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: Mud pulse telemetry systems and methods that employ some combination of modulated pulse positions, modulated pulse widths, and modulated pulse amplitudes to increase telemetry data rates. In at least some of the employed coding techniques, information is conveyed by the positions of both the upward and downward transitions. In some embodiments, fixed symbol intervals are used to convey combinatorial coded waveforms. In other embodiments, variable length symbol intervals include both a pulse position interval and a pulse width interval. The two intervals can be independently varied to convey telemetry data. Subject to specific system constraints, optimal coding efficiencies may be expected at data rates of between four and seven bits per symbol interval.

Abstract: An apparatus and method for performing high transverse resolution voltage measurements in downhole logging tools utilized to determine the resistivity of an adjacent portion of a borehole wall. Two current electrodes 508 and 509 are energized by an excitation source to create an oscillatory electric field in a borehole wall. The voltage drop from each voltage electrode in a row of laterally spaced voltage electrodes 604 is measured relative to a shared voltage electrode 606 longitudinally spaced from the row of electrodes. The differential voltage is used in combination with a measured current flow to determine a resistivity value for the borehole. A second row of laterally spaced voltage electrodes 608 having electrodes laterally offset from the electrodes of the first row is included to provide high transverse resolution. A common mode voltage at the shared voltage electrodes is measured and utilized to minimize the resistivity measurement error.

Abstract: A decision-feedback equalizer (DFE) can be operated at higher frequencies when parallelization and pre-computation techniques are employed. Disclosed herein is a DFE design that operates at frequencies above 10 GHz, making it feasible to employ decision feedback equalization in optical transceiver modules. An adaptation technique is also disclosed to maximize communications reliability. The adaptation module can be treated as a straightforward extension of the pre-computation unit. At least some method embodiments include, in each time interval: sampling a signal that is partially compensated by a feedback signal; comparing the sampled signal to a set of thresholds to determine multiple speculative decisions; selecting and outputting one of the speculative decisions based on preceding decisions; and updating a counter if the sampled signal falls within a window proximate to a given threshold. Once a predetermined interval has elapsed, the value accumulated by the counter is used to adjust the given threshold.

Abstract: Disclosed herein are electromagnetic resistivity logging systems and methods that employ an antenna configuration having at most two transmitter or receiver antenna orientations that rotate relative to the borehole. The measurements made by this reduced-complexity antenna configuration enable the determination of at least seven components of a coupling matrix, which may be determined using a linear system of equations that express the azimuthal dependence of the measurements. For increased reliability, measurement averaging may be performed in azimuthally spaced bins. The coupling matrix components can then be used as the basis for determining logs of various formation parameters, including vertical resistivity and anisotropy.

Abstract: Logging tools having protected tilted antennas are disclosed, along with construction methods therefor. In one method embodiment, a tilted antenna on a retrievable segment of a downhole tool is constructed by: forming an elliptical recess on the segment; forming an antenna within the elliptical recess; and forming an elliptical pattern of windows over and perpendicular to the axis of the elliptical antenna. Some tool embodiments comprise a retrievable segment of a downhole tool having an elliptical recess; an elliptical antenna disposed within the elliptical recess; and an elliptical pattern of windows formed over and perpendicular to the plane of the elliptical antenna.

Abstract: Front wheel drive vehicles, bicycles or motorized scooters, include an enclosed drive belt connected to provide power to the front wheel through a chain, where the vehicle is steered by way of a front fork extending outside and over the head tube of the frame, and methods of use thereof. Movable linkages, which may be belts, chains, or other linkages, provide power generated using pedals or a motor to the front wheel. The belts are preferably enclosed within the frame or the front fork to prevent interference or damage. A chain is preferably used to drive the front wheel. Having the front fork outside the head tube allows for the head tube to route the linkage from the frame to the front fork without interference by the steering connection to the front wheel, allowing for a full range of motion of the front wheel.

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: An apparatus and method for minimizing the effects of a common mode voltage signal in downhole logging tools utilized to determine the resistivity of an adjacent portion of a borehole wall. Two current electrodes are energized by an excitation source to create an oscillatory electric field in a borehole wall. A voltage drop across a segment of the borehole wall is measured by two voltage electrodes, and the differential voltage is used in combination with a measured current flow to determine a resistivity value for the borehole wall. A common mode voltage in front of the two voltage electrodes is measured and minimized by controlling the excitation source, thereby reducing the resistivity measurement error.

