AU2015234298B2

AU2015234298B2 - Controlled rotation centraliser

Info

Publication number: AU2015234298B2
Application number: AU2015234298A
Authority: AU
Inventors: Michael Charles AYRIS
Original assignee: Imdex Tech Pty Ltd
Current assignee: Imdex Technologies Pty Ltd
Priority date: 2014-10-16
Filing date: 2015-09-29
Publication date: 2020-07-02
Anticipated expiration: 2035-09-29
Also published as: AU2015234298A1

Abstract

A controlled rotation centraliser apparatus for attachment to a survey tool or protective apparatus encasing the survey tool, The apparatus comprises a plurality of centraliser arms, wherein each centraliser arm comprises a first arm component, second arm component and roller bearing attached to the first arm component. Each roller bearing is orientated at a pitch angle so that the apparatus rotates the survey tool when the survey tool is conveyed through a drill rod. 1/4 f-0 `7 00 Co c CM> CCM A CMj C\o k~zC CCYr rN \ ssP"s~S,,,x* SIC V'Y,, -)C C-cj

Description

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AUSTRALIA

PATENTS ACT 1990

COMPLETE SPECIFICATION

FOR A STANDARD PATENT (Original)

APPLICATION NO: LODOED: COMPLETE SPECIFICATION LODGED: ACCEPTED: PUBLISHED: RELATED ART: NAME OF APPLICANT: DHS (AUST) PTY LTD

ACTUAL INVENTOR: Michael Charles Ayris

ADDRESS FOR SERVICE: LORD AND COMPANY, Patent and Trade Mark Attorneys, of PO Box 530, West Perth, Western Australia, 6872, AUSTRALIA.

INVENTION TITLE: "CONTROLLED ROTATION CENTRALISER" DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO'S:

Australian Provisional Patent Application Number 2014904140 filed on 16 October 2014

The following Statement is a full description of this invention including the best method of performing it known to me/us:

I TITLE "CONTROLLED ROTATION CENTRALISER" FIELD OF INVENTION

[0001] The present invention relates to a controlled rotation centraliser. More particularly, the present invention relates to a controlled rotation centraliser apparatus for downholesurvey tools.

BACKGROUNDART

[0002] In underground mining and drilling operations, boreholes are drilled in order to cut and extract core samples that enable geologists to determineunderground geological composition and rock mechanics.

[0003] Once a borehole has been drilled, a survey tool is commonly used to measure and profile the trajectory of the borehole, typically by measuring the borehole's depth, inclination (pitch) and bearing (azimuth) at various intervals along its length. Geologists and engineers use this information to ascertain andverify the course of the borehole and the position and orientation of any core samples taken. This provides a better understanding of the formation of minerals and rock strata in the drilling area.

[0004] To profile a borehole, a survey tool is, firstly, fed into the mouth of the drill rod that has been used to drill the borehole at the ground's surface. The survey tool is then conveyed down and up the length of the drill rod one or more times using known mechanical means, such as a winched wireline. Measurements are taken at regular designated intervals, commonly referred to as survey"stations" and the information collected is transmitted from the survey tool back to drilling personnel at the surface using known wireless or wired communication means and standards, such as electromagnetic signals, Wi-Fi, mud pulse telemetry or coaxial cable.

[0005] To obtain accurate measurements, the survey tool must be kept at a position located centrally in the drill rod equidistant from the drill rod's circumferential inner walls. Further, the longitudinal length of the survey tool must be aligned substantially parallel to the longitudinal length of the drill rod while the tool is conveyed along its course.

[0006 Keeping a survey tool centralised and aligned can be difficult, particularly for directional boreholes that do not have a fixed course and/or cross sectional area. Strictures and other physical obstructions inside the course of the drill rod (for example, at rod sectionjoints) may also impede accurate centralisation and alignment of the survey tool.

[0007] Survey tools typically employ gyroscopic sensing means used to take orientation measurements at survey stations. For example, rotary or vibrating structure gyroscopes (such as micro-electromechanical (MEMS) systems) or optical gyroscopes are commonly used.

