Borehole orientation measurement apparatus and methods

Abstract

An apparatus for determining orientation measurements associated with a borehole. The apparatus comprises a sensing unit and a controller. The sensing unit has at least one or more sensors arranged relative to a measurement axis of the apparatus, the measurement axis determining an orientation of the apparatus. The controller is configured to receive or determine an expected rate of change of the orientation of the apparatus for operating the sensing unit to determine the orientation measurements. The controller is further configured to determine a measurement mode of the sensing unit based on the expected rate of change of the orientation of the apparatus, where the measurement mode defines a rate range and / or bandwidth of the one or more sensors. The controller is further configured to operate the sensing unit in the measurement mode to generate the orientation measurements from data collected by the one or more sensors.

Description

"Borehole orientation measurement apparatus and methods"

[0001] The present application claims priority from Australian Provisional Patent Application No. 2024903543 filed on 31 October 2024, the contents of which are incorporated herein by reference in their entirety.Technical Field

[0002] The present disclosure relates to the development and exploration of a borehole, and specifically to determining orientation measurements associated with the borehole in a plurality of measurement use cases, such as for example during drill rig alignment prior to drilling the borehole and post-drilling surveying of the borehole.Background

[0003] The term “borehole” is used to collectively refer to any of the various types of holes that may be drilled into a ground surface. Boreholes are created by a drilling process generally performed by a drill rig, for example in order to perform resource extraction or geotechnical investigation or assessment of an environmental site, such as a mine site, for example to enable the collection of soil samples, water samples or rock cores, or to install monitoring wells or piezometers.

[0004] The development, exploration and production of a mine site requires various measurements to be conducted at different steps of the workflow in relation to an individual borehole. Prior to drilling the borehole, measurements are performed to align the drill rig with the surface of the mine site, such that the borehole is formed in the surface according to a desired direction and depth. The desired direction and depth of the borehole may be determined by pre-drilling data, which may also specify additional characteristics of the borehole such as, for example, a collar location.

[0005] Measurements, such as for example depth measurement values, may be obtained during the drilling of the borehole. This may include directional-drillingmeasurements, e.g., for decision support for the wellbore path (generally referred to as “measurement while drilling” (MWD) data), and data related to the geological formations penetrated while drilling (generally referred to separately as “logging while drilling” (LWD) data). The various data that are obtained during the drilling of the borehole are referred to collectively as “hole drilling data” herein.

[0006] In addition, it is often desirable to obtain measurements from the borehole in its post-drilled state. Measurements of the geological parameters of the interior of the borehole (generally referred to as “logging”) are obtained via a post-drilling survey of the borehole, which typically involves the insertion of a measurement device at least partially into the hole, and the transmission of the obtained data to instruments on or above the surface. The measurements obtained by the hole logging process provide additional information of the hole and its surrounding strata, that are unable to be measured at the time of drilling.

[0007] By logging many holes it is possible to build up a model of one or more geological formations or bodies beneath the surface in terms of their properties. Specifically, this data enables a picture of the geological formations to be created in the form of a geological block model. The geological block model provides utility for assessing the surface and each individual borehole within, such as by assisting with increased efficiencies in planning and operating a mine site.

[0008] Determining measurements associated with a borehole (i.e., as obtained for the borehole either in its pre-drilled or post-drilled state) typically involves determining an orientation of an apparatus or device, such as a survey instrument or a rig alignment device, in relation to the borehole.

[0009] For example, to conduct a borehole survey gyroscopes, accelerometers, and / or other inertial sensors of the survey instrument are used to determine the azimuth and the inclination of the borehole. Orientation measurements may be combined with measurements of the depth of the borehole, or indications of the depths at which particular features of the borehole occur (e.g., the occurrence of mineral deposits).Similarly, during drill rig alignment the orientation of an alignment device, which is coupled to the drill rig, is measured thereby providing an indication of the orientation of the borehole to be drilled by the drill rig.Summary

[0010] There is provided an apparatus for determining orientation measurements associated with a borehole, the apparatus comprising: a sensing unit having at least one or more sensors arranged relative to a measurement axis of the apparatus, the measurement axis determining an orientation of the apparatus; and a controller configured to: receive or determine an expected rate of change of the orientation of the apparatus for operating the sensing unit to determine the orientation measurements; determine a measurement mode of the sensing unit based on the expected rate of change of the orientation of the apparatus; and operate the sensing unit in the measurement mode to generate the orientation measurements from data collected by the one or more sensors, wherein the measurement mode defines a rate range and / or bandwidth of the one or more sensors to generate the orientation measurements.

[0011] In some embodiments, determining the measurement mode comprises switching between a plurality of predetermined measurement modes.

[0012] In some embodiments, the plurality of predetermined measurement modes comprise: a first measurement mode defining a first range rate and / or bandwidth of the one or more sensors and having a corresponding first accuracy; and a second measurement mode defining a second range rate and / or bandwidth greater than the first range rate and / or bandwidth of the one or more sensors and having a corresponding second accuracy being less than the first accuracy.

[0013] In some embodiments, the one or more sensors comprise at least a plurality of gyroscopes each having a sensing axis arranged relative to the measurement axis of the apparatus.

[0014] In some embodiments, operating the sensing unit in the determined measurement mode comprises: selecting at least one fixed rate gyroscope of the plurality of gyroscopes with a rate range and / or bandwidth corresponding to the determined measurement mode; and obtaining output data from each of the selected at least one fixed rate gyroscope.

[0015] In some embodiments, the plurality of gyroscopes comprises at least one rate adjustable gyroscope, and wherein operating the sensing unit in the determined measurement mode comprises adjusting the rate range and / or bandwidth of the at least one rate adjustable gyroscope to the rate range and / or bandwidth corresponding to the determined measurement mode.

[0016] In some embodiments, the plurality of gyroscopes comprise at least three gyroscopes in a mutually orthogonal configuration, wherein at least one of the gyroscopes has a preferred rate range of less than lOOdeg / sec and at least one of the gyroscopes has a preferred rate range of greater than 200deg / sec.

[0017] In some embodiments, the controller is configured to operate the sensing unit to blend outputs produced by two or more of the plurality of gyroscopes to generate the orientation measurements.

[0018] In some embodiments, the controller is configured to set or adjust the measurement mode of the sensing unit based at least in part on one or more of a measurement use case; and a measurement operation, in which the sensing unit generates the orientation measurements.

[0019] In some embodiments, the controller is configured to receive or determine the expected rate of change of the orientation of the apparatus, in response to a change in the measurement use case.

[0020] There is also provided a method for determining orientation measurements associated with a borehole using a borehole measurement apparatus comprising asensing unit having at least one or more sensors arranged relative to a measurement axis of the apparatus, the measurement axis determining an orientation of the apparatus, the method comprising: (i) receiving or determining an expected rate of change of the orientation of the apparatus for operating the sensing unit to determine the orientation measurements; (ii) determining a measurement mode of the sensing unit based on the expected rate of change of the orientation of the apparatus; and (iii) operating the sensing unit in the determined measurement mode to generate the orientation measurements associated with the borehole, wherein the measurement mode defines a rate range and / or bandwidth of the one or more sensors for generating the orientation measurements.

[0021] In some embodiments, the method further comprises repeating steps (i) to (iii) in response to a deviation in the expected rate of change of the orientation of the apparatus.

[0022] In some embodiments, determining the measurement mode of the sensing unit comprises switching the measurement mode between a plurality of predetermined measurement modes.

[0023] In some embodiments, the plurality of predetermined measurement modes comprise: a first measurement mode defining a first range rate and / or bandwidth of the one or more sensors and having a corresponding first accuracy; and a second measurement mode defining a second range rate and / or bandwidth greater than the first range rate and / or bandwidth of the one or more sensors and having a corresponding second accuracy being less than the first accuracy.

[0024] In some embodiments, the one or more sensors comprise at least a plurality of gyroscopes each having a sensing axis arranged relative to the measurement axis of the apparatus.

[0025] In some embodiments, operating the sensing unit comprises selecting at least one fixed rate gyroscope of the plurality of gyroscopes with a rate range and / orbandwidth corresponding to the determined measurement mode; and obtaining output data from each of the selected at least one fixed rate gyroscope.

[0026] In some embodiments, operating the sensing unit further comprises adjusting the rate range and / or bandwidth of at least one gyroscope of the plurality of gyroscopes to the rate range and / or bandwidth corresponding to the determined measurement mode.

[0027] In some embodiments, the plurality of gyroscopes comprises at least three gyroscopes in a mutually orthogonal configuration, wherein at least one of the gyroscopes has a preferred rate range of <100deg / sec and at least one of the gyroscopes has a preferred rate range of >200deg / sec.

[0028] In some embodiments, operating the sensing unit further comprises blending the outputs produced by two or more of the plurality of gyroscopes in the determined measurement mode to generate the orientation measurements.

[0029] In some embodiments, the method further comprises receiving or determining the expected rate of change of the orientation of the apparatus based on a measurement use case in which the sensing unit is operated to generate the orientation measurements.

[0030] There is also provided an apparatus for determining orientation measurements associated with a borehole, the apparatus comprising: a sensing unit having at least one or more sensors collectively configured to generate the orientation measurements according to a measurement mode; and a controller configured to set or adjust the measurement mode between a plurality of measurement modes corresponding to a plurality of borehole measurement use cases and / or borehole measurement operations of the apparatus, wherein the measurement mode defines a rate range and / or bandwidth of the one or more sensors.

[0031] There is also provided an instrument for use in determining orientation measurements to align a drilling apparatus to drill a borehole and to survey theborehole, the instrument comprising: one or more sensors arranged relative to a measurement axis of the instrument, the measurement axis determining an orientation of the instrument, wherein the one or more sensors are collectively configured to determine the orientation measurements according to a measurement mode, wherein the measurement mode defines a rate range and / or bandwidth of the one or more sensors, wherein the one or more sensors are communicatively coupled to a controller configured to: set or adjust the measurement mode based on an expected rate of change of the orientation of the instrument during the determination of the orientation measurements; and operate the one or more sensors in the measurement mode to generate the orientation measurements from data collected by the one or more sensors.Brief Description of Drawings

[0032] Some embodiments are described herein below with reference to the accompanying drawings, wherein:

[0033] Figure la is a block diagram of an orientation measurement apparatus, according to some embodiments;

[0034] Figure lb is a schematic diagram of a particular implementation of components of the orientation measurement apparatus shown in Figure la, according to some embodiments;

[0035] Figure 1c is a schematic diagram of a first implementation of the orientation measurement apparatus of Figure lb as a rig alignment tool;

[0036] Figure Id is a schematic diagram of a second implementation of the orientation measurement apparatus of Figure lb as a borehole surveying tool;

[0037] Figure 2a is a first schematic diagram illustrating the generation of orientation measurements associated with a pre-drilled borehole by using the orientationmeasurement apparatus in a drill rig alignment use case, according to some embodiments;

[0038] Figure 2b is a second schematic diagram illustrating the generation of orientation measurements associated with a pre-drilled borehole by using the orientation measurement apparatus in a drill rig alignment use case, according to some embodiments;

[0039] Figure 2c is a third schematic diagram illustrating the generation of orientation measurements associated with a pre-drilled borehole by using the orientation measurement apparatus in a drill rig alignment use case, according to some embodiments;

[0040] Figure 2d is a first schematic diagram illustrating the generation of orientation measurements associated with a post-drilled borehole by using the orientation measurement apparatus in a surveying use case, according to some embodiments;

[0041] Figure 2e is a second schematic diagram illustrating the generation of orientation measurements associated with a post-drilled borehole by using the orientation measurement apparatus in a surveying use case, according to some embodiments;

[0042] Figure 2f is a third schematic diagram illustrating the generation of orientation measurements associated with a post-drilled borehole by using the orientation measurement apparatus in a surveying use case, according to some embodiments;

[0043] Figure 2g is a fourth schematic diagram illustrating the generation of orientation measurements associated with a post-drilled borehole by using the orientation measurement apparatus in a surveying use case, according to some embodiments;

[0044] Figure 3a is a flow diagram of a method for determining orientation measurements associated with a borehole using a borehole measurement apparatus, according to some embodiments;

[0045] Figure 3b is a schematic diagram illustrating a first exemplary user interface configured to provide an expected rate of change of orientation of the orientation measurement apparatus, according to some embodiments;

[0046] Figure 3c is a schematic diagram illustrating a second exemplary user interface configured to provide an expected rate of change of orientation of the orientation measurement apparatus, according to some embodiments;

[0047] Figure 3d is a schematic diagram illustrating a third exemplary user interface configured to provide an indication of a measurement use case of the orientation measurement apparatus, according to some embodiments;

[0048] Figure 4a is a schematic diagram illustrating a set of candidate measurement modes used by the orientation measurement apparatus to determine the measurement mode associated with the expected rate of change of orientation, according to some embodiments;

[0049] Figure 4b is a flow diagram of a method for determining a measurement mode using an expected rate of change of orientation value of the method for determining orientation measurements of Figure 3a;

[0050] Figure 4c is a flow diagram of an exemplary method for performing comparison testing to determine the measurement mode, according to some embodiments;

[0051] Figure 4d is a flow diagram of a method for determining a measurement mode based on the combination of an indication of a measurement use case and an associatedmeasurement operation, of the method for determining orientation measurements of Figure 3 a;

[0052] Figure 5 is a flow diagram of a method performed by a sensing unit for generating orientation values in response to receiving measurement control signal(s) from a controller, of the method for determining orientation measurements of Figure 3 a;

[0053] Figure 6a is a schematic diagram of a first implementation of a sensing unit of the orientation measurement apparatus of Figure la;

[0054] Figure 6b is a schematic diagram of a second implementation of a sensing unit of the orientation measurement apparatus of Figure la;

[0055] Figure 7 is a flow diagram of a sequence of operations performed by the orientation measurement apparatus to measure a borehole, according to some embodiments;

[0056] Figure 8a is a flow diagram of a method for performing a North seeking measurement operation of the sequence of operations of Figure 7;

[0057] Figure 8b is a flow diagram of a method for performing a sensor tuning adjustment operation of the sequence of operations of Figure 7; and

[0058] Figure 8c is a flow diagram of a method for performing a navigation measurement operation of the sequence of operations of Figure 7.Description of Embodiments

[0059] An issue with conventional approaches to developing and exploring a borehole on a mine site is that distinct devices or instruments are required to determine orientation measurements across each of the different steps of the borehole workflow.

[0060] For example, the borehole workflow typically requires the generation of orientation measurements in at least the use cases of: (i) drill rig alignment, during which a rig alignment device is used to determine the orientation of the rig to drill in a desired direction; (ii) and exploratory borehole surveying, during which a borehole surveying device is used to determine its orientation, and therefore that of the borehole, when the device is passed into the borehole. Other use cases for obtaining orientation measurements in relation to a borehole include: blast surveying, where a blast hole surveying device is used; tripping pipe, where a logging while tripping device is used; and performing orientation of drilling equipment, such as for example orienting the arms of a drilling and blasting rig, and orienting a tunnel boring machine.

[0061] The use of separate devices to determine orientation measurements in each of the different stages of a borehole workflow has several disadvantages. Equipment providers must provide fleets of multiple different expensive measurement devices that are used for only one step of the process, which increases the total number of devices required to service the entire scope of work necessary to explore, develop and produce a mine. The increased total number of measurement devices required on the mine site increases capital costs of deployment, as well as production and maintenance costs for the equipment provider.

[0062] Further, the utilization rate for each device type is difficult to optimize as the particular device may only be used for obtaining measurements during a small time or during part of the total workflow. Thus there is additional overhead expense for each separate device and associated support servicing reducing profitability for equipment providers. The low utilization is compounded for a device that can be used only in exploration and not in production operations as during typical industry cyclical downturns exploration only devices will tend to be far under-utilized.

[0063] It is therefore desired to use a single device to determine orientation measurements across all steps and measurement use cases of the borehole workflow. However, there are technical challenges associated with the use of a single orientation measurement device across multiple workflow stages, including the need to account fora differing form factor, operating conditions, and other specific characteristics of each of the workflow stages.

[0064] Previous approaches have focused on designing mechanisms and devices to enable an instrument that is designed and configured for a particular borehole measurement use case to be used for another. For example, mounting clamps or brackets have been developed for attaching a borehole survey instrument to a drill rig to allow the instrument to produce measurements during drill rig alignment.

