Abstract: Various embodiments include apparatus and methods of operation with respect to well logging. Apparatus and methods include a tool having an arrangement of transmitters and receivers to capture a signal from a first region relative to the tool such that signal contributions from a second region relative to the tool are cancelable, based on placement of the transmitters and receivers with respect to each other. Additional apparatus, systems, and methods are disclosed.

Abstract: Sensors, systems and methods for downhole electromagnetic field detection, including a downhole micro-opto-electro-mechanical system (MOEMS) electromagnetic field sensor that includes a first surface that is at least partially reflective, a second surface that is at least partially reflective and suspended by one or more flexible members to define an optical cavity having a variable distance between the first and second surfaces, and a magnetically polarized layer attached to the second surface. A magnetic field passing through the optical cavity interacts with the magnetically polarized layer and a gradient in the magnetic field produces a displacement of the second surface that alters the variable distance and causes a spectrum variation in light exiting the sensor.

Abstract: Sensors, systems and methods for downhole electromagnetic field measurement, including a downhole micro-opto-electro-mechanical system (MOEMS) electromagnetic field sensor that includes a first surface that is at least partially reflective, a second surface that is at least partially reflective and suspended by one or more flexible members to define an optical cavity having a variable distance between the first and second surfaces, a first conductive layer attached to the first surface, and a second conductive layer attached to the second surface. The first and second conductive layers have an electrical potential proportional to an electromagnetic field within a formation surrounding the sensor. The electrical potential produces an electric field that displaces the second surface to alter the variable distance and cause a spectrum variation in light exiting the sensor.

Abstract: Multi-array laterolog tool systems and methods acquire a set of array measurements sufficient to provide laterolog tool measurements of differing array sizes. Such systems and method offer multiple depths of investigation while offering greater measurement stability in borehole environments having high resistivity contrasts. In at least some system embodiments, a wireline or LWD tool body has a center electrode positioned between multiple pairs of guard electrodes and a pair of return electrodes. At least some of the guard electrodes are positioned between component electrodes of associated split monitor electrodes that enable more accurate measurement of the guard electrode potential. The tool's electronics provide a current from the center electrode to the pair of return electrodes and currents from each pair of guard electrodes to the pair of return electrodes. Each of the currents may be distinguishable by frequency or distinguishable by some other means.

Abstract: A system and method for improving the accuracy of galvanic tool measurements is described. The system (300) may include a survey electrode (A0) and a first monitor electrode (M1?) positioned above the survey electrode. A second monitor electrode (M1) may be positioned below the survey electrode, and a first conductive wire (307) may couple the first monitor electrode to the second monitor electrode. A first measurement point (302) may be located on the conductive wire, and a first resistive element (Rm1) may be coupled to the conductive wire.

Abstract: Calibration tools and procedures that provide one or more calibration methods for multi-component induction tools can include use of a tilted elliptical loop and a circular loop. Measurement signals may be used for analytic calibration of a multicomponent induction tool. Additional apparatus, systems, and methods are disclosed.

Abstract: Various systems and methods for implementing and using a full tensor micro-impedance downhole imaging tool that includes downhole emitters that induce, at azimuthally-spaced positions on a borehole wall, fields having components in three different non-coplanar directions within a formation and directionally sensitive downhole sensors that sense the components caused by each emitter. The tool further includes a downhole controller that processes signals received from the directionally sensitive downhole sensors to provide a set of measurements representative of a 3×3 impedance tensor at each position.

Abstract: Various systems and methods are disclosed for implementing and using a multi-axial induction borehole imaging tool that includes emitters that induce, at azimuthally-spaced positions on a borehole wall, a plurality of fields having components in three non-coplanar directions within a formation. The tool also includes directionally sensitive inductive sensors that sense the components caused by each of the one or more inductive emitters, and a downhole controller that processes signals received from the directionally sensitive inductive sensors to provide a set of measurements representative of an impedance tensor at each position.

Abstract: A method and system to compensate for inaccuracies in crosswell tomography is presented. The method includes obtaining data from at least two receivers in response to transmissions from at least two transmitters. Next, at least one compensated value is derived based on the responses of the receivers to the transmitters. Finally, an inversion is performed based at least in part on the compensated value derived. This method eliminates inaccuracies that can be caused by sensor gain and phase variations in the inversion process. Inversion results with gain and phase compensation produce better imaging results that can better help determine the shape and boundaries of the reservoir.

Abstract: Various embodiments include apparatus and methods to provide a skin-effect correction. The skin-effect correction can be based on a pre-calculated correction coefficient library. In various embodiments, a skin-effect correction procedure can be applied that only uses a single-frequency R-signal measurement. In addition, an embodiment of a skin-effect correction procedure using a single-frequency R-signal measurement can be applied whenever the quality of the data from one of the multiple frequencies normally used in a multi-frequency method is reliable. Additional apparatus, systems, and methods are disclosed.

Abstract: Sensors, systems and methods for downhole electromagnetic field detection, including a downhole micro-opto-electro-mechanical system (MOEMS) electromagnetic field sensor that includes a first surface that is at least partially reflective, a second surface that is at least partially reflective and suspended by one or more flexible members to define an optical cavity having a variable distance between the first and second surfaces, and a magnetically polarized layer attached to the second surface. A magnetic field passing through the optical cavity interacts with the magnetically polarized layer and a gradient in the magnetic field produces a displacement of the second surface that alters the variable distance and causes a spectrum variation in light exiting the sensor.

