Abstract: A retrievable tool for steering through an earth formation includes a first tool assembly and a tilted antenna attached to the first tool assembly. The tool also includes a second tool assembly attached to the first tool assembly and a tilted antenna attached to the second tool assembly. The first tool assembly attaches to the second tool assembly so that the antennas are tilted in predetermined directions. The tilted antennas are transmitter antennas or receiver antennas. Each tool assembly is a tubular cylinder with a longitudinal axis running the length of the cylinder, wherein the tubular cylinder has two ends, each end including a rotational attachment mechanism. The tool assemblies attach to each other through their rotational attachment mechanisms. The rotational attachment mechanism may be a screw-on mechanism, press-fit mechanism, or welded mechanism.

Abstract: A disclosed fracture characterization method includes: collecting three-dimensional resistivity measurements of a volume surrounding an open borehole; analyzing the measurements to determine parameters describing fractures in the volume; and providing a report to a user based at least in part on said parameters. A fluid with a contrasting resistivity is employed to make the fractures detectable by a directional electromagnetic logging tool in the borehole. illustrative parameters include fracture direction, height, extent, length, and thickness. The resistivity measurements can be augmented using a borehole wall image logging tool. Also disclosed are fracturing methods that include: positioning a directional electromagnetic logging tool proximate to a formation; fracturing the formation; monitoring fracture progression with said tool; and halting the fracturing when measurements by said tool indicate that a predetermined set of criteria have been satisfied.

Abstract: In some embodiments, an apparatus (200) includes a tubular to operate downhole. The tubular has a longitudinal axis and has a cutout (210N) that has a direction that is other than 90 degrees to the longitudinal axis of the tubular. The apparatus also includes an antenna (202A) positioned in the cutout of the tubular. The antenna is to perform at least one of a transmission or reception of an electromagnetic signal that has a path that is to traverse a subsurface formation.

Abstract: An apparatus for measuring a resistivity of a formation comprising an instrumented bit assembly coupled to a bottom end of the apparatus. At least one first electromagnetic wave antenna transmits an electromagnetic wave signal into the formation. At least one second electromagnetic wave antenna located on the instrumented bit assembly and longitudinally spaced apart from the at least one first electromagnetic wave antenna receives the electromagnetic wave signal transmitted through the formation. Electronic circuitry is operably coupled to the at least one second electromagnetic wave antenna to process the received signal to determine a resistivity of the formation proximate the instrumented bit assembly.

Abstract: Methods and systems that compensate for magnetic interference in azimuthal tool measurements. At least some method embodiments include a downhole logging method that includes taking measurements as a function of orientation from inside a borehole. The measurements are associated with different azimuthal bins, and an azimuthal direction is determined for each azimuthal bin. Because the tool rotates at a constant rate, the relative number of measurements associated which the different bins can be used to measure the effective sizes of the different bins and to redetermine the effective angles of the bins in the presence of magnetic interference. The tool measurements may include, but are not limited to, formation resistivity, magnetic field, and formation density.

Abstract: Methods and systems for determining the horizontal resistivity, vertical resistivity, and relative dip angle of anisotropic earth formations. Some of the disclosed methods and systems measure sinusoidal variation of azimuthally sensitive resistivity logging tool measurements, determine parameters representative of the sinusoidal variation, and perform inversion based on the sinusoidal parameters. When cast in this manner, the inversion process may yield more accurate and consistent resistivity and dip angle estimates. The sinusoidal parameters preferably take the form of average and peak-to-peak measurements, but may also take other forms. Moreover, use of such sinusoidal parameters enables a condensed representation of the resistivity logging tool measurements, enabling significantly more efficient communication and storage of these measurements. The condensed representations continue to enable directional boundary detection and geosteering.

Abstract: This invention is directed to a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. The present invention accomplishes this objective by using an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. This invention also relates to a method and apparatus for steering a downhole tool during a drilling operation in order to maintain the borehole within a desired earth formation.