[0065] However, as the mounting device needs to support the survey instrument when attached to the drill rig, once attached the apparatus is often large and cumbersome, and in some cases this introduces an undesired angular offset between the instrument sensors and the drill rod when coupled to the same.

[0066] Conversely, the use of instruments that are designed and configured for drill rig alignment are generally unsuitable for other borehole measurement use cases, such as surveying. This is because the form factor of a specialized drill rig alignment instrument is generally incompatible for use within a borehole. For example, the rig alignment device may have a larger width dimension as compared to the diameter of the borehole.

[0067] Another significant issue is that the accuracy requirements and the degree of deviation of the orientation measurements varies across different borehole workflow steps. For most orientation sensing components (e.g., gyroscopes and / or accelerometers) there is a trade-off between the ability to provide measurements at a high accuracy, and the rate change over which the orientation values can be effectively detected and measured. The inventors have discovered this to be a particular issue for the use of conventional borehole survey instruments in other orientation measurement use cases of the borehole workflow, such as rig alignment using the aforementioned approach, since this requires an ability of the tool to measure orientations during both high and low rate changes. However, the configuration and operation of the sensor components (e.g., gyroscopes and / or accelerometers) of a conventional surveyinstrument is typically predetermined and specialized for the intended surveying use case.

[0068] As a result, the orientation measurements that are obtained when using a conventional survey instrument across multiple use cases in the borehole workflow are unsuitable (i.e., are inaccurate and / or have an improper range for at least some of the use cases). It is desired to develop apparatus and methods that address one or more of these problems, or one or more other drawbacks of the prior art, or that at least provide a useful alternative.Overview

[0069] Disclosed herein are embodiments of apparatus, instruments, and methods for determining orientation measurements of a borehole on a mine site in either a pre- or post-drilled state and across a plurality of workflow stages. As shown in Fig. la, a computer processing device (the “controller”) 120 is configured to operate a sensing unit 110 comprising one or more sensors 112 that provide output data indicating orientation measurements (e.g., values of an azimuth, an inclination, and optionally a toolface (TF)) associated with the borehole.

[0070] The sensing unit 110 is configured to generate the orientation measurements according to a particular measurement functionality of the sensing unit 110 (referred to herein as a “measurement mode”). In some embodiments, the controller 120 is configured to determine the measurement mode based on an expected rate of change of the orientation of the apparatus 100 during the determination of the orientation measurements. For example, the controller 120 may receive an indication of the expected rate of change of the orientation of the apparatus to determine the orientation measurements, such as from an input signal received from a user device or other computing system.

[0071] In some embodiments, the controller is configured to automatically determine the expected rate of change of the orientation, such as by processing the detected changes in the actual orientation over a given time period, or based on a predeterminedroutine. In some embodiments, the controller 120 determines the measurement mode by first determining the expected rate of change of the orientation in response to receiving an indication of a measurement use case and / or a measurement operation for which to generate the orientations.

[0072] The controller 120 controls the sensing unit 110 to operate it in the determined measurement mode to generate the orientation measurements associated with the borehole. To operate the sensing unit 110 the controller 120 generates measurement control signals, which may specify for a given sensor: a rate range and / or bandwidth of the sensor, an activation state of the sensor, or any other measurement property that is configurable with respect to the sensor, to generate the orientation measurements.

[0073] This advantageously accounts for the change in orientations likely to be experienced during a use case of conducting measurement associated with a borehole, and during individual measurement operations performed in the use case. For example, the changes in the measured orientation values that can be expected when navigating the apparatus during an alignment use case are significantly greater than those when navigating the instrument during a surveying use case.

[0074] Accordingly, the proposed technology provides apparatus, methods, and instruments that, through the use of a sensing unit with dynamically configurable sensors, are suitable for obtaining orientation measurements across a plurality of borehole workflow stages without compromising on measurement accuracy or rate range capability. For example, the apparatus and instruments may be used during an alignment use case to align a drilling apparatus to drill a borehole. The instrument may also be used in a surveying use case to survey an as drilled borehole.

[0075] Further, the proposed technology enables the same single apparatus or device to perform north seeking and navigation measurement operations at all required attitudes and environmental conditions (rotation rates, shock, vibration, temperature, magnetic interference, underground operation) across all intended use cases.Adjustable mode sensing

[0076] The one or more sensors 112 each generate data representing measurements of the orientation values when the sensing unit 110 is operated in a measurement mode. The measurement mode defines a set of one or more parameters of the sensing unit 110 (“sensing unit parameters”) to perform orientation measurement. Preferably, the measurement mode defines at least a rate range value and / or a bandwidth value of the one or more sensors 112 as used to generate the orientation measurements by the sensing unit 110. However, the measurement mode may also define one or more other parameters of the one or more sensors 112, including but not limited to a measurement wait time.

[0077] In some embodiments, the measurement mode includes a rate range and / or a bandwidth of the one or more sensors 112, and optionally a wait time of the sensing unit 110 between successive measurements in an operation. For example, the wait time may be determined by a time taken to average data obtained from the one or more sensors 112 (“averaging time”) during a North seeking operation and / or drift tuning. In some embodiments, the sensing unit 110 may have a configurable averaging time providing a trade-off against the accuracy of the resulting orientation measurements. Each of the one or more sensors 112 generates measurements based on one or more individual sensor parameters. In some embodiments, to operate the sensing unit 110 the controller 120 maps the sensing unit parameters specified by the measurement mode to the corresponding individual sensor parameters of the sensor(s) 112.

[0078] In some embodiments, the controller 120 determines (e.g., sets or adjusts) the measurement mode by switching between a plurality of predetermined measurement modes. For example, the predetermined measurement modes may include: a first measurement mode (a “low rate range mode”) defining a first range rate and / or bandwidth of the one or more sensors 112, and having a corresponding first accuracy; and a second measurement mode defining a second range rate and / or bandwidth greater than the first range rate and / or bandwidth of the one or more sensors and having a corresponding second accuracy being less than the first accuracy (a “high rate range mode”).

[0079] For example, the controller 120 may be configured to a preset measurement mode (e.g., to either a high rate range mode or a low rate range mode in some embodiments) in response to determining or receiving the expected rate of change of the orientation measurements. In some embodiments, the controller 120 receives an indication of the expected rate of change comprising a non-numerical indicator, such as for example a classification of the expected rate of change as one of a number of categories (e.g., as ‘large’, ‘moderate’, or ‘small’). The controller 120 may map the classification to one of the plurality of predetermined measurement modes, for example to determine a low rate range mode in response to the expected rate of change being indicated as ‘small’.

[0080] In some embodiments, the indication of the expected rate of change of the orientations comprises a numerical value, for example representing an estimated or predicted rate of change of the orientations to be encountered during measurement. The controller 120 may map the expected rate of change value to one of the plurality of predetermined measurement modes. In one example, the controller 120 compares the expected rate of change value to one or more of the sensing unit parameters of each candidate measurement mode, such as the rate range and / or bandwidth defined by the respective candidate measurement mode, and selects the candidate mode with the closest value to the expected rate of change value. In some implementations, the controller 120 compares the expected rate of change value to one or more thresholds (e.g., in one or more comparison tests) and determines a measurement mode based on the outcome of the comparison tests (e.g., using a mapping of the measurement modes to the thresholds).

[0081] In some embodiments, the controller 120 is configured to receive or determine the expected rate of change of the orientation of the apparatus 100 based at least in part on a measurement use case in which the sensing unit 110 is operated to generate the orientation measurements.

[0082] This advantageously allows the controller 120 to control the operation of the sensing unit 110 (i.e., to switch between a plurality of rate ranges and / or bandwidths ofthe unit) to accommodate for the differences in orientation changes in across measurement operations and / or workflow use cases (as described herein). Specifically, the sensing unit 110 is able to detect and measure both ‘macro’ changes in orientation (i.e., using a high rate range mode) that occur, for example, during a navigation operation in drill rig alignment, and also ‘micro’ changes in orientation (i.e., using a low rate range mode) that occur, for example, during a north seeking operation or during a navigation operation when surveying the borehole.Measurement use cases and operations

[0083] The controller 120 operates the sensing unit 110 to generate orientation measurements according to one or more borehole workflow use cases. Exemplary use cases include: (i) drill rig alignment; and (ii) surveying. The surveying use case may have sub-cases including exploration surveying, blast surveying, and logging while tripping.

[0084] In each use case, the determination of orientation measurements may involve conducting one or more distinct measurement operations using the sensor(s) 112, including: (i) north seeking, and (ii) navigation. North seeking (also called “gyrocompassing”) is conducted to obtain a reference set of orientation measurements representing a direction of the apparatus with respect to North and of the earth’s gravity vector (e.g., as NED earth coordinates). During a subsequent navigation operation, the sensor(s) 112 track changes in orientation (e.g., as values of the azimuth, the inclination, and optionally the toolface) with respect to the references obtained during the prior North seeking operation.

[0085] In various examples, the controller 120 receives or determines the expected rate of change of the orientation of the apparatus 100 in response to receiving an indication of one or more of: a measurement use case (rig alignment, or surveying); and a measurement operation (e.g., north seeking or navigation), in which the sensing unit 110 is operated to generate the orientation measurements.

[0086] For example, the controller 120 may receive an input signal indicating that measurement is to occur for a combination of a use case and a measurement operation. The controller 120 may then determine the expected rate of change of the orientation for the use case and measurement operation (e.g., as a predetermined or assigned value for the combination), and subsequently determine the measurement mode based on the same.

[0087] This advantageously allows the use of a different rate range and / or bandwidth to obtain orientations during the same measurement operation (e.g., North seeking or navigation) conducted in the context of a different use case (e.g., exploration surveying and blast hole surveying). For example, since the speed of conducting measurements is more important for blast hole surveying, a North seeking operation may be sped up by using a lower rate range mode compared to conducting North seeking during exploration surveying.Modular orientation instrument

[0088] In some embodiments, the apparatus 100 is configured as a modular orientation instrument with a size and form factor that is adaptable to each borehole measurement use case.

[0089] In some embodiments, the apparatus 100 comprises a base module having an outer housing containing the sensing unit 110, and optionally the controller 120. The apparatus 100 comprises one or more add-on modules that each contain one or more functional components that enable or assist orientation measurement over a plurality of use cases including at least (i) drill rig alignment of a pre-drilled borehole, and (ii) surveying of the post-drilled borehole.

[0090] The one or more add-on modules are removably attachable to one another, and to the base module, in a manner that permits a communicative coupling between the functional components of the add-on modules and base module (i.e., the sensing unit 110, and optionally the controller 120). The apparatus 100 is configured for a measurement use case by mutual attachment of one or more add-on modules and thebase module together to form an instrument configured for the generation of orientation measurements in the given measurement use case.

[0091] This advantageously allows for a single common sensing module to be used as an instrument for determining orientation measurements associated with a borehole, where the capability of the instrument to conduct measurements is adapted by the addition of other functional components that are appropriate for any one of a number of measurement use cases across the borehole workflow. This permits the generation of improved orientation measurements while customizing the properties of the instrument, such as but not limited to its size and form factor, to the applicable use case.Orientation measurement apparatus

[0092] Fig. la is a block diagram of an orientation measurement apparatus 100 according to some embodiments. The orientation measurement apparatus 100 includes a sensing unit 110 comprising one or more sensors 112 configured to generate orientation values relative to a measurement axis 103 of the apparatus 100. The apparatus 100 further includes a controller 120 communicatively coupled with the one or more sensors 112 of the sensing unit 110. The controller 120 is configured to operate the sensing unit 110 to generate orientation data during a measurement operation associated with a borehole, in accordance with the methods and techniques described herein.

[0093] In some embodiments, the sensing unit 110 and the controller 120 are in local proximity within a single instrument, such as a survey device or a rig alignment device. In other examples, the controller 120 is located remotely to the one or more sensors 112. For example, the sensing unit 110 may be deployed as part of an instrument that is oriented during the measurement process (e.g., a rig alignment device or a survey device being respectively deployed onto the drill rig or into the borehole), while the controller 120 is deployed as an edge processing device that is physically separated from the instrument (e.g., located on the surface of the site).

[0094] The one or more sensors 112 each have a sensing axis 107 that is arranged relative to the measurement axis 103 to enable measurement of the earth's rate of rotation with adequate accuracy. That is, although in the depiction of Fig. la the sensing axis 107 is shown as arranged perpendicular to the measurement axis 103, it will be appreciated that the sensing axis 107 may be arranged with any configuration, and at any angle, relative to the measurement axis 103, for example depending on the properties and / or configuration of the respective sensor in the sensing unit 110.

[0095] The measurement axis 103 determines the orientation of the apparatus 100 during a measurement use case. That is, orientation measurements generated by apparatus 100 are with reference to the measurement axis 103. For example, during drill rig alignment the sensing unit 110 is attached to, or otherwise held in a fixed position relative to, the drill rig such that the measurement axis 103 is coincidental with the longitudinal axis of the drill rig. The values of the azimuth and inclination (and optionally the toolface) therefore represent an orientation of the drilling direction of the borehole in this use case.

[0096] In some embodiments, the sensing unit 110 is attached to a drilling assembly in order to orient the drilling assembly to drill in a particular direction (e.g., towards an intended target). For example, the sensing unit 110 may be configured to generate measurements for the orientation of: a wedge that is used to deflect the drilling assembly in a particular direction; a directional core drilling assembly; and a rotary steerable system.

[0097] By contrast, during surveying, the measurement axis 103 is coincidental with the longitudinal axis of a borehole surveying tool that is inserted into the borehole. In this use case, the values of the azimuth and inclination (and optionally the toolface) therefore represent an orientation of the interior of the borehole (i.e., at a given depth).

[0098] Fig. lb is a schematic diagram of a representation of an example of the orientation measurement apparatus 100, including exemplary implementations of the sensing unit 110 and controller 120.Sensing unit

[0099] In some embodiments, the sensing unit 110 comprises a set of one or more accelerometers 114 (e.g., linear accelerometers) configured to generate accelerometer data representing acceleration values of the sensing unit 110 over time. The one or more sensors 112 also comprise a set of rate sensors, such as one or more gyroscopes 116, configured to generate gyroscope data during a measurement operation. For example, the gyroscope(s) 116 may include one or more rate gyroscopes configured to generate data representing the angular velocity of the sensing unit 110 to enable determination of the attitude and heading of the accelerometers 114 in a chosen navigation reference coordinate frame. The raw measurement data generated by the sensor(s) 112 of the sensing unit 110, including the accelerometer data and the gyroscope data, is referred to as “orientation data” in some embodiments. The orientation data indicates orientation values, including for example at least an azimuth and an inclination relative to the measurement axis 103.

[0100] In some embodiments, the accelerometers 114 and gyroscopes 116 of sensing unit 110 are configured as a strap-down system. In other embodiments, the accelerometers 114 and gyroscopes 116 are attached to a sensor platform connected to a chassis or housing of the sensing unit 110 by one or more gimbals. In such embodiments, the gimbal may be stabilized with respect to gravity such that the roll or gravity TF of the sensor platform is held constant with respect to gravity which may reduce the effects of some sensor errors such as, for example, residual sensor misalignments (e.g. remaining error in alignment of the sensitive axis of the sensor after calibration has been applied) by reducing or eliminating fluctuations in the component of gravity in the sensor output due to rotation of the sensing unit 110 during the measurement operation.

[0101] For example, the one or more sensors 112 may comprise at least a set of three gyroscopes and a set of three accelerometers, such that the sensing unit 110 is configured as a 6-degree of freedom (DOF) inertial measurement unit (IMU). The set of three gyroscopes are arranged in a mutually orthogonal configuration. The one or more sensors 112 may comprise additional sets of gyroscopes and / or accelerometerseach having a different fixed or adjustable rate range and / or bandwidth. In some embodiments, the one or more sensors 112 include a set of magnetometers, for example three magnetometers having a tri-axial configuration such that the sensing unit 110 is a 9-DOF IMU.

[0102] In some embodiments, at least one gyroscope is mounted on a rotatable platform, where the rotation of the platform causes a corresponding rotation of the sensing axis 107 of the at least one gyroscope in order to remove any fixed bias drift errors present.