[0008] Like other types of sensor systems, measurements taken by a gyroscopic sensor will contain some inherent error. For gyroscope sensors, these errors are conventionally referred to as bias errors and the accuracy and reliability of modem gyroscopes are often described in terms of their bias drift or bias instability. Bias errors grow linearly with time so, unless abated, they will accumulate as and when a gyroscope is used continually causing an increasingly significant reduction in survey accuracy.

[0009] Bias errors exhibited by gyroscope-based sensors may be positive (i.e., over measurements taken) or negative (i.e., under-measurements taken) depending on how the sensor is orientated in three-dimensional space. The amount of bias error exhibited by a sensor that is configured to measure a specific orientation value (for example, pitch or azimuth) varies in a sinusoidal manner as and when the sensor is rotated about a fixed axis in two-dimensional space. This means that the sensor exhibits its maximum amount of positive bias at a rotational position that is exactly 1800 degrees from the position at which it exhibits its maximum amount of negative bias.

[0010] The aggregate amount of positive bias of a sensor will match the aggregate amount of negative bias if the sensor is rotated completely about 360 degrees in a uniform manner. Bias errors can, therefore, be effectively eliminated by rotating the survey tool at a constant rotational speed about a longitudinal axis parallel to the drill rod while the tool is conveyed along its course. These rotations result in the positive bias errors effectively compensating for the negative bias errors (and vice-versa) which yields a set of sample readings from which accurate mean estimations of borehole orientation can be calculated.

[0011] Various techniques and apparatuses are currently employed in an effort to centralise and rotate survey tools while they are conveyed along the length of a borehole.

[0012] In one known manual method, the survey tool (or an apparatus housing the tool) is locked at a fixed central position inside the drill rod The rod is manually rotated about its longitudinal axis by the drilling operator using mechanical means at each of the survey stations. Typically, the rod will be rotated by 90° degrees at each survey station, thus achieving one full 3600 rotation every four survey stations, This process is time consuming for the drilling operator and rotating the rod accurately can be difficult. Over~ rotations and misalignments are common and drilling operators may even omit rotations at survey stations by mistake.

[0013] As an alternate to manual methods, a centraliser apparatus may be used to support and guide the survey tool while it is independently fed along the course of the drill rod.

[0014] One known type of centraliser apparatus commonly used is known as a bow (or basket spring) type centraliser. Bow centralisers typically comprises two collars that are each fixed around the circumference of the survey tool. The collars are connected together by, and spaced apart by, a plurality of outwardly directed staves, springs or bows which press against the wall of the drill rod wall in an effort to keep the survey tool centred within the drill rod.

[0015] Bow centralisers suffer from several significant shortcomings. They are prone to collapsing when being used to guide a survey tool along flat or horizontal directional borehole as the majority of the survey tool's weight will act on the lower-most bows contacting the drill rod wall. This leads to decentralising of the survey tool causing inaccurate readings and accumulation of errors.

[0016] Further, bow-type centralisers having springs or bows with a large bowed height are not suitable for guiding survey tools through narrow drill rods or drill rod sections. This is because, in use, the bowed portion of each spring presses inwardly towards the casing in which the survey tool ishoused. With a large bowed height, a very large compressive force is required to deflect the spring bow close to the casing. This makes it difficult to pass the centraliser apparatus through narrow drill rods and drill rod strictures and makes the apparatus and its springs vulnerable to wear and tear.

[0017] Further, most bow-type centralisers do not permit rotation of the survey tool. Bow-type centralisers that are designed to facilitate some rotation fail to do so in a controlled or uniform manner. Often, only random or intermittent rotations may be achieved which causes bias errors to remain substantially manifest in the survey readings.

[0018] A further alternative type of centraliser design commonly used is a roller bogie type centraliser. This typically comprises a chassis having a plurality of wheels that contact with the walls of the drill rod. The suvey tool is secured to the chassis and then conveyed down the drill rod using mechanical means.

