Abstract: This disclosure may generally relate to systems and methods systems and methods for determining drill bit position while drilling. A bit-position-while-drilling system may include: a drill bit; a gyroscope unit coupled to the drill bit to measure angular velocity about three axes, wherein the gyroscope unit is coupled to the drill bit in a known relationship to the drill bit; and an information handling system operable to receive gyroscope measurements from gyroscope unit and determine position of the drill bit in a borehole based at least partially on the gyroscope measurements.

Abstract: Apparatus, systems, and methods for ranging operate to use a wireline active ranging system to initially determine a relative distance and relative direction from a first well (e.g., ranging well) to a second well (e.g., target well) and an EM azimuthal logging tool to maintain or adjust the distance from the target well while drilling the ranging well. Additional apparatus, systems, and methods are disclosed.

Abstract: A method for establishing downlink telemetry communication to a downhole system involves placing into a drillstring a telemetry transcoder, and advancing the drillstring so the telemetry transcoder is below the surface. The method then transmits downlink EM telemetry signals from surface equipment. These signals are received at the telemetry transcoder which retransmits the signals as mud pulse signals. The mud pulse signals are received at the downhole system.

Abstract: A seismic data recording unit. The seismic data recording unit may include a housing and retractable arms coupled to the housing. The seismic data recording unit may include a respective seismic sensor coupled proximate the end of a retractable arm. The retractable arm may move from a position on or proximate the housing to a position away from the housing.

Abstract: A magnetic pulse actuation arrangement configured for use in a downhole system, the arrangement including: a workpiece; a layer placed on a portion of the workpiece, the layer having a different magnetic permeability than the workpiece; and, an inductor including a coil and configured to deliver a magnetic pulse to the workpiece to urge the workpiece in a direction, the layer facing the coil.

Abstract: A downhole tool is provided for measuring accelerations at a location within a subterranean borehole. The tool is rotatable around the longitudinal direction of the borehole. The tool includes four accelerometers, each accelerometer measuring acceleration in a respective direction and being arranged such that at least a component of its measured acceleration is normal to the longitudinal direction. The accelerometers are further arranged such that no more than any two of the four accelerometers have their respective components parallel to the same direction. The tool also includes a first device which measures the rotational speed of the tool. The tool also includes a processor unit which relates the acceleration measured by each accelerometer to the true acceleration at that accelerometer by a respective scaling term and a respective offset, and combines the measured accelerations and the tool rotational speed to re-calibrate the scaling terms as the tool rotates.

Abstract: A method for performing contamination monitoring through estimation wherein measured data for optical density, gas to oil ratio, mass density and composition of fluid components are used to obtain plotting data and the plotting data is extrapolated to obtain contamination levels.

Abstract: A steering tool may include a tool body, gimbal body rotatably coupled to the tool body, and an angular positioning device to rotate the gimbal body relative to the tool body. One or more sensors may be coupled to the gimbal body. The sensors may be one or more gyros, accelerometers, and magnetometers. A gyro may be aligned with the axis of rotation of the gimbal body and may be used to detect rotation of the gimbal body. The detected rotation may be used to stabilize the gimbal body by using the angular positioning device. A gimbal toolface angle relative to a reference frame may be determined based on readings of one or more of the sensors. The gimbal body may be rotated to align with a reference position by the angular positioning device and rotated to one or more other gimbal toolface angles, at which sensor readings may be taken.

Abstract: A method is provided for selectively enabling inertial measurement unit (IMU) sensors. The method comprises enabling a gyroscope of the IMU sensors for generating a device orientation output estimate, selectively enabling an accelerometer of the IMU sensors for improving the device orientation output estimate when a magnitude of an angular velocity is less than a centripetal velocity threshold, an accelerometer jitter error estimate is less than a gyroscopic orientation error estimate, a filled accelerometer filter length is less than a full length of an accelerometer filter, and a filled magnetometer filter length is less than a full length of a magnetometer filter. The method also includes enabling a magnetometer of the IMU sensors when the accelerometer is enabled, and an accelerometer gravitational error angle is less than a predetermined accelerometer gravitational error angle threshold.

