Abstract: A logging while drilling tool includes a directional resistivity antenna and an antenna shield having. The shield has at least one slot having at least one electrically open end formed therein. The antenna shield may include a base portion and a plurality of spaced apart fingers extending away from the base portion such that the finger ends are electrically isolated from the tool body and from one another. The antenna shield may alternatively include a plurality of spaced apart plates that are electrically isolated from the tool body and from one another. These antenna shields have been found to provide suitable physical protection for sensitive antenna components while at the same time being substantially transparent to both z-mode and x-mode electromagnetic waves.

Abstract: A directional resistivity tool includes a pair of transmitters deployed between at least one pair of receivers. Each of the transmitters and receivers preferably includes collocated z-mode and x-mode antennae. Exemplary embodiments may further include additional receivers, for example, additional pairs of receivers deployed axially about the transmitters or one or more deep reading receivers deployed on one axial end of the transmitters. Tools in accordance with the invention enable directional resistivity measurements to be acquired at multiple depths of investigation using fewer transmitter firings than conventional tools.

Abstract: A microresistivity logging tool includes a dual function electrode deployed between a guard electrode and a return electrode. A drive circuit enables the electrical potential of the dual function electrode to be independently controlled so as to control a depth of investigation of a microresistivity measurement. The depth of investigation tends to increase with increasing electrical potential of the dual function electrode.

Abstract: Methods for making calibrated microresistivity logging measurements in nonconductive drilling fluid are disclosed. A calibrated measurement parameter (e.g., a calibrated electrical impedance or a calibrated potential difference) is obtained and further utilized to compute a formation resistivity. The methods tend to be particularly well suited for drilling applications in which the borehole environment is highly resistive (i.e., boreholes in which both the drilling fluid and the formation have a high resistivity).

Abstract: A method for estimating at least one formation parameter from a directional resistivity measurement includes computing a plurality of hypothetical directional resistivity values at a corresponding plurality of formation parameter values. The computation makes use of a forward model having at least one analytical expression that relates a directional resistivity measurement to the formation parameter. The analytical expression includes at least one image source term. Comparison of computed directional resistivity values with measured direct resistivity values enables a value of at least one formation parameter to be selected. The method may be implemented on a downhole processor.

Abstract: A method for providing an image of a formation surrounding a wellbore, includes: obtaining an apparent conductivity curve from main components of resistivity measurements of the formation; performing fitting for cross-components of the resistivity measurements; calculating scaling factors from the cross-component data; scaling apparent conductivity data by the calculated scaling factors; and plotting the scaled conductivity data to provide the image of the anisotropic formation. A system and a computer program product are disclosed.

Abstract: A method for forming a borehole image includes fitting logging sensor measurements residing in each of a plurality of azimuthal windows with corresponding mathematical fitting functions. The functions may then be evaluated at one or more corresponding azimuthal positions to obtain at least one sector value for each of the azimuthal windows. A two dimensional borehole image may be formed by repeating the procedure at multiple measured depths in the borehole.

Abstract: An instrument disposed into a drill string for imaging an earth formation includes: at least one band antenna disposed over an intermediate layer disposed into a groove in an outer surface of the drill string. A method of fabrication is provided.

Abstract: A downhole measurement tool includes at least one non-planar antenna configured for transmitting and/or receiving electromagnetic radiation. The non-planar antenna includes at least one non-planar loop of antenna wire deployed about a tool body. In one exemplary embodiment, the non-planar antenna may be thought of as being bi-planar in that it includes first and second sections defining first and second intercepting geometric planes. In another exemplary embodiment, the axial separation between the non-planar loop of antenna wire and a circular centerline of the antenna varies substantially sinusoidally with respect to an azimuth angle about the circumference of the tool. Exemplary non-planar antennae in accordance with the invention may be advantageously configured to transceive substantially pure x-, y-, and z-mode radiation.

Abstract: A method for making directional resistivity measurements and forming a directional resistivity image of a subterranean formation includes processing a plurality of directional resistivity measurements and corresponding azimuth angles to calculate a first order harmonic representation at selected azimuth angles. A two dimensional borehole image may be formed by repeating the procedure at multiple measured depths in the borehole.

