DOWN HOLE SURVEYING

Abstract

In one aspect, there is disclosed an apparatus for indexing a device about an indexing axis, the apparatus comprising an indexing drive mechanism comprising a drive portion configured in driving engagement with a driven member for indexing the device about the indexing axis. The driven member is arranged in operable association with an assembly comprising at least one resilient element arranged so as to be capable of transitioning to/from a state of bias such that exposure of the device to any undesirable physical forces is reduced to at least some extent.

Claims

1. An apparatus for indexing a device about an indexing axis, the apparatus comprising: an indexing drive mechanism comprising a drive portion configured in driving engagement with a driven member for indexing the device about the indexing axis, the driven member arranged in operable association with an assembly comprising at least one resilient element arranged so as to be capable of transitioning to/from a state of bias such that exposure of the device to any undesirable physical forces is reduced to at least some extent.

2. An apparatus according to claim 1, wherein said assembly is configured so as to resiliently associate the driven member with a support, the support arranged so as to be fixed or restrained from movement relative the indexing axis.

3. An apparatus according to claim 1 or claim 2, wherein the indexing mechanism is configured for indexing of the device between first and second index positions about the indexing axis, the first and second index positions configured so as to allow a scope of travel therebetween of about 180 degrees.

4. An apparatus according to any one of the preceding claims, wherein the driven member is of tubular form and arranged to surround a portion of a body of the device, the driven member and the body of the device aligned concentric with the indexing axis, the driven member and the device configured so as to be capable of rotation relative one another about the indexing axis.

5. An apparatus according to claim 4 when dependent on claim 2, wherein the support is of tubular form and arranged so as to surround a portion of the body of the device adjacent to the driven member, the support and the second portion of the device aligned concentric with the indexing axis.

6. An apparatus according to claim 5, wherein said assembly comprises first and second resilient coupling elements configured so as to resiliently couple the driven member with the support, the first and second resilient coupling elements arranged in a symmetrical manner about a region of the body relative to the indexing axis so as to provide an arrangement in which both resilient coupling elements co-operate to, at least in part, dampen or reduce any vibrational and/or shock forces which might be imparted to the device during operation.

7. An apparatus according to claim 6, wherein the first and second resilient coupling elements comprise opposite free ends, one free end of each of the first and second resilient coupling elements attached to the driven member adjacent each other, and the alternate free end of each of the first and second resilient coupling elements attached to the support adjacent each other, the points of attachment provided with the driven member substantially opposing the points of attachment provided with the support relative to the indexing axis.

8. An apparatus according to claim 7, wherein the first and second resilient coupling elements are arranged having substantially equivalent tension so that their respective coupling or biasing forces existing between the driven member and the support are substantially equal when the device is at a position intermediate the first and second index positions.

9. An apparatus according to any one of the preceding claims when dependent on claim 3, wherein the apparatus comprises a limit means configured so as to confirm the device in the first or second index positions when indexed thereto.

10. An apparatus according to claim 9, wherein the limit means comprises a stop member fixed relative to the device and projecting radially away therefrom, the limit means configured so that rotation of the device allows the stop member to be brought to bear against a first region of the support to confirm registration of the device in the first index position when indexed thereto, and against a second region of the support to confirm registration of the device in the second index position when indexed thereto.

11. An apparatus according to claim 10, wherein the first and second regions of the support are provided in the form of opposing regions of a circumferentially aligned slot provided with the support.

12. An apparatus according to any one of the preceding claims when dependent on claim 6, wherein the driven member is operable with the first and second resilient coupling elements such that driving of the driven member beyond one of the first or second index positions causes the device to be biased to the intended index position when driving of the driven member is ceased.

13. An apparatus according to any one of the preceding claims, wherein the device is arranged to carry one or more sensors comprising any of the following: accelerometers, gyroscopes, physical switches, magnetometers, vibration sensors, inclinometers, inductive RPM sensors.

14. An apparatus according to any one of the preceding claims, wherein the device is configured so as to carry the indexing drive mechanism.

15. An apparatus according to claim 14, wherein the drive portion comprises a drive element configured for mounting with the device eccentrically relative to the indexing axis.

16. An apparatus according to any one of the preceding claims, wherein transfer of drive to the driven member is by way of a ring gear assembly having an annular ring gear associated with the driven member and operable with a pinion gear associated with the indexing drive mechanism.

17. A down hole surveying instrument comprising an apparatus arranged in accordance with any one of claims 1 to 16.

18. A method for performing a down hole surveying operation using a survey instrument, the method comprising: recording data measured from a sensor when provided at a first measurement position and a second measurement position; acknowledging the time the data was recorded by way of a first timer; acknowledging by way of a second timer, a point in time during the surveying operation, the first and second timers arranged so as to be synchronised with one another; and identifying data recorded after said recorded point in time for use in preparing a survey report.

19. A method according to claim 18, wherein acknowledging the time the data was recorded by way of the first timer comprises associating the time the data was recorded with the corresponding recorded data.

20. A method according to claim 18 or claim 19, wherein the instrument alternates recording of measured data between the first and the second measurement positions (or vice versa) during a survey period.

21. A method according to claim 20, wherein the survey period is arranged to commence following insertion of the instrument into the hole.

22. A method according to any one of claims 18 to 21, wherein the first timer is associated with the instrument and the second timer is remote from the instrument during operation.

23. A method according to any one of claims 18 to 22, wherein the second timer is synchronised with the first timer associated with the instrument prior to insertion of the instrument into the borehole.

24. A method according to any one of claims 18 to 23, wherein the method includes the use of a controller module provided remote from the instrument during the surveying operation, the second timer being associated with the controller module.

25. A method according to any one of claims 18 to 24, wherein the sensor comprises a gyroscope.

26. A method according to any one of claims 18 to 25 when dependent on claim 20, wherein following retrieval of the instrument from the borehole, the recorded data is processed by the controller module for preparing the survey report.

27. A method according to any one of claims 18 to 26, wherein the survey report is prepared using data measured at the first measurement position and the second measurement position when taken in a consecutive manner.

28. A method according to any one of claims 18 to 27, wherein the instrument is a down hole surveying instrument according to claim 17.

29. A system for conducting a survey of a portion of a bore hole, the system comprising: a survey instrument arranged for recording data measured from a sensor carried by the instrument when indexed between a first measurement position and a second measurement position during a survey period, the instrument having a first timer, a controller module provided remote from the instrument, the controller module having a second timer arranged so as to be substantially synchronised with the first timer, the controller module configured for identifying data recorded by the instrument from about a known point in time during the survey period, the controller module further configured for processing the identified data for providing a survey report.