[0019] Roller bogie devices typically position the survey tool on the low side of the borehole meaning that the tool is not truly centralised. The minority of devices that are able to achieve a central position are not capable of adapting to changes in drill rod shape and/or cross-sectional area, for example due to narrow strictures or drill rod joints.

[0020] Furthermore, roller bogie type centralisers do not rotate the survey tool meaning that bias errors accumulate as the tool is used over time.

[0021] The present invention attempts to overcome, at least in part, the aforementioned disadvantages of previous centraliser apparatuses.

SUMMARY OF INVENTION

[0022] In accordance with one aspect of the present invention, there is provided a controlled rotation centraliser apparatus for attachment to a survey tool or protective apparatus encasing the survey tool, the apparatus comprising a plurality of centraliser arms, wherein each centraliser arm comprises a: first arm component; second arm component; and roller bearing attached to the first ann component, and wherein each roller bearing is orientated at a pitch angle so that the apparatus rotates the survey tool when the survey tool is conveyed through a drill rod.

[0023] The first arm component of each centraliser arm may be shorter than the second arm component of the centraliser arm.

[0024] The controlled rotation centraliser apparatus may comprise at least four centraliser arms, wherein:

at least two centraliserarms are arranged such that their first arm components are disposed towards a first end of the apparatus; and at least two centraliser arms are arranged such that their second arm components are disposed towards a second end of the apparatus.

[0025] The first arm component of each centraliser arm may be attached to the second arm component of the centraliser arm by a revolute or pin joint at an attachment point.

[0026] The attachment point of each centraliser arm may be located away from a distal end of the first arm component ofthe centraliser ann.

[0027] The second arm component of each centraliser arm may comprise a recess, wherein the recess is adapted to receive the roller bearing that is attached to the first arm component of the centraliser arm when the centraliser arms are in a retracted state.

[0028] The controlled rotation centraliser apparatus may also comprise a: static arm support; moving arm support; and compression spring, wherein the compression spring and moving arm support biases the centraliser arms in an expanded state.

[0029] The controlled rotation centraliser apparatus may also comprise an elongated supporting shaft extending between the first and second ends ofthe apparatus.

[0030] The controlled rotation centraliser apparatusmayalsocompriseatensioning nut for increasing energy stored in the compression spring.

[0031] In accordance with one further aspect of the present invention, there is provided a method for centralising a survey tool within a drill rod, the method comprising the steps of:

attaching a first controlled rotation centraliser, as described above, to a first end of the survey tool or a protective apparatus encasing the survey tool; attaching a second controlled rotation centraliser, as described above, to a second end of the survey tool or protective apparatus; and conveying the survey tool and the attached first and second controlled rotation centralisers along the length of the drill rod.

BRIEF DESCRIPTION OF DRAWINGS

[0032] The foregoing summary, as well as the following detailed description of the illustrated embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an exemplary embodiment which illustrates what is currently considered to be the best mode for carrying out the invention, it being understood, however, that the invention is not limited to thespecific instruments disclosed. In the drawings:

Figure 1 is a perspective view of a controlled rotation centraliser according to a preferred embodiment of the present invention;

Figure 2 is a first side view of the controlled rotation centraliser in Figure I where centraliser arms of the controlled rotation centraliser are shown in an expanded state and pressing against the inside walls of a drill rod;

Figure 3 is a second side view of the controlled rotation centraliser in Figure 1 where the centraliser arms are shown in a retracted state and pressing against the supporting shaft of the controlled rotation centraliser; and

Figure 4 is a perspective view of two controlled rotation centralisers, each as shown in Figure 1, attached to opposite ends of a survey tool.

DETAILED DESCRIPTION OF THE DRAWINGS

[0033] Referring to Figures 1 to 3, there is shown a controlled rotation centraliser 10 according to the present invention.

[0034] The controlled rotation centraliser 10 comprises a centraliser arm apparatus 12 having a first end 14, a second end 16 and an elongated supporting shaft 18 extending between the first and second ends 14, 16.