[0103] In some embodiments, the controller 120 determines and optionally corrects for any bias errors in the output data generated by at least one gyroscope. For example, the controller 120 may operate the sensing unit 110 to generate sensor data representing multiple orientation measurements at a number of arrangements of the sensing axis 107 relative to the measurement axis 103. In some embodiments, the controller 120 is configured to perform a reversal of signal polarity for at least one gyroscope (e.g., a mode reversal for MEMs gyros or spin reversal for spinning mass gyros), to account for error in the output data, such as error due to zero-rate offset (see [1]).

[0104] The sensing unit 110 generates orientation data as a set of discrete measurement values obtained at corresponding sample time instants over the duration of a measurement operation. The sensing unit 110 is configured to obtain measurements from accelerometers 114 and gyroscopes 116, and to generate corresponding orientation data values periodically according to a sampling period. Depending on the sampling period, zero, one or more sample measurements may be generated during an arbitrary contiguous time interval of the measurement operation. For example, the sensing unit 110 may average the values obtained from the one or more sensors 112, or a subset thereof, over an averaging time window to generate the orientation data.

[0105] The sensing unit 110 includes a sensor interface 118 configured to transmit data to, and receive data from, an external device. For example, the sensor interface118 may be configured to: receive sensor parameter data from a sensor I / O connector of the controller 120 to control the operation of one or more of the sensors 112, and to transmit orientation data generated by the one or more of the sensors 112 to the controller 120. In some embodiments, the sensing unit 110 exchanges data with the controller 120 via a connection between the sensor interface 118 and an intermediate system, such as a wireless communication system.

[0106] The sensing unit 110 includes a power supply 115 configured to provide power to the sensor(s) 112. For example, the power supply 115 may be a power source such that the sensing unit 110 self-powers the sensor(s) 112 to permit the generation of orientation measurements. Alternatively, the power supply 115 may be implemented as an interface, such as a connection port, permitting the sensing unit 110 to receive power from an external source.Controller

[0107] The controller 120 is configured to control the functionality of the sensing unit 110 to generate orientation measurements associated with the borehole, by: receiving or determining an expected rate of change of the orientation of the apparatus 100 for operating the sensing unit 110; determining a measurement mode of the sensing unit 110 based on the expected rate of change of the orientation of the apparatus; and operating the sensing unit 110 in the determined measurement mode to generate the orientation measurements.

[0108] The controller 120 is communicatively coupled to the sensing unit 110, such as for example via a wireless or wired communication medium that enables the exchange of data between the same. In some embodiments, the components of the controller 120 are configured as an embedded system with the processor 122 and memory system 125 implemented as an integrated microcontroller with a RISC architecture, and the sensing unit 110 configured as a peripheral device providing data to, and receiving control data from, the microcontroller.

[0109] In some embodiments, controller 120 is implemented as a standalone computing device, and comprises a central system bus (not shown), a memory system 125, a processor (e.g., CPU) 122, communications module 123, and I / O device interfaces 124. The processor 122 may be any microprocessor which performs the execution of sequences of machine instructions, and may have architectures consisting of a single or multiple processing cores such as, for example, a system having a 32- or 64-bit Advanced RISC Machine (ARM) architecture (e.g., ARMvx). The processor 122 issues control signals to other device components via the system bus, and has direct access to at least some form of the memory system 125.

[0110] The memory system 125 provides internal media for the electrical storage of the machine instructions required to execute the user application. The memory system 125 may include random access memory (RAM), non-volatile memory (such as ROM or EPROM), cache memory and registers for fast access by the processor 122, and high volume storage subsystems such as hard disk drives (HDDs), or solid state drives (SSDs).

[0111] The processes executed by the controller 120 are implemented as programming instructions of one or more software modules stored on non-volatile storage of the memory system 125. The one or more software modules includes a mode control module (MCM) 121 configured to: receive input data relating to any one or more of a measurement use case, a measurement operation, and an expected rate of change of orientation during orientation measurement associated with a measurement use case and / or a measurement operation; determine one or more parameters of the sensing unit 110, and / or the sensor(s) 112, as a measurement mode of the sensing unit 110, either in response to receiving the input data, or to receiving or generating some other data; and generate and transmit control instructions to the sensing unit to operate the sensing unit 110 according to the determined parameters.

[0112] In some embodiments, the MCM 121 is further configured to determine an expected rate of change of orientation during orientation measurement, for example in response to receiving input data specifying a measurement use case and / or ameasurement operation for the orientation measurement. In some embodiments, the processes may be executed by one or more dedicated hardware components, such as field programmable gate arrays (FPGAs) and / or application-specific integrated circuits (ASICs).

[0113] Memory system 125 may also include one or more general application programs providing methods, data structures, or other software services that define data or perform functions as required by the controller 120 (e.g., an operating system). The data and instructions may reside in multiple parts of the memory system 125, including registers, cache, main memory, and high volume storage.

[0114] In some embodiments, the memory system 125 includes one or more data storage modules including one or more data structures configured to store data including one or more of: data generated by the MCM 121; and optionally orientation data generated by the sensing unit 110. In some embodiments, the data structures are also configured to store other data generated, received and / or processed by the controller 120.

[0115] The I / O device interface 124 provides functionality enabling the user to interact with the controller 120 via one or more I / O devices. In some embodiments, the controller 120 includes one or more onboard input devices such as a touchpad or touch screen enabling a user to interact with the controller 120. The I / O device interface 124 also provides functionality for the controller 120 to instruct output peripherals, which may include displays, and audio devices.

[0116] In some embodiments, the controller 120 is connected to the sensing unit 110 via a sensor I / O connector of I / O device interface 124 enabling the transfer of control instructions from the controller 120 to the sensing unit 110 in real-time, or substantially real-time. For example, the control instructions may include instructions for operating the sensing unit 110 in a determined measurement mode, such as according to a determined rate range and / or bandwidth of the sensor(s) 112, a measurement wait timefor the sensing unit 110, and / or any other functional parameter(s) determining a capability of the sensing unit 110 to measure orientations.

[0117] In some embodiments, the controller 120 is configured to receive measurement data, including orientation data, from the sensing unit 110, and optionally to store the measurement data values as a function of time in order to enable postprocessing of the data.

[0118] Communications module 123 is a modem or transceiver device configured to enable the establishment of a logical connection between the controller 120 and other computing devices through a wireless or wired transmission media. For example, in some embodiments the controller 120 is configured to receive data associated with a borehole, such as for example hole planning data, hole drilling data, and / or logging data of the borehole from an external system 180, such as for example a bench management system (BMS), via a wide area network 150.

[0119] The controller 120 implements one or more service modules including a structured query language (SQL) support module (e.g., MySQL) enabling data to be stored in, and retrieved from, a data store (such as an SQL database). In some embodiments, the data store is formed within the memory system 125 and includes data tables, or other structures, configured to store, data for one or more boreholes, including at least orientation data generated by the sensing unit 110 from orientation measurements in association with the borehole(s).

[0120] The skilled person in the art will appreciate that many other embodiments may exist including variations in the hardware configuration of controller 120, and the distribution of program data and instructions to execute the orientation measurement methods described herein.Example apparatus configurations

[0121] Fig. 1c is a schematic diagram of a first exemplary implementation of the apparatus 100 according to the described embodiments. In particular, Fig. 1c shows theapparatus 100 implemented as a rig alignment tool 102 where the sensing unit 110 is coupled with a plurality of auxiliary systems and components 130, 131, 132. In this configuration, the rig alignment tool 102 is configured to generate orientation measurements during a drill rig alignment workflow use case of a borehole, as described herein.

[0122] In some embodiments, the rig alignment tool 102 includes a coupling system 130 in the form of a mechanical system configured to removably attach the rig alignment tool 102 to a drill rig. For example, the coupling system 130 may be implemented as a clamp, brace, or any other suitable mechanical means for fastening the rig alignment tool 102 to a part of the drill rig.

[0123] In some embodiments, the coupling system 130 is configured to attach the rig alignment tool 102 to other portion of the drill apparatus, such as a drill string and / or a drill rod. For example, the coupling system 130 may comprise a fastening mechanism configured to lock the portion of the apparatus 100 forming the rig alignment tool 102 onto, around a part of, or into an internal volume of, a drill rod, preferably a collar drill rod that is used to commence the drilling of the borehole.

[0124] In particular, inserting the rig alignment tool 102 into the drill rod improves the accuracy of the alignment process by enabling the length of the drill rod to be used in the alignment movements. Further, utilising the internal diameter of the drill rod whilst the drill rig is aligning itself assists with the rig alignment tool 102 maintaining alignment during the movement of the drill rig, thereby advantageously reducing or eliminating angular offset (i.e., by achieving axial co-inci dent alignment of both the drill rod and the rig aligner).

[0125] In some embodiments, the rig alignment tool 102 includes a localization system 131 configured to provide a global location, and optionally a pose, of the rig alignment tool 102. The localization system 131 includes components configured to receive a location and pose signal (e.g., an antenna, not shown), and components to process received location and orientation data. In one example, the localization system131 includes a global navigation satellite system (GNSS) and an inertial navigation (IMU) system configured to determine an exact position and orientation of a portion of the rig alignment tool 102 in a coordinate space of the localization system 131. In some embodiments, the localization system 131 also includes a kinematic linkage positioning and measurement system configured to determine relative positions and orientations of a fixed predetermined point on the rig alignment tool 102.

[0126] In some embodiments, the rig alignment tool 102 includes a communication system 132 configured to communicate with the controller 120 and / or one or more other computing devices. The communication system 132 includes a modem or transceiver configured to perform a data transfer over a wired or wireless communication media. In some embodiments, the sensing unit 110 is connected to the communication system 132 via the sensor interface 118 to enable the exchange of data with the controller 120 (e.g., via communication module 123). For example, the communication system 132 may have a network interface implementing the IEEE 802. xx family of networking protocols enabling the exchange of information wirelessly with the controller device 222 (e.g., over technologies such as Wi-Fi).

[0127] The communication and data transfer capability of the communication system132 may be configurable depending on the configuration of the rig alignment tool 102. For example, the communication system 132 may be configured to exchange data according to a particular protocol and / or using a particular network or medium depending on the physical distance between the controller 120 and the sensing unit 110 during measurement.

[0128] Fig. Id is a schematic diagram of a second exemplary implementation of the apparatus 100 according to the described embodiments. In particular, Fig. Id shows the apparatus 100 implemented as a borehole surveying tool 104 where the sensing unit 110 is coupled with a plurality of auxiliary systems and components 133, 134, 135, 136. In this configuration, the surveying tool 104 is configured to generate orientation measurements during a borehole survey workflow use case of a borehole, as described herein.

[0129] Exemplary components of the surveying tool 104 include: a deployment connector 133, such as for example a spear point module that provides a coupling for the attachment of a wireline provided with an overshot to the surveying tool 104 enabling the surveying tool 104 to be lowered into the borehole; one or more geological sensors 135a, 135b (e.g., electrical or electronic sensors) and one or more instruments 135c collectively configured for geological or geophysical parameter surveying; the sensing unit 110 comprising the one or more sensors 112 and having a sensing axis 107 arranged relative to the measurement axis 103 to generate orientation measurements during the surveying; and a housing 139 that encapsulates the components. The housing 139 is composed of a resilient material, such as a metal, composite, or hard plastic, to provide protection to the internal modules during movements of the surveying tool 104 within the borehole (e.g., as the surveying tool 104 is lowered into the borehole and as it is extracted).

[0130] The geological sensors may be grouped into one or more sensor sets 135a, 135b positioned at physically distinct locations along the axial length of the surveying tool 104. For example, geological sensing modules 135a, 135b form sets of electromagnetic sensors that are collectively configured to generate data representing one or more geological data measurements of the borehole, and / or the formation / strata surrounding the borehole, during the surveying process. Exemplary embodiments may include, for example, a total gamma system 135a configured to detect gamma radiation through the scintillation of light produced by the interaction of the gamma rays with a scintillator crystal material.

[0131] The surveying tool 104 may also include a magnetic susceptibility and conductivity system 135b, including at least one receiver coil responsive to at least one transmitter coil to obtain both magnetic susceptibility and conductivity measurements from a region surrounding the surveying tool 104.

[0132] In some embodiments, either or both of geological sensor sets 135a 135b may include a temperature sensor, a water sensor, a deviation sensor that can sense pitch, roll and heading, or any other number of varying sensors or modules. For example, thegeological sensors 135a may include an infrared (IR) sensor. In some embodiments, the IR sensor measures temperature associated with the borehole which is then processed to produce an electrical signal providing an indication of a temperature associated with the borehole (e.g., a temperature at the collar or an interior surface).

[0133] In some embodiments, the instruments 135c of the sensors 135 include one or more mechanical or electromechanical devices configured to make physical contact with the formation / strata of a borehole during the measurement process. For example, the instruments 135c may include a caliper set having a number of caliper fingers that, when activated, extend outwards from a body of the surveying tool 104 to collectively provide a measurement of the diameter of the borehole.

[0134] Under normal operation of the caliper set, each caliper finger deploys to an extended length until the finger is stopped by an abutment (e.g., the side of the borehole wall). The amount of extension of each finger that may be detected thereby providing a measurement of the distance between the housing 139 of the surveying tool 104 and the borehole 101. This enables the generation of distance measurements representing a diameter of the borehole 101.

[0135] lin some embodiments, the instruments 135c includes a modified caliper (either as an addition to, or replacement of, the standard caliper described above). The modified caliper may provide extended and / or additional functionality to that of a standard caliper. In some embodiments, the modifed caliper includes one or more components that enable the modified caliper to generate measurement data without physical contact between the caliper and the borehole during movements of the surveying process. The components of the modified caliper may include, for example, one or more imaging devices (such as cameras), one or more emitter / detector devices (such as IR or acoustic subsensors), or any other device configured to take measurements of a surface or region of the borehole.

[0136] In one example, the modified caliper is configured with components attached to an end of corresponding fingers, and operates by extending each finger towards theside of the borehole wall, but stopping the extension prior to physical contact with the wall. This is advantageous in that the component is placed close to the borehole interior wall thereby improving the accuracy of the measurements obtained by the component, without requiring physical contact of the same with the borehole (and thereby avoiding potential damage or wear).

[0137] In some embodiments, the sensors 135 include one or more imaging devices or sensors configured to generate data representing images of the interior of the borehole. For example, sensors 135 may include one or more cameras, such as monographic cameras, stereographic cameras, or laser scanning devices, and / or radar, or light-based radar (LiDAR) devices that generate imaging data related to shape, color, depth, and / or other features of object(s) of the borehole that are in the line of the sensors. The imaging data may be processed, by the local controller 136, the controller 120, or another computing device to assist with understanding the nature of the borehole according to the methods described herein. In some embodiments, some or all of the imaging devices or sensors are configured as components of the modified caliper. In other embodiments, the imaging devices are configured as one or more sensor groups, which may be located, for example, on the body or at the base of the surveying tool 104.

[0138] In some embodiments, the surveying tool 104 is provided with one or more deployment components 134. Each of the one or more deployment components 134 is a physical instrument, device, or apparatus that is configured to control the deployment characteristics of the surveying tool 104 in the borehole. The deployment characteristics generally refer to the properties of the surveying tool 104, other than those which determine the collection of surveying data within the borehole.

[0139] For example, the deployment components 134 may include bracing and / or stabilizing devices that, when activated, cause the surveying tool 104 to be oriented or positioned in a certain way relative to one or more interior surfaces of the borehole. One or more deployment components 134 may be activated in combination with one or more of the sensors 135a, 135b and / or instruments 135c. For example, a bracing devicemay be activated to position a sensor 135a against the interior wall of the borehole. In some embodiments, one or more of the instruments 135c are also deployment components 134. For example, a caliper set of the surveying tool 104 may act as a sensor to provide a measurement of the diameter of the borehole. The caliper set of the surveying tool 104, when activated, may also force the surveying tool 104 into a particular alignment relative to the axial path X of the borehole, or provide a degree of stability to the movement of the surveying tool 104 (thereby influencing the deployment characteristics).

[0140] In some embodiments, the surveying tool 104 is provided with one or more centralizers at, or adjacent to, proximate and distal ends of the surveying tool 104 that are positioned about the housing 139. Centralizers may be arranged to bind an inner section containing the sensing unit 110 and / or geological sensor(s) 135a, 135b which are powered by one or more power sources such as a battery (not shown). The centralizers 134 maintain the surveying tool 104 in a central position relative to the core barrel innertube if used and / or the drill rod, such that the surveying tool 104 is firmly held within the drill string, such that on the occurrence of any lateral movement (e.g., shaking of the string) the surveying tool 104 is held firmly in place.