30. A system according to claim 29, wherein the instrument is a down hole surveying instrument according to claim 17.

31. A system according to claim 29 or claim 30, wherein the system is configured operable so as to carry out the method according to any one of claims 18 to 28.

32. A method for operating an apparatus arranged for indexing a device about an indexing axis for use in a down hole surveying operation, the method comprising: providing an apparatus arranged in accordance with any one of claims 1 to 16; associating the apparatus with a down hole survey instrument so that the apparatus is operable therewith; causing the apparatus to drive the device about the indexing axis to, toward, or from an index position.

33. A method according to claim 32, wherein the method comprises causing the apparatus to hold the device at an index position for a predetermined period of time before driving the device toward another index position so as to be held there at for about the predetermined period of time.

34. A method according to claim 32 or claim 33, wherein the method comprises causing the apparatus to reduce the speed of driving the device about the indexing axis as the device approaches an intended index position.

35. A method according to any one of claims 32 to 34, wherein the method further comprises: causing the apparatus to continue to drive the device in the direction of an intended index position once said intended index position has been reached; and causing the apparatus to cease driving of the device such that the device is biased at the intended index position.

36. A method according to any one of claims 32 to 35, wherein the method comprises driving the device between a first index position and a second index position in a consecutive manner during the course of a predetermined period of time.

37. A method according to any one of claims 32 to 36, wherein the method comprises causing the apparatus to drive the device to a park or inactive position, the apparatus configured in a manner in which exposure of the device to any undesirable physical forces when the device is in said park or inactive position is substantially reduced.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0318] Further features of the present invention are more fully described in the following description of a non-limiting embodiment. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

[0319] FIG. 1 is a perspective view of one embodiment of an apparatus arranged for indexing a sensor used in a down hole surveying apparatus;

[0320] FIG. 2 is another perspective view of the embodiment of the apparatus shown in FIG. 1, when sectioned along the axis X;

[0321] FIG. 3 is a further perspective view of the embodiment of the apparatus shown in FIG. 1 and FIG. 2, having a collar removed;

[0322] FIG. 4 is a perspective view of a cross section X.sub.1-X.sub.2 (see FIG. 2) of the embodiment of the apparatus shown in FIGS. 1 to 3;

[0323] FIG. 5 is a perspective view of one side of the embodiment of the apparatus shown in FIGS. 1 to 4, with attention focused on the ring gear set assembly;

[0324] FIG. 6 shows a further perspective view of that shown in FIG. 5 with the chassis hidden;

[0325] FIG. 7 is a flow diagram showing one implementation of a method of performing a down hole survey of a bore hole;

[0326] FIG. 8 depicts a schematic diagram of a controller module used in the method shown in FIG. 7; and

[0327] FIG. 9 depicts a simplified system diagram of a system implementing the method shown in FIG. 7.

[0328] In the Figures, like structures are referred to by like numerals throughout the views provided. The drawings shown in the Figures are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention as exemplified in the embodiments described.

DESCRIPTION OF EMBODIMENTS

[0329] The present invention is not to be limited in scope by any specific embodiment described herein. The embodiments described are intended for the purpose of exemplification only. Functionally equivalent products, and methods are clearly within the scope of the invention as described herein.

[0330] Embodiments of the invention described herein may include one or more range of values (eg. size, displacement and field strength etc). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent to the range which lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range.

[0331] Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention relates.

[0332] FIGS. 1 to 6 show one embodiment of an apparatus 5 arranged for indexing a device configured for carrying a sensor (such as for example a gyroscope (not shown)) between two index positions about an indexing axis X (shown in FIG. 2).

[0333] The apparatus 5 comprises an indexing drive mechanism 15 having a motor unit 10 and gearbox arrangement 12 configured for providing drive to a driven portion which is provided in the form of a first collar 35. Drive is provided to the first collar 35 by way of a mating pinion and a ring gear set assembly 45. The indexing mechanism 15 also includes an encoder assembly 16.

[0334] The apparatus 5 also includes a body provided in the form of a chassis 25, which is configured to support the motor 10, gearbox arrangement 12, and encoder assembly 16. The chassis 25 has a longitudinal axis which is aligned substantially concentric with the indexing axis X. The first collar 35 is arranged relative a region of the chassis 25 so that it may rotate thereabout by drive provided by the motor 10 and gearbox arrangement 12. As shown in FIGS. 1 and 2, the motor 10, gearbox arrangement 12 and encoder 16 assembly are arranged so as to be supported by the chassis 25 in an off-axis manner relative to the longitudinal axis of the chassis 25 so that the motor drive can engage with the ring gear set assembly 45. In this regard, FIG. 5 and FIG. 6 each serve to show the operable association of the annular ring gear 47 with the pinion 48 driven by motor 10 by way of gearbox 12.

[0335] The sensor carrying device is provided in the form of a second collar 65 which is operably associated with the first collar 35 in a manner which seeks to substantially reduce the susceptibility of the second collar 65 (and the sensor(s) it carries) becoming subject to any undesirable physical forces which might result while the sensor is operable in a measurement process: when provided at one of the index positions, during indexing of the second collar 65 about the indexing axis X to one of the index positions, and/or when in a ‘parked’ position (generally in a region between the index positions).

[0336] Undesirable or adverse external/system forces may include, but need not be limited to, any adverse vibrational and/or shock forces to which the second collar 65 may become subject to during the course of operation (eg. measurement being undertaken by one or more sensors carried by the second collar 65 when at either index position and/or during indexing about the index axis X). Vibration forces may include induced physical movement/forces resulting from prime movers such as, for example, electric motors. As one example, servo or stepper motors are usually driven by a chopped drive current to allow accurate control of their speed and position. In such instances, the chopped current can cause small vibrations of the motor shaft even when stationary. Thus, if such a motor is directly coupled to a sensor carrying device such as the second collar 65 which is used to drive the sensor to a desired index position, when held at that position the residual vibrations of the motor drive shaft can be transferred to the sensor carrying device causing unwanted sensor ‘noise’ when the sensor is performing a measuring operation. As the skilled reader will appreciate, it is important that the sensor (eg. gyroscope) remains substantially stationary during measurement.

[0337] Shock forces may include various external forces applied to the apparatus 5 during its movement into, within, and/or out of the target drilled borehole for measurement purposes. In some instances, shock forces may be less of a threat to the operation of the sensor carrying device (collar 65) during indexing so long as the motion of the drive motor is smooth.

