Abstract: A measurement and communication system for use with a tubular string, comprises a tubular string having a plurality of self-powered, autonomous telemetry stations disposed at predetermined locations along the tubular string. Each autonomous telemetry station is adapted to receive at least one first signal and transmit at least one second signal related to the at least one first signal. Power is extracted from potential energy sources proximate each autonomous telemetry station. A method of communicating information along a tubular string comprises, disposing an autonomous telemetry station at predetermined locations along the tubular string. A preferred transmission path is autonomously determined at each of the autonomous telemetry stations. Information is transmitted along the tubular string according to the autonomously determined preferred path.

Abstract: An imaging tool made includes a pad whose curvature is chosen based on the expected range of borehole radius and the pad size so as to maintain the maximum standoff below a desired value. The curvature may be adjusted using fasteners.

Abstract: An apparatus, method and computer-readable medium for evaluating an earth formation are disclosed. The apparatus includes at least one coil on a logging tool conveyed in a borehole in the earth formation. Passage of a current through the coil induces an electrical current in the earth formation. At least two electrodes associated with the logging tool and in proximity to a wall of the borehole have a potential difference in response to the induced electrical current that is indicative of a property of the earth formation. The at least one coil may be mounted on a mandrel of a downhole assembly. The electrodes may be positioned on a first pad extendable from a mandrel of the downhole assembly.

Abstract: An apparatus, method and computer-readable medium for obtaining a resistivity image of an earth formation. The apparatus includes a downhole assembly configured to be conveyed in a borehole penetrating the earth formation; a plurality of sensor electrodes on the downhole assembly, each of the plurality of sensor electrodes having a different capacitance to a wall of the borehole; and at least one processor configured to: (i) process measurements using each of the sensor electrodes; (ii) process a subset of the measurements substantially unaffected by the different capacitances to produce an image of the borehole wall; and (iii) record the image on a suitable medium.

Abstract: Disclosed is an apparatus for estimating a property of an earth formation penetrated by a borehole having a substantially non-conducting liquid. The apparatus includes: a downhole tool having a transmitter electrode configured to convey an electric current into the earth formation. A measurement electrode is configured to receive the electric current from the earth formation, wherein the electric current bridges as least one of a first gap between the transmitter electrode and the formation and a second gap between the measurement electrode and the formation. A compensating circuit coupling the transmitter electrode to the measurement electrode is configured to reduce a reactive component of a total current received by the measurement electrode. A receiver coupled to the measurement electrode is configured to measure the total current to estimate the property.

Abstract: An apparatus for imaging a subsurface material traversed by a borehole, the apparatus including an imaging pad deployed by a logging instrument, the pad including a plurality of measuring sets, each measuring set including a first current injector electrode, a second current injector electrode, a pair of sensor electrodes disposed between the first current injector electrode and the second current injector electrode, and an output for coupling to an electronics unit adapted for producing the imaging of the subsurface material.

Abstract: An apparatus and method for reducing an electric current leakage in a logging tool, particularly relating to reducing electric current leakage by altering a phase difference between a biasing element and an electric current produced by a first power source. The apparatus may include one or more measure electrodes for imparting electric current into a formation, a current meter, at least one current return electrode, a controller, and a biasing element. The method includes adjusting a phase angle difference between the current leaving the measure electrode and a biasing signal applied to the biasing element from a second power source to reduce the current leakage of the apparatus.

Abstract: A reactance is introduced into a flow path of axial currents in an induction logging tool. The reactance may be a capacitor or an inductor. A transmitter antenna is operated at a frequency defined by a cutoff frequency related to the reactance.

Abstract: Calibration of the arrays of a multicomponent induction logging tool is achieved by positioning the tool horizontally above ground. The upper and lower housings of the tool are connected by a borehole conductivity simulator which as a resistance comparable to that of a borehole. Axial and radial positioning of the transmitter coils is done by monitoring outputs at receiver coils to achieve a minimum.

Abstract: An induction logging device is provided with additional electrodes. One set of electrodes provides voltages that are indicative of the current distribution in the borehole. The output of the first set of electrodes may be used for estimating formation resistivity. A second set of electrodes may be used to provide an image of the formation.