Abstract: The disclosure includes an inductive conductivity sensor for measuring the specific electrical conductivity of a medium with a transmitter coil energized by an input signal, a receiver coil coupled with the transmitter coil via the medium, which receiver coil supplies an output signal that is a measure for the conductivity of the medium, and a housing enclosing the transmitter coil and the receiver coil, which housing comprises at least one housing section designed to be immersed in the medium, the housing wall of said housing section surrounding the transmitter coil and the receiver coil. The housing is made of a magnetic plastic or resin for inductively decoupling the transmitter coil from the receiver coil. In certain embodiments, the housing may be made of a ferromagnetic material. Another aspect of the disclosure includes a method for manufacturing the conductivity sensor.

Abstract: A downhole control device is configured to activate downhole equipment requiring control signals. The device having a housing adapted to protect electronic components; a transducer configured to measure one or more of pressure and temperature; an accelerometer; and control circuitry in communication with the transducer and the accelerometer and configured to control the operation of a downhole tool depending on data from one or more of the transducer and accelerometer. The transducer, the accelerometer and at least part of the control circuitry are mounted on a chassis that is removably inserted within the housing.

Abstract: A method and apparatus for a rugged three-axis inclinometer for determining an object's orientation with respect to a gravitational field. Components of the apparatus include but not limited to a magnet, a non-magnetic casing, a ferrofluid, one or more non-magnetic gravitational field aligning materials attached to the magnet and a plurality of angle sensors attached to the non-magnetic casing. In this regard, when the apparatus is rotated, the gravitational field aligning materials maintain a constant orientation of the magnet and the angle sensors experience different magnetic field strengths as they rotate around the magnet. The position of the apparatus, with respect to the gravitational field can then be calculated based on the angle sensor outputs.

Abstract: A method for surveying a formation includes conveying a survey instrument into the wellbore; measuring one or more parameters of interest relating to a wellbore tubular in the wellbore; and operating the survey instrument after the measured parameter of interest indicates that the wellbore tubular is being tripped out of the wellbore.

Abstract: A system for monitoring a drilling rig operation includes a drilling rig assembly and at least one sensor coupled to a member of the drilling rig assembly to sense a parameter related to operation of the drilling rig assembly. A client device coupled to the at least one sensor includes a data acquisition device for receiving data from the at least one sensor. The client device also includes a first radio, which is coupled to the data acquisition device. A base station located a distance from the client device comprises a second radio that communicates wirelessly with the first radio in order to transfer data between the data acquisition device and the base station.

Abstract: A method of predicting a well trajectory wherein the method utilises a series of parameters to calculate the trajectory. The method is characterised in that the parameters include the angle of a drill bit (23) relative to a well bore (27), and the variation of said angle during drilling wherein the variation of said angle is related to the moment on the bit (23).

Abstract: A six-direction indicator is provided in an XYZ rectangular coordinate system and includes a shaft on an X axis, a rotation member rotatable around an axis inclined with respect to a rotation axis, guide pins provided upright on the rotation member, and a guide member provided around the X-axis to surround the rotation member. The guide member has a zigzag slit track bent alternately in a mountain-like shape and a valley-like shape in the X direction at intervals of 60° around the X-axis. The guide pins are inserted in the slit track and move around on the slit track by rotation of the shaft. The device indicates one of the positive and negative directions on the U, V, and W axes crossing one another at intervals of 60° around the X-axis.

Abstract: Casing or work string orientation indicating apparatus and methods. A system for indicating orientation of a structure in a wellbore includes an orientation indicating device responsive to fluid flow through the device, whereby fluid flow through the device at a selected flow rate produces a reduced pressure differential across the device when the device is at a preselected azimuthal orientation, compared to an increased pressure differential across the device produced by fluid flow through the device at the selected flow rate when the device is not at the azimuthal orientation. A method of detecting orientation of a structure in a wellbore includes the steps of: flowing fluid at a selected flow rate through an orientation indicating device interconnected to the structure; and observing a substantially constant pressure differential across the device during the flowing step, thereby indicating that the structure is at a predetermined azimuthal orientation.

Abstract: Tools and methods for subsurface operations. Circuit arrangements providing a damping effect against undesired vibration effects on inertial data signals derived from inertial sensors disposed in a downhole tool.

Abstract: A centralizer for an instrument such as an in-place inclinometer is described. The centralizer has a clamp with an inner receptacle configured for coupling to the instrument housing, and a plurality of elongate fingers extending from the clamp that center the instrument in the casing. The fingers carry rollers that fit into grooves in the instrument casing. The fingers are arcuate and provide a spring-like contact force that causes the rollers to abut the instrument casing and stabilize the instrument.