[0035] Substantially towards the first end 14, there is provided a first connector 20 which is used to attach removably the centraliser ann apparatus 12 to a survey tool (not shown) or to a protective apparatus encasing the survey tool such as, for example, a pressure barrel (not shown).

[0036] The first connector 20 comprises an elongated male threaded portion 22 that is received into, and engages with, a complementary female threaded portion on the survey tool to attach the centraliser arm apparatus 12 to the survey tool.

[0037] Substantially towards the second end 16, there is provided a second connector 24 which is used to attach removably the centraliser arm apparatus 12 to a known deployment means, such as a winched wireline (not shown), for conveying the centraliser arm apparatus 12 (and, therefore, the attached survey tool) down and along the course of a drill rod.

[0038] The second connector 24 comprises a substantially cylindrical boss 26 having an internally threaded cavity therein 28 that receives, and engages with, a complementary elongated male threaded portion (not shown) on the deployment means.

[0039] In use, a pair of centraliser arm apparatuses 12 will be disposed at opposite ends of, and attached to, the survey tool or protective apparatus encasing the tool.

[0040] The centraliser arm apparatus 12 further comprises a tensioning nut 30 disposed adjacent the second connector 24, The tensioning nut 30 comprises a collar having an internal threaded portion that engages with a complementary threaded portion on the supporting shaft 18, such that rotating the tensioning nut 30 causes the tensioning nut 30 to travel along the threaded portion on the supporting shaft 18.

[0041] The centraliser arm apparatus 12 further comprises a plurality of asymmetrical centraliser arms 32 arranged substantially about a centre section of the supporting shaft 18.

[0042] In the preferred embodiment shown in Figures 1 to 3, the centraliser rm apparatus 12 comprises a set of four centraliser arms. It will be appreciated, however, that in alternative embodiments of the present invention, a different number of centraliser arms may be used provided always that a minimum of at least three centraliser arms are used.

[0043] The centraliser arms 32 are disposed between, and each individual arm 40 is attached to and spans, a static arm support 34 and a moving arm support 36.

[0044] The static arm support 34 is disposed adjacent the first connector 20 and is immovably fixed to the supporting shaft 18 by, for example, welding.

[0045] The moving arm support 36 comprises a substantially cylindrical collar that is disposed around the supporting shaft 18 and may travel freely along at least a portion of the supporting shaft 18.

[0046] The centraliser arm apparatus 12 further comprises a compression spring 38 that is disposed around the supporting shaft 18 and is arranged between, and abuts each of, the moving armsupport 36 and the tensioning nut30. When the compression spring 38 is in a compressed state, energy stored in the compression spring 38 causes a force to be exerted on the moving arm support 36 thereby biasing the moving arm support 36 towards a centre position of the supporting shaft 18. This, in turn, causes the moving arm support 36 to exert a corresponding lateral force on the centraliser arms 32.

[0047] Rotating the tensioning nut 30 in one direction causes the tensioning nut 30 to travel along the supporting shaft 18 away from the second end 16 of the centraliser arm apparatus 12. This increases the compression of, and energy stored in, the compression spring 38 and, in turn, the corresponding lateral force exerted by the moving arm support 36 on the centraliser arms 32.

[0048] Conversely, rotating the tensioning nut 30 in the opposite direction reduces the energy stored in the compression spring 38 and the corresponding lateral force exerted by the moving arm support 36 on the centraliser arms 32.

[0049] Each individual centraliser arm 40 comprises a short arm component 42 and a long arm component 44. An end of each arm component 42,44 is attached to an arm support 34,36 by means of a revolute or pin joint 46. Further, each short arm component 42 is attached to its corresponding long arm component 44 also using a revolute or pin joint 48,

[0050] Each short arm component 42 comprises a roller bearing 50 that is attached to a distal end 52 of the short arm component 42 by roll pin 54.