[0141] In some embodiments, the surveying is conducted with the survey tool 104 located within a drill string of the drilling apparatus used to drill the borehole (as described below). The surveying tool 104 may include an engagement member to hold the survey tool 104 in place in the string. The drill string engagement member is located towards the lower most end of the surveying tool 104, so that the surveying tool 104 is retained at the end of the drill string. However, the geological sensor(s) 135a may be positioned at the lower most end of the surveying tool 104 (i.e., beyond the engagement member) to enable the geological sensor(s) 135a to extend beyond the corresponding engagement end of the drill string, such that the drill string does not interfere with the operation of the geological sensor(s) 135a.

[0142] In some embodiments, the surveying tool 104 includes additional components, including for example a latch assembly that provides a coupling for the releasableattachment of the surveying tool 104 to the drill string. In some embodiments, the surveying tool 104 is configured to abut against a bitstop of the drill bit for the coupling of the surveying tool 104 to the drill string.

[0143] In some embodiments, the surveying tool 104 includes a communication system 136 configured to communicate with the controller 120 (e.g., via the communication module 123) and / or one or more other computing devices. The communication system 136 of the surveying tool 104 may be configured analogously or differently compared to the communication system 132 of the rig alignment tool 102. For example, the communication system 136 may be optionally configured to receive data from other components, such as the geological sensors 135a, 135b, and / or instruments 135c, and to transmit the same to the controller 120, or another computing device.

[0144] The communication and data transfer capability of the communication system 136 may be configurable depending on the configuration of the surveying tool 104. For example, the communication system 136 may be configured to exchange data according to a particular protocol and / or using a particular network or medium depending on the physical distance between the controller 120 and the sensing unit 110 during measurement.

[0145] In some embodiments, components of the surveying tool 104 are arranged in interconnected sections enabling the attachment and detachment of discrete modules comprising one or more components, such as for example the sensing unit 110 and one or more auxiliary components or systems respectively, in accordance with a desired surveying function and / or deployment of the surveying tool 104. Housing 139 may be similarly configurable to permit adjustment of the total size, weight and / or form-factor of the surveying tool 104.Borehole workflow use cases

[0146] The orientation measurements generated by the apparatus 100 comprise a set of N orientation values O = {O1(ON}, each value (f being determined at a sampletime instant t. In the described embodiments, the orientation values include: an azimuth value i , as the angle of the measurement axis 103 with respect to true North, which is the projection of the spin vector of the earth onto the horizontal plane; and an inclination value 0, as the angle of the measurement axis 103 with respect to gravity.

[0147] Each orientation value OLoptionally includes a value of a toolface (TF), as used, for example, to determine the orientation of a core so the features on the core can be oriented to the formation of the borehole, or to determine the direction that a drilling tool will drill towards. In some embodiments, the value of the toolface is a gravity TF (also referred to as “high side TF”) value, which is the angle about the measurement axis 103 of the apparatus 100 with respect to gravity.

[0148] In some embodiments, the value of the toolface is a gyroscope TF value, which is the angle about the measurement axis 103 with respect to true North. Gravity TF may be used, for example, when the measurement axis 103 of the apparatus 100 is > 5 degrees (deg) off of vertical and gyroscope TF when < 5 deg. In some embodiments, the value of the toolface is a magnetic TF value, which is an alternative in the vertical case when magnetometers are used instead of gyroscopes.

[0149] The apparatus 100 is used to generate the orientation values O in the respective measurement use cases of drill rig alignment for drilling a borehole, and surveying of the as drilled borehole (i.e., as implemented within the rig alignment tool 102 and surveying tool 104 respectively).Drill rig alignment

[0150] Figs. 2a to 2c illustrate an exemplary drill rig alignment use case in which a rig alignment tool 102 is used to generate orientation measurements associated with a borehole 101. The borehole 101 is in a pre-drilling state with respect to the surface 109 (i.e., prior to the borehole creation within the surface 109). Although Figs. 2a to 2c illustrate the application of the proposed orientation measurement to a borehole in an above ground mining site, this can be extended to other situations where there is a needto conduct orientation measurements associated with a borehole either prior to or after drilling.

[0151] As shown in Fig. 2a, the borehole 101 is created by a drilling apparatus 140 comprising a drill rig 141 configured to position and control the operation of a drilling device 142 including a drill string 146 with a drill bit (not shown) attached at the end of the drill string 146 that carries out the drilling. In some embodiments, one or more systems are coupled to the drill rig 141, or drill device 142, such as a drill guidance system 143 and a drill operation system 145 implemented as one or more computing devices. The drill guidance system 143 includes a navigation component for the drill rig 141, enabling the drill rig 141 to move to particular positions on the surface 109 to drill the one or more holes (including borehole 101) in accordance with a drilling plan that includes pre-determined locations to drill the boreholes.

[0152] In some embodiments, the drill guidance system 143 also includes a location component configured to determine location co-ordinate values of: the drill rig 141 and the drill device 142. For example, the location component is configured to determine the location for the as drilled position (A) of the collar of borehole 101. These location co-ordinate values determined by the drill guidance system 143 may be the same or different to the drilling plan. Differences may arise due to unforeseen differences on the drilling site, such as for example wear of the drill bit, slight misalignment of the drill rig 141, uneven terrain or other circumstances that arise during drilling vs the optimal circumstances on which the drilling plan was based upon.

[0153] The drill operation system 145 controls the operation of the drill rig 141 enabling the drilling of one or more holes, including borehole 101. In some embodiments, the drill operation system 145 is configured to process data (i.e., hole pattern data) to determine particular drilling operations required for hole creation. For example, the drill operation system 145 may dynamically configure the drilling apparatus 140 by selecting a particular drill bit, and mode of drilling with the selected bit, based on the desired characteristics of the borehole 101 and / or mine site requirements (e.g., hole length and width).

[0154] The rig alignment tool 102 is attached to a portion of the drilling device 142 in a manner that permits measurement of orientation of the drill device 142, and therefore of the (pre-drilled) borehole 101, in relation to the surface 109. During rig alignment, the pose of the drill device 142 is varied by the drilling apparatus 140 to vary the alignment of the borehole 101 that is to be drilled, such as for example to achieve a desired orientation of a primary (i.e., longitudinal) axis X of the borehole 101.Variation of the orientation of the drill device 142 results in a corresponding variation of the orientation of the rig alignment tool 102, as measured with respect to the measurement axis 103.

[0155] In some configurations, the rig alignment tool 102 is positioned relative to the drill device 142 such that the measurement axis 103 is coincident with the axis X of the borehole 101 to be drilled by the drill device 142 in the corresponding pose. In the examples depicted by Figs. 2a to 2c, the rig alignment tool 102 is inserted into a portion of the drill rod sitting within the drill device 142. In other configurations, the rig alignment tool 102 is coupled to another part of the drill device 142 resulting in an offset between the measurement axis 103 and the borehole primary axis X.

[0156] Drill rig alignment commences in accordance with a drilling plan that identifies a desired alignment of the drill device 142 for forming the borehole 101 (e.g., from identification of an area of interest of the sub-surface). A desired orientation of the drill device 142 is therefore determined based on the drilling plan such that the borehole 101 will have a desired alignment when drilling commences.

[0157] With reference to Fig. 2a, the drill rig alignment process commences with the drill device 142 in a known or initial pose. A user of the drill apparatus 140 controls the drill apparatus 140 to vary the orientation of the drill device 142 and also operates the rig alignment tool 102 via the controller 120 (which may be located on the drill apparatus 140).

[0158] The drill rig alignment use case commences with a North seeking measurement operation to determine orientations of true North and the Earth’s gravity.The user provides input to the orientation measurement apparatus 100 indicating an expected rate of change of the orientation of the apparatus 100 (referred to as an “expected rate of change input”) for performing North seeking as part of the drill rig alignment. For example, the user may indicate or otherwise select a ‘Low rate range’ option or preset for operating the sensing unit 110, which reflects the expectation of relatively small changes in orientation during North seeking. The controller 120 processes the expected rate of change input to determine a corresponding measurement mode of the sensing unit 110, and then operates the sensing unit 110 in this measurement mode to cause the sensor(s) to generate orientation values.

[0159] The drill apparatus 140 holds the drill device 142 stationary during North seeking, and the rig alignment tool 102 generates a series of orientation values ONSaccording to at least a rate range and / or bandwidth specified by the corresponding measurement mode. In some embodiments, the rig alignment tool 102 transmits the generated orientation values to the controller 120 in real-time or substantially real-time for processing and / or provision to the user (e.g., via an interactive display component). In some embodiments, the rig alignment tool 102 is detached from the drilling device 142 during North seeking, then reattached to the drilling device 142 to perform one or more other measurement operations. For example, the rig alignment tool 102 may be located on the ground during North seeking and then coupled to the drill rig during navigation.

[0160] Figs. 2b and 2c depict a navigation measurement operation performed with the rig alignment tool 102 comprising the apparatus 100. Prior to the commencement of navigation, the user provides the controller 120 with an expected rate of change input for the orientation measurements. For example, the user may indicate or otherwise select a ‘High rate range’ option or preset for operating the sensing unit 110, which reflects the expectation of relatively large changes in orientation associated with orienting the drill device 142 (and therefore the rig alignment tool 102) during this part of the drill rig alignment process. The controller 120 processes the expected rate of change input to determine a corresponding measurement mode of the sensing unit 110, which may be different to the measurement mode used for North seeking, and thenoperates the sensing unit 110 in this measurement mode to cause the sensor(s) to generate orientation values.

[0161] As shown in Fig. 2b, at timethe user operates the drill apparatus 140 to vary the orientation of the drill device 142, and therefore the measurement axis 103, resulting in the generation of orientation values representing an azimuth i1(i.e., the angle between the projection of the measurement axis 103 and a reference direction, such as the true North direction ‘N’, at time t-^ and an inclination of (i.e., the angle between the measurement axis 103 and a vertical direction of gravity ‘G’ at time t-^. At a further time t2, the orientation of the drill device 142, and therefore the measurement axis 103, changes resulting in the generation of orientation values representing an azimuth ip2and an inclination of 02. Variations to the orientation of the drill device 142, and therefore the measurement axis 103, may be performed during the drill rig alignment process in response to the user receiving the orientation values from the controller 120 (e.g., by viewing the orientation values, and / or a depiction of the same, on the display component).

[0162] The drill rig alignment process ceases once the drill device 142 is oriented to have the desired alignment for drilling of the borehole 101. In the example shown by Figs. 2a to 2c, the desired alignment is represented by the orientation values (I / J2, 02). The borehole 101 is then drilled according to the desired alignment to have an orientation that, ideally, corresponds to the orientation values (I / J2, 02). In practice, the interior of the borehole 101 is often not drilled with a constant alignment, and there is consequently a need to determine orientation measurements at different depth values within the as-drilled borehole 101.Borehole surveying

[0163] Figs. 2d to 2g are respective schematic diagrams of an exemplary borehole surveying use case in which a surveying tool 104 is used to generate orientation measurements associated with the borehole 101.

[0164] Figs. 2d to 2g depict the borehole in its post-drilling state following the completion of the drilling operation, but prior to drill string extraction. The borehole 101 extends into the ground of surface 109 at the first position A and terminates at a second position A’ forming the as drilled borehole 101. At the completion of the excavation of the borehole 101 (i.e., once the end of the borehole 101 is formed at the second position A’), the drill string 146 is disposed within the borehole 101, such that the drill bit resides at the hole end position A’. The drill string will then be extracted to then drill the next hole in the pattern.

[0165] Borehole surveying may be performed to determine orientation measurements at different depth values within the as-drilled borehole 101. This may be useful to determine whether drilling has accurately followed the drilling plan, thereby allowing the borehole 101 to hit the area of interest or anticipated ore body.

[0166] Figs. 2d to 2g depict a logging-while-tripping surveying use case occurring as part of a drill string extraction procedure following drilling of the borehole 101. Surveying tool 104 is placed into the distal end of the drill string 146, for example as coupled to the end most part of a drill string 146. Drill string 146 is comprised of a plurality of interconnected drill rods 146a to 146f. An extraction means, such as a cable, or a drill rod handler on a drill rig is tethered to the drill string 146 at the proximal end of drill rod 146f, located at or around position A at the hole collar. Drill string extraction involves the operation of the extraction means to exert a pulling force on the drill string 146, causing the removal of a portion of the drill string 146 from the borehole 101 (i.e., the removed portion being that which exits the borehole 101 in response to the pulling force). The removal and detachment of drill rods of the drill string 146 proceeds repeatedly until the final drill rod, as represented by 146a in Figs. 2d-2g, has been extracted.

[0167] Fig. 2d depicts the surveying at an initial time t0, in which the series of rods 146a to 146f fully occupies the interior of the borehole 101, such that surveying tool 104 is adjacent to the end position A’. A user operates the orientation measurement apparatus 100 via the controller 120 (which may be implemented as an edge processingdevice above the surface 109), such as for example to provide an expected rate of change input to the controller 120 for operating the surveying tool 104 to determine the orientation measurements during at least a portion of the surveying. The controller 120 processes the expected rate of change input to determine a corresponding measurement mode of the sensing unit 110, and then operates the sensing unit 110 in this measurement mode to cause the sensor(s) to generate orientation values.

[0168] In some examples, the surveying use case commences with a North seeking measurement operation. The controller 120 receives an expected rate of change input from the user for performing North seeking during surveying (e.g., a ‘Low rate range’ indication, which reflects the expectation of relatively small changes in orientation during North seeking). Drill rig extraction is delayed until North seeking completes, such that the surveying tool 104 remains stationary during the operation. Alternatively, if North seeking has already been conducted with the surveying tool 104 located at the top of the borehole 101 (i.e., near position A), then the same reference orientation data may be used as the reference point for the borehole surveying use case.

[0169] In some examples, North seeking is performed intermittently during the surveying to reset or otherwise recalibrate the reference orientation data. In some examples, the reference orientation data is derived from measurement operations conducted using the sensing unit 110 during the rig alignment use case. In some examples, the reference orientation data is obtained from data received from an external source.

[0170] Figs. 2e to 2g depict a navigation measurement operation performed with the surveying tool 104 comprising the apparatus 100. The controller 120 receives an expected rate of change input from the user for performing navigation during surveying (e.g., a ‘Low rate range’ indication, which reflects the expectation of relatively small changes in orientation associated with navigating the surveying tool 104). The drill string 146 is extracted from the borehole 101 by the removal of successive drill rods, resulting in the surveying tool 104 traveling from end position A’ towards collar position A.

[0171] As shown in Fig. 2e, at time txthe drill rods 146f and 146e have been extracted from the borehole 101 resulting in a movement of surveying tool 104 and therefore the measurement axis 103, providing orientation values representing an azimuth ip1and an inclinationat time t1. As shown in Fig. 2f, at time t2the drill rods 146d and 146c have been extracted from the borehole 101 resulting in a further movement of surveying tool 104 and therefore the measurement axis 103, providing orientation values representing an azimuth i2and an inclination of 02at time t2. Then, as shown in Fig. 2g, at time t3the drill rods 146b and 146a have been extracted from the borehole 101 resulting in a movement of surveying tool 104 and therefore the measurement axis 103, to the collar position A, providing orientation values representing an azimuthand an inclination of 03at time t3.

[0172] The orientation of the measurement axis 103 typically varies continuously during a navigation operation of the surveying use case, such that the apparatus 100 generates corresponding orientation values Ot., 0ti) for sample timesE [t0, t3] reflecting the variation in the alignment of the borehole 101 as a function of the depth of the surveying tool 104 within the borehole 101 (which varies over time).

[0173] It will be appreciated that the apparatus 100 may be used for other surveying use cases in which the surveying tool 104 is not coupled to the drill string 146. For example, in a drill pipe exploration survey the surveying tool 104 is deployed into the borehole 101 via a cable to generate orientation measurements at a time after drill string extraction has occurred. In some embodiments, the surveying tool 104 comprises a spearpoint, a battery, the sensing unit 110, one or more geological sensors (e.g., gamma sensors), and an overshot to attach to the spearpoint of a core barrel for retrieval.