Abstract: A method and system for azimuth measurements using one or more gyro sensors is disclosed. The method includes acquiring a first data from each of the gyro sensors with an input axis aligned to a first angular orientation and acquiring a second data from each of the gyro sensors with the input axis flipped to a second angular orientation opposite to the first angular orientation. An earth rate component at the first angular orientations is determined based on a difference between the first data and the second data to cancel out bias of each of the gyro sensors. The method may include acquiring a third data of the gyro sensor with the input axis aligned to the same angular orientation as the first angular orientation. An average of the first data and the third data may be used instead of the first data for determining the earth rate component.

Abstract: A gyroscopically-oriented survey tool, includes a housing having an axis. Three accelerometers are mounted in the housing with their axis set orthogonally. A first of the axis is aligned to the axis of the housing. A second of the axis is perpendicular to the first. A third of the axis is perpendicular to both of the first and the second. Three gyroscopes are mounted pseudo-orthogonally in the housing with their axis set at relative angles of other than 90 degrees. None of the axis of the gyroscopes are mounted parallel to the axis of the accelerometers. This configuration permits data from the accelerometers to be used to check the quality of data from the gyroscopes.

Abstract: Aspects of this invention include methods for surveying a subterranean borehole. In one exemplary aspect, a change in borehole azimuth between first and second longitudinally spaced gravity measurement sensors may be determined directly from gravity measurements made by the sensors and a measured angular position between the sensors. The gravity measurement sensors are typically disposed to rotate freely with respect to one another about a longitudinal axis of the borehole. Gravity MWD measurements in accordance with the present invention may be advantageously made without imposing any relative rotational constraints on first and second gravity sensor sets. The present invention also advantageously provides for downhole processing of the change in azimuth between the first and second gravity sensor sets. As such, Gravity MWD measurements in accordance with this invention may be advantageously utilized in closed-loop steering control methods.

Abstract: Methods and related systems are described for use for determining orientation of a measurement tool in a cased borehole. The measurement tool is deployed in a cased section of a borehole. The tool includes a volume containing a reference fluid having a first density, and a marker within the fluid having a different density. The position of the marker within volume containing the reference fluid is senses, and orientation information of the measurement tool is determined based at least in part on combining information relating to the position of the marker with prior recorded data representing orientation measurements made while the section of the borehole was not yet cased.

Abstract: A Centralizer based Survey and Navigation (CSN) device designed to provide borehole or passageway position information. The CSN device can include one or more displacement sensors, centralizers, an odometry sensor, a borehole initialization system, and navigation algorithm implementing processor(s). Also, methods of using the CSN device for in-hole survey and navigation.

Abstract: A method and system for azimuth measurements using one or more gyro sensors is disclosed. The method includes acquiring a first data from each of the gyro sensors with an input axis aligned to a first angular orientation and acquiring a second data from each of the gyro sensors with the input axis flipped to a second angular orientation opposite to the first angular orientation. An earth rate component at the first angular orientations is determined based on a difference between the first data and the second data to cancel out bias of each of the gyro sensors. The method may include acquiring a third data of the gyro sensor with the input axis aligned to the same angular orientation as the first angular orientation. An average of the first data and the third data may be used instead of the first data for determining the earth rate component.

Abstract: A Centralizer based Survey and Navigation (CSN) device designed to provide borehole or passageway position information. The CSN device can include one or more displacement sensors, centralizers, an odometry sensor, a borehole initialization system, and navigation algorithm implementing processor(s). Also, methods of using the CSN device for in-hole survey and navigation.

Abstract: Casing or work string orientation indicating apparatus and methods. A system for indicating orientation of a structure in a wellbore includes an orientation indicating device responsive to fluid flow through the device, whereby fluid flow through the device at a selected flow rate produces a reduced pressure differential across the device when the device is at a preselected azimuthal orientation, compared to an increased pressure differential across the device produced by fluid flow through the device at the selected flow rate when the device is not at the azimuthal orientation. A method of detecting orientation of a structure in a wellbore includes the steps of: flowing fluid at a selected flow rate through an orientation indicating device interconnected to the structure; and observing a substantially constant pressure differential across the device during the flowing step, thereby indicating that the structure is at a predetermined azimuthal orientation.