[0338] The first collar 35 is arranged so as to freely rotate about a region of the chassis 25 by way of a ball race assembly 50 (see FIG. 2) mounted between the first collar 35 and an elongate portion 55 (see FIG. 2) of the chassis 25. The first collar 35 is arranged concentric with the second collar 65 about the indexing axis X and coupled together by way of an assembly of a pair of coil springs 75, 77. As shown in FIG. 3, coil springs 75, 77 are arranged opposite one another at the outer periphery of a support element 85, which is provided between the first 35 and the second 65 collars. The support element 85 sits about a spacer 86, which in turn is provided about a region of the elongate portion 55. A grooved region 95 is provided within the support element 85 at its periphery and serves to, at least in part, accommodate the coil springs 75, 77.

[0339] The first collar 35 includes a pair of pins 105A, 105B provided near its periphery at one of its ends as shown in at least FIG. 3. Similarly, the second collar 65 includes a pair of pins 115A, 115B provided near its periphery at one of its ends as shown. Pins 105A, 105B and 115A, 115B extend outward from the first 35 and the second 65 collars respectively and are arranged substantially symmetrical about the indexing axis X (or so as to oppose one another about the axis X as shown in the Figures).

[0340] The coupling between the first 35 and the second 65 collars is achieved by a first end 75A of the coil spring 75 attaching to pin 115A of the second collar 65, and a second end 75B of the spring 75 attaching to pin 105A of the first collar 35. Similarly, a first end 77A of the spring 77 attaches to pin 115B of the second collar 65, and a second end 77B of spring 77 attaches to pin 105B of the first collar 35.

[0341] As shown in the Figures, the coil springs 75, 77 are arranged about opposite sides of the support element 85 seated on spacer 86. In this manner, either coil spring 75, 77 is operably responsive (operable so as to be extensible) when acted upon by the first collar 35 when driven by motor 10 about the axis X. When either spring 75, 77 is extended by movement of the first collar 35, its resilient nature serves to revert it towards its original or unextended state thereby causing a biasing force which biases the second collar 65 toward and in response to movement of the first collar 35.

[0342] The second collar 65 is capable of freely rotating about the elongate portion 55 of the chassis 25 by way of a pair of ball race bearing assemblies 125, 135 provided between the inner surface 145 of the second collar 65 and the outer surface 155 of elongate portion 55 of chassis 25. The ball race bearing assemblies 125, 135 are retained in position by a retainer 136 which threadingly engages with a threaded portion provided at an end 140 of the elongate portion 55 (of the chassis 25). Ball race bearing assemblies 125, 135 are separated by a spacer 138 arranged about the elongate portion 55. All ball race bearing assemblies may be provided, for example, in the form of Timken Torque Tube 1219 bearing assemblies. It will be appreciated that other makes and sizes of bearing assemblies would be satisfactory or could be adapted/configured to work with different embodiments of the apparatus 5.

[0343] In the presently described embodiment, the second collar 65 is configured so as to carry a sensor, such as for example a gyroscope. However, in an alternate arrangement (discussed below), the sensor (or other like sensor) can be arranged so as to be associated with or carried by the chassis 25. The skilled reader will appreciate that the sensor may be a device of any appropriate type; for example, the sensor device may comprise one or more of the following: accelerometers, gyroscopes, physical switches, magnetometers, vibration sensors, inclinometers, inductive RPM sensors, flow sensors and pressure sensors, or any suitable combination. The latter examples are not to be taken as being an exhaustive list as the skilled reader would readily appreciate the scope of sensors which could find utility in application with the subject apparatus.

[0344] In operation, torque applied by way of the motor 10 provided with the encoder assembly 16 to the first collar 35 is transferred to the second collar 65 due to the bias force resulting from the extension of one of the coil springs 75, 77 (and the corresponding reduction of extension of the alternate or opposing coil spring). In this manner, the second collar 65, and the sensor (eg. gyroscope) carried thereby, can be rotated using motor 10 until one of two limit pins, 180, 185 is brought into engagement with a mechanical stop provided in fixed relationship with the chassis 25 in the form of pin 170. Limit pins 180, 185 are embedded in collar 65 and define two indexing positions/limits and are typically positioned to allow the second collar 65 a range of rotational movement of about 180 degrees of travel.

[0345] Thus, the coil springs 75, 77 couple the first collar 35 and the second collar 65 in such a way so that each coil spring is provided substantially symmetrical about the elongate portion 55. In this manner, the first collar 35 and the second collar 65 are coupled together in an arrangement which allows for the second collar 65 to follow the movement of the first collar 35, regardless of the direction the first collar 35 is moved.

[0346] As the skilled reader will readily appreciate, movement of the first collar 35 serves to place one of the coil springs 75,77 into a state of bias whereby the response (due to its resilient nature) of the relevant coil spring is to bias the second collar 65 to follow the movement of the first collar 35. Thus, movement of the first collar 35 has the effect of the extending the relevant coil spring 75, 77 (or modifying its shape from its original form) which, due to its resilient nature, seeks to revert toward its original or steady state condition. Thus, continual movement of the first collar 35 (assuming no limit position is provided) will continue to bias the second collar 65 so as to follow the movement of the first collar 35 when driven. It will be appreciated that substantially the same physical response occurs for both coil springs 75, 77 when either are placed into a state of bias—which will of course depend upon which index position the second collar 65 is to be biased toward. It follows that the alternate coil spring (75, 77) (that not extended) offers less of a biasing influence to the second collar 65 when following the movement of the first collar 35.

[0347] During an indexing operation in which the second collar 65 is being moved to one of the index positions, once one of limit pins (180, 185) engages with pin 170, therefore confirming that an index position has been reached; additional driving of the first collar 35 (by way of the motor 10) increases the extension of one of the springs 75, 77. This additional driving of the first collar 35 serves to provide a biasing force for holding the second collar 65 (by way of whichever limit pin 180, 185 is relevant) against the pin 170. Once the required biasing or holding force is achieved, power to the motor 10 can be removed and/or the motor's electrical connections shorted together to provide an electromechanical braking effect. In this manner, operation of the motor 10 ceases allowing the sensor carried by the second collar 65 to operate (for measurement/recording purposes) in an environment which is substantially free from any undesirable vibrational/shock forces which might occur due to standard operation of the motor.