[0051] As most clearly shown in Figure 2, thetrce exerted by the moving arm support 36 on the centraliser arms 32 due to the compression spring 38 causes the centraliser arms 32 to expand radially away from the supporting shaft 18, thus biasing the centraliser arms 32 in a substantially expanded state. This causes the roller bearing of each centraliser ann to push against an internal circumferential wall 56 of a drill rod into which the centraliser ann apparatus 12 has been inserted. This, in turn, causes the centraliser aims 32 to exert an equal corresponding force inwardly on the arm supports 34,36.

[0052] By appropriately adjusting the tensioning nut 30 and, therefore, energy stored in the compression spring 38, the survey tool may be held firmly in a central position in the drill rod when the survey tool is conveyed along the course of the drill rod.

[0053] As shown more particularly in Figure 3, in situations where significant compressive forces are acting on the centraliser arms 32 by the drill rod wall 56, the centraliser arms 32 retract inwardly towards the supporting shaft 18.

[0054] The centraliser arn apparatus 12 is, therefore, capable of withstanding and operating effectively in circumstances where the shape, cross sectional area and/or direction of the drill rod wall 56 changes significantly along its course.

[0055] Each long arm component 44 of each centraliser arm 40 is connected to its corresponding short arm component 42 by pin or revolute joint 48 at a position that is located away from the distal end 52 of the short arm component 42. Further, as shown in Figure 1, each long arm component 44 includes a recess 58. The recess 58 is adapted to receive the distal end 52 and roller bearing 50 of the corresponding short arm component 42 when the centraliser arms 32 are compressed sufficiently by the drill rod wall 56 causing the centraliser arms 32 to retract and lie flat against the supporting shaft 18, as is shown in Figure 3.

[0056] When the centraliser arms 32 are in the retracted state, this allows each centraliser arm apparatus 12 to pass through very narrow sections of the drill rod and overcome strictures and other physical obstacles that may be encountered in the drill rod,

II

such as mechanical joints connecting drill rod sections together, when the survey tool is being conveyed.

[0057] Referring to Figure 2, the four centraliser arms 32 comprise a first pair 60 and a second pair 62 of centraliser arms. The first pair 60 are arranged such that the short arm component 42 and roller bearing 50 of each centraliser ar in the first pair 60 are disposed towards the first end 14 of the centraliser arm apparatus 12. Preferably, the two centraliser arms in the first pair 60 are each disposed on opposite sides of the longitudinal length of the centraliser ann apparatus 12 with respect to one another.

[0058] In contrast to the first pair 60, the second pair 62 of centraliser arms are arranged such that the short arm component 42 and roller bearing 50 of each centraliser ann in the second pair 62 are disposed towards the second end 16 of the centraliser am apparatus 12. The two centraliser arms in the second pair 62 are also each preferably disposed on opposite sides of the longitudinal length of the centraliser arn apparatus 12 with respect to one another.

[0059] Having the first and second pairs 60,62 of centraliser arms offset from one another in this manner additionally facilitates the passage of each centraliser arm apparatus 12 past any mechanical joints encountered when the survey tool is being conveyed along the course of the drill rod, When the centraliser arm apparatus 12 passes over a mechanical joint, the arrangement provides that there is always at least two roller bearings 50 in contact with the inner wall 56 of the drill rod at any one point in time.

[0060 Referring to Figure 1, each roller bearing 50 rotates about a rotational axis defined by its roll pin 54, The rotational axis is orientated such that it is offset slightly (not shown) from an angle that is perpendicular to the longitudinal length of the centraliser arm apparatus 12.

[0061] In one embodiment of the present invention, this offset or"pitch" angle is achieved by adjusting the angle of each roll pin 54 relative to its corresponding centraliser ann 40. In an alternative embodiment, the pitch angle is achieved by adjusting the angle of the short arm component 42 of each centraliser arm 40 relative to the longitudinal length of the centraliser arm apparatus 12.

[0062] The pitch angle causes the centraliser arms 32 to exert a rotational force on the ann supports 34,36 when the survey tool is conveyed along the course of the drill rod. This causes each centraliser arm apparatus 12 and, therefore, the survey tool to rotate at a controlled and uniform helicoidal manner along the course of the drill rod. This rotation eliminates the accumulation of any bias errors in the survey tool's sensors.