Abstract: Sequential measurements are made using a two terminal resistivity imaging device wherein the measure electrodes are activated sequentially with the remaining electrodes in a floating mode. This eliminates the hardware requirements for focusing electrodes, prevents galvanic leakage between proximal electrodes and the effects of mutual coupling between circuits including proximal electrodes.

Abstract: An apparatus, method and computer-readable medium for evaluating an earth formation are disclosed. A logging tool which has two coplanar antennas disposed at a known distance from an axis of the logging tool is conveyed into a borehole. The presence of a borehole effect is determined from a difference between outputs of the two antennas. The borehole effect may include eccentering of the logging tool in the borehole. Measurements made by an additional antenna and/or the two coplanar antennas may be corrected for the effects of eccentering. Horizontal and vertical formation resistivity as well as additional petrophysical properties may be determined.

Abstract: A method for correcting a measurement of a property of a subsurface material includes: selecting an instrument that includes a test circuit and a separate sensor, the test circuit configured for providing a standard for referencing to generate correction information, the sensor configured for: transmitting an electric signal into the subsurface material; and receiving a data signal from the subsurface material; wherein the test circuit and the sensor are switchably coupled to an electronics unit of the instrument; receiving the electric signal from the test circuit in the electronics unit; using the electronics unit, measuring at least one output characteristic of the instrument; and applying the correction information to the data signal according to the measured output characteristic.

Abstract: A method and apparatus for evaluating an earth formation penetrated by a borehole comprises taking resistivity measurements using a plurality of resistivity arrays or pads positioned within the borehole proximal the borehole wall. In one embodiment, pads are spaced apart azimuthally around the perimeter of a tool body, each pad carrying at least one electrode thereon. A sequence of resistivity measurement operations are performed involving sequentially operating each pad, in turn, as a transmitter, with remaining pads and electrodes operated as return electrodes. The sequence preferably involves a succession of adjacent pads around the perimeter of the tool body, resulting in a full rotational (360°) imaging of the formation penetrated by the borehole. In one embodiment, the pads include at least two electrodes spaced vertically apart from one another, such that helical current paths are defined between transmitting electrodes and return electrodes.

Abstract: A mixed mode tool uses an inductive source and detects galvanic currents and/or potentials at electrodes in proximity to a borehole wall to produce a resistivity image of the earth formation. Alternative, the magnetic field produced by a galvanic current is detected by an antenna coil and used to produce a resistivity image.

Abstract: An apparatus, method and computer-readable medium are provided for estimating a resistivity property of an earth formation. A logging tool includes a first antenna arrangement and a second antenna arrangement of the logging tool; and at least one device for maintaining the first antenna arrangement and the second antenna arrangement in proximity to a wall of the borehole. The first antenna arrangement and the second antenna arrangement may be at substantially the same axial location on the logging tool. Alternately, the first antenna arrangement and the second antenna arrangement may be at different axial positions on the logging tool. Extendible arms of the logging tool are configured to extend one or more of the first antenna arrangement and the second antenna arrangement against a face of the borehole.

Abstract: A power source for use in a downhole environment. The power source can include a microgenerator, where the microgenerator is comprised of a motive source, a rotor, a stator, and an electrical load. The motive source can be compressed gas, liquid, two-phase fluid, or combustion gases. The rotor may comprise a magnet and the stator may comprise a coil, such that rotating the rotor coaxially proximate to the stator produces electrical current. The electrical load includes any device used in downhole exploration and production that requires electrical energy.

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: A method for correcting a measurement of a property of a subsurface material includes: selecting an instrument that includes a test circuit and a separate sensor, the sensor adapted for transmitting an electric signal into the subsurface material and receiving a data signal from the subsurface material, wherein the test circuit and the sensor are switchably coupled to an electronics unit of the instrument; receiving the electric signal from the test circuit in the electronics unit; using the electronics unit, measuring at least one output characteristic of the instrument; and applying a correction to the data signal according to the measured output characteristic. An instrument and an additional method are provided.

Abstract: Measurements made by a multi-component induction logging tool are corrected for tool eccentricity in a deviated borehole. The eccentricity angle is determined from single frequency skin-effect corrected data and is then used to correct multifrequency data. Multifrequency focusing is then applied to the corrected multifrequency data. An inversion is then used to recover formation resistivity and relative dip and azimuth of the borehole.