[0348] The first collar 35 may be configured controllable so that it decelerates to a lower speed as the second collar 65 approaches a desired limit position so as to substantially reduce or minimise any shock force as the limit position is reached (ie. when engagement between either of pins 180, 185 with limit pin 170 occurs). Thereafter, the motor 10 can be arranged to accelerate again so as to provide the additional drive to the first collar 35 in order to stretch or extend the relevant coil spring (75, 77) so as to apply the holding force for biasing either of the pins 180, 185 of the second collar 65 against the limit pin 170.

[0349] As will be apparent, the coil springs 75, 77 coupling the first 35 and second 65 collars are arranged in an a symmetrical relationship about the elongate portion 55 providing a substantially cooperative arrangement which, at least in part, serves to dampen or reduce any undesirable vibration and/or shock forces which might be imparted to the second collar 65 and any sensor carried thereby during any measurement and/or indexing operation. Furthermore, such arrangements may also serve to reduce the transfer of any torque impulses to the second collar 65 or elongate portion 55 when drive is provided to the first collar 35.

[0350] At times when the sensor carried by the second collar 65 is not required to be held at either indexing position, the second collar 65 can be driven to an intermediate or park position (shown in FIG. 4). As discussed below, when in this position, operation of the coil springs 75, 77 in the configuration shown, at least in part, affords protection to the sensor/gyroscope against undesirable vibrational and/or shock forces (eg. torque impulses).

[0351] The resilient association between the first 35 and second 65 collars by way of the dual coil spring (75, 77) coupling causes the collar 65 to follow movement of the collar 35. In one respect, this resilient association is operable so that the second collar 65 maintains or seeks to maintain a predetermined alignment with the first collar 35 during indexing of collar 65 about the indexing axis X. The coil springs 75, 77 can be arranged so that both are balanced such that substantially little or no net force is applied to the second collar 65. In this balanced state, the second collar 65 and the first collar 35 are aligned with one another in an equilibrium like condition at the desired or predetermined alignment (between collars 35, 65). Thus, the second collar 65 and the first collar 35 are arranged relative one another in a manner which defines a desired or predetermined state of alignment between both components. For the embodiment of the apparatus 5 described, this alignment between both components is substantially intermediate the index positions, but could be arranged so as to be biased toward either if required.

[0352] In operation, movement of the first collar 35 causes the second collar 65 to follow therewith in an effort to maintain or seek the steady state alignment. Due to the resilient nature of each coil spring 75, 77, the second collar 65 is unlikely to cease movement at the instant the first collar 35 ceases movement. Instead, although the biasing force applied to the second collar 65 by the relevant coil spring 75, 77 substantially reduces, the collar 65 is likely to overrun the stop position of the collar 35 due to the acquired rotational inertia. Once the second collar 65 overruns the stop position of the collar 35, a biasing response is provoked from the alternate coil spring 75, 77 which then serves to bias the collar 65 toward the stop position of the collar 35.

[0353] It will be appreciated that, depending on the dynamic circumstances surrounding the cessation of the movement of the first collar 35, and the degree of resilience of the coil springs 75, 77, the second collar 65 might oscillate about the equilibrium state a number of times until a steady or balanced state between both coil springs 75, 77 is reached. Thus, until the balanced state is reached, both coil springs 75, 77 could transition through varying degrees of bias until the steady state condition is attained.

[0354] Having specific regard to the form of coil springs 75, 77, one test embodiment has shown that favourable performance can be achieved if coil springs 75, 77 are extended to approximately 50% of their maximum extension when the collars 35, 65 are in a rest or balanced state (when alignment as desired). Thus, both springs 75, 77 are initially provided in a preloaded equilibrium. In this configuration, a sufficiently responsive coupling arrangement has been found to be provided—for example, as one spring stretches the alternate spring retracts or relaxes. The arrangement of the coil springs 75, 77 is such that the coils of the retracted or retracting coil spring never close up completely so as to cause the coil spring to bulge outward from the apparatus 5. It will be appreciated that the rest state as referred to here may be the desired or predetermined steady state alignment between the first 35 and second 65 collars. As noted, the desired or steady alignment between the first 35 and second 65 collars could be one that is biased toward either limit/index position.

[0355] A range of spring constants within the allowable space have been tested and found to be not substantially critical so long as the desired holding force—that which holds either of the pins 180, 185 against the limit pin 170—can be achieved with an acceptable amount of additional motor drive.

[0356] The above described arrange represents, broadly, a first implementation of operation in which the chassis 25 is arranged stationary relative to the indexing axis X. However, other embodiments of the apparatus 5 (ie. the second implementation embodiments described above) can be realized in which the chassis 25 is provided with freedom to rotate about the indexing axis X, and the collar 65 is arranged to be fixed or stationary relative to the indexing axis (which will often be, for example, by way of rigid connection with a housing or similar of a down hole survey instrument or survey tool). In such arrangements, the chassis 25 is arranged to carry a sensor device/arrangement in a similar manner to that of collar 65. In arrangements of this nature, it will be understood that the same relative movements as described above are applicable and thus many of the structural, operational, and conceptual features previously described continue to apply to the case where the chassis 25 rotates about the indexing axis X, and second collar 65 is fixed relative to the indexing axis X.

[0357] In operation of such arrangements, movement of the chassis 25 remains by way of drive provided by the indexing drive mechanism 15 as discussed above. In this regard, the structural relationship of the chassis 25 and the indexing mechanism 15 is the substantially same. As the reader will appreciate, in embodiments where second collar 65 is held fixed relative to the indexing axis X, drive provided by the indexing mechanism 15 to the collar 35 serves to cause relative movement there between. With the second collar 65 stationary relative to the indexing axis X and the association between the first collar 35 and the collar 65 sufficiently resilient, drive provided by the indexing mechanism 15 to drive collar 35 serves to rotate the chassis 25 about the indexing axis X. In this manner, it is the pin 170 that moves about the indexing axis X to or toward a stationary limit pin 185/180 (depending of course on which of the index positions the chassis 25 is to be moved to or toward), as opposed to, in the first implementation described above, the limit pins 180/185 in collar 65 being rotated to engage the pin 170.

[0358] Movement of the chassis 25 about the indexing axis X will continue until the pin 170 is brought into engagement with one of the limit pins 180/185. Once this engagement occurs, further driving of the collar 35 serves to test the resilience of the association between the collar 65 and the collar 35. Further driving of the collar 35 begins to rotate the collar 35 about the indexing axis X. As such, the association between the collar 35 and the collar 65 serves to bias or urge the chassis 25 (by way of pin 170) against a limit pin 180/185 of a respective limit position. In this manner, the chassis 25 is effectively held (biased or urged) against the limit pin (180/185) of the corresponding intended index position.