[0063] The pitch angle may be easily adjusted to control the rate of rotation, thus permitting the centraliser arm apparatus 12 to be used inside drillrods of a range of different diameters.

[0064] The pitch angle will typically be set so that the centraliser arm apparatus 12 produces a rotation of 900 degrees for every 5 metres of travel. In this configuration, one full rotation is achieved for every 20 metres of travel (at which point any bias errors in the sensors will be effectively eliminated).

[0065] The rotation that is achieved using the present invention is sufficiently accurate and uniform such that it may also be used as a check or reference for measuring borehole depth, which is of fundamental importance in borehole surveying. An estimated borehole depth may be calculated by dividing the number of rotations achieved during a survey run by the known number ofrotations per metre. Where two or more survey runs are conducted, the accuracy of the estimated depth can be improved by averaging the sum of the depth calculations obtained for the complete sequence of runs.

[0066] Referring to Figure 4, there is shown a pair of centraliser arm apparatuses 12 that have been attached to opposite ends of an elongated length of a survey tool 64 or protective apparatus enclosing the survey tool (for example, a pressure barrel).

[0067] The first connector 20 of each centraliser ann apparatus 12 has been attached to the survey tool 64. In use, known deployment means, such as a winched wireline, will be attached to the second connector 24 of one of the centraliser arm apparatuses 12 (not shown). The deployment means will then used to convey the centraliser apparatus down and along the course of the drill rod in the borehole that is to be surveyed. Each centraliser arm apparatus 12 will keep the survey tool positioned centrally in the drill rod and rotate the survey tool continually in a controlled manner, thus eliminating the accumulation of any bias errors in the survey tool's sensors.

[0068] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

L A controlled rotation centraliser apparatus for attachment to a survey tool or protective apparatus encasing the survey tool, the apparatus comprising a plurality of centraliser arms, wherein each centraliser arm comprises a: first arm component; second arm component; and roller bearing attached to the first arm component, and wherein each roller bearing is orientated at a pitch angle so that the apparatus rotates the survey tool when the survey tool is conveyed through a drill rod.
2. A controlled rotation centraliser apparatus according to claim 1, wherein the first arm component of each centraliser arm is shorter than the second arm component of the centraliser arm.
3. A controlled rotation centraliser apparatus according to claim 2, wherein the apparatus comprises at least four centraliserarms, wherein: at least two centraliser arms are arranged such that their first ann components are disposed towards a first end of the apparatus; and at least two centraliser arms are arranged such that their second ann components are disposed towards a second end of the apparatus.
4. A controlled rotation centraliser apparatus according to any preceding claim, wherein thefirst arm component of each centraliser arm is attached to the second arm component of the centraliser arm by a revolute or pin joint at an attachment point.
5. A controlled rotation centraliser apparatus according to claim 4, wherein the attachment point of each centraliser arm is located away from a distal end of the first arm component of the centraliser arm.
6. A controlled rotation centraliser apparatus according to claim 5, wherein the second arm component of each centraliser arm comprises a recess, wherein the recess is adapted to receive the roller bearing attached to the first arm component of the centraliser aim when the centraliser arms are in aretracted state.
7. A controlled rotation centraliser apparatus according to any preceding claim, comprising a: static arm support; moving arm support; and compression spring, wherein the compression spring and moving arm support biases the centraliser arms in an expanded state.
8. A controlled rotation centraliser apparatus according to claim 7, comprising a tensioning nut for increasing energy stored in the compression spring.
9. A controlled rotation centraliser apparatus according to any preceding claim, comprising an elongated supporting shaft extending between the first and second ends of the apparatus.
10. A method for centralising a survey tool within a drill rod, the method comprising the steps of: attaching a first controlled rotation centraliser according to any preceding claim to a first end of the survey tool or a protective apparatus encasing the survey tool; attaching a second controlled rotation centraliser according to any preceding claim to a second end of the survey tool or protective apparatus; and conveying the survey tool and the attached first and second controlled rotation centralisers along the length of the drill rod.