Abstract: An apparatus for making azimuthally sensitive resistivity measurements of a subterranean formation is disclosed. The apparatus includes a magnetically permeably ring deployed about an electrically conductive tool body. An AC voltage supply is coupled to the tool body on opposing sides of the magnetically permeable ring, with at least one connecting conductor crossing outside the ring. Exemplary embodiments of this invention may further include one or more current sensing electrodes deployed in and electrically isolated from an outer surface of the tool body and may be utilized to make azimuthally resolved formation resistivity measurements.

Abstract: Aspects of this invention include a downhole tool (such as a steering tool) including first and second sensor sets for measuring substantially instantaneous drill string rotation rates. Each of the sensor sets includes at least one accelerometer disposed to measure cross-axial acceleration components. Embodiments of this invention advantageously enable gravitational and tool shock/vibration acceleration components to be cancelled out, thereby improving accuracy. Moreover, exemplary embodiments of this enable stick/slip conditions to be detected and accommodated.

Abstract: An apparatus for obtaining tool face angles on a rotating drill collar in substantially real time is disclosed. In one exemplary embodiment the apparatus includes a magnetoresistive magnetic field sensor deployed in a tool body. The apparatus further includes a programmed processor configured to calculate tool face angles in substantially real time from the magnetic field measurements. The programmed processor may optionally further be configured to correlate the calculated tool face angles with logging while drilling measurements for use in borehole imaging applications.

Abstract: Aspects of this invention include a downhole tool having first and second radially offset ultrasonic standoff sensors and a controller including instructions to determine at least one of a drilling fluid acoustic velocity and a drilling fluid attenuation coefficient from the reflected waveforms received at the standoff sensors. The drilling fluid acoustic velocity may be determined via processing the time delay between arrivals of a predetermined wellbore reflection component at the first and second sensors. The drilling fluid attenuation coefficient may be determined via processing amplitudes of the predetermined wellbore reflection coefficients. The invention advantageously enables the acoustic velocity and attenuation coefficient of drilling fluid in the borehole annulus to be determined in substantially real-time.

Abstract: Methods for determining the distance and relative axial position between twin and target wells are disclosed. In one exemplary embodiment the magnitude and direction of the interference magnetic field vector are processed to determine the distance and the axial position. In another exemplary embodiment, a change in direction of the interference magnetic field vector between first and second longitudinally spaced magnetic field measurements may be processed to determine the distance and axial position. In still another exemplary embodiment of the invention, a component of the magnetic field vector aligned with the tool axis may be measured in substantially real time during drilling and utilized to determine the distance between the two wells. Embodiments of this invention improve the accuracy and/or the frequency of distance determination between twin and target wells.

Abstract: A method for estimating an azimuthal dependence of a parameter of a borehole using logging sensor measurements acquired as a function of azimuth of the logging sensors is provided. The method includes acquiring at least one logging sensor measurement and a corresponding azimuth from a downhole tool. The method further includes processing a convolution of the logging sensor measurement and corresponding azimuth with a predetermined filter to determine convolved logging sensor data for at least one azimuthal position. Certain embodiments of this invention may be advantageously utilized in LWD imaging applications to provide for superior image resolution and noise rejection as compared to prior art imaging techniques.

Abstract: A loop antenna useful, for example, in investigation of earth formations. Embodiments of the invention provide a loop antenna circuit comprising a loop antenna disposed to generate, in response to an electromagnetic wave, a pick-up signal on an output node. Loop antenna circuit further includes a tuning network coupled to the loop antenna. The tuning network is disposed to provide simultaneous tuning at a plurality of interrogation frequencies. Further embodiments include a preamplifier circuit coupled to the loop antenna. The preamplifier circuit is disposed to receive the pick-up signal on an input node and provide a high impedance load to the loop antenna for a first of the plurality of interrogation frequencies to reduce the secondary radiation from the loop antenna to below a predetermined value at the said first interrogation frequency.

Abstract: An azimuthally sensitive logging while drilling tool is disclosed. The tool may be suitable, for example, to measure azimuthal variations of electrical properties of a subterranean formation. The tool includes at least one transmitter disposed to transmit electromagnetic energy and a longitudinally spaced receiver array. The receiver array includes a plurality of discrete magnetic field sensors deployed about a circumference of the tool body. In one exemplary embodiment, the tool includes six or more magnetic field sensors selected from either giant magnetoresistive sensors or anisotropic magnetoresistive sensors.

Abstract: A downhole steering tool is disclosed. The steering tool includes a rotatable shaft, a substantially non-rotating tool body deployed about the shaft, and a plurality of force application members deployed on the steering tool body. The steering tool further includes a bendable section deployed in the steering tool body. The bendable section is disposed to bend preferentially relative to the steering tool body under an applied bending load. The use of a steering tool body having a bendable section tends to advantageously reduce bending stresses in the steering tool body during use. Moreover, tools embodying this invention may be suitable for higher dogleg severity applications.

Abstract: Aspects of this invention include a downhole tool having first and second members disposed to translate substantially linearly with respect to one another. A magnet is deployed on the first member and a plurality of magnetic field sensors is deployed on the second member. The magnetic field sensors are spaced in a direction substantially parallel with a direction of translation between the first and second members. The tool typically further includes a controller disposed to determine a linear position of the first and second members with respect to one another from magnetic flux measurements made at the magnetic field sensors. Exemplary position sensor embodiments of the present invention are non-contact and therefore are not typically subject to mechanical wear. Embodiments of the invention therefore tend to advantageously provide for accurate and reliable linear position measurements.