[0359] As noted above, the motor unit 10 can be configured (in the manner described above) to be electrically shorted so as to brake the motor and maintain the biased state. In this state, when the association between the collar 35 and the collar 65 is resilient in nature, exposure of any undesirable forces to any sensor carried on the chassis is, at least in part, reduced. Similarly, when driving toward an intended limit position, the indexing mechanism can be configured so as to control the speed of the approach to the limit position such the shock of any contact with the pin 170 is reduced, before then returning to an appropriate speed to cause collar 35 to rotate beyond the index position so that the necessary biasing/holding force can be applied (as described above).

[0360] As described above, the indexing mechanism 15 may be operable to drive the chassis 25 to a position which is substantially intermediate the index positions —such as a ‘park’ position. In this manner, the association between the collar 35 and the collar 65 is configured such that exposure of the chassis 25 (and the sensor(s) carried thereby) to any undesirable forces is, at least in part, reduced.

[0361] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variations and modifications. The invention also includes all of the steps, and features referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0362] The skilled reader will appreciate that coil springs 75, 77 could be readily replaced by any suitable coupling means of resilient character capable of being deformable in some manner so that it can store energy therein. For example, any type of flexible coupling element made from rubber, silicone, or polymer, could be configured for suitable use. It will be appreciated that arrangements using gas or pneumatic coupling assemblies having sufficient resilient character could be configured for use.

[0363] Other configurations which couple first 35 and second 65 collars together in a resilient like manner will be possible. In one alternative embodiment, the coil springs 75, 77 could be replaced by a single piece sleeve formed from a resilient material (such as, for example, rubber) and arranged so as to couple the first 35 and second 65 collars together at opposing ends at or near their peripheries. As with the above described operation, biasing of the second collar 65 so as to follow the movement of the first collar 35 (or vice versa) occurs due to the extensible and resilient nature of the sleeve. In at least one embodiment, one or more portions or regions of the sleeve would serve to provide the biasing effect when extended by movement of the first collar 35.

[0364] Any method for operating embodiments of the apparatus 5 may broadly involve providing an embodiment of apparatus 5 and associating it with a down hole surveying tool or surveying instrument so that the apparatus is operable therewith, and causing or operating the apparatus to drive the sensor carrying device (either collar 65 or chassis 25 depending on which implementation is relevant) about the indexing axis X to, toward, or from an index position.

[0365] When the sensor is at the intended index position, the apparatus may be caused or operated to hold the device at the index position for a predetermined period of time for measurement purposes before driving the device toward another index position for about the same predetermined period of time for measurement purposes.

[0366] As discussed above, the apparatus 5 may be caused or operated so as to reduce the speed of driving the device about the indexing axis X as the device approaches the intended index position. This is so as to reduce any impact forces as the limit pins 180/185 engage with the pin 170. Furthermore, the speed of driving the device about the indexing axis may be increased in the direction of the intended index position once the device has reached the index position. In this manner, further driving of the collar 35 rotates the collar about the indexing axis X. As such, the association between the collar 35 and the collar 65 is arranged so as to bias or urge the chassis 25 at a respective limit position. In this manner, the chassis 25 is effectively held (biased or urged) against the limit pin (180/185) in the intended index position.

[0367] In another embodiment, any operative method may comprise driving the device between a first index position and a second index position in a consecutive manner during the course of a survey operation.

[0368] When the sensor carried by the device (collar 65 or chassis 25) is not operable, the apparatus may be caused or operated to drive the device to a park or inactive position. In this manner, the resilient nature of the coupling between collar 35 and collar 65 serves to, at least in part, limit exposure of the sensor to any undesirable physical forces when the device is in the ‘park’ or inactive position.

[0369] It will be appreciated that survey devices or instruments incorporating embodiments of apparatus 5 will comprise a plurality of components, subsystems and/or modules operably coupled via appropriate circuitry and connections to enable the apparatus 5 to perform the functions and operations herein described. This will include suitable components, such as computing means having associated storage, necessary to receive, store and execute appropriate computer instructions such as a method of performing a down hole surveying operation using a survey instrument in accordance with an embodiment of the invention. This will include sufficient electronics for measuring various types of information and recording such information (for example, recording data to one or more appropriate memory modules) for subsequent processing. Further, such electronics will also include suitable controllers programmed to carry out any such measuring, recording, and/or processing of information as might be required.

[0370] As the skilled person will appreciate gyroscopes such as dynamically tuned gyroscopes (DTGs) based on north seeking survey instruments will typically need to index the gyroscope between two measurement positions in order to allow any static bias errors to be reduced or eliminated.

[0371] Gyroscopic data acquisition in each measurement position may typically take in the order of about 40 seconds, and movement from one position to the other may typically take a further (about) 10 seconds. Thus, a survey process from initiation to completion may take about 90 seconds in total, ie. consisting of about 40 seconds in the first index position, about 10 seconds traversing between the first index position and a second index position, and about 40 seconds in the second index position.

[0372] One embodiment of a method 300 proposed for conducting a survey of a borehole using a survey instrument is shown in FIG. 7. For the arrangement shown, the survey instrument is configured so as to incorporate apparatus 5 for indexing a sensor device carried by the second collar 65 between first 350 and second 360 index positions (such as for example index positions which correspond to pins 180, 185 as described above).

[0373] In broad terms, the proposed method 300 seeks to provide a convenient means of performing a down hole surveying operation comprising recording data measured from the sensor (such as for example a gyroscope) when provided at the first and second index positions. The survey instrument is arranged so as to measure the data at each index position in a continuous and consecutive manner.

[0374] The method 300 further comprises acknowledging the time the data was recorded by way of a first timer which is arranged so as to be associated with the survey instrument. In a typical arrangement, acknowledging the time the data was recorded by the survey instrument is achieved by way of associating the time the data was recorded with the corresponding recorded data (such as by recording the time the data was measured to an appropriate memory module).

[0375] The method 300 further comprises, by way of a further timer, acknowledging a point in time while the survey instrument is down hole during the surveying operation. It will be understood that such acknowledgement represents a user or operator requesting a survey report to be prepared based on the data measured down hole following the request being made. The means by which the request is made may be by way of, for example, an input into an appropriate controller 330 provided at the surface by the user/operator.