Abstract: Nearby conductors such as pipes, well casing, etc., are detectable from within a borehole filled with an oil-based fluid. At least some method embodiments provide a current flow between axially-spaced conductive bridges on a drillstring. The current flow disperses into the surrounding formation and causes a secondary current flow in the nearby conductor. The magnetic field from the secondary current flow can be detected using one or more azimuthally-sensitive antennas. Direction and distance estimates are obtainable from the azimuthally-sensitive measurements, and can be used as the basis for steering the drillstring relative to the distant conductor. Possible techniques for providing current flow in the drillstring include imposing a voltage across an insulated gap or using a toroid around the drillstring to induce the current flow.

Abstract: Methods and apparatus for detecting nearby conductors such as pipes, well casing, etc., from within a borehole. A nearby casing string can be detected by transmitting an electromagnetic signal from a first antenna on a downhole logging tool and measuring a response signal with a second antenna. As the tool rotates, the transmitting and measuring are repeated to determine the azimuthal dependence of the response signal. The azimuthal dependence is analyzed to determine an diagonal component and a cross component. The amplitude of the diagonal component is indicative of distance to the conductive feature. Direction can be determined based on the diagonal component alone or in combination with the cross component. Sinusoidal curve fitting can be employed to improve accuracy of the distance and direction estimates. At least one of the antennas is preferably tilted. Measurement results are presented for parallel tilted and perpendicular tilted antennas.

Abstract: Downhole tools and techniques acquire information regarding nearby conductors such as pipes, well casing, and conductive formations. At least some method embodiments provide a current flow along a drill string in a borehole. The current flow disperses into the surrounding formation and causes a secondary current flow in the nearby conductor. The magnetic field from the secondary current flow can be detected using one or more azimuthally-sensitive antennas. Direction and distance estimates may be obtainable from the azimuthally-sensitive measurements, and can be used as the basis for steering the drillstring relative to the distant conductor. Possible techniques for providing current flow in the drillstring include imposing a voltage across an insulated gap or using a toroid around the drillstring to induce the current flow.

Abstract: A drill string can include at least one transmit antenna and at least one receive antenna. The transmit antenna transmits at least one electromagnetic signal into a region of an earth formation. The receive antenna receives the signal from the region of the earth formation. The transmit antenna comprises one of a magnetic dipole and an electric dipole, and the receive antenna comprises the other of the magnetic dipole and the electric dipole. At least one characteristic of the region of the earth formation is determined, based at least partially on the signal received by the receive antenna. A homogenous part of the electromagnetic signal may be reduced, to thereby increase a depth of detection of the characteristic.

Abstract: Logging tools and methods for obtaining a three-dimensional (3D) image of the region around a borehole. In at least some embodiments, a 3D imaging tool rotates, transmitting pulses that are approximately a nanosecond long and measuring the time it takes to receive reflections of these pulses. Multiple receivers are employed to provide accurate triangulation of the reflectors. In some cases, multiple transmitters are employed to obtain compensated measurements, i.e., measurements that compensate for variations in the receiver electronics. Because reflections occur at boundaries between materials having different dielectric constants, the 3D imaging tool can map out such boundaries in the neighborhood of the borehole. Such boundaries can include: the borehole wall itself, boundaries between different formation materials, faults or other discontinuities in a formation, and boundaries between fluids in a formation.

Abstract: Oil-based mud imaging systems and methods having leakage current compensation. In some embodiments, disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between at least two current electrodes that create an electric field in a borehole wall, and is further provided with electronics coupled to the current electrodes to determine a differential voltage between the voltage electrodes in response to different current frequencies from the current electrodes. From the voltage measurements at different frequencies, the computing facilities determine borehole wall resistivity as a function of depth and azimuth, and may display the resistivity as a borehole wall image.