Abstract: A method for correcting subterranean resistivity measurements to account for tool bending includes processing at least one coupling component and at least one cross-coupling component in combination with a tool bending angle. Such processing may, for example, remove one or more coupling components from a cross-coupling component. Removal of the coupling component(s) tends to increase the sensitivity of directional resistivity measurements to remote boundaries.

Abstract: An apparatus for measuring one or more earth formation properties during applications including formation evaluation and geosteering applications is provided. The apparatus includes: an elongated body; at least one recessed portion on a periphery of the elongated body; an electrically conductive coil forming a closed loop, at least a portion of the coil extending through the at least one recessed portion; and a u-shaped magnetically permeable and non-conductive material disposed between the coil and the at least one recessed portion, the u-shaped material partially surrounding the coil in the at least one recessed portion. A system for measuring one or more properties of an earth formation is also provided.

Abstract: One exemplary embodiment of a method for making directional resistivity measurements includes transmitting an axial electromagnetic wave in a borehole and receiving substantially pure axial and transverse components of the wave. A ratio of the axial and transverse components is computed and may be utilized as an indicator of various formation parameters. The invention advantageously enables the moment of the transmitting antenna to be canceled and therefore can result in improved accuracy.

Abstract: A microresistivity logging tool includes a shield electrode deployed between a guard electrode and a return electrode. A measuring electrode is deployed in and electrically isolated from the guard electrode and first and second potential electrodes are deployed in and electrically isolated from the shield electrode. The tool further includes at least one switch configured to switch the tool between distinct first and second microresistivity measurement modes. The first measurement mode is configured for making microresistivity measurements in conductive (water based) drilling fluid and the second measurement mode is configured for making microresistivity measurements in non-conductive (oil based) drilling fluid, thereby enabling the tool to be utilized in either type of drilling fluid.

Abstract: A method for making acoustic logging measurements includes grouping received acoustic waveforms into one of a plurality of groups, each group being representative of a measured borehole condition (e.g., a range of measured standoff values and/or a range of measured azimuth angles). The waveforms stored in at least one of the groups are stacked so as to obtain an averaged waveform. The averaged waveform may be further processed, for example, via a semblance algorithm to obtain at least one acoustic wave slowness.

Abstract: A closed-loop method for geosteering includes acquiring logging while drilling data and processing the logging while drilling data downhole while drilling to obtain a geosteering correction (a correction to the drilling direction based upon the LWD measurements). The geosteering correction is further processed downhole to obtain new steering tool settings which are then applied to the steering tool to change the direction of drilling. These steps are typically repeated numerous times without the need for uphole processing or surface intervention.

Abstract: A downhole tool includes circumferentially spaced and/or angled transducer elements. In one embodiment a standoff sensor has at least three piezoelectric transducer elements, at least a first element of which is configured to both transmit and receive ultrasonic energy. At least second and third of the elements are configured to receive ultrasonic energy transmitted by the first element in pitch catch mode. An electronic controller is configured to calculate a standoff distance from the ultrasonic waveforms received at the first, the second, and the third piezoelectric transducer elements. The controller may further be configured to estimate the eccentricity of a measurement tool in the borehole. Exemplary embodiments of the invention may improve borehole coverage and data quality and reliability in LWD caliper logging. In particular, the invention may advantageously reduce or even eliminate blind spots when logging eccentric bore holes.

Abstract: Cross-component measurements in combination with standard propagation resistivity measurements are processed to estimate the vertical and horizontal resistivities, relative dip and relative azimuth of an anisotropic earth formation.

Abstract: An antenna system for a downhole tool has an antenna that is configured to operate at a plurality of frequencies. The tuning circuit is on the interior of the tool and shielded from borehole fluids. The tuning circuit is coupled to the antenna by a transformer circuit.

Abstract: A directional resistivity tool includes at least one receiver deployed axially asymmetrically between at least one pair of transmitters. The transmitters are configured to transmit electromagnetic waves at first and second correspondingly distinct frequencies f1 and f2 such that: f1/f2=L2/L1, where L1 and L2 represent the corresponding axial distances between the first and second transmitters and the receiver. Exemplary embodiments of the invention further include a method for reducing the near-bed anisotropy effect. The anisotropy effect may be advantageously reduced (or removed) while at the same time providing for freedom in selecting the axial transmitter and receiver spacing.