[0376] Once the survey instrument has been retrieved and is back on the surface, the method 330 further comprises identifying data recorded by the survey instrument after the request was made by the user/operator for use in preparing the survey report. This process of identifying the data recorded by the survey instrument after the request was made by the user/operator may be carried out by, for example, synchronising the controller 330 with the survey instrument so that the data stored in the survey instrument can be interrogated in an appropriate manner.

[0377] Use of the apparatus 5 in the proposed method is advantageous in that it is necessary to ensure that the data measured by one or more sensors carried by the apparatus 5 is less exposed to undesirable noise components caused, at least in part, due to physical forces resulting from vibrational/forces emanating from internal/external sources. The skilled reader will appreciate the need to ensure that the sensor remains as stationary as possible while operational for measurement purposes.

[0378] The method 300 is shown in the form of a multiple component flow chart, reflecting events occurring down-hole 310 by the surveying instrument, and those occurring at the surface 320 by the controller 330.

[0379] Similarly to the apparatus 5, the controller 330 comprises a plurality of components, subsystems and/or modules operably coupled via appropriate circuitry and connections to enable the controller 330 to perform the functions and operations herein described. The controller 330 comprises suitable components necessary to receive, store and execute appropriate computer instructions such as a method of performing a down hole surveying operation using a survey instrument in accordance with at least one embodiment described herein.

[0380] Particularly, and as shown in FIG. 8, the controller 330 comprises computing means which in this embodiment comprises processing means in the form of a processor 500 and storage 510 for storing electronic program instructions for controlling the controller 330, and information and/or data; a display 520 for displaying a user interface 530; and input means 540; all housed within a container or housing 550, so as to provide a controller module.

[0381] The storage 510 comprises read only memory (ROM) and random access memory (RAM).

[0382] The controller 330 is capable of receiving instructions that may be held in the ROM or RAM and may be executed by the processor 500. The processor 500 is operable to perform actions under control of electronic program instructions, as will be described in further detail below, including processing/executing instructions and managing the flow of data and information through the controller 330.

[0383] In the embodiment, electronic program instructions for the controller 330 are provided via a single software application (app) or module which may be referred to as a surveying app. The surveying app can be downloaded from a website (or other suitable electronic device platform) or otherwise saved to or stored on storage 510 of the controller 330.

[0384] In some embodiments, the controller 330 comprises a smartphone such as that marketed under the trade mark IPHONE® by Apple Inc, or by other provider such as Nokia Corporation, or Samsung Group, having Android, WEBOS, Windows, or other Phone app platform. Alternatively, the controller 330 may comprise other computing means such as a personal, notebook or tablet computer such as that marketed under the trade mark IPAD® or IPOD TOUCH® by Apple Inc, or by other provider such as Hewlett-Packard Company, or Dell, Inc, for example, or other suitable processing apparatus.

[0385] The controller 330 also includes an operating system which is capable of issuing commands and is arranged to interact with the surveying app to cause the controller 330 to carry out the respective steps, functions and/or procedures in accordance with the embodiment described herein. The operating system may be appropriate for the controller 330. For example, in the case where the controller 330 comprises an IPHONE® smartphone, the operating system may be iOS.

[0386] With reference to FIG. 9, the controller 330 is operable to communicate via one or more communications link(s) 560, which may variously connect to the apparatus 5, and optionally one or more other remote devices and/or systems 570 such as servers, personal computers, terminals, wireless or handheld computing devices, landline communication devices, or mobile communication devices such as a mobile (cell) telephone. At least one of a plurality of communications link(s) may be connected to an external computing network through a telecommunications network.

[0387] The surveying app and other electronic instructions or programs for the computing components of the controller 330, and the apparatus 5, can be written in any suitable language, as are well known to persons skilled in the art. For example, for operation on a controller comprising an IPHONE® smartphone, the surveying app may be written in the Objective-C language. In some embodiments, the electronic program instructions may be provided as stand-alone application(s), as a set or plurality of applications, via a network, or added as middleware, depending on the requirements of the implementation or embodiment.

[0388] In alternative embodiments, the software may comprise one or more modules, and may be implemented in hardware. In such a case, for example, the modules may be implemented with any one or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA) and the like.

[0389] The computing means can be a device or system of any suitable type, including: a programmable logic controller (PLC); digital signal processor (DSP); microcontroller; personal, notebook or tablet computer, or dedicated servers or networked servers.

[0390] The processor can be any custom made or commercially available processor, a central processing unit (CPU), a data signal processor (DSP) or an auxiliary processor among several processors associated with the computing means. In some embodiments, the processing means may be a semiconductor based microprocessor (in the form of a microchip) or a macro processor, for example.

[0391] In some embodiments, the storage can include any one or combination of volatile memory elements (e.g., random access memory (RAM) such as dynamic random access memory (DRAM), static random access memory (SRAM)) and non-volatile memory elements (e.g., read only memory (ROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), programmable read only memory (PROM), tape, compact disc read only memory (CD-ROM), etc.). The respective storage may incorporate electronic, magnetic, optical and/or other types of storage media. Furthermore, the storage can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the processing means. For example, the ROM may store various instructions, programs, software, or applications to be executed by the processing means to control the operation of the controller and the RAM may temporarily store variables or results of the operations.

[0392] The use and operation of computers using software applications is well-known to persons skilled in the art and need not be described in any further detail herein except as is relevant to the presently described embodiment.

[0393] Any suitable communication protocol can be used to facilitate connection and communication between any subsystems or components of the controller 330, any subsystems or components of the apparatus 5, and the controller 330 and apparatus 5 and other devices or systems, including wired and wireless, as are well known to persons skilled in the art and need not be described in any further detail.

[0394] In one embodiment, the display 520 for displaying the user interface and the user input means 530 are integrated in a touchscreen 580. In alternative embodiments these components may be provided as discrete elements or items.

[0395] The touchscreen 580 is operable to sense or detect the presence and location of a touch within a display area of the controller 330. Sensed “touchings” of the touchscreen 580 are inputted to the controller 330 as commands or instructions. It should be appreciated that the user input means 530 is not limited to comprising a touchscreen, and in alternative embodiments any appropriate device, system or machine for receiving input, commands or instructions and providing for controlled interaction may be used, including, for example, a keypad or keyboard, a pointing device, or composite device, and systems comprising voice activation, voice and/or thought control, and/or holographic/projected imaging.