[0174] The surveying tool 104 is deployed into the borehole 101 on the cable, starting at collar position A and finishing at the end position A’. The surveying tool 104 is then extracted from the borehole 101 by retracting the cable (e.g., via a winch). Logging of the borehole 101 may be conducted during an inward movement and / or during an outward movement of the surveying tool 104 (i.e., a movement from the end positionA’ to the collar position A), in which its movement is analogous to the logging-whiletripping process shown in Figs. 2d to 2g. A user operates the apparatus 100 via the controller 120 (which may be implemented as an edge processing device above the surface 109), such as for example to provide an expected rate of change input to the controller 120 for operating the surveying tool 104 during at least the portion of the exploration survey in which the borehole 101 is logged.

[0175] For logging-while-tripping surveying, exploration surveying, or another surveying use case, the controller 120 executes a control application that is in communication, typically wirelessly, with the sensing unit 110. The control application programs the surveying tool 104 to perform a sequence of measurement operations (e.g., North seeking, drift tuning, then navigation for a first time period, followed by drift tuning, then navigation for a second time period, etc.), which in some embodiments may be analogous to the operations performed for the logging-whiletripping process shown in Figs. 2d to 2g.

[0176] For exploration surveying, the controller 120 is also connected to a wireline encoder that tracks the depth of the survey tool 104 within the borehole 101. In addition, the controller 120 tracks the measurement operation sequence that was programmed on the surveying tool 104. The controller 120 is configured to alert the operator when the surveying tool 104 needs to be held still (for drift tuning or North seeking) and when movement is permitted. The surveying tool 104 is extracted from the borehole 101, and the measurement data logged on the surveying tool 104 is extracted and correlated to the depth recorded in the control application (both as a function of time) to obtain an orientation vs depth (and optionally a geological measurement vs depth) log.

[0177] In some embodiments, the apparatus 100 is configured to perform blast hole surveying according to any of an above ground blast hole surveying use case; and an underground blast hole / drill hole surveying use case.

[0178] In some embodiments, the apparatus 100 is configured to perform one or more of (a) high temperature surveying; and (b) wireline surveying, of a borehole 101. For a high temperature survey, the sensing unit 110 is housed in a heat shielding casing, and, typically, conducting high speed measurements is more important than conducting measurements with high accuracy (e.g., to reduce self-heating). Therefore, the controller 120 may program the sensing unit 110 to reduce North seeking time, for example by selectively deactivating one or more high accuracy sensors to reduce power consumption and / or self-heating.

[0179] For a wireline survey, both power and communication are typically provided through the wireline used to deploy the surveying tool 104 into the borehole 101. In some embodiments, the sensing unit 110 is configured to transmit orientation data, as generated during the survey when the sensing unit 110 is within the borehole 101, to the controller 120, as located at the surface, in real-time or substantially real-time.

[0180] It will be appreciated that the examples depicted in the figures and described herein are non-exhaustive, and that there are other configurations, deployments and use cases of the apparatus 100 for generating orientation measurements.Method for determining orientations associated with a borehole

[0181] Fig. 3a is a flow diagram of a method 300 for determining orientation measurements associated with a borehole 101 using a borehole measurement apparatus 100 according to the proposed technology.Expected rate of change of orientation

[0182] At step 302, the controller 120 receives, or otherwise determines, an expected rate of change of the orientation of the apparatus 100 for operating the sensing unit 110 to determine the orientation measurements. In some embodiments, the controller 120 receives an indication of the expected rate of change of orientation (referred to as an “indicated expected ROC”) as input data, such as for example data received from a user interaction with a user interface (UI) component of the controller 120 via I / O device interface 124, or as data transmitted to the controller 120 from another computingdevice (via communications module 123). In such embodiments, the controller 120 processes the input data to generate expected ROC data comprising a numerical representation of the expected rate of change of the orientation of the apparatus (referred to as an “expected ROC” value).

[0183] Fig. 3b is a schematic diagram of a first exemplary user interface 310 having a UI display panel 311 with elements 312-316 that each may be activated to provide the controller 120 with a corresponding non-numerical indication of the expected ROC. The UI display panel 311 allows a user to select one or more rendered elements, in this case comprising ‘Large’ 312, ‘Moderate’ 314, and ‘Small’ 316 elements. In the embodiment shown in Fig. 3b the non-numerical indicator elements 312-316 form a set of classifications of the expected ROC of orientations as a relative level of change. This is advantageous in permitting variable control over the expected ROC of orientations in scenarios where the user of the apparatus 100 does not know, and cannot approximate, the expected ROC numerically. The controller 120 maps the indicated expected ROC provided by the input data (i.e., comprising a selection of one of categories 312, 314 and 316) to an expected ROC value such as for example using a predetermined non- numerical ROC indicator table or structure maintained in memory system 125.

[0184] Fig. 3c is a schematic diagram of a second exemplary user interface 320 having a panel 311’ with elements 322-329 that may each be activated to provide the controller 120 with a corresponding numerical indication of the expected ROC. The numerical indications may each comprise one or more discrete or continuous values representing the expected ROC of orientations, or representing an interval in which the expected ROC of orientations occurs. The numerical values may be determined from a set of predetermined representative values (or representative intervals), or alternatively may be specified arbitrarily by the user.

[0185] For example, Fig. 3c shows numerical indications in the form of a first ROC interval defining a range less than 50 deg / sec (element 322), a second ROC interval defining a range from 50 to 100 deg / sec (element 324), a third ROC interval defining a range from 100 to 200 deg / sec, and a fourth ROC interval defining a range of over 200deg / sec (element 328). In some examples, the start and / or end values of an indicated expected ROC interval are configurable (e.g., in response to input from the user). Fig. 3c further shows a UI element 329 of the panel 311’ that provides a numerical indication in the form of a single representative value X that may be set or selected by the user. For example, the value of X may be a sample value taken from a predetermined number of values, or a value that is arbitrarily determined by the user.

[0186] The user selects a numerical indication from the set of indications 322-329 rendered on the panel 311’ to cause the generation of data, comprising at least the representative values, which is received by the controller 120 as expected ROC input data. The controller 120 is configured to derive an expected ROC value from the numerical value(s) of the expected ROC input data. For example, the controller 120 may map the numerical values to an indicated expected ROC interval (e.g., corresponding to one of elements 322, 324, 326, 328 and 329) to the expected ROC value (i.e., by using either of the start or end values as the expected ROC value, or by calculating the expected ROC value as a point within the interval, such as the midpoint). In other examples, the controller 120 may use a single representative value of the indicated expected ROC (e.g., value X corresponding to element 329) as the expected ROC value.

[0187] In some embodiments, the controller 120 receives an indication of expected ROC of orientations by means other than the user selecting the indication from a user interface, or otherwise providing the indication to the controller 120. For example, the controller 120 may be configured to receive orientation history data representing orientation values previously generated over a known prior time interval. The controller 120 may process the orientation values of the orientation history data to determine an expected ROC value for the future measurements (e.g., by averaging the previously generated orientation values).

[0188] In some embodiments, the controller 120 is configured to determine the expected rate of change of the orientation of the apparatus 100 in response to receiving an indication of a workflow use case and / or a measurement operation in which thesensing unit 110 is operated (or is to be operated). In some embodiments, the controller 120 receives the indication of the workflow use case and / or measurement operation as input data, such as for example as data received from a user interaction with the controller 120 (e.g., via the I / O device interface 124), or as data transmitted to the controller 120 from another computing device (e.g., via the communications module 123). In such embodiments, the controller 120 processes the input data to generate a corresponding expected ROC value.

[0189] Fig. 3d is a schematic diagram of a third exemplary user interface 330 having a panel 311” with elements corresponding to one or more workflow use cases 331, and one or more measurement operations 333, in which the sensing unit 110 may be operated. The user of the apparatus 100 may select a UI element corresponding to a workflow use case, such as drill rig alignment 332 or post-drill surveying 334, and an element corresponding to a measurement operation, such as North seeking 336 or navigation 338. The indicated workflow use case and / or operation is provided by the interface 330 to the controller 120 as input data.

[0190] In some embodiments, the controller 120 processes the indicated workflow use case and / or operation to determine an expected ROC value, such as for example using a mapping table or structure maintained in memory system 125. In some embodiments, the mapping table or structure comprises the non-numerical ROC indicator map used by the controller 120 to translate non-numerical indications of an expected ROC to the expected ROC value.

[0191] For example, the controller 120 may map an indication of a navigation operation occurring in a drill rig alignment use case to the same expected ROC value that is associated with an indication of a ‘Large’ non-numerical indication of expected ROC of orientation. This advantageously enables the controller 120 to receive or determine an expected rate of change of the orientation of the apparatus 100, and subsequently a measurement mode (as described below), from an indication of a measurement use case and / or a measurement operation of the sensing unit 110.Measurement mode determination

[0192] With reference to Fig. 3a, at step 304 the controller 120 determines a measurement mode of the sensing unit 110 based on the expected rate of change of the orientation of the apparatus 100 for generating the orientation values. The expected rate of change of the orientation is represented by an expected ROC value determined according to step 302. The controller 120 is configured to invoke the MCM 121 to determine the measurement mode by processing the expected ROC value.

[0193] Fig. 4a is a schematic diagram illustrating a set 400 of candidate measurement modes M used by the MCM 121 to determine the measurement mode associated with the expected ROC value. Each measurement mode 401-405 defines a set of one or more parameters of the sensing unit 110 for generating the orientation measurements. Preferably, the set of parameters of the sensing unit 110 includes a rate range (R) and / or a bandwidth (B) of the one or more sensors 112. The specified rate range R and / or bandwidth B determines the range of the change in orientations (R determining the magnitude and B determining the frequency) that are detectable by the sensing unit 110 to a desired degree of accuracy. Optionally, the set of one or more parameters of the sensing unit 110 also includes a wait time (W) to generate a set of orientation measurements at each particular sample time instant. The sensing unit 110 may be configured to use a default or existing wait time value (e.g., if a wait time is not explicitly specified).

[0194] In some embodiments, each measurement mode 401-405 defines additional parameters of the sensing unit 110, the one or more sensors 112, and / or of any other components of the sensing unit 110, to generate the orientation measurements. In some examples, the parameters of the sensing unit 110 may include, but are not limited to: (i) a list of sensors that will be powered (activated) in North seeking and / or navigation operations; (ii) an indication of whether a drift tuning operation is to be performed after North seeking and, if so, a time period to average the sensor output values during the drift tuning operation; and (iii) an indication of whether or not to enable a space stabilization loop of a platform of the sensing unit 110 (as discussed below), and, if so, one or more properties of the loop (e.g., the bandwidth).

[0195] In some embodiments, the parameters of the sensing unit 110, the one or more sensors 112, and / or any other components of the sensing unit 110, are determined in part based on the measurement use case. For example, in the logging while tripping use case, the space stabilization may be enabled and at relatively high bandwidth, such that the orientation of the depth determining accelerometers remains more constant with respect to gravity which increases accuracy.

[0196] In some embodiments, the controller 120 determines the measurement mode by switching between a plurality of predetermined measurement modes. The MCM 121 identifies the predetermined measurement modes from the candidate set of modes 400. Example set 400 depicted in Fig. 4a shows a first mode (“low rate range mode”) M1(401) having a first range rate (401a) and a bandwidth (401b) of the one or more sensors 112, and a second mode (“high rate range mode”) M2defining a second range rate (402a) and a bandwidth (402b), where the rate range and bandwidth of the mode M2are greater than those of the mode M1. In some implementations, when operating in the second (high rate range) mode, the sensor(s) 112 will have a corresponding second accuracy less than a first accuracy of the first (low rate range) mode.

[0197] In some embodiments, the set of candidate measurement modes comprises N = 2 modes, such as the low rate range mode M1and the high rate range mode M2, which are respectively suitable for generating orientation measurements when the apparatus measures corresponding low and high expected rates of change of orientation. In some embodiments, the set of candidate measurement modes includes N > 2 modes defining a corresponding set of rate ranges and / or bandwidths of the sensor(s) 112.

[0198] For example, the set of candidate measurement modes 400 may include one or more measurement modes defining a rate range and / or bandwidth with a value between a minimum and maximum value defined by corresponding modes. The MCM 121 may be configured to store the set of candidate modes 400 in a mode data structure, such as an array, list, or table. The mode data structure may be configured to index the candidate modes as an ordered set M = {M1, M2, MN} according to one or morecorresponding defined parameters, such as rate ranges R = {R1, R2, ... , RN} and / or bandwidths B = {B1, B2, ... , BN}, where MNdefines the highest rate range (and / or bandwidth) mode and M1defines the lowest rate range (and / or bandwidth) mode.

[0199] In some embodiments, the predetermined measurement modes comprise other modes in addition to the set of modes {M1, M2, ... , MN} that are ordered according to rate ranges and / or bandwidth values. For example, the predetermined measurement modes may include one or more modes that combine values of rate range and / or bandwidth of a low rate range or a high rate range mode (e.g., M1and M2) with values of a wait time (W).

[0200] Fig. 4a depicts measurement modes M1Land M1Sdefining a low rate range (and bandwidth) according to the parameters of mode M1, with different respective wait time values. This advantageously allows the sensing unit 110 to measure micro range orientation changes with relatively long and short wait times (e.g., for use in North seeking operations during alignment and different types of surveying).

[0201] In some embodiments, the MCM 121 is configured to process the expected ROC value (E) to select the determined measurement mode as one of the plurality of candidate modes 400. For example, the MCM 121 may select one of the plurality of predetermined modes of set 400 using (i) parameter matching or (ii) thresholding, of the expected ROC value E. In some embodiments, selecting a predetermined measurement mode using parameter matching comprises comparing the expected ROC value E to one or both of the rate range and / or bandwidth of each of the plurality of measurement modes. For example, the MCM 121 may calculate a difference value dtbetween the expected ROC value E and each rate range RlE {R1, ... , RN} (i.e.,=\E — 7?11 , V 1 < i < N) and then select the measurement mode which minimizes this difference.

[0202] Fig. 4b is a flow diagram of a method 420 for determining a measurement mode using thresholding of an expected rate of change of orientation value. At step 422, the MCM 121 retrieves a set of measurement modes from the plurality ofpredetermined modes. The retrieved set of measurement modes may be ordered according to corresponding rate range values (or bandwidth values). At steps 424 and 426 respectively, the MCM 121 performs comparison testing to compare the expected ROC value E to a set of one or more thresholds T corresponding to the retrieved set of measurement modes M, and selects a measurement mode from the set based on the outcome of the testing.

[0203] Fig. 4c is a flow diagram of an exemplary method 450 for performing the comparison testing using a set of N — 1 thresholds T = {T1, ... , Tw-1} to select a determined mode from a set of N ordered measurement modes, where the thresholds are of ascending value (i.e., each threshold value Tl+1> Tlfor all i). At step 452, a first comparison test is performed between modes M1and M2using threshold T1. If E is less than T1, then corresponding rate range R1is deemed to be representative of E, and mode M1is selected (at step 453).

[0204] Otherwise, and for a set size of N > 2, a second comparison test is performed at step 454 between modes M2and M3using threshold T2> T1. If E is less than T2, then corresponding rate range R2is deemed to be representative of E, and mode M2is selected (at step 455). Subsequent steps are performed to conduct additional comparison tests as necessary, where the final test is performed at step 460 between modes and MNusing threshold Tw-1> TN~2. If E is less than TN~ then corresponding rate range RN-1is deemed to be representative of E, and mode Mw-1is selected (at step 461). Otherwise, rate range RNis deemed to be representative of E, and mode MNis selected (at step 462).

[0205] It will be appreciated that the parameter matching and thresholding processes described herein are exemplary techniques, and that the controller 120 may perform other techniques to operate the MCM 121 to switch between the plurality of measurement modes in response to receiving or determining the expected ROC value. By determining the measurement mode in this manner, the controller 120 advantageously sets or adjusts the functionality of the sensing unit 110 in accordancewith a number of predetermined functionalities that may correspond to allowed or desired configurations of the sensor(s) 112.

[0206] In some embodiments, the MCM 121 determines the measurement mode (i.e., at step 304 of method 300) by generating an arbitrary (or “custom”) measurement mode having at least a rate range and / or bandwidth value that is derived from the expected ROC value.

[0207] Fig. 4a shows a custom measurement mode Mzfor which rate range value 405a is set to the expected ROC value (i.e., Rz= E). In some embodiments, the rate range value (405a), the bandwidth value (405b), or any one or more other parameters of a custom measurement mode Mzare generated using a function maintained by the MCM 121, and having an input including one or more of: the expected ROC value E; an indication of the measurement use case (e.g., drill rig alignment or surveying); and an indication of the measurement operation (e.g., North seeking or navigation).