Abstract: An apparatus and method for compensation of the effects of various bias errors encountered by inertial rate gyroscopes, particularly vibrating element gyroscopes, configured to detect heading relative to true north. Certain embodiments are suitable for reducing rotational dynamic errors associated with rotating gyroscopes. Other embodiments may include compensation of biases not related to rotational dynamics, such as thermal drift. The various methods disclosed may also account for the bias by sampling the rotational vector of the earth at an arbitrary heading, and at a heading that is 180° offset from the arbitrary heading. The sequence may be repeated numerous times to compensate for bias drift. The bias drift may be constant with respect to time (linear) or changing over time (non-linear) during the data acquisition sequence. Some embodiments include methods that utilize data from accelerometers to infer the bank and elevation angles as well as earth latitude location relative to the equator.

Abstract: Aspects of this invention include methods for surveying a subterranean borehole. In one exemplary aspect, a change in borehole azimuth between first and second longitudinally spaced gravity measurement sensors may be determined directly from gravity measurements made by the sensors and a measured angular position between the sensors. The gravity measurement sensors are typically disposed to rotate freely with respect to one another about a longitudinal axis of the borehole. Gravity MWD measurements in accordance with the present invention may be advantageously made without imposing any relative rotational constraints on first and second gravity sensor sets. The present invention also advantageously provides for downhole processing of the change in azimuth between the first and second gravity sensor sets. As such, Gravity MWD measurements in accordance with this invention may be advantageously utilized in closed-loop steering control methods.

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: An apparatus for determining the orientation of a borehole at a point along the borehole, includes a tiltmeter for measuring the inclination of the borehole relative to the vertical, a vector magnetic sensor for measuring the amplitude of the component of the Earth's magnetic field along the axis of the borehole, and means for computing the orientation of the tubular sonde from the measurements of inclination and amplitude of the component of the Earth's magnetic field aligned with axis of the sonde.

Abstract: A system and method for using a survey tool within a borehole is provided. The survey tool includes a plurality of rotation sensors each having a sensing axis and a direction of least acceleration sensitivity. The sensing axes of the plurality of rotation sensors are generally parallel to one another and the directions of least acceleration sensitivity of the plurality of rotation sensors are generally non-parallel to one another.

Abstract: A system for determining the location of and communicating with a downhole tool assembly. A tracker assembly comprises a vertical transmitting antenna, a plurality of receiving antennas, and a processor. The downhole tool assembly has a beacon assembly comprising a plurality of receiving antennas, a transmitting antenna, an orientation sensor, and a processor. The transmitter in the tracker transmits a substantially vertical dipole field. The beacon assembly detects the vertical field and processes the signals to determine the location of the beacon relative to the tracker. The beacon assembly transmits the beacon location and operational information to the tracker assembly. The tracker assembly displays the beacon location and operational information on a visual display. The tracker assembly may also transmit operational commands or requests for information to the beacon assembly.

Abstract: Methods are disclosed for drilling a first well and a second well. The method includes measuring direction and inclination for at least one of the bottom hole assemblies (BHAs) in the wells, generating a magnetic field in at least one of the BHAs and measuring the magnetic field at the other BHA. The method includes determining the geometrical relationship of one BHA with respect to the other BHA. The method further includes determining the position of one BHA with respect to the Earth's geology or geometry. The method further includes automatically positioning one well with respect to the other well to maintain a predetermined geometrical relationship between them.

Abstract: A method for determining a rate of change of longitudinal direction of a subterranean borehole is provided. The method includes positioning a downhole tool in a borehole, the tool including first and second surveying devices disposed thereon. The method further includes causing the surveying devices to measure a longitudinal direction of the borehole at first and second longitudinal positions and processing the longitudinal directions of the borehole at the first and second positions 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.

Abstract: A two-axis gyroscope used on a bottom hole assembly can be used for determining a rate of rotation about the rotational axis of a BHA. The method takes advantage of possible misalignment of at least one axis of the two axis gyroscope from orthogonality with respect to the rotational axis of the BHA, resulting in the misaligned gyro being sensitive to BHA rotation.

