Device for centering a sensor assembly in a bore

Abstract

A centraliser comprises arm assemblies pivotally connected between first and second support members. Each arm assembly comprises a first arm and a first pivot joint having a first pivot axis, a second arm and a second pivot joint having a second pivot axis, the first and second arms pivotally attached together via a third pivot joint having a third pivot axis. The arm assemblies are arranged in diametrically opposed pairs. In some embodiments the first arm comprises a fork section to position the first pivot axis coincident with the central longitudinal axis of the device, or so that the first pivot axis and the third pivot axis are positioned on opposite sides of a plane coincident with the central longitudinal axis of the device.

Claims

1. A device for centering a sensor assembly in a bore, the device comprising: a first support member and a second support member axially spaced apart along a central longitudinal axis of the device, one or both of the first and second support members configured to move axially along the central longitudinal axis, a first pair of diametrically opposite arm assemblies and a second pair of diametrically opposite arm assemblies orthogonal to the first pair of diametrically opposite arm assemblies, each arm assembly comprising: a first arm and a first pivot joint having a first pivot axis, a second arm and a second pivot joint having a second pivot axis, the first and second arms pivotally attached together via a third pivot joint having a third pivot axis, and wherein the first arm comprises a fork section, and for each arm assembly in the first pair of diametrically opposite arm assemblies: the first arm is pivotally connected to the first support member by the first pivot joint, and the second arm is pivotally connected to the second support member by the second pivot joint, and the fork section extends around opposite sides of the first support member to position the first pivot axis coincident with a first plane coincident with the central longitudinal axis of the device or so that the first pivot axis and the third pivot axis are positioned on opposite sides of the first plane, and for each arm assembly in the second pair of diametrically opposite arm assemblies: the first arm is pivotally connected to the second support member by the first pivot joint, and the second arm is pivotally connected to the first support member by the second pivot joint, and the fork section extends around opposite sides of the second support member to position the first pivot axis coincident with a second plane coincident with the central longitudinal axis of the device or so that the first pivot axis and the third pivot axis are positioned on opposite sides of the second plane, wherein the second plane is orthogonal to the first plane.

2. The device as claimed in claim 1, wherein, in the first pair of diametrically opposite arm assemblies, the first pivot axes are coincident with the first plane, and in the second pair of diametrically opposite arm assemblies, the first pivot axes are coincident with the second plane.

3. The device as claimed in claim 1, wherein in each pair of diametrically opposite arm assemblies, the first pivot axes of the pair of arm assemblies are colinear, such that the first arms pivot on the respective first or second support member on a common pivot axis.

4. The device as claimed in claim 3, wherein in each pair of diametrically opposite arm assemblies: one of the first arms comprises a pair of colinear pivot pins spaced apart by the fork section, the other one of the first arms comprises a pair of colinear eyes spaced apart by the fork section, the eyes received on the pins, and the pins received in corresponding bearing portions on opposed sides of the respective first or second support member to pivotally connect the first arms to the respective first or second support member to pivot on the respective first or second support member on a common pivot axis.

5. The device as claimed in claim 1, wherein the first pair of diametrically opposite arm assemblies comprises a first said arm assembly and a second said arm assembly, and the first pivot axis of the first arm assembly is colinear with the first pivot axis of the second arm assembly, and the second pair of diametrically opposite arm assemblies comprises a third said arm assembly and a fourth said arm assembly, and the first pivot axis of the third arm assembly is colinear with the first pivot axis of the fourth arm assembly.

6. The device as claimed in claim 1, wherein, in the first pair of diametrically opposite arm assemblies, the first pivot axis and the third pivot axis are positioned on opposite sides of the first plane, and in the second pair of diametrically opposite arm assemblies, the first pivot axis and the third pivot axis are positioned on opposite sides of the second plane.

7. The device as claimed in claim 6, wherein the first pivot axes of the first pair of diametrically opposite arm assemblies are axially aligned at the first support member, and the first pivot axes of the second pair of diametrically opposite arm assemblies are axially aligned at the second support member.

8. The device as claimed in claim 6, wherein the fork sections of the first pair of diametrically opposite arm assemblies laterally cross over such that the first pivot axis and the third pivot axis of each arm assembly in the first pair of diametrically opposite arm assemblies are positioned on opposite sides of the first plane, and the fork sections of the second pair of diametrically opposite arm assemblies laterally cross over such that the first pivot axis and the third pivot axis of each arm assembly in the second pair of diametrically opposite arm assemblies are positioned on opposite sides of the second plane.

9. The device as claimed in claim 1, wherein the first arm of each arm assembly comprises an elongate section extending between the fork section and the third pivot joint.

10. The device as claimed in claim 1, wherein in each pair of diametrically opposite arm assemblies, the forked section of one first arm is received radially inside the fork section of the other first arm.

11. The device as claimed in claim 1, wherein the device comprises one or more spring elements to bias the first and second pairs of diametrically opposite arm assemblies radially outwards.

12. A device for centering a sensor assembly in a bore, the device comprising: a first support member and a second support member axially spaced apart along a central longitudinal axis of the device, one or both of the first and second support members configured to move axially along the central longitudinal axis, a plurality of arm assemblies pivotally connected between the first and second support members, wherein each arm assembly comprises: a first arm pivotally attached to one of the first and second support members by a first pivot joint having a first pivot axis, a second arm pivotally attached to the other one of the first and second support members by a second pivot joint having a second pivot axis, the first and second arms pivotally attached together via a third pivot joint having a third pivot axis, and wherein the first arm comprises a fork section extending around opposite sides of the respective first or second support member to position the first pivot axis coincident with the central longitudinal axis of the device.

13. A device for centering a sensor assembly in a bore, the device comprising: a first support member and a second support member axially spaced apart along a central longitudinal axis of the device, one or both of the first and second support members configured to move axially along the central longitudinal axis; a first pair of diametrically opposite arm assemblies and a second pair of diametrically opposite arm assemblies orthogonal to the first pair of diametrically opposite arm assemblies, each arm assembly comprising a first arm and a first pivot joint having a first pivot axis, a second arm and a second pivot joint having a second pivot axis, the first and second arms pivotally attached together via a third pivot joint having a third pivot axis, and for each arm assembly in the first pair of diametrically opposite arm assemblies: the first arm is pivotally connected to the first support member by the first pivot joint, the second arm is pivotally connected to the second support member by the second pivot joint, and the first pivot axis is coincident with a first plane coincident with the central longitudinal axis of the device, and for each arm assembly in the second pair of diametrically opposite arm assemblies: the first arm is pivotally attached to the second support member by the first pivot joint, the second arm is pivotally connected to the first support member by the second pivot joint, and the first pivot axis is coincident with a second plane coincident with the central longitudinal axis of the device, the second plane orthogonal to the first plane.

14. The device as claimed in claim 13, wherein the first arm of each arm assembly comprises a fork section extending around opposite sides of the respective first or second support member.

15. The device as claimed in claim 13, wherein the first pair of diametrically opposite arm assemblies comprises a first said arm assembly and a second said arm assembly, and the first pivot axis of the first arm assembly is colinear with the first pivