the plurality, determining a first difference and a second difference of the electric potential between points of the collected data; when each of the transmitters is excited, acquiring a focused measurement by simultaneously calculating a combination of at least one orthogonally weighted measurement and at least one axially weighted measurement obtained by the receiver, wherein the weighting is obtained from a condition of equipotentiality in four outer electrodes of the receiver; and, applying a time-differentiation technique to obtain deep measurements that exhibit low noise contribution from shallow features. An apparatus is also disclosed.

Abstract: A sensor device includes a first electrode, a second electrode, a gap forming member and a functional element. The first electrode is composed of a first metallic material. The second electrode is spaced apart from the first electrode, and composed of a second metallic material. The gap forming member is arranged with a gap being formed between the gap forming member and a portion of a surface of the first electrode. The functional element is configured and arranged to measure a difference in electric potential between the first electrode and the second electrode so that a state of a measurement site to be measured is measured based on the difference in electric potential as measured by the functional element.

Abstract: The invention is concerned with a tool for imaging a formation, the tool comprising: a pad capable of alignment adjacent a wall of the formation. The pad has located thereon an imaging electrode for injecting current into the formation. There is a first return electrode separated from the imaging electrode for receiving the injected current. There is at least one recessed electrode that is located at a different distance from the wall of the formation as the other electrodes.

Abstract: A method for marine electromagnetic surveying includes transmitting a first electromagnetic field oriented in a first direction into a body of water. A second electromagnetic field oriented in a second direction is transmitted into the body of water, wherein the second direction is substantially transverse to the first direction. A parameter related to electromagnetic field amplitude is detected at a plurality of longitudinally and laterally spaced apart positions behind a vessel. The components of the detected electromagnetic field parameter are resolved into components along the first and second directions by using the geometrical symmetries and asymmetries of the transmitting source. Systems for implementing such methods are also provided.

Abstract: In order to increase result accuracy the noise effect during vessel motion is reduced, wherefore direct current pulses are excited the parameters of which are set basing on section conductivity and deposit depth, the electric field is measured simultaneously on pairs of receiving electrodes basing on the spatial averaging of potential of double electric layer that is generated on the boundary of electrode and water during the pulses and pauses between them, and geoelectrical parameters are determined.

Abstract: A tool 1 is used in electrical investigation of geological formations GF surrounding a borehole BH. The tool 1 is comprised in a string of tools TS. The tool 1 comprises a current injection section CIS and a current return section CRS. The string of tools TS comprises at least one other section OS1. The current injection section CIS is electrically decoupled from the current return section CRS. The current injection section CIS is electrically decoupled from the at least one other section OS1 when the current injection section CIS and the at least one other section OS1 are adjacent to each other. The current return section CRS is electrically decoupled from the at least one other section OS1 when the current return section CRS and the at least one other section OS1 are adjacent to each other.

Abstract: A method for significantly reducing measurement time for electrical resistivity profiling and logging without degrading the quality of the measurement includes simultaneously transmitting a current from multiple points to underground and carrying out mathematic processing to calculate a potential obtained when a current is transmitted independently from any transmission point, based on observed response potential waveforms. Further current waveforms having a covariance of zero are selected. Then, a possible response obtained independently at transmission point can be determined by dividing the covariance of the observed potential waveform and the current waveform by the variance of the current waveform. As the waveform zeroing the covariance, an M-sequence code with zero added to the end thereof is applied.

Abstract: A method of accurately measuring earth resistance even when the composition state of soil that affects the installation of a metering device for measuring earth resistance is unknown. The method comprises measuring a potential at a first potential electrode point, measuring a potential at a second potential electrode point, calculating a voltage slope corresponding to a change rate of potential difference, using a potential difference between the first and second potential electrode points, and setting a potential point according to voltage slope characteristics and measuring earth resistance. A measurement approximating an accurate value of earth resistance can be performed even when soil composition characteristics are unknown at a site.

Abstract: Method for removing air wave noise from shallow water controlled source electromagnetic survey data, using only the measured data and conductivity values for sea water (140) and air. The method is a calculation performed numerically on CSEM data and resulting in an estimate of those data that would have been acquired had the water layer extended infinitely upward from the seafloor. No properties of the sub-sea sediments are used. Synthetic electromagnetic field data are generated for (a) an all water model (141) and (b) an air-water model (146-147) of the survey region. These simulated results are then used to calculate (148-150) electromagnetic field values corresponding to a water-sediment model with water replacing the air half space, which represent measured data adjusted to remove air wave noise.

Abstract: The average current at a plurality of measure electrodes of a resistivity imaging tool is determined and subtracted from the individual measure currents to give a resistivity image with improved dynamic range.