[0208] For example, the bandwidth value 405b of the custom measurement mode Mz405 may be generated using a bandwidth mapping function FBand(E) to determine a bandwidth of the one or more sensors 112 from the expected ROC value E (i.e., to determine whether the sensors will conduct measurements with low or high accuracy at the corresponding rate range). In some embodiments, the wait time 405c of the custom measurement mode Mz405 may be set, for example to a default value, to a value based on the expected ROC value E, or to a value determined in response to any other data (e.g., user input data).

[0209] This advantageously permits the MCM 121 to adapt the functionality of the sensing unit 110 to utilize an arbitrary rate range and / or bandwidth for a corresponding configuration of the sensor(s) 112 (e.g., in implementations where at least one sensor 112 has a configurable rate range and / or bandwidth). In some embodiments, the controller 120 is configured to store the custom measurement mode Mzin memory 125 (e.g., in the mode data structure) for use as a predetermined mode in future measurements.

[0210] In some embodiments, the MCM 121 is configured to select a predetermined measurement mode, or to generate a custom measurement mode, based at least in part on an indication of the measurement use case and / or the measurement operation performed to generate the orientations. For example, the MCM 121 may be configured to process an indication of the measurement use case and / or a particular measurement operation to filter the set of candidate measurement modes of set 400 from which the determined mode is selected. Alternatively, or in addition, the MCM 121 processes the indication of the measurement use case and / or particular measurement operation to determine one or more parameters of a measurement mode, such as for example a wait time value (W).

[0211] With reference to Fig. 3a, instead of performing steps 302 and 304, in some embodiments the controller 120 is configured to perform an alternative step 304’.

[0212] Fig. 4d is a flow diagram of a method performed by the MCM 121 for performing alternative step 304’ to determine the measurement mode based on the combination of an indication of the measurement use case and the associated measurement operation for generation orientation.

[0213] At step 472, the controller 120 receives an indication of the measurement use case (e.g., drill rig alignment, exploration surveying, blast surveying, or any other appropriate use case of measuring orientations associated with the borehole 101).

[0214] At step 474, optionally the controller 120 receives an indication of the measurement operation (e.g., North seeking or navigation). In some embodiments, the indications of the use case and optional measurement operation are received as input data, such as for example resulting from the selection of interactive elements on a UI, as described herein.

[0215] At step 476, the controller 120 selects or determines a measurement mode for generating the orientation values from the indicated measurement use case and / or measurement operation. The measurement mode determines the one or moreparameters of the sensing unit 110 and / or sensor(s) 112, such as for example values for: the rate range and / or bandwidth of the sensor(s) 112 during one or more measurement operations, such as both the North seeking operation and the navigation operation, or one of the operations if specified at step 474; the wait / averaging time; a set of sensors used to perform the one or more measurement operations, including the measurement operation specified at step 474 (e.g., gyro-compasses to perform North seeking); whether or not to drift tune after North seek and a time period for conducting the drift tuning; and whether or not to stabilize the sensor platform and if so a bandwidth to of the stabilization control loop.

[0216] For example, the MCM 121 may be configured to map the indication of the use case, and optionally the measurement operation, to particular modes of the set of candidate modes, or a subset of the same that are available for mode selection. In some embodiments, the low rate range mode M1is selected in response to receiving an indication of a North seeking operation in combination with an indication of either a drill rig alignment or surveying use case. In some embodiments, the high rate range mode M2is selected in response to receiving an indication of a navigation operation in combination with an indication of a drill rig alignment use case.Operating the sensing unit

[0217] With reference to Fig. 3a, at step 306 the controller 120 operates the sensing unit 110 in the measurement mode determined in step 304 to generate orientation measurements related to the borehole 101. Controller 120 generates one or more measurement control signals comprising measurement parameters, calibration parameters, bias parameters, and / or other parameters for controlling the generation of data by the sensor(s) 112, and transmits the measurement control signal(s) to the sensing unit 110. The control signal(s) are received by the sensor interface 118 and are subsequently processed by the sensing unit 110 to control the operation of the one or more sensors 112 for generating orientation values.

[0218] Fig. 5 is a flow diagram of a method 500 performed by the sensing unit 110 for generating orientation values in response to receiving the measurement controlsignal(s) from the controller 120. The controller 120 determines measurement parameters for each of the sensor(s) 112 which are set by the sensing unit 110 at step 502. The measurement parameters may include a rate range and / or bandwidth of the sensor 112 and / or an activation state of the sensor 112. The rate range value represents the maximum angular velocity that a rate sensor, such as a gyroscope, can measure in degrees per second (deg / sec). The bandwidth refers to the frequency range over which the sensor 112 conducts measurements. Typically for most rate sensors a lower rate range and bandwidth generally results in a lower noise level which results in a higher accuracy of the sensor 112.

[0219] The activation state of the sensor 112, as ‘enabled’ or disabled’, indicates whether or not respectively the sensor is configured to operate to generate output data as part of a measurement conducted by the sensing unit 110. For example, the orientation values generated at step 506 are comprised of measurements from the one or more sensors that are in the ‘enabled’ state.

[0220] The controller 120 determines the rate range and / or bandwidth of the sensor(s) 112 based on the rate range and / or bandwidth specified by the determined measurement mode. For example, in some embodiments where the one or more sensors 112 comprise a plurality of rate gyroscopes each having respective fixed or preferred rate ranges and / or bandwidths, the controller 120 may be configured to selectively activate at least one rate gyroscope with a rate range and / or bandwidth corresponding to the rate range and / or bandwidth of the determined measurement mode (i.e., by setting an activation state of the selected at least one rate gyroscope to the ‘enabled’ state, and an activation state of the other rate gyroscopes to the ‘disabled’ state).

[0221] In some embodiments, the one or more sensors 112 comprise at least one rate adjustable sensor, such as a rate adjustable gyroscope, and the controller 120 is configured to adjust the rate range and / or bandwidth of the at least one rate adjustable sensor to the rate range and / or bandwidth corresponding to the determined measurement mode. For example, to operate in a determined measurement mode M1of Fig. 4a, the sensor interface 118 processes the measurement control signal(s) todetermine the desired rate range value (25 deg / sec) and sets the sensor-specific rate range of the at least one rate adjustable sensor to the same value.

[0222] In some embodiments, the controller 120 generates measurement parameters to operate individual sensors of the sensing unit 110. For example, the controller 120 may be configured to switch the rate range of a rate adjustable gyroscope of sensing unit 110 between: a first (low) rate range value; and a second (high) rate range value, wherein said second (high) rate range value being relatively higher than the first rate range value.

[0223] In some embodiments, the controller 120 generates measurement parameters to operate one or more groups of sensors, and / or use the output data generated by those groups of sensors, depending on the operating rate range and / bandwidth of the sensor(s) and the determined measurement mode. Preferably, the one or more groups of sensors are predetermined, for example based on one or more characteristics or functional capabilities of the sensors and / or the measurement mode(s). For example, a first group of sensors with a low rate range and / or bandwidth may be activated, or have corresponding output data used, for a “low rate” measurement mode (e.g., Mode M1401 in set 400 of Fig. 4a). Conversely, a second group of sensors with a relatively higher rate range and / or bandwidth may be activated, or have corresponding output data used, for a “high rate” measurement mode (e.g., Mode M2402 in set 400 of Fig. 4a).

[0224] In some embodiments, at least one gyroscope has a relatively low rate range, such as preferably less than lOOdeg / sec, and at least one gyroscope has a high rate range, such as preferably more than 200deg / sec. In some embodiments, the at least one gyroscope with a relatively low rate range has a low bandwidth, such as preferably less than 30Hz, and the at least one gyroscope with a high rate range has a high bandwidth, such as preferably at least 30Hz. The lower rate range low bandwidth gyroscope(s) may provide a reduced noise level which can be used to either obtain a more accurate measurement over the same time period or obtain the same accuracy of measurement over a shorter time period. This advantageously improves the speed and accuracy withwhich the sensing unit 110 determines orientation measurements during North seeking while also permitting accurate measurement of macro movements.

[0225] At step 504, the sensing unit 110 sets one or more calibration and / or bias parameters for one or more of the sensor(s) 112. In some embodiments, one or more factory calibration parameters may be stored in a non-volatile memory of the sensing unit 110. In some embodiments, the controller 120 is configured to store the one or more factory calibration parameters in memory system 125 and to transmit the parameters to the sensing unit 110 as measurement control signals. In some embodiments, the controller 120 is configured to apply the parameters to data received from the sensing unit 110 as a post-processing operation.

[0226] At step 506, the sensing unit 110 operates the sensor(s) 112 with the determined rate range and / or bandwidth parameters, and the calibration and bias parameters, to generate orientation values.

[0227] At step 508, the sensing unit 110 transmits the generated orientation values to the controller 120. Optionally, the controller 120 is configured to process the orientation values generated by the sensor(s) 112 to adjust the rate range and / or bandwidth parameters, or the calibration and bias parameters, of the sensor(s) 112 by transmitting further measurement control signals to the sensing unit 110.Example sensing unit implementation

[0228] The sensing unit 110 is configurable to utilize sensors, including one or more gyroscopes and accelerometers, that are configurable in their relative arrangement within the sensing unit 110 and in their respective parameters (e.g., the sensor rate range and / or bandwidth). This advantageously allows the apparatus 100 to be adapted to produce orientation measurements in response to changing operational requirements (e.g., preferences for measurement accuracy vs. speed) across a plurality of use cases. Various exemplary implementations of the sensing unit 110 are described below.Single rotatable sensor platform

[0229] Fig. 6a is a schematic diagram illustrating a first example implementation of the sensing unit 110 of an apparatus 100 in accordance with the proposed technology, the sensing unit 110 comprising a case 601 containing a sensor platform 610 and supporting components 602, 604, 606, 608.

[0230] The sensor platform 610 is free to rotate about a sensor platform axis 610’, which is nominally aligned parallel to the measurement axis 103 of the apparatus 100, through one or more support bearings 606. The sensor platform 610 is configured to mount the one or more sensors 112 of the sensing unit 110. The sensor platform 610 further comprises a local gyroscope 612, such as for example a single axis MEMS gyroscope, such as the ADXRS646 available from Analog Devices Inc., that is mounted with an axis nominally aligned with the axis of rotation 610’ of the sensor platform 610, typically coincident with the measurement axis 103, such that the local gyroscope 612 measures the rate of rotation of the sensor platform 610.

[0231] A motor 604 provides a means to control rotation of the sensor platform 610 about the sensor platform axis 610’ through the support bearings 606. One or more electrical connectors 602, such as for example an electric slip ring, provide electrical connections between the platform mounted sensor group 112 and the local gyroscope 612 and the controller 120 of the apparatus 100. A resolver 608 measures a relative angle between the sensing unit case 601 with the support components and the rotating sensor platform 610.

[0232] In some embodiments of the example of Fig. 6a, first platform 610 includes at least one low rate range / high accuracy gyroscope each having a sensing axis 107 (not shown in Fig. 6a) substantially perpendicular to the measurement axis 103 of the apparatus 100. For example, the sensor platform 610 includes two high accuracy gyroscopes each having sensing axis 107 substantially perpendicular to the measurement axis 103 and substantially perpendicular to each other.

[0233] This advantageously increases the speed with which North seeking can be performed as two orthogonal measurements are made during the same sampling period, thus fewer sampling periods are required to make the necessary bias removed non- colinear (preferably orthogonal) measurements of rate about the measurement axis 103. The accuracy of orientation measurements made in a navigation operation is also increased both by direct use of the sensor outputs (e.g., when the rate range of the gyro corresponds to the measurement mode) and by correcting lower accuracy measurements.

[0234] In some embodiments of the example of Fig. 6a, the first platform 610 also includes a first set of at least one high rate range (lower accuracy) tri -axial gyroscope with mutually orthogonal input axes and one axis substantially parallel to the measurement axis 103. A second set of tri-axial gyroscopes may be included having an even higher rate range (and therefore lower accuracy) than the first set of tri-axial gyroscopes. This allows accurate measurements for very high rate measurement modes. Each set of low or high rate tri-axial gyroscopes may have respective gyroscopes with either fixed rates or adjustable rates.

[0235] In the case that one or more fixed rate gyroscopes are implemented, the sensing unit 110 may be configured to select one or more of the fixed rate gyroscopes in each set to contribute outputs to the orientation data generated by the sensing unit 110, according to the measurement mode (e.g., by matching a specified rate range of the measurement mode to the fixed rate range of the selected gyroscope(s)).

[0236] In the case that one or more adjustable rate gyroscopes are implemented, the sensing unit 110 may be configured to adjust the rate range of the one or more adjustable rate gyroscopes to a rate range specified by the measurement mode (provided that the specified rate range is within an adjustable rate range interval of the respective gyroscope). The one or more adjustable rate gyroscopes subsequently contribute outputs to the orientation data generated by the sensing unit 110, according to the measurement mode.

[0237] In some implementations, each tri-axial gyroscope is comprised of 3 single axis gyroscope sensors with individual measurement axes in a mutual relative alignment as appropriate. Alternatively, each tri-axial gyroscope is implemented as a 6- degrees of freedom (DOF) or 9-DOF IMU (e.g., as an integrated circuit incorporating a triaxial accelerometer and a triaxial magnetometer respectively).

[0238] In some embodiments of the example of Fig. 6a, the first platform 610 also includes a high bandwidth and high dynamic range gyroscope (i.e., local gyroscope 612) having a bandwidth of preferably no less than 1 KHz, and with a sensing axis oriented substantially along the measurement axis 103 of the apparatus 100. The high bandwidth gyroscope may be configured as the highest bandwidth gyroscope of any of the sets of high rate range tri-axial gyroscopes with a sensing axis 107 aligned with the measurement axis 103. This advantageously reduces the size of the sensing unit 110 and the power requirements by avoiding the implementation of an additional sensor.

[0239] The high bandwidth gyroscope may be used to space stabilize the sensor platform 610, such as, for example, according to a process described in United States Patent 9,714,548. Space stabilization using a high bandwidth single axis gyroscope may isolate the lower bandwidth (higher accuracy) gyroscopes of the sensor platform 610 from high roll rates about the measurement axis 103 of the apparatus 100. This results in improved accuracy of orientation measurements when performing a navigation operation.

[0240] In conventional approaches, the high rate range / bandwidth sensors are typically not used to generate orientation measurements, but are instead used to provide feedback to de-rotate the sensor platform so that high rates are not measured along the measurement axis when used in navigation operations to measure changes in orientation.

[0241] By contrast, in embodiments of the proposed technology the highest range / bandwidth gyroscope may be used for space stabilization together with its output to generate orientation measurements (e.g., during navigation). The inclusion of outputfrom the higher rate range / bandwidth gyroscope lowers the bandwidth of the stabilization loop, as the sensor will not saturate when allowing a larger portion of the roll rates about the measurement axis 103 to be observed on the sensor platform 610. The lowering of the bandwidth of the stabilization loop in turn allows some of the roll rotation of the case 601 to be observed by the gyroscopes on the sensor platform 610. This advantageously reduces power consumption, as the power consumed by the motor 604 to perform the space stabilization is a significant portion of the power budget of the apparatus 100. This results in the ability to utilize a smaller power source (e.g., battery) thereby reducing the size and weight of the sensing unit 110. Additionally, a smaller motor 604 can be used to meet the lower stabilization loop bandwidth requirement.

[0242] The use of the highest range / bandwidth gyroscope in the manner described for some embodiments of the proposed technology also advantageously allows for the configuration of the stabilization loop bandwidth according to the measurement use case. For example, when the bandwidth is higher, more power is consumed and a larger battery is required. High bandwidth stabilization allows the gyroscopes with lower rate range and higher accuracy to be utilized for a greater portion of time during a navigation operation, resulting in more accurate orientation measurements (which is beneficial for the exploration borehole surveying case in the vertical orientation).

[0243] High bandwidth stabilization also provides advantages for the geophysical logging while tripping surveying sub-case, as the sensing axis 107 is held constant with respect to gravity with greater precision resulting in more accurate depth measurements. For example, the accelerometers and gyroscopes of sensor platform 610 may be connected to the case 601 by one or more gimbals. In such embodiments, the gimbal may be stabilized with respect to gravity such that the roll or gravity toolface of the sensor platform 610 is held constant with respect to gravity. This may advantageously reduce the effects of some sensor errors such as, for example, residual sensor misalignments (e.g. remaining error in alignment of the sensitive axis of the sensor after calibration has been applied), by reducing or eliminating fluctuations in the component of gravity in the sensor output due to rotation of the sensing unit 110 during measurement.