[0396] The method 300 serves to reduce or eliminate (if possible) the need to provide a pre-set trigger for the survey process, and therefore mitigate against any need to pre-plan when the survey should take place. As the skilled reader will appreciate, traditional methods generally involve the user predicting the time at which the survey instrument will be in position, stationary and ready to commence the survey. The user would then set a time delay within the survey instrument before it is inserted into the borehole. The skilled reader will appreciate that a significant drawback with this method is that valuable rig time can be wasted if the user's initial prediction of when the survey instrument will be in position is too long, or the survey results can be useless if the user's prediction is ultimately found to be too short. The present described method seeks to avoid the need for the user or operator to make any such prediction.

[0397] With reference again to FIG. 7, once the survey instrument is inserted 340 into the borehole, the instrument is configured so as to continuously measure and record data for substantially the entire time it is down-hole 310. During this measurement process, the survey instrument is alternating or indexing between the first 350 and second 360 index positions. During the measurement process (eg. a measurement cycle), the survey instrument is sought to be held as still as possible.

[0398] Other arrangements are also possible. It will be appreciated that the survey instrument could be configured to measure continuously over a finite period of time. In one such arrangement, the survey instrument may be configured so that the finite of time period commences at a time, for example, when the operator believes or predicts that the survey instrument is likely to be in a position down hole at a location in the borehole where a survey report is required.

[0399] The survey instrument includes a timer (survey timer) which is arranged so as to be synchronised with a timer located on the surface (surface timer). In the embodiment, the surface timer is a component of the controller 330. Thus, in one arrangement, the survey instrument and the controller 330 are synchronised with one another so as to become ‘initialized’—this being the process of ensuring that the survey timer and the surface timer are synchronised.

[0400] Once ‘initialized’, the survey instrument continuously moves the sensor from one indexing position to the other. The time spent by the sensor at each index position for measurement purposes is for a known period of time (in one embodiment, this known time period may be in the order of substantially 40 seconds). A single survey comprises two consecutive measurements taken at the two index positions.

[0401] The survey report is determined or processed using the information measured by the sensor unit(s) at each index position (350, 360) consecutively. In some configurations, preparation of the survey report is based on a preselected reference index position. In one arrangement, one of the index positions is selected to serve as the reference index position, eg. the first 350 index position. Arrangements of this type will require, for example, a survey report to be prepared using data taken from the first 350 index position, followed by data taken from the second 360 index position consecutively. In these embodiments, it will be understood that the sensor requires indexing back to the reference or first 350 index position before another survey report can be sought/prepared.

[0402] For the example outlined above for the case where the sensor comprises a gyroscope, gyroscopic data acquisition in each measurement position may typically take in the order of about 40 seconds, and movement from one position to the other may typically take a further 10 seconds. Thus, a survey process from initiation to completion may take about 90 seconds in total, ie. consisting of about 40 seconds in the first index position, about 10 seconds traversing between the first index position and a second index position, and about 40 seconds in the second index position. In such arrangements, a new survey may commence on a substantially regular basis (for example, every two minutes). In this manner, the survey start or commencement times can be readily determined; for example, for the present case where the survey commences substantially every two minutes, the relevant survey commencement times will be in two minute intervals (eg. 0-2-4-6-8 minutes (etc)) after initialization.

[0403] Other configurations might also be realised. In another embodiment, the preparation of the survey report can be configured so as to consider consecutive sets of measured data regardless of any stipulation for a reference index position. In such embodiments, a fresh survey report can be prepared using measurement data taken from either index (350, 360) position provided that the following set of measured data is taken from the alternate index position in a consecutive manner—both sets of measurement data will then be used to prepare the survey report. Thus, in arrangements of this nature, a new survey report can be prepared by not requiring the sensor to be indexed back to a required reference index position.

[0404] As the skilled reader will appreciate, arrangements of this nature can be advantageous in that a valid survey result can be prepared independent of what survey measurement (ie. survey measurement data taken from either the first or second index positions) was used as the reference index position for the survey (ie. as compared with the need to move the sensor back to the same index position in other embodiments described above). Accordingly, using the time periods outlined above, a new survey report can be commenced at approximately minute intervals.

[0405] Using the present method, at the surface 320, if at any time the operator/user wishes to record or request 380 a survey start time (for example, by pressing a button 390 provided on the touchscreen 580 to record 400 the relevant timestamp in the controller 330), the controller 330 will, in response, commence the surface timer that is configured so as to finish after the next full survey (for example, once two consecutive measurements have been taken) is expected to be completed. The survey instrument may not be moved during this period. The operator/user will generally only wish to request a survey if the survey instrument is thought to be in a stationary position.

[0406] However, the survey instruction could also be configured so that actuation of a survey is triggered by one of the sensors sensing the current state of the survey instrument when down hole. The occurrence of any current state of the survey instrument (and/or change in current state when down hole) could be detected by way of any signal(s) received from any of the on-board sensors.

[0407] For example, rather than continuously commencing a measurement cycle at pre-defined time intervals (as described above), the survey instrument could be configured to employ its on-board sensor unit(s) to make a determination as to whether the survey instrument is stationary. Such a determination could be made, for example, by the survey instrument seeking to determine whether it has remained substantially stationary (or has remained sufficiently stationary according to defined criteria) for a specified period of time during which signals from one or more sensor units associated with the survey instrument are monitored (monitoring period). Such a monitoring period may be in the order of, for example, 10 seconds, but could be any appropriate nominated time period considered sufficient for making such a determination. It would be appreciated that various practical factors could inform the quantum of such a time period, such as for example, power consumption considerations, the type of sensor being relied upon, and/or the geologic nature of the site sought to be surveyed.

[0408] The survey instrument could be configured so as to monitor signals from an accelerometer unit with the signals being processed in a manner which provides an indication of physical vibration experienced by the survey instrument when the accelerometer unit is operational during the monitoring period. If, for example, a measured signal is considered to be indicative of a stationary state during the monitoring period, the determination is made that the survey instrument is stationary and a measurement cycle can commence.

[0409] If, however, a measured signal is considered to reflect a non-stationary state, the survey instrument may be configured so that a measurement cycle is unable to commence. In such cases, the survey instrument may be configured so as to recommence the monitoring period (either automatically or at a specified future time therefrom).

[0410] If the determination is made that the instrument is stationary, and a measurement cycle is commenced, the survey instrument may be configured to continue testing or monitoring for a change in its state for the remainder of the current measurement cycle. If, for example, the state of the survey instrument were to change from being stationary to non-stationary, then the survey instrument could be configured to cease recording data and the monitoring period recommenced. Alternatively, the survey instrument could be configured to continue measuring for the remainder of the current measurement cycle and any measurement data recorded during this time associated with an appropriate indicator indicating that the data may be compromised. The data could, however, simply be deleted or discarded in an appropriate manner.