Abstract: Acoustic telemetry devices and methods that provide directional detection. In one embodiment, a disclosed acoustic telemetry device comprises at least two acoustic sensors and an electronics module. The electronics module combines the detection signals from the acoustic sensors to obtain a combined signal that substantially excludes signals propagating in a direction opposite to the communication signal. The disclosed systems and methods can be trained in the field and will readily accommodate an irregular and unknown signal transmission medium between the two acoustic sensors.

Abstract: A displaced electrode amplifier (“DEA”) for measuring signals from high impedance sources. The amplifier may include an operational amplifier (“op-amp”) configured as a unity gain buffer, with a feedback path to the non-inverting input to at least partly compensate for a parasitic input shunt impedance. In cases where the device is to measure AC signals in high ambient temperatures, the non-inverting input may be coupled via a large resistance to a ground reference that is driven with a second feedback signal to magnify the effective value of the large resistance. Where a differential configuration is desired, one or more tuning resistors may be provided to match responses of different input buffer stages, thereby maximizing the common mode rejection. The disclosed amplifier is suitable for use in oil-based mud resistivity imaging tools but is also suitable for other applications.

Abstract: A wellbore drilling system includes a weight on bit controller configured to generate a normalized weight on bit output, a drilling torque controller configured to generate a normalized toque on bit output, and a differential pressure controller configured to generate a normalized differential pressure output. The system further includes a rate of penetration controller that is configured to multiply a rate of penetration setpoint with the normalized weight on bit output, the normalized torque on bit output, and the normalized differential pressure output to generate a rate of penetration output.

Abstract: Systems and methods for frequency-domain compensation in optical communication systems. In pre-equalization embodiments, the transmitter transforms the data stream into a frequency domain signal and applies a compensation filter before transforming it back into a pre-distorted time domain signal. As the pre-distorted time domain signal propagates through the optical channel, optical dispersion effects counter the pre-distortion, producing an equalized signal at the channel output. In post-equalization embodiments, the receiver transforms the received signal into a frequency domain signal and applies a compensation filter before transforming it back into an equalized time domain signal. Pre-equalization may prove less expensive due to the square-law characteristic of photodetectors employed by most receivers.

Abstract: Multipole acoustic logging-while-drilling (LWD) tools and associated methods are disclosed herein. In some embodiments, the disclosed acoustic LWD tool comprises a transmitter array and at least one receiver array. The transmitter array generates acoustic waves with an excitation pattern having a cutoff frequency greater than about 3 kHz. The receiver array is spaced apart from the transmitter array and is configured to detect said acoustic waves. Some of the disclosed method embodiments comprise: generating multipole acoustic waves in a fluid-filled borehole using an excitation pattern with a cutoff frequency greater than about 3 kHz; selectively detecting acoustic waves that propagate with said excitation pattern; and determining an acoustic shear wave slowness for a formation penetrated by the borehole.

Abstract: A migration method using hybrid one-way and full-way (HOF) wave equation propagation. The HOF method extrapolates seismic wavefields in less complex media with a one-way wave equation propagator and extrapolates seismic wavefields in extremely complex media with a full-way wave equation propagator. For prestack depth migration, the HOF extrapolates source-side and receiver-side wavefields independently. Frequency-space domain and time-space domain imaging conditions are applied to the one-way and the full-way extrapolated wavefields, respectively. A suitable amplitude matching factor is introduced to combine the one-way and full-way images. The HOF method is a cost-effective migration that produces superior image quality with less noises and less computational resources.

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: 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: 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: Disclosed drilling systems offer multiple methods providing access to the open borehole without first tripping the drill string. In some embodiments, a drill bit has a tool port that is blocked by a plug during normal drilling operations. When a tool is deployed through the interior of the drill string, the tool port opens, enabling the tool to enter the borehole beneath the drill string and perform logging or sampling operations. The plug may be attached to the drill bit by a hinge or pivot, or alternatively, the plug may be discarded and a replacement seated in place after the tool is retracted into the drill string. In other embodiments, the drill bit itself is detachable, allowing the bit to be parked in the hole or in a side bore. If desired, the bit can be re-attached by lowering the drill string to the bottom of the hole.

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.