[0244] Alternatively, or in addition, a gravity indexing feedback loop may be created based on an error signal between measured and control sensor values, which is used to determine a rotation of the sensor platform 610 until a roll axis feedback signal is driven to zero, thereby achieving a consistent roll attitude with respect to gravity (as described in United States Patent No. 9,714,548).

[0245] In some use cases where minimizing or reducing the size and / or weight of the sensing unit 110 is more important than maximizing or increasing the accuracy of the measurements (e.g., for blast hole surveying), the stabilization loop may be disabled since high rate range measurements can be accommodated with the high rate range sensors (albeit with less accuracy in navigation operations).

[0246] In some embodiments of the example of Fig. 6a, the first platform 610 also includes a first set of at least one tri-axial accelerometer having a low dynamic range (high accuracy) and with mutually orthogonal sensing axes and one axis parallel to the measurement axis 103. The low dynamic range tri-axial accelerometer is used to determine orientation with respect to gravity (i.e., dip angle and gravity toolface), and, optionally, for determining depth in the geophysical logging while tripping use case (see International Patent Publication No. WO2023115151).

[0247] In some embodiments, the low dynamic range tri-axial accelerometer is implemented as three separate accelerometers or a tri-axial package (e.g., on an integrated circuit which advantageously has a reduced size and power consumption compared to three separate sensors). In some embodiments, an accelerometer from an IMU may be selected as the low dynamic range (high accuracy) tri-axial accelerometer.

[0248] In some embodiments of the example of Fig. 6a, the first platform 610 also includes a second set of at least one accelerometer having a higher dynamic range / bandwidth (and lower accuracy), relative to the first set of at least one accelerometer, with a sensing axis 107 substantially parallel to the measurement axis 103 of the apparatus 100.

[0249] The first and second sets of accelerometers form a plurality of accelerometers of the sensing unit 110. In some embodiments, the dynamic ranges and / or bandwidths of the plurality of accelerometers vary (i.e., no two accelerometers of the sensing unit 110 have identical values). The sensing unit 110 is configured to generate, in a time period, accelerometer data by using output data generated by a first accelerometer of the plurality of accelerometers, the first accelerometer being dynamically selected based on the one or more control signal (e.g., as specifying a measurement mode) and the detection capabilities of the plurality of accelerometers.

[0250] In some embodiments of the example of Fig. 6a, the sensing unit 110 is configured to generate accelerometer data by selecting between or by blending the outputs of the plurality of accelerometers with nested dynamic ranges / bandwidths. The sensing unit 110 processes the output of each of the plurality of accelerometers, or absence of an output, at each sample time instant to determine accelerometer data.

[0251] For example, the sensing unit 110 may take, as the generated accelerometer data, the output of the accelerometer with the lowest dynamic range and / or bandwidth that is capable of generating reliable data at the particular sample time of a measurement operation. Alternatively, the sensing unit 110 may calculate accelerometer data values as a weighted average to blend any two or more of the accelerometer outputs, for example based on one or more of the range and / or the bandwidth of the measurement mode and corresponding ranges and / or bandwidths of the accelerometers, and the expected accuracy of each accelerometer during the measurement operation.

[0252] In some embodiments of the example of Fig. 6a, the sensing unit 110 is configured to determine the accuracy and / or reliability of an accelerometer output at a given sample time instant by comparing the values of the accelerometer output magnitude and / or frequency to one or more of (i) a manufacturer supplied specification of the dynamic range and / or bandwidth; and (ii) a sensitivity function indicating acceleration magnitude and frequency as determined by conducting validation tests on the accelerometer(s).

[0253] For example, the sensing unit 110 may be configured to compare the output of each accelerometer to a reliability or accuracy threshold, where the comparison is performed according to ascending dynamic range and / or bandwidth. By selecting the first output value that satisfies the comparison check as the sampled accelerometer data, the sensing unit 110 achieves a degree of resilience against shock and vibration effects (i.e., by using data output by a higher range / bandwidth accelerometer at times when these effects occur) while prioritizing the use of more accurate accelerometer data in the absence of these effects.

[0254] In some embodiments of the example of Fig. 6a, the sensing unit 110 is configured to dynamically correct the output of the second set of higher dynamic range / bandwidth accelerometers using samples from the relatively lower dynamic range accelerometers during measurement instants when the acceleration of the sensing unit 110 is in range of both sets of accelerometers. In some embodiments, the sensing unit 110 is configured to perform an analogous process of dynamically correcting sensor outputs for the sets of gyroscopes with relatively higher and lower rate ranges. For example, in a navigation operation, the outputs of the gyroscopes and / or accelerometers may be respectively blended to obtain more accurate orientation measurements, and, in the case of the logging while tripping use case, more accurate displacement measurements using the accelerometers.

[0255] In some embodiments of the example of Fig. 6a, the first and second sets of one or more accelerometers each include one or more tri-axial accelerometers, and the sensing unit 110 is configured to perform blending to combine the outputs of the tri- axial high dynamic range accelerometer(s) with the corresponding low dynamic range tri-axial accelerometer(s). For example, in the blast hole logging use case the sensing unit 110 may integrate the blended outputs over time (e.g., twice) to more accurately determine 3-dimensional displacement of the sensing unit 110 (i.e., where the displacement from borehole to borehole can be measured as a check against the operator measured displacements). In some embodiments, the high dynamic range tri- axial accelerometers are implemented by using the accelerometers of the high dynamic range 6-DOF IMU.Multiple rotatable sensor platforms

[0256] Fig. 6b is a schematic diagram illustrating a second example implementation of sensing unit 110, which is analogous to the first implementation of Fig. 6a, and which includes a second sensor platform 620 that is separate from the first sensor platform 610 and is free to rotate about a second sensor platform axis 620’. The second sensor platform axis 620’ is nominally aligned perpendicular to the measurement axis 103 of the apparatus 100.

[0257] The first sensor platform 610 is configured to mount one or more sensors of a first sensor group 112a including all, or a subset of, the one or more sensors 112 of the sensing unit 110. The second sensor platform 620 is configured to mount one or more sensors of a second sensor group 112b including all, or a subset of, the one or more sensors 112 of the sensing unit 110 that are not part of the first sensor group 112a. The second sensor platform 620 further comprises a local gyroscope 622 that is mounted with an axis nominally aligned with the axis of rotation 620’ of the second sensor platform 620 such that the local gyroscope 622 measures the rate of rotation of the second sensor platform 620.

[0258] A first motor 603 provides a means to control rotation of the first sensor platform 610 about the first sensor platform axis 610’, and second motor 605 provides a means to control rotation of the second sensor platform 620 about the second sensor platform axis 620’, through the support bearings 607. The one or more electrical connectors 602 provide electrical connections between the platform mounted sensor groups 112a and 112b and the local gyroscope 612 and the controller 120 of the apparatus. A resolver 608 measures a relative angle between the sensing unit case 601 with the support components and each of the rotating first and second sensor platforms 610 and 620.

[0259] With reference to the example of Fig. 6b, an exemplary configuration of the second sensor platform 620 is described in United States Patent No. 4,197,654, and in United States Patent No. 6,347,282. The use of a second sensor platform 620 separate to the first sensor platform 610 advantageously allows for the horizontal North seekingfunctionality to be implemented as a separate module and deployed as part of the apparatus 100 only when needed (e.g., for the surveying tool 104).

[0260] In some embodiments of the example of Fig. 6b, the second platform 620 is rotatably coupled to the first sensor platform 610, such as for example according to the configuration described in United States Patent No. 4,197,654, and in United States Patent No. 6,895,678. The use of the second sensor platform 620 allows manipulation of the sensing axis 107 (not shown in Fig. 6b) of a single high accuracy gyroscope mounted on the second sensor platform 620 into three orthogonal positions. The sensing unit 110 determines a bias from two 180 deg apart positions of the single high accuracy gyroscope and generates bias corrected high accuracy orthogonally oriented rates in each of the three positions. The sensing unit 110 utilizes the bias corrected orientation measurements in conjunction with accelerometer measurements to improve the accuracy of orientation data, such as for example during North seeking, at all attitudes including horizontal.

[0261] In some embodiments of the example of Fig. 6b, the second platform 620 has mounted a tri-axial accelerometer or a 6-DOF IMU (i.e., including a tri-axial gyroscope and a tri-axial accelerometer) in addition to the single high accuracy gyroscope.

[0262] With reference to the example of Fig. 6a, in some embodiments the first platform 610 has an additional high accuracy gyroscope mounted at a fixed position on the sensor platform 610 (“fixed high accuracy gyroscope”) with a sensing axis 107 aligned with the measurement axis 103 of the apparatus 100.

[0263] The sensing unit 110 may be configured to perform one or more bias estimation techniques to estimate the bias of the fixed high accuracy gyroscope sensor. For example, the sensing unit 110 may perform mode reversal (as described in [1]) to estimate the bias. Alternatively, or in addition, the sensing unit 110 may be configured to generate an estimate of the bias using information about the factory calibration vs temperature of the sensor, .subject to an assumption of a relatively low change in theinitial bias of the gyroscope each time it is powered on (i.e., the turn on to turn on bias variability is low).

[0264] The accuracy of the azimuth values of the orientation measurements generated by the sensing unit 110 is dependent on the accuracy of the estimate of the bias. However, generating and utilizing an estimate of the bias, even if the estimate is of low accuracy, may be desirable in some use cases (e.g., in blast surveying) as an alternative to increasing the size and / or weight of the sensing unit 110 (i.e., as a consequence of using a second sensor platform). For other applications, however, such as rig alignment, the increased size and / or weight of the sensing unit 110 may be preferred in order to achieve the desired accuracy.

[0265] The use of a single or multiple rotatable sensor platforms provides the sensing unit 110 with the following advantages: 1) the ability to rotate the one or more sensors (e.g., gyroscopes) of respective sensor groups 112a, 122b to accurately determine bias during a North seeking operation; 2) the ability to de-rotate the sensor platform(s) to decouple high roll rates from the sensor(s) oriented along the measurement axis 103 and maintain alignment of the sensor(s) with respect to gravity; and 3) the possibility of reducing the number of high accuracy gyroscopes for North seeking (i.e., to avoid the need for a separate gyroscope to measure Earth's rotation in a minimum of two non- colinear non-vertical orientations).Fixed sensor platform

[0266] In some embodiments, the sensing unit 110 is implemented with a single sensor platform, analogous to the first example implementation of Fig. 6a, but where the sensor platform 610 is held in a fixed position rather than being free to rotate. For example, the sensor platform 610 may be mounted to the sensing unit case 601. This advantageously eliminates the need for support components including the motor 604, resolver 608, and support bearings 606, thereby leading to a reduction in size and complexity of the sensing unit 110.

[0267] In some embodiments in which the sensor platform 610 is held in a fixed position, the sensing unit 110 is configured to account for bias in the output of one or more high accuracy gyroscopes (and / or accelerometers) using an assumption that the turn on to turn on bias variability is low (e.g., < 0.25 deg / hr for gyroscopes and < 3mG for accelerometers), and / or by performing mode reversal for the respective sensors.

[0268] In some embodiments where the sensor platform(s) are fixed or rotatable, the sensing unit 110 may optionally include one or more components configured to isolate and / or reduce the effects of shock and vibration. For example, one or more shock insulating or dampening components may be applied to the exterior of the sensing unit 110 (e.g., to the case 601) or internally within the unit (e.g., to encase particular sensors 112 or to shock isolate the sensor platform 610) to reduce or eliminate the effects of shock and vibration. In some embodiments, the sensor platform 610 is held in a fixed position by a mounting of the sensor platform 610 to the sensing unit 110 via the one or more shock insulating or dampening components.Additional sensors

[0269] In some embodiments, the one or more sensors 112 of the sensing unit 110 includes one or more additional sensors other than gyroscopes and accelerometers. For example, at least one tri-axial magnetometer may be included on the first sensor platform 610 or on second sensor platform 620. The sensing unit 110 may be configured to use the output of the at least one tri-axial magnetometer to perform one or more quality control (QC) operations, for example to adjust the output of one or more gyroscopes in response to sensitivity to magnetic fields.

[0270] The sensing unit 110 may be further configured to use the output of the at least one tri-axial magnetometer to provide an independent measure of the azimuth, which can be used to correct for gyroscope drift (for example, by use of a Kalman filter, MARG (magnetic angular rate) algorithm, or other sensor fusion algorithm).Alternatively, or additionally, the sensing unit 110 may be configured to use the output of the at least one tri-axial magnetometer to measure magnetic field distortions caused by the formation surrounding a borehole 101 (e.g., in a surveying use case).Example of a North seeking to navigation sequence

[0271] Fig. 7 is a flow diagram of a sequence of operations 700 performed by the apparatus 100 to measure a borehole 101. At steps 702 and 706 the apparatus 100 sequentially performs a North seeking measurement operation and a navigation operation respectively, such as for example as part of one or more of the workflow drill rig alignment and / or surveying use cases described herein.

[0272] At steps 701 and 704, the apparatus 100 optionally performs a sensor tuning operation prior to a respective measurement operation. The sequence is performed to generate orientation measurements using the apparatus 100 with a sensing unit 110 comprising a plurality of gyroscopes 116 and a plurality of accelerometers 114.

[0273] Fig. 8a is a flow diagram of a method 800 for performing the North seeking measurement operation (e.g., at step 702 of the sequence 700 depicted by Fig. 7).

[0274] At step 802, the controller 120 sets the rate ranges and / or bandwidths of the sensor(s) 112 for generating orientations during the North seeking operation. For example, the controller 120 may set the sensor(s) 112 to use a relatively low rate range (e.g., 1 to 25 deg / sec) and a low bandwidth (e.g., a bandwidth of ~30Hz) resulting in a high accuracy. In some examples, the rate range is set to the lowest rate that is not expected to result in overrating during North seeking as this enables the greatest accuracy and fastest time to achieve a particular accuracy.

[0275] At step 804, the controller 120 sets one or more calibration parameters of the sensor(s) 112. For example, the factory determined temperature calibration parameters (e.g., bias, scale factor, mis-alignment angles, and acceleration sensitivity) are used for the low rate range for the specific sensor of sensor(s) 112, including one or more gyroscopes 116.

[0276] At step 806, the controller 120 determines biases of one or more of the sensors 112. Sensor biases are removed from calibrated measurements to determine rates and accelerations in tool coordinate frame according to the following process.

[0277] While the value of biases may be predetermined for a particular temperature during the manufacturing of the sensor, and / or configuration of the sensing unit 110, there is typically an offset or DC shift in this value that occurs at random in response to power cycling the sensor(referred to as the “turn on” bias). Thus, the change in bias vs temperature is determined by the factory calibration parameter while the turn-on bias offset is determined during alignment or North seeking.

[0278] The turn-on bias offset may be estimated by obtaining average sensor measurements while stationary in two positions 180 degrees apart. When this is done, the output of the sensor due to the earth's field (i.e., rotation for gyroscopes, gravity for accelerometers, and magnetic field for magnetometers) changes sign but the bias does not. The bias is estimated by adding the two 180deg separated measurements and dividing by 2. Alternatively, more than two measurements can be made which adds the potential for improved quality control as more than one bias estimate can be obtained. Additionally, angles less than 180deg can be used, for example three measurements 120deg apart or four measurements 90deg apart.

[0279] The averaging time at each position may be increased to improve accuracy but the improvement diminishes as the averaging time approaches the time at which the bias instability is reached (e.g., normally 20 - lOOsec depending generally on the ARW of the gyroscope). As a result, more than one set of positional measurements may be taken and the resulting attitudes averaged.

[0280] Some gyroscopes (e.g., MEMs gyroscopes) exhibit a decreased turn on bias variability, such that the factory calibrated biases may be used for these gyroscopes 116 during North seeking, thereby eliminating the need to rotate the gyroscope 116 to calculate bias values. The accuracy of bias and attitude determination using this method may be lower than that achievable via rotation of the gyroscopes 116, but the total time required to perform the North seeking operation is reduced since the rotation no longer needs to be conducted. For some use cases, increasing the speed of conducting North seeking is more important than increasing the accuracy of the corresponding orientation measurements, and this method may be advantageous in those cases.

