Abstract: Improved receiver antennas are disclosed for long offset tensor induction army logging tools. The disclosed antennas include a bobbin which accommodates a ferromagnetic core. The outer surface of the bobbin is wrapped around a binding so that winding is thicker or includes more turns towards a center of the bobbin and is thinner or includes less turns towards the outer ends of the bobbin. The result is that the primary winding with a curved or parabolic profile that enhances the effective magnetic permeability and magnetic moment of the antenna. A secondary winding may also be utilized for flux feedback compensation. The elimination of winding turns towards the ends of the magnetic coil result in reduced DC resistance and the reduction in parasitic capacitance of the antennas. The disclosed antennas may be used in x-y-z receiver arrays.

Abstract: Sensor assemblies including transmitter and receiver antennas to respectively transmit or receive electromagnetic energy. The sensor assemblies are disposed in downhole tools adapted for subsurface disposal. The receiver is disposed at a distance less than six inches (15 cm) from the transmitter on the sensor body. The sensor transmitter or receiver includes an antenna with its axis tilted with respect to the axis of the downhole tool. A sensor includes a tri-axial system of antennas. Another sensor includes a cross-dipole antenna system.

Abstract: An induction or propagation apparatus for performing measuring the tensor resistivity of a sample of matter includes a non-conductive, generally cylindrical tubular member adapted to receive the matter therein, a triaxial transmitter, at least one triaxial receiver, and an electronic module. The electronic module is adapted to energize the triaxial transmitter, control acquisition of signals by the at least one triaxial receiver, and perform anisotropic measurements and analysis. The triaxial transmitter and the at least one triaxial receiver are disposed on the generally cylindrical tubular member in axial spaced relationship.

Abstract: A well logging instrument housing includes an electrically non-conductive tube and at least one layer of fiber embedded in a matrix surrounding an exterior of the tube. The at least one fiber layer includes at least one carbon fiber. The at least one or carbon fiber is arranged to have substantially no closed loops.

Abstract: An induction or propagation apparatus for performing measuring the tensor resistivity of a sample of matter includes a non-conductive, generally cylindrical tubular member adapted to receive the matter therein, a triaxial transmitter, at least one triaxial receiver, and an electronic module. The electronic module is adapted to energize the triaxial transmitter, control acquisition of signals by the at least one triaxial receiver, and perform anisotropic measurements and analysis. The triaxial transmitter and the at least one triaxial receiver are disposed on the generally cylindrical tubular member in axial spaced relationship.

Abstract: Improved receiver antennas are disclosed for long offset tensor induction army logging tools. The disclosed antennas include a bobbin which accommodates a ferromagnetic core. The outer surface of the bobbin is wrapped around a binding so that winding is thicker or includes more turns towards a center of the bobbin and is thinner or includes less turns towards the outer ends of the bobbin. The result is that the primary winding with a curved or parabolic profile that enhances the effective magnetic permeability and magnetic moment of the antenna. A secondary winding may also be utilized for flux feedback compensation. The elimination of winding turns towards the ends of the magnetic coil result in reduced DC resistance and the reduction in parasitic capacitance of the antennas. The disclosed antennas may be used in x-y-z receiver arrays.

Abstract: Sensor assemblies including transmitter and receiver antennas to respectively transmit or receive electromagnetic energy. The sensor assemblies are disposed in downhole tools adapted for subsurface disposal. The receiver is disposed at a distance less than six inches (15 cm) from the transmitter on the sensor body. The sensor transmitter or receiver includes an antenna with its axis tilted with respect to the axis of the downhole tool. A sensor includes a tri-axial system of antennas. Another sensor includes a cross-dipole antenna system.

Abstract: Techniques for calibrating an electromagnetic logging tool equipped with a plurality of antennas, with at least one antenna having its axis at an angle with respect to a tool axis, include disposing a test loop about the tool such that an axis of the tool and a plane on which the test loop lies form a tilt angle that is between about 0 and 90 degrees. An induced signal is measured at one of the antennas by energizing another of the antennas. Embodiments analyze the induced signal corresponding to a max or min extrema associated with a coupling effect due to the test loop. In other embodiments a corrected signal is compared with a calculated signal.

Abstract: An antenna for an electromagnetic tool having a longitudinal axis and a core. The antenna includes a flexible dielectric substrate flexibly conformed about the core and an electrical conductor disposed on the dielectric substrate. The electrical conductor is disposed on the substrate such that the antenna has a dipole moment having any desired direction relative to the longitudinal axis of the tool.

Abstract: Sensor assemblies including transmitter and receiver antennas to respectively transmit or receive electromagnetic energy. The sensor assemblies are disposed in downhole tools adapted for subsurface disposal. The receiver is disposed at a distance less than six inches (15 cm) from the transmitter on the sensor body. The sensor transmitter or receiver includes an antenna with its axis tilted with respect to the axis of the downhole tool. A sensor includes a tri-axial system of antennas. Another sensor includes a cross-dipole antenna system.