Abstract: Two embodiments of marine geo-electric probe methods for hydrocarbon deposits survey comprise—excitation of electromagnetic field in a surveyed medium by transmitting two rectangular current pulses therethrough, the first—during forward traveling of a probe device along a profile and the second—during backward traveling thereof,—measuring instant values of the first and second electric potential differences during the time between the pulses, wherein, the equal-zero condition of the electric potential differences along the profile is ensured,—calculating three sets of normalized electrical parameters based on difference values,—solving an inverse problem via a differential equation for the dipole source voltage in an electrochemically polarizable medium using the parameters,—producing data according to said electrical parameters, and—determining conductivity of the medium, induced-polarization factor and decay time constant of the polarization potential difference.

Abstract: Disclosed herein is an apparatus and method for measuring a specific soil resistance for distribution grounding by a three-electrode method. The apparatus uses three electrodes to measure a specific soil resistance as well as an earth resistance based on a three-electrode method in specific soil resistance measurement that is the most basic but likely to be overlooked in a practical distribution work.

Abstract: Dynamic gain setting is provided for a multiphase flow measuring device that measures in-phase and quadrature signals. The average current at a plurality of measure electrodes is determined and subtracted from the individual measure currents to give a measurement with improved dynamic range.

Abstract: A galvanic resistivity tool with one or more measurement electrodes and guard electrodes, and one or more shielding electrodes. The potential difference between the measurement electrodes and the guard electrodes is controlled to minimize current flow between the measurement electrodes and the shielding electrodes. This provides improved focusing and avoids effects of contact impedance.

Abstract: Process for determining the resistivity (Rt) of a formation (9) surrounding a well (10) equipped with a casing (11) consisting of several casing segments (11.i, 11.

Abstract: The object of the present invention is to realize a low-invasive underground exploration apparatus, system, and method which are capable of specifying the kind, three-dimensional position, and amount of a substance present in the ground. The underground exploration apparatus, system, and method includes: measuring, at multiple points, a high frequency voltage that appears upon conduction of high frequency current through the ground to obtain measurement results at two or more frequency levels; employing an ground model using the finite element method, the boundary element method, an impedance network, or the like to estimate a substance in the ground by changing unknown quantities of the ground model such as local dielectric constant and electric conductivity so as to make an error between the actual measured value and the calculated value smaller; and displaying input information of the ground model and results of the estimation processing two-dimensionally or three-dimensionally.

Abstract: A method and apparatus for minimizing direct coupling between transmitters and receivers on a downhole logging tool are disclosed. One embodiment includes a transmitter, a bucking device, and a plurality of receivers, where signals may be directly coupled from the transmitter into the receivers and signals may be indirectly coupled from the transmitter into the receivers through the formation and borehole environment. The bucking device minimizes the magnitude of the signals that are directly coupled from the transmitter into multiple receivers within the plurality. By varying the current in the bucking device, the bucking device minimizes the magnitude of the directly coupled signal of each receiver in the plurality, and each receiver may utilize a common bucking device.

Abstract: The present invention relates to a drill string fitted with information transmission means. The hollow rods of conductive material have their inside faces covered in an insulating material. The transmission means comprise a first electrical unit having at least a first annular electrode secured to the insulating inside face of the drill string, said electrode being in electrical contact with the mud contained inside the drill string so as to establish a flow of current in the conductive mud; and a second electrical unit disposed in said borehole, close to the top end of the drill string in order at least to receive the information contained in said electrical current.

Abstract: A method for determining the resistivity of earth formations penetrated by a wellbore. Electrical current is imparted to the wellbore and the earth formations from a first electrode located on a mandrel disposed in the wellbore. The electrical current is returned at a second electrode on the mandrel at a spaced apart location from the first electrode. Voltage differences are measured between a first pair and a second pair of electrodes located on the mandrel between the first and the second electrodes. Circuits used to measure the voltage differences are adjusted until the measured voltage difference between the second pair is substantially the same as the measured voltage difference between the first pair. Then the electrical current is returned to an electrode at the earth's surface or other location distal from the first electrode, and measuring the voltage differences is repeated. A difference of the voltage differences is then calculated.

Abstract: A method and apparatus for determining leaks in sewage pipes. The apparatus includes a measuring probe having several radially arranged measuring electrode segments, the measuring probe being positioned in the sewage pipe. With the probe sections and electrode segments being arranged in such radial manner, the electrical probe, once electrically powered, measures a leakage current emitted by the probe's central section with several probes sections at a same electrical potential, and divides the measured leakage currents of the probe's central section in a mathematical operation into two or more electrode segments to determine both an axial and radial location for defects within the sewage pipe. A higher leakage current in one segment indicates the location of a leak, and the amplitude of the leakage current indicates the volume of the leak.

Abstract: A conductivity measuring device comprises a low-potential intermediate electrode which is capable of being in connected state by a switch and which is disposed between a couple of measuring electrodes for transmitting and receiving. Each of said electrodes is made contact with a body to be tested so that the conductivities of the surface and the inner portion of said body to be tested can be measured, respectively.