Abstract: Apparatus and techniques are described, such as for obtaining information indicative of a formation resistivity, such as using an array laterolog apparatus. For example, an electrical excitation is coupled from a well tool in a borehole to a geologic formation through which the borehole extends, the excitation coupled through excitation electrodes on the well tool selected according to a specified excitation mode, and induced voltages are received from the geologic formation resulting from the excitation using monitor electrodes selected according to the specified excitation mode. In some examples, a voltage difference between a first pair of monitor electrodes is estimated through use of the induced voltage received through at least one additional monitor electrode.

Abstract: A tool for providing modifiable structures in a wellbore using ferrofluids in a downhole system is provided. The downhole system can include a tool body, a source of ferrofluid, and a magnet. The magnet can magnetically couple with the ferrofluid from the source for arranging the ferrofluid adjacent for modifying a parameter of an object coupled with or in the tool body when the tool body is positioned in the wellbore.

Abstract: A tool for enhancing or directing magnetic fields using ferrofluids in a downhole system is provided. The downhole system can include a tool body, a source of ferrofluid, and a positioning magnet. The positioning magnet can magnetically couple with the ferrofluid from the source for enhancing or directing a magnetic field through at least a portion of an annulus between the tool body and a wellbore formation.

Abstract: A tool for isolating objects in a wellbore using ferrofluids in a downhole system is provided. The downhole system can include a tool body, a source of ferrofluid, and a magnet. The magnet can magnetically couple with the ferrofluid from the source for arranging the ferrofluid adjacent to the tool body for isolating an object positioned in a wellbore from effects of fluids present in the wellbore.

Abstract: A tool for influencing electrically conductive paths using ferrofluids in a downhole system is provided. The downhole system can include a tool body, a source of ferrofluid, and a magnet. The magnet can provide a magnetic field that influences an electrically conductive path within an annulus between the tool body and a wellbore formation by arranging the ferrofluid from the source in the annulus.

Abstract: Apparatus and methods to visualize formation properties and distances associated with formations can be implemented in a variety of applications. In various embodiments, one or more visualization schemes and systems arranged to implement such schemes can use a combination of visual structures to provide information about measured formations. Additional apparatus, systems, and methods are disclosed.

Abstract: Various embodiments include apparatus and methods related to finding a position in an underground formation. Apparatus and methods can include receiving signals from a receiver in an underground formation in response to signals generated from transmitting sources, each of the transmitting sources located at a known position; and processing the received signals, based on the signals generated from the transmitting sources, to determine the position of the receiver. A number of techniques can be applied to processing the received signal. Additional apparatus, systems, and methods are disclosed.

Abstract: According to aspects of the present disclosure, systems and methods for optimizing deep resistivity measurements are described herein. The method may include obtaining one or more first multi-component measurements from a downhole tool disposed in a bore-hole. The downhole tool may comprise multi-component antennae. A relative structural dip angle, ?, of the downhole tool relative to formations may be determined, for example, through the use of an additional downhole tool, or computationally using the one or more first multi-component measurements. A tilt angle of at least one of the multi-component antenna may be adjusted, with the adjusted tilt angle being based on the dip angle. The method may further include obtaining one or more second multi-component measurements associated with the adjusted tilt angle, and determining a formation characteristic based, at least in part, on the one or more second multi-component measurements, without including or considering formation anisotropy effects.

Abstract: Various embodiments include apparatus and methods related to finding a position in an underground formation. Apparatus and methods can include receiving signals from a receiver in an underground formation in response to signals generated from transmitting sources, each of the transmitting sources located at a known position; and processing the received signals, based on the signals generated from the transmitting sources, to determine the position of the receiver. A number of techniques can be applied to processing the received signal. Additional apparatus, systems, and methods are disclosed.

Abstract: Various embodiments include apparatus and methods related to finding a position in an underground formation. Apparatus and methods can include receiving signals from a receiver in an underground formation in response to signals generated from transmitting sources, each of the transmitting sources located at a known position; and processing the received signals, based on the signals generated from the transmitting sources, to determine the position of the receiver. A number of techniques can be applied to processing the received signal. Additional apparatus, systems, and methods are disclosed.

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: 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 ranging system utilizes gradiometric data to determine the direction to and distance between a first and second well without any knowledge or involvement of the borehole or formation characteristics in order to intersect and/or avoid the second well. In general, this is achieved by deploying a downhole assembly comprising transmitters and receivers having magnetic dipoles, along with bucking receivers positioned between the transmitters and receivers.

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: In some embodiments, an apparatus and a system, as well as a method and an article, may operate to acquire multiple output values provided by at least one elongated, unitary acoustic sensor operating as a secondary propagation medium. The sensor has multiple mechanical-to-electrical conversion probe points along its length, to provide corresponding multiple output values proportional to mechanical movement along the length of the sensor, the mechanical movement being induced by acoustic waves in a primary propagation medium comprising a geological formation and borehole fluid. Further activity may include processing the output values to determine slowness in an acoustic wave propagating between at least two of the probe points. Additional apparatus, systems, and methods are disclosed.

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.

Abstract: A system and method for measuring a formation property in a wellbore is disclosed. In the method, an acoustic measurement tool is introduced into a wellbore. The acoustic measurement tool may include a transmitter and a plurality of sensors. At least one of the plurality of sensors may be positioned in a non-uniform spacing configuration. The transmitter may transmit energy into the formation. The plurality of sensors may measure energy received from the formation. Additionally, a time semblance of the formation may be determined using at least one time semblance algorithm generalized for non-uniform sensor spacing.

Abstract: Various embodiments include apparatus and methods to land a well in a target zone with minimal or no overshoot of target zone. The well may be directed to a target in the target zone based on the separation distance between a transmitter sensor (212) and a receiver sensor (214) being sufficiently large to detect a boundary of the target zone from a distance from the boundary of the target zone such that collected received signals from activating the transmitter sensor (212) can be processed in a time that provides minimal or no overshoot of a target zone. Additional apparatus, systems, and methods are disclosed.