Abstract: Aspects of this invention include a steering tool having a controller configured to provide closed-loop control of hydraulic fluid pressure. In one exemplary embodiment, closed-loop control of a system (reservoir) pressure may be provided. In another embodiment, closed-loop control of a blade pressure may be provided while the blade remains substantially locked at a predetermined position. Other exemplary embodiments may incorporate rule-based-intelligence such that pressure control thresholds may be determined based on various measured and/or predetermined downhole parameters. The invention tends to reduce the friction (drag) between the blades and the borehole wall and thereby also tends to improve drilling rates. Moreover, the invention also tends to improve the service life and reliability of downhole steering tools.

Abstract: An electronic assembly for use in a downhole tool includes a damming boot deployed about at least one integrated circuit component on a circuit board. The boot is disposed to house the integrated circuit leads and solder joints in a substantially sealed cavity between the circuit board, the integrated circuit body, and an inner surface of the damming boot. The boot is also disposed to support the integrated circuit body and thereby improve the shock and vibration resistance of various electronic assemblies used in downhole tools. The invention also tends to improve the reworkability of downhole electronic assemblies.

Abstract: A technique of estimating electrical parameters of an earth formation accounts for spatial inhomogeneities and frequency dispersion. The results are achieved using a model which is evaluated to generate predicted values for a plurality of electrical signals measured in a borehole in an earth formation as a function of a first set of model electrical parameters, a second set of model electrical parameters and model spatial coordinates of boundaries between regions of the earth formation. Transformations are applied to the measured electrical signals and the predicted values. The electrical parameters and spatial coordinates are selected to cause approximate agreement between the transformed measurements and the transformed predicted values.

Abstract: An azimuthally sensitive electromagnetic measurement tool is provided. The tool may be suitable, for example, to measure azimuthal variations of electrical properties of a subterranean formation. The tool includes a transmitter disposed to transmit electromagnetic energy into a subterranean formation and a longitudinally spaced receiver. At least one of the transmitter and the receiver includes a sector antenna. The sector antenna includes an exposed length of antenna wire that forms an arc about a portion of a circumference of the tool body. In one exemplary embodiment, the receiver includes first and second sector antennae, which, in combination, subtend a circular angle of about 360 degrees about the circumference of the tool body without substantially overlapping one another.

Abstract: An apparatus for magnetizing a wellbore tubular includes a plurality of co-axial magnetizing coils deployed on a frame. The coils are typically deployed about a track on which the tubular may be traversed. Exemplary embodiments may further include a magnetic field sensor disposed to measure the imparted magnetic field along the length of the tubular as it is removed from the track after magnetization. Exemplary embodiments of this invention provide for semi-automated control of tubular magnetization and thereby enable a repeatable magnetic pattern to be imparted to each of a large number of wellbore tubulars.

Abstract: Aspects of this invention include a rotary steerable steering tool having a sensor arrangement for measuring downhole dynamic conditions. Rotary steerable tools in accordance with this invention include a rotation rate measurement device disposed to measure a difference in rotation rates between a drive shaft and an outer, substantially non-rotating housing. A controller is configured to determine a stick/slip parameter from the rotation rate measurements. Exemplary embodiments may also optionally include a tri-axial accelerometer arrangement deployed in the housing for measuring lateral vibrations and bit bounce. Downhole measurement of stick/slip and other vibration components during drilling advantageously enables corrective measures to be implemented when dangerous dynamic conditions are encountered.

Abstract: A method for determining a rate of change of longitudinal direction of a subterranean borehole includes positioning a downhole tool in a borehole, the tool including first and second longitudinally spaced surveying devices disposed thereon. The method further includes causing the surveying devices to measure longitudinal directions of the borehole at first and second longitudinal positions and processing the longitudinal directions of the borehole to determine the rate of change of longitudinal direction of the borehole between the first and second positions. The method may further include processing the measured rate of change of longitudinal direction of the borehole and a predetermined rate of change of longitudinal direction to control the direction of drilling of the subterranean borehole. Exemplary embodiments of this invention tend to minimize the need for communication between a drilling operator and the bottom hole assembly, thereby advantageously preserving downhole communication bandwidth.

Abstract: A method for compressing borehole image data is disclosed. In one exemplary embodiment, the method includes acquiring image data downhole, selecting a block of the image data to compress, applying at least one filter to the block, selecting a subset of pixels from the block, and quantizing each of the subset of pixels. Exemplary methods in accordance with this invention may advantageously provide for sufficient data compression to enable conventional telemetry techniques to be utilized for transmitting borehole images to the surface in substantially real time. Moreover, exemplary methods in accordance with this invention reduce data latency and the susceptibility to telemetry errors as compared to the prior art.

Abstract: A method for locating casing string joints using a measurement while drilling tool is disclosed. The method includes deploying an MWD tool in a wellbore and measuring the magnetic field along a length of the wellbore. Changes in the magnetic field along the length of the wellbore are evaluated to determine the location of at least one casing joint. Embodiments of this invention may be advantageously utilized, for example, in sidetracking operations to avoid milling through a casing joint. Use of this invention may obviate the need for a separate wireline run to locate the casing joints.

Abstract: A method for determining a borehole geometry parameter vector and/or lateral tool displacement vectors in a borehole is provided. The method includes acquiring at least one set of standoff measurements at a corresponding time. The method also includes processing a system of equations to determine the parameter vector and/or the lateral displacement vector(s). The system of equations may include variables representative of the parameter vector, the lateral tool displacement vector(s), and the standoff measurements. Exemplary embodiments of this invention advantageously enable the borehole parameter vector and/or the lateral displacement vector to be determined substantially contemporaneously.