Abstract: A system and method for determining an orientation of the survey tool within a borehole utilizes a survey tool including a plurality of rotation sensors each having a sensing axis and a direction of least acceleration sensitivity. The plurality of rotation sensors are mounted in a housing with their sensing axes generally parallel to one another and with their directions of least acceleration sensitivity generally non-parallel to one another. The survey tool further includes a controller adapted to calculate a weighted average of the detected angular rotation rates from the plurality of rotation sensors. The weighted average includes the detected angular rotation rate of each rotation sensor about its sensing axis weighted by the detected acceleration along its direction of least acceleration sensitivity.

Abstract: A system for determining the location of and communicating with a downhole tool assembly. A tracker assembly comprises a vertical transmitting antenna, a plurality of receiving antennas, and a processor. The downhole tool assembly has a beacon assembly comprising a plurality of receiving antennas, a transmitting antenna, an orientation sensor, and a processor. The transmitter in the tracker transmits a substantially vertical dipole field. The beacon assembly detects the vertical field and processes the signals to determine the location of the beacon relative to the tracker. The beacon assembly transmits the beacon location and operational information to the tracker assembly. The tracker assembly displays the beacon location and operational information on a visual display. The tracker assembly may also transmit operational commands or requests for information to the beacon assembly.

Abstract: A method for determining a borehole azimuth in a borehole is disclosed. In one exemplary embodiment, the method includes acquiring at least one standoff measurement and a tool azimuth measurement at substantially the same time. Such measurements are then processed, along with a lateral displacement vector of the downhole tool upon which the sensors are deployed in the borehole, to determine the borehole azimuth. The computed borehole azimuths may be advantageously correlated with logging sensor data to form a borehole image, for example, by convolving the correlated logging sensor data with a window function. As such, exemplary embodiments of this invention may provide for superior image resolution and noise rejection as compared to prior art LWD imaging techniques.

Abstract: A system and method for determining an orientation of the survey tool within a borehole utilizes a survey tool including a plurality of rotation sensors each having a sensing axis and a direction of least acceleration sensitivity. The plurality of rotation sensors are mounted in a housing with their sensing axes generally parallel to one another and with their directions of least acceleration sensitivity generally non-parallel to one another. The survey tool further includes a controller adapted to calculate a weighted average of the detected angular rotation rates from the plurality of rotation sensors. The weighted average includes the detected angular rotation rate of each rotation sensor about its sensing axis weighted by the detected acceleration along its direction of least acceleration sensitivity.

Abstract: A method for determining a borehole azimuth in a borehole is disclosed. In one exemplary embodiment, the method includes acquiring at least one standoff measurement and a tool azimuth measurement at substantially the same time. Such measurements are then processed, along with a lateral displacement vector of the downhole tool upon which the sensors are deployed in the borehole, to determine the borehole azimuth. The computed borehole azimuths may be advantageously correlated with logging sensor data to form a borehole image, for example, by convolving the correlated logging sensor data with a window function. As such, exemplary embodiments of this invention may provide for superior image resolution and noise rejection as compared to prior art LWD imaging techniques.

Abstract: An omnidirectional borehole navigation system is provided that includes a housing that can be placed within the smaller diameter drill pipes used towards the bottom of a borehole, an outer gimbal connected to the housing, and at least two or more stacked inner gimbals that are nested in and connected to the outer gimbal, the inner gimbals each having an axis parallel to one another and perpendicular to the outer gimbal. The inner gimbals contain electronic circuits, gyros whose input axes span three dimensional space, and accelerometers whose input axes span three dimensional space. There are an outer gimbal drive system, an inner gimbal drive system for maintaining the gyro input axes and the accelerometer input axes as substantially orthogonal triads, and a processor responsive to the gyro circuits and the accelerometer circuits to determine the attitude and the position of the housing in the borehole.

Abstract: A method for surveying a subterranean borehole is provided. The method includes determining tool face angles at first and second longitudinal positions in the borehole. The method further includes processing the tool face angles to determine a change in borehole azimuth between the first and second positions. Exemplary embodiments of this invention provide a direct mathematical solution for the change in azimuth and therefore provide for improved accuracy and reliability of azimuth determination (as compared to the prior art) over nearly the entire range of possible borehole inclination, azimuth, tool face, and dogleg values.