Abstract: Logging tools and methods employing an at-bit loop antenna to acquire azimuthal resistivity measurements proximate to the bit enable low-latency geosteering signals to be generated. In some embodiments, the at-bit antenna is part of a bottom hole assembly that includes a drill bit, a mud motor, and a resistivity tool. The mud motor is positioned between the at-bit antenna and the resistivity tool. The resistivity tool includes at least one loop antenna that is not parallel to the at-bit loop antenna. The at-bit antenna is part of an at-bit module that, in some embodiments, transmits periodic electromagnetic signal pulses for the resistivity tool to measure. In other embodiments, the at-bit module measures characteristics of electromagnetic signal pulses sent by the resistivity tool and communicates the measured characteristics to the resistivity tool via a short hop telemetry link.

Abstract: Disclosed dielectric logging tools and methods employ three or more receive horn antennas positioned between at least two transmit antennas, which can also be horn antennas. The logging tools can operate in the range between 100 MHz and 10 GHz to provide logs of formation permittivity, formation conductivity, standoff distance, and electrical properties of material in the standoff gap. Logs of water-saturated porosity and/or oil movability can be readily derived. The presence of additional receive antennas offers a significantly extended operating range, additional depths of investigation, increased measurement accuracy, and further offers compensation for tool standoff and mudcake effects. In both wireline and logging while drilling embodiments, at least some disclosed dielectric logging tools employ a set of three axially-spaced receive antennas positioned between pairs of axially-spaced transmit antennas.

Abstract: Various disclosed resistivity imaging tools and methods provide a high-resolution electrode configuration for imaging in oil-based imaging in oil-based muds. Some tool embodiments have a sensing surface that comprises: a measurement electrode, a focus electrode surrounding the measurement electrode, and a return electrode surrounding the focus electrode. The sensing surface can be provided on an extendable sensor pad or on the wall-contacting portion of a stabilizer. Some method embodiments include measuring the measurement electrode current while driving a voltage signal between the measurement electrode and the return electrode. The voltage signal may simultaneously or sequentially provide energy at different frequencies. The resistivity measurements are combined with tool position and orientation measurements to form a borehole wall image.

Abstract: This invention is directed to a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. The present invention accomplishes this objective by using an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. Although this invention is primarily intended for MWD or LWD applications, this invention is also applicable to wireline and possibly other applications.

Abstract: Multimodal geosteering systems and methods are disclosed. Some disclosed tool embodiments include first and second transmitter-receiver arrangements that make geosteering measurements using different forms of energy (such as acoustic and electromagnetic energy) to provide geosteering measurements that at least indicate a boundary direction but may also indicate a boundary distance. Some disclosed method embodiments include: determining a direction to a bed boundary using measurements with different energy types; and adjusting a drilling direction based at least in part on said determination. Combinations of (or selections between) the different measurements may be made based on, inter alia, measurement range, resolution, and contrast. Some disclosed system embodiments include a memory and a processor. The memory stores geosteering display software that configures the processor to generate an image with different regions based on the different types of geosteering measurements.

Abstract: Borehole data presentation systems and methods that facilitate communication of volumetric logging data to a surface processing system for presentation to a driller or other user interested in visualizing the formations surrounding a borehole. The disclosed systems optionally tailor the telemetry stream to match the chosen display technique, thereby maximizing the logging system utility for the driller. Variable opacity of certain data regions or certain data discontinuities greatly facilitates data comprehension, particularly when true three-dimensional display technologies are employed. Holographic or stereoscopic display technologies may be employed to show the three-dimensional dependence of measured formation properties such as resistivity, density, and porosity. Alternatively, the radial axis can be used to represent a formation parameter value, thereby enabling cylindrical cross-plots of multiple measurements.

Abstract: Systems and methods for look-ahead boundary detection and distance estimation are disclosed. In some embodiments, a drilling method includes extending a borehole with a drill string that includes a resistivity logging tool. The logging tool makes upward-looking and downward-looking resistivity measurements based on radial current flow. The upward looking and downward looking resistivity measurements are processed to estimate the distance to approaching bed boundaries, and drilling can be halted when the estimated distance reaches a desired value. Such information can be used to anchor casing at advantageous points and can further be used to avoid penetrating water-containing formations below a hydrocarbon reservoir.