Abstract: Sensors, systems and methods for downhole electromagnetic field measurement, including a downhole micro-opto-electro-mechanical system (MOEMS) electromagnetic field sensor that includes a first surface that is at least partially reflective, a second surface that is at least partially reflective and suspended by one or more flexible members to define an optical cavity having a variable distance between the first and second surfaces, a first conductive layer attached to the first surface, and a second conductive layer attached to the second surface. The first and second conductive layers have an electrical potential proportional to an electromagnetic field within a formation surrounding the sensor. The electrical potential produces an electric field that displaces the second surface to alter the variable distance and cause a spectrum variation in light exiting the sensor.

Abstract: Sensors, systems and methods for downhole electromagnetic field detection, including a downhole micro-opto-electro-mechanical system (MOEMS) electromagnetic field sensor that includes a first surface that is at least partially reflective, a second surface that is at least partially reflective and suspended by one or more flexible members to define an optical cavity having a variable distance between the first and second surfaces, and a first conductive layer attached to the second surface and having a first electric charge. An electric field passing through the optical cavity interacts with the first electric charge and displaces the second surface to alter the variable distance and cause a spectrum variation in light exiting the sensor.

Abstract: Various resistivity logging tools, systems, and methods are disclosed. At least some system embodiments include a logging tool and at least one processor. The logging tool provides transmitter-receiver coupling measurements that include at least direct coupling along the longitudinal tool axis (Czz), direct coupling along the perpendicular axis (Cxx or Cyy), and cross coupling along the longitudinal and perpendicular axes (Cxz, Cyz, Czx, or Czy). The processor combines a plurality of the coupling measurements to obtain inversion parameters. Based at least in part on the inversion parameter, the processor performs an inversion process to determine a vertical conductivity and, based in part on the vertical conductivity, determines borehole corrected values for said transmitter-receiver coupling measurements. One or more of the borehole corrected values can be provided as a function of borehole position.

Abstract: Multi-array laterolog tool systems and methods acquire a set of array measurements sufficient to provide laterolog tool measurements of differing array sizes. Such systems and method offer multiple depths of investigation while offering greater measurement stability in borehole environments having high resistivity contrasts. In at least some system embodiments, a wireline or LWD tool body has a center electrode positioned between multiple pairs of guard electrodes and a pair of return electrodes. At least some of the guard electrodes are positioned between component electrodes of associated split monitor electrodes that enable more accurate measurement of the guard electrode potential. The tool's electronics provide a current from the center electrode to the pair of return electrodes and currents from each pair of guard electrodes to the pair of return electrodes. Each of the currents may be distinguishable by frequency or distinguishable by some other means.

Abstract: A method and system to compensate for inaccuracies in crosswell tomography is presented. The method includes obtaining data from at least two receivers in response to transmissions from at least two transmitters. Next, at least one compensated value is derived based on the responses of the receivers to the transmitters. Finally, an inversion is performed based at least in part on the compensated value derived. This method eliminates inaccuracies that can be caused by sensor gain and phase variations in the inversion process. Inversion results with gain and phase compensation produce better imaging results that can better help determine the shape and boundaries of the reservoir.

Abstract: A disclosed subsurface electromagnetic field monitoring system employs at least one fiberoptic cable to optically communicate measurements from an array of electromagnetic field sensors in a borehole. A data processing system that receives the measurements and responsively models the subsurface electromagnetic field, which in at least some cases is generated by a controlled source such as a downhole electric or magnetic dipole source or a casing that serves as an electrode for injecting a distributed current into the formation.

Abstract: Tools, systems, and methods are disclosed for multi-component induction logging with iterative analytical conversion of tool measurements to formation parameters. At least some system embodiments include a logging tool and at least one processor. The logging tool provides transmitter-receiver coupling measurements that include at least diagonal coupling measurements (Hzz, Hxx, and/or Hyy) and cross-coupling measurements (Hxy, Hxz, and Hyz). The processor employs an iterative analytical conversion of the cross-coupling measurements into formation resistive anisotropy and dip information. The processor may further provide one or more logs of the resistive anisotropy and/or dip information.

Abstract: A logging tool and method for winding a multi-component induction (MCI) antenna is presented. The method eliminates unwanted dipole signals that are created by the voltage drop that takes place in the transmitter. The antenna is made of at least two parts physically separated, one on each side of the mandrel. The winding method is performed in a way that creates at least four windings arranged to eliminate dipole signals attributable to an asymmetric voltage distribution. The midpoint of the conductive wire that for is the antenna windings may be electrically attached to the tool body. This method is suitable for the winding of the cross-components X and Y of the MCI coil arrays.

Abstract: Disclosed herein are multicomponent borehole radar tools and methods. At least some tool embodiments employ at least two antennas that receive reflections of electromagnetic pulses transmitted from the tool. A processor processes the receive signals to identify reflection signals and to determine a direction and/or distance to the sources of the reflection signals. Possible sources include formation boundaries, fluid boundaries, cased wells, and other features that cause contrasts in electromagnetic properties. In addition to reflection signals, the measured responses may include direct signal measurements that are useful for determining formation resistivity and permittivity. Each of the antennas may transmit and receive, and they may be collocated to reduce tool size and reduce processing complexity. Disclosed logging tool examples employ both electric and magnetic dipole antennas.