Abstract: A method for surveying a borehole is disclosed which uses first and second gravity measurement devices disposed at corresponding first and second positions in the borehole and a supplemental reference measurement device disposed at the first position. Exemplary supplemental reference measurement devices include magnetometers and gyroscopes. The method includes determining a reference borehole azimuth at the first position using the supplemental reference measurement device, determining a change in borehole azimuth between the first and second positions using the first and second gravity measurement devices and determining the borehole azimuth at the second position by applying the change in borehole azimuth the reference azimuth. A system adapted to execute the disclosed method and a computer system including computer-readable logic configured to instruct a processor to execute the disclosed method are also provided.

Abstract: A compact navigation system for a rover is provided. The navigation system includes a housing configured to be transported by the rover; a gimbal system having two or more gimbals that includes at least an outer gimbal connected to the housing and an inner gimbal nested in and connected to the outer gimbal; a solid state three-axis gyro assembly mounted on the inner gimbal; a solid state three-axis accelerometer assembly mounted on the inner gimbal; a gyro logic circuit responsive to the three-axis gyro assembly for producing an inertial angular rate about each gyro input axis; an accelerometer logic circuit responsive to the three-axis accelerometer assembly for producing a non-gravitational acceleration along each accelerometer input axis; and a processor responsive to the gyro logic circuits and the accelerometer logic circuits for determining the attitude and the position of the housing to provide for long term accuracy of the attitude and the position for navigation of the rover.

Abstract: An omnidirectional borehole navigation system is provided which features a housing for traversing a borehole; a gimbal system including at least one outer gimbal connected to the housing and at least one inner gimbal nested in and connected to the outer gimbal; a solid state three-axis gyro assembly mounted on the inner gimbal; a solid state three-axis accelerometer assembly mounted on the inner gimbal; gyro logic circuits on the inner gimbal responsive to the three-axis gyro assembly to produce the inertial angular rate about each gyro input axis; accelerometer logic circuits on the inner gimbal to produce the non-gravitational acceleration along each accelerometer input axis; and a microprocessor responsive to the gyro logic circuits and the accelerometer logic circuits for determining the attitude and the position and velocity of the housing in its borehole.

Abstract: The invention relates to a method and an apparatus for use in surveying boreholes. The method of the invention comprises the following steps: providing an instrument package in a leading end of a drillstring, the instrument package comprising first and second single-axis sensors mounted for rotation with the drillstring about the rotational axis of the drillstring, the first sensor being an accelerometer and the second sensor being a magnetic fluxgate or a rate gyro; rotating the drillstring; deriving from the first sensor the inclination angle of the drillstring at the instrument package; and deriving from the second sensor the azimuth angle of the drillstring at the instrument package.

Abstract: An autonomous down hole survey tool and method for determining deviation angles of a well bore while tripping. The instrument package assembly is carried in a commercially available running gear and utilizes a low voltage solid state electronic apparatus in cooperation with a method for detecting and correlating desired measurements such as pitch, roll, azimuth and temperature taken from a bored hole in an autonomous manner and electronically recovering such data from the instrument upon its return to the surface. The apparatus includes electronic measurement sensing circuitry that includes a compass/magnetometer utilizing a tilt compensated linear/compass, dual axis tilt system, housed in a high tensile strength non-metallic casing sleeve with a self centering capability. The system further includes electronic communications programming and retrieval cabling and a portable computer processor unit.

Abstract: A device and a method for the measurement of the angle of drift of a borehole that extends from the surface of the ground downwardly into the earth. The device comprises a generally hollow protective exterior casing, a microprocessor control; and, a sensor pack. At least the microprocessor control and the sensor pack are received and contained within the exterior casing. The sensor pack includes one or more accelerometers mounted upon a sensor chassis that is positioned within the casing and situated generally parallel to its longitudinal axis. The sensor chassis has one or more mounting surfaces for receiving and securing the one or more accelerometers to the sensor chassis. The mounting surfaces are configured such that the one or more accelerometers when secured to the chassis are held and retained at an inclined angle relative to the longitudinal axis of the exterior casing and the device.

Abstract: A continuous measurement-while-drilling surveying apparatus includes a fiber optic gyroscope sensitive to rotation about the tool spin axis of the bottom hole assembly and a second fiber optic gyroscope sensitive to rotation of the bottom hole assembly about an axis normal to the tool spin axis. The first gyroscope may be shaped as a torus to accommodate flow of drilling mud through the bottom hole assembly. The outputs of the first and second gyroscopes are processed together with acceleration signals from three accelerometers in a microprocessor which determines the orientation, velocity and position of the bottom hole assembly on a continuous basis.