[0411] The survey instrument may be configured so that any adverse change in its state detected during a measurement cycle and/or the monitoring period has the effect of restarting the monitoring period. Any data recorded can either be discarded/deleted or retained with an appropriate caveat.

[0412] Once the survey instrument has been retrieved and the survey data open to interrogation, the controller 330 is arranged so as to receive 410 the data for synchronisation 420 purposes. The purpose of the synchronisation stage is to identify data that is associated with the period of time initiated by the user (survey start and expected completion time). The identified data may then be isolated or extracted 430 for processing purposes (eg. for preparing a survey report).

[0413] In embodiments described above where the measurement cycle can be triggered by testing for the current state of the survey instrument when down hole, the timers associated with the survey instrument and the controller still remain synchronized with one another. When a survey report is required, the operator records the time during the survey period when it is considered (by the operator/user at the surface) that the survey instrument is stationary at the desired location down hole. The controller at the surface then seeks to capture or record the time so as to be able to identify and/or isolate the relevant measured survey data once synchronised with the survey instrument when it is back at the surface.

[0414] The controller 330 may be arranged so as to provide and display a further timer to the operator indicating the estimated elapsed time as the measurement cycle progresses. For example, the controller 330 may be configured to display a timer to the operator/user showing an appropriate wait time (eg. being in the order of about 2 minutes) per measurement cycle.

[0415] All data acquired by the on-board gyroscope sensor is recorded to an appropriate memory module and may include relevant information which corresponds to the time each set of gyroscope data was taken (ie. all data recorded by the gyroscope should be appropriately time stamped).

[0416] Thus, in effect, the two complete and consecutive measurements following the time at which the survey was requested 400 are extracted 430 and used to compute the survey results 440. The results can then be processed and used 450 to determine the appropriate calculation for the first index position 350, followed by the second index position 360, or vice versa.

[0417] In some environments, efficient use of the time available for measuring purposes can be advantageous. For embodiments where the survey instrument is configured to test for the current state of the survey instrument (eg. a non-stationary state), the measurement cycle may be arranged to commence once the time duration of the monitoring period expires. Thus, in these arrangements, the time needed for the survey instrument to remain stationary for measuring is the time duration of the monitoring period plus the normal time duration of the measurement cycle.

[0418] To seek to reduce any undue delay, the survey instrument could be configured so as to measure data during the monitoring period at the same time the instrument is testing, for example, to determine whether the instrument is in a stationary state. The survey instrument could therefore be configured so as to continuously record signals received from any measuring sensor during the monitoring period. Thus, the signals from the sensor(s) may be continuously recorded into a buffer module during the monitoring period. The buffer module may have a prescribed size so as to have sufficient capacity for retaining measured data recorded during the monitoring period.

[0419] When the monitoring period expires, and the survey instrument is affirmed, for example, as being in a stationary state (as described above), then the measured data recorded to the buffer module may be used in the preparation of the survey report. In this manner, the measured data recorded during the monitoring period becomes part of the data used for preparing the survey report. Use of the data measured and recorded during the monitoring period therefore serves to reduce the time needed for the survey instrument to remain stationary for measuring purposes.

[0420] In one arrangement, the survey instrument could continuously store the current sensor signals into the buffer module having a given size (eg. having a capacity of about 10 seconds of data). When a stationary period of 10 seconds occurs, then the data in the buffer forms a valid portion of the survey measurement. Thus, the measurement time in the initial index position will not have to be extended by the time of the monitoring detection period (eg. 10 seconds).

[0421] Processing of the raw measured data can require the need for calibration. For the case where the sensor comprises a gyroscope, the raw measured data can be corrected using a calibration file that can be stored or associated with the survey instrument. The calibration file could also be stored or associated with the controller 330 on the surface 320. In some embodiments, the calibration file can be stored or associated with a handheld unit when serving as the controller 330.

[0422] Where an accelerometer is included, for example, the accelerometer data can be corrected using the calibration file. In some arrangements, error terms in the gyroscope data may need to be corrected using the accelerometer data. With the corrected sensor signals, the static bias can be estimated/determined. For configurations where there is provided substantially 180 degrees of rotation between the two indexing positions, it can be assumed that the corrected gyroscope signals have the substantially same magnitude but opposing signs. By way of a brief simple example, a simplified equation might look like this:

wx1=+wx+Bias  Gyroscope data in index position 1:

wx2=−wx+Bias  Gyroscope data in index position 2:

Bias=(wx1+wx2)/2

[0423] For situations where the bias is known, the azimuth can be derived from either one of the index positions.

[0424] It will be appreciated that the recording of the data down-hole would be stored on a memory module of any suitable configuration provided with the survey instrument. Thus, in one form, the input 410 of the recorded data into the controller 330 and synchronisation 420 with the controller data could comprise a transfer from the memory module to a memory module within the controller 330. The skilled reader would appreciate that any data synchronisation (and associated hardware) solution could be used.

[0425] To assist the operator while the survey is being made, the controller 330 would use knowledge (generated via processing of relevant data and/or information under control of the electronic program instructions) of the synchronised events occurring in the survey instrument when down-hole to advise the operator once two complete consecutive measurements had been acquired and the survey was therefore complete.

[0426] Because the operator could request a survey at any arbitrary time, and this could potentially occur part way through a measurement, a short delay of up to one acquisition period may be required for the in-process measurement to complete and the survey to properly commence.

[0427] Where the terms “system”, “device”, and “apparatus” are used in the context of the invention, they are to be understood as including reference to any group of functionally related or interacting, interrelated, interdependent or associated components or elements that may be located in proximity to, separate from, integrated with, or discrete from, each other.

[0428] Where the words “store”, “hold” and “save” or similar words are used in the context of the present invention, they are to be understood as including reference to the retaining or holding of data or information both permanently and/or temporarily in the storage means, device or medium for later retrieval, and momentarily or instantaneously, for example as part of a processing operation being performed.

[0429] Furthermore, in embodiments of the invention, the word “determining” is understood to include receiving or accessing the relevant data or information.

[0430] Throughout this specification, and the claims which follow, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0431] Furthermore, throughout the specification, and the claims which follow, unless the context requires otherwise, the word “include” or variations such as “includes” or “including”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0432] Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.