Abstract: A well logging tool and method are disclosed comprising a conductive mandrel, an antenna array disposed around the conductive mandrel, wherein the antenna array comprises a plurality of antennas disposed on insulating supports and at least one contact spacer, the at least one contact spacer having at least one conductor channel having a contact assembly disposed therein, a sleeve disposed over the antenna array, wherein the sleeve includes at least one electrode assembly, the at least one electrode and the contact assembly adapted to provide a radially conductive path from an exterior of the well logging tool to the conductive mandrel and wherein the electrode assembly comprises a first conductor exposed to the exterior of the well logging tool and at least one second conductor conductively connected to the first conductor and exposed to an inner surface of the sleeve, wherein at least one of the first conductor or the second conductor being in sealed contact with the sleeve to prevent the passage of fluid th

Abstract: An apparatus for measuring fluid resistivity includes a flow line adapted to be in fluid communication with formation fluids, wherein the flow line includes a first section comprising a first conductive area, a second section comprising a second conductive area, and an insulating section disposed between the first section and the second section to prevent direct electrical communication between the first section and the second section; a first toroid and a second toroid surrounding the flow line around the first section and the second section, respectively, wherein the first toroid is configured to induce an electrical current in a fluid in the flow line and the second toroid is configured to measure the electrical current induced in the fluid in the flow line; and an electronic package to control functions of the first toroid and the second toroid.

Abstract: An induction tool includes a conductive mandrel; at least one array including a transmitter, a bucking coil, and a receiver disposed in an insulating tool body surrounding the conductive mandrel; and an electrode disposed on the insulating tool body at a selected location between the bucking coil and the receiver, wherein the selected location is spaced from the transmitter at a distance corresponding approximately to the harmonic mean of the distance between the transmitter and the bucking coil and the distance between the transmitter and the receiver, and wherein the electrode includes a contact forming a conductive path to the conductive mandrel. Additional electrodes may be disposed above and below each transmitter and receiver coil to reduce sensitivity to eccentricity of the tool in the borehole.

Abstract: A logging tool includes a tool body; a simple transmitter comprising a single antenna disposed on the tool body; four simple receivers, each comprising a single antenna, disposed on the tool body and spaced apart from the simple transmitter to form four arrays; and an electronic module for controlling operation of the four arrays, wherein the simple transmitter is configured to generate a magnetic field having a transverse component, wherein each of the four simple receivers is sensitive to the magnetic field generated by the simple transmitter, and at least one of the four simple receivers is sensitive to the transverse component of the magnetic field generated by the simple transmitter, and wherein the four arrays are configured to provide measurements at at least three depths of investigation.

Abstract: A sensor for measuring mud resistivity in a borehole includes a transmitter having a magnetic moment in a first direction; and a receiver having a magnetic moment in a second direction, wherein the first direction and the second direction are substantially different, wherein the transmitter and the receiver are disposed in an insulating collar of a downhole tool, and wherein the transmitter is disposed at a selected distance no more than 10 inches from the receiver along a longitudinal axis of the downhole tool.

Abstract: A composite shell adapted to cover a source or sensor, particularly for subsurface applications. The shell provides transparency to the passage of signals to or from the source or sensor. The shell is adapted with a uniform semi-conductive surface providing a path for electric currents flowing within a subsurface borehole to short near the source or sensor.

Abstract: A well logging tool and method are disclosed comprising a conductive mandrel, an antenna array disposed around the conductive mandrel, wherein the antenna array comprises a plurality of antennas disposed on insulating supports and at least one contact spacer, the at least one contact spacer having at least one conductor channel having a contact assembly disposed therein, a sleeve disposed over the antenna array, wherein the sleeve includes at least one electrode assembly, the at least one electrode and the contact assembly adapted to provide a radially conductive path from an exterior of the well logging tool to the conductive mandrel and wherein the electrode assembly comprises a first conductor exposed to the exterior of the well logging tool and at least one second conductor conductively connected to the first conductor and exposed to an inner surface of the sleeve, wherein at least one of the first conductor or the second conductor being in sealed contact with the sleeve to prevent the passage of fluid th

Abstract: A well logging tool includes a housing; at least one piston moveably disposed on the housing; at least one sensor disposed on the at least one piston; a pressure compensation system coupled to the at least one piston such that a pressure at a back side of the at least one piston is substantially identical to a pressure outside the well logging tool; and a piston deployment mechanism for deploying the at least one piston. A method for well logging using a logging tool having at least one piston and a pressure compensating system, wherein the at least one piston includes at least one sensor, the method includes disposing the well logging tool in a borehole; deploying the at least one piston to establish a contact between the at least one piston and a wall of the borehole; and measuring a formation property using the at least one sensor.

Abstract: The invention provides an apparatus for making an electromagnetic measurement from within a subsurface borehole. The apparatus comprises an elongated support having electrically conductive segments and adapted for disposal within the borehole; an antenna adapted to transmit electromagnetic energy disposed on the support such that its axis is tilted or perpendicular with respect to the axis of the support; a sensor disposed on the support and adapted to detect a current flow along the support when the antenna is activated to transmit electromagnetic energy; and means to process the detected current flow to provide an indication of the measurement quality or the position of the support within the borehole.

Abstract: Methods and apparatus for detecting and monitoring the borehole effect in subsurface measurements. Toroidal sensor configurations address the undesired axial electric currents that travel along the borehole when antennas with tilted or transverse axes are used to make electromagnetic measurements. Embodiments use currents measured along the instrument to determine the quality of measured logs, the borehole size, and instrument position or orientation within the borehole.