[0281] In some embodiments, the controller 120 is configured to estimate bias using mode reversal for Coriolis Vibratory Gyroscope (CVG) with symmetric resonating structures (e.g., rings, hemisphere / wine glass, even beams).

[0282] At step 808, the controller 120 determines azimuth and inclination values from bias and calibration corrected data of the sensor(s) 112. For example, this involves determining the dip angle and gravity TF values from corrected acceleration measurements, relative to the measurement axis 103 of the apparatus 100. Then, the controller 120 uses the dip angle and gravity TF to project rates measured in the coordinate frame of the apparatus 100 into the horizontal plane of Earth's frame from which azimuth is determined. In some embodiments, the controller 120 is configured to calculate the gyro TF value directly from the sensor measurements when the measurement axis is vertical.

[0283] Fig. 8b is a flow diagram of a method 820 for performing an optional drift tuning operation prior to a navigation measurement operation (e.g., at step 704 of the sequence 700).

[0284] At step 822, the controller 120 sets the sensor(s) 112 to use a relatively high rate range (typically between 25 and 500 deg / sec) and a low accuracy corresponding to the rate range that would be used during the navigation.

[0285] At step 824, the controller 120 sets one or more calibration parameters of the sensor(s) 112. For example, the factory determined temperature calibration parameters (e.g., bias, scale factor, mis-alignment angles, and acceleration sensitivity) are used for the high rate range implementation of the specific sensor of sensor(s) 112, including one or more gyroscopes 116.

[0286] At step 826, the controller 120 performs drift tuning to determine and / or update biases of the sensor(s) 112. The controller 120 maintains the measurement instrument 102, 104 of the apparatus 100 stationary for an additional period of time (e.g., lOsec to 60sec; referred to as "drift tune") while at least the gyroscope(s) 116generate data at the relatively high rate range. When the rate range of the gyroscope(s) 116 is changed, the bias offset from the calibrated value is likely to shift. Drift tuning measures this change in bias and subtracts the change from the gyroscope outputs when navigating to improve the accuracy of the orientation values obtained.

[0287] To estimate bias during a drift tune, dip, gravity TF and azimuth of the apparatus 100 is determined during the prior North seeking operation (i.e., at step 702) to calculate the theoretical value of earth's rotation rate that would be observed on each gyroscope 116. The determined theoretical value is then subtracted from the average output measurement of the gyroscope 116 to obtain an updated bias estimate.

[0288] In addition to the changed bias, there may also be some error in the attitude determined during the North seeking operation, for example due to residual error in the sensors and inexact positioning of the sensors. As part of performing drift tuning, the controller 120 may therefore include both the changed bias and the portion of Earth's rate due to error in attitude.

[0289] Fig. 8c is a flow diagram of a method 840 for performing a navigation operation (e.g., at step 706 of the sequence 700 depicted by Fig. 7). At step 842, the controller 120 sets the rate ranges and / or bandwidths of the sensor(s) 112 for generating orientations during the navigation operation. For example, the controller 120 may set the sensor(s) 112 to use a relatively high rate range and low accuracy. As described herein, the rate ranges and / or bandwidths of sensor(s) 112 are determined by the measurement mode. The controller 120 generates measurement control signals to translate sensing unit specific parameters of the measurement mode, including at least the rate range and bandwidth, to sensor-specific parameters of the sensor(s) 112. Determination of the sensor rate ranges and bandwidth values depends on the configuration and type of the gyroscope(s) 116.

[0290] For adjustable rate sensor (i.e., an adjustable gyroscope), the noise level may increase and accuracy may decrease as the rate range of the sensor is increased. Therefore, to achieve the highest accuracy during navigation the rate range should beset to the lowest maximum expected rate of change of orientation for the particular use case of the apparatus 100. In some embodiments, the controller 120 sets the rate range based on heuristic knowledge of the expected rate ranges for a particular application.

[0291] For example, drill rig alignment typically involves changes in orientation (i.e., rate ranges) of less than 500deg / sec, while borehole surveying, logging while tripping, and blast hole surveying have typical rates of 25deg / sec, 50deg / sec and lOOdeg / sec respectively. In some embodiments, the controller 120 determines the rates by processing one or more statistical metrics compiled on measured rates for a use case. The statistical metrics may encompass data that is specific to a region or location of the workflow use case (i.e., to account for higher or lower than normal rates for a particular application or site).

[0292] For implementations in which the set of one or more gyroscopes 116 includes adjustable rate and fixed rate devices, the controller 120 is configured to set the adjustable gyroscopes to have a rate range and / or bandwidth based on the noise level of the one or more gyroscope 116 as well as the amount of time that the gyroscopes are expected to operate at a particular rate while navigating. The controller 120 may calculate an expected amount of time of operation of the sensors within different rate ranges, for example as a heuristic estimate or prediction based on the application / use case. Alternatively, or in addition, the controller 120 determines the rates by processing one or more statistical metrics compiled on measured rates for a use case. Based on the historical or prediction data, the controller 120 sets or determines an optimal adjustable rate for the one or more adjustable rate gyroscopes 116, which may be specific to a region or location of the workflow use case.

[0293] For implementations in which the set of one or more gyroscopes 116 includes only fixed rate devices, the rate range of each gyroscope 116 is predetermined (e.g., at design or manufacture time). In some embodiments, the controller 120 is configured to select one or more of the fixed rate gyroscopes 116 that has a rate range and / or bandwidth that corresponds to the desired rate range (e.g., the rate range specified by the sensing unit measurement mode, or determined either from the measurement mode,or by other data related to the navigation operation and the relevant use case such as historical or prediction data). The controller 120 may be configured to obtain output data from each of the selected fixed rate gyroscopes.

[0294] Optionally, at step 844 the controller 120 blends outputs produced by two or more gyroscopes 116 to generate the orientation measurements. For example, in some implementations the set of one or more gyroscopes 116 are configured with nested rate ranges and accuracies. In some embodiments, when the measured rate range is within the range of all gyroscopes 116, the controller 120 is configured to generate a blended rate estimate based on relative uncertainties of each gyroscope via a minimum variance unbiased estimator. The weights of each gyroscope 116 are the unity gain normalized version of Wj = — X t Vt is the uncertainty of each gyroscope output vi related to both noise level and bias instability.

[0295] The controller 120 adaptively corrects the outputs of the high rate range / low accuracy gyroscopes using outputs of the low rate range / high accuracy gyroscopes (e.g., via least squares, iterative least squares, Kalman filtering, etc.). In some embodiments, the controller 120 uses data from the North seeking and / or initialization operation as previously conducted. In some embodiments, the controller 120 adaptively adjusts the error term estimates while orientation values are generated during navigation.

[0296] In some embodiments, for a desired rate range that is outside of the range of low rate range / high accuracy configured gyroscope(s) the controller 120 is configured to use only the high rate / low accuracy gyroscopes, but may correct the output of the same by most recently received output data of the low rate range / high accuracy gyroscope(s).

[0297] At step 846, the controller 120 generates corrected orientation data using updated bias and calibration parameters of the sensor(s) 112. The controller 120 subtracts the updated bias estimates and the determined theoretical earth's rate calculated from the drift tune operation (i.e., method 820 of Fig. 8b) from the outputvalues of the one or more gyroscopes 116 to generate compensated gyroscope outputs. The controller 120 integrates the compensated gyroscope outputs to obtain changes in the attitude value of the apparatus 100. The controller 120 compensates for the dip and gravity TF error due to gyro drift (bias change over time) using a determined Dip and gravity TF of the accelerometers 114 (e.g., using one or more Complimentary, Kalman, or Madgwick filters).

[0298] In some embodiments, the controller 120 is configured to power down or deactivate one or more of the sensors 112, either during or prior to a measurement operation. For example, the controller 120 may deactivate one or more of the low rate range / high accuracy gyroscopes 116 to perform measurements, such as during navigation, for the blast hole surveying use case in which the accuracy requirement is lower than for navigation. This advantageously reduces the power consumption of the apparatus 100 and permits a reduced form factor (e.g., through minimization of the size of the battery).

[0299] In some embodiments, the apparatus 100 may be deployed as a rig alignment tool 102, or a surveying tool 104, to perform any of the methods 700, 800, 820, 840. Numerous advantages are provided by the apparatus 100 in such embodiments. For example, when performing an above ground blast hole surveying use case, the surveying tool 104 advantageously enables fast North seeking and handling of higher rates expected in these larger diameter boreholes. When performing an underground blast hole surveying use case, the surveying tool 104 advantageously enables faster North seeking, handling of higher rates that sometimes occur at the end of the short drill holes when the assembly hits the end of the borehole 101.

[0300] Further, during an underground surveying case, conventional surveying tools typically perform North seeking at the opening of each borehole 101 which takes considerable time. The proposed surveying tool 104 advantageously avoids the need to perform the time consuming North seeking operation at the commencement of measurement of each borehole 101, due to an ability to optimally switch to and / or blend higher rate outputs from a plurality of the sensor(s) 112. That is, the surveyingtool 104 is able to remain configured for navigation while moving between boreholes during which high rates are encountered, thus saving the operator the time required to North seek at each hole (i.e., North seeking can instead be carried out periodically, such as between measurement of every three to five boreholes).

[0301] The surveying tool 104 has an additional advantage for accurately North seeking to measure a borehole 101 that is aligned very close to horizontal. The ability to navigate from one hole to the next enables the surveying tool 104 to North seek at an attitude closer to vertical (or at least >30deg from horizontal) where the single degree of freedom sensor platform embodiment of sensing unit 110 (as shown in Fig. Id) can be used to find North accurately. After this, when in navigation mode, the surveying tool 104 is oriented into the near horizontal position and no additional North seeking operation is required to survey the next borehole in the horizontal position.

[0302] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.References[1] NASA Jet Propulsion Laboratory, “Continuous Tuning and Calibration of Vibratory Gyroscopes”, NASA Tech Briefs, October 2003, NPO-30449, page 26.

Claims

CLAIMS:

1. An apparatus for determining orientation measurements associated with a borehole, the apparatus comprising: a sensing unit having at least one or more sensors arranged relative to a measurement axis of the apparatus, the measurement axis determining an orientation of the apparatus; and a controller configured to: receive or determine an expected rate of change of the orientation of the apparatus for operating the sensing unit to determine the orientation measurements; determine a measurement mode of the sensing unit based on the expected rate of change of the orientation of the apparatus; and operate the sensing unit in the measurement mode to generate the orientation measurements from data collected by the one or more sensors, wherein the measurement mode defines a rate range and / or bandwidth of the one or more sensors to generate the orientation measurements.

2. The apparatus of claim 1, wherein determining the measurement mode comprises switching between a plurality of predetermined measurement modes.

3. The apparatus of claim 2, wherein the plurality of predetermined measurement modes comprise: a first measurement mode defining a first range rate and / or bandwidth of the one or more sensors and having a corresponding first accuracy; anda second measurement mode defining a second range rate and / or bandwidth greater than the first range rate and / or bandwidth of the one or more sensors and having a corresponding second accuracy being less than the first accuracy.

4. The apparatus of any of claims 1 to 3, wherein the one or more sensors comprise at least a plurality of gyroscopes each having a sensing axis arranged relative to the measurement axis of the apparatus.

5. The apparatus of claim 4, wherein operating the sensing unit in the determined measurement mode comprises: selecting at least one fixed rate gyroscope of the plurality of gyroscopes with a rate range and / or bandwidth corresponding to the determined measurement mode; and obtaining output data from each of the selected at least one fixed rate gyroscope.

6. The apparatus of any of claims 4 to 5, wherein the plurality of gyroscopes comprises at least one rate adjustable gyroscope, and wherein operating the sensing unit in the determined measurement mode comprises adjusting the rate range and / or bandwidth of the at least one rate adjustable gyroscope to the rate range and / or bandwidth corresponding to the determined measurement mode.

7. The apparatus of any of claims 4 to 6, wherein the plurality of gyroscopes comprise at least three gyroscopes in a mutually orthogonal configuration, wherein at least one of the gyroscopes has a rate range of less than lOOdeg / sec and at least one of the gyroscopes has a rate range of greater than 200deg / sec.

8. The apparatus of claim 7, wherein the controller is configured to operate the sensing unit to blend outputs produced by two or more of the plurality of gyroscopes to generate the orientation measurements.

9. The apparatus of any of claims 1 to 8, wherein the controller is configured to set or adjust the measurement mode of the sensing unit based at least in part on one ormore of: a measurement use case; and a measurement operation, in which the sensing unit generates the orientation measurements.

10. The apparatus of claim 9, wherein the controller is configured to receive or determine the expected rate of change of the orientation of the apparatus, in response to a change in the measurement use case.

11. A method for determining orientation measurements associated with a borehole using a borehole measurement apparatus comprising a sensing unit having at least one or more sensors arranged relative to a measurement axis of the apparatus, the measurement axis determining an orientation of the apparatus, the method comprising:(i) receiving or determining an expected rate of change of the orientation of the apparatus for operating the sensing unit to determine the orientation measurements;(ii) determining a measurement mode of the sensing unit based on the expected rate of change of the orientation of the apparatus; and(iii) operating the sensing unit in the determined measurement mode to generate the orientation measurements associated with the borehole, wherein the measurement mode defines a rate range and / or bandwidth of the one or more sensors for generating the orientation measurements.

12. The method of claim 11, further comprising repeating steps (i) to (iii) in response to a deviation in the expected rate of change of the orientation of the apparatus.

13. The method of claim 12, wherein determining the measurement mode of the sensing unit comprises switching the measurement mode between a plurality of predetermined measurement modes.

14. The method of claim 13, wherein the plurality of predetermined measurement modes comprise: a first measurement mode defining a first range rate and / or bandwidth of the one or more sensors and having a corresponding first accuracy; and a second measurement mode defining a second range rate and / or bandwidth greater than the first range rate and / or bandwidth of the one or more sensors and having a corresponding second accuracy being less than the first accuracy.

15. The method of any of claims 11 to 14, wherein the one or more sensors comprise at least a plurality of gyroscopes each having a sensing axis arranged relative to the measurement axis of the apparatus.

16. The method of claim 15, wherein operating the sensing unit comprises selecting at least one fixed rate gyroscope of the plurality of gyroscopes with a rate range and / or bandwidth corresponding to the determined measurement mode; and obtaining output data from each of the selected at least one fixed rate gyroscope.

17. The method of claim 16, wherein operating the sensing unit further comprises adjusting the rate range and / or bandwidth of at least one gyroscope of the plurality of gyroscopes to the rate range and / or bandwidth corresponding to the determined measurement mode.

18. The method of any of claims 15 to 17, wherein the plurality of gyroscopes comprise at least three gyroscopes in a mutually orthogonal configuration, wherein at least one of the gyroscopes has a preferred rate range of <100deg / sec and at least one of the gyroscopes has a preferred rate range of >200deg / sec.

19. The method of claim 18, wherein operating the sensing unit further comprises blending outputs produced by two or more of the plurality of gyroscopes in the determined measurement mode to generate the orientation measurements.

20. The method of any of claims 11 to 19, further comprising receiving or determining the expected rate of change of the orientation of the apparatus based on a measurement use case in which the sensing unit is operated to generate the orientation measurements.

21. An apparatus for determining orientation measurements associated with a borehole, the apparatus comprising: a sensing unit having at least one or more sensors collectively configured to generate the orientation measurements according to a measurement mode; and a controller configured to set or adjust the measurement mode between a plurality of measurement modes corresponding to a plurality of borehole measurement use cases and / or borehole measurement operations of the apparatus, wherein the measurement mode defines a rate range and / or bandwidth of the one or more sensors.

22. An instrument for use in determining orientation measurements to align a drilling apparatus to drill a borehole and to survey the borehole, the instrument comprising: one or more sensors arranged relative to a measurement axis of the instrument, the measurement axis determining an orientation of the instrument, wherein the one or more sensors are collectively configured to determine the orientation measurements according to a measurement mode, wherein the measurement mode defines a rate range and / or bandwidth of the one or more sensors, wherein the one or more sensors are communicatively coupled to a controller configured to:set or adjust the measurement mode based on an expected rate of change of the orientation of the instrument during the determination of the orientation measurements; and operate the one or more sensors in the measurement mode to generate the orientation measurements from data collected by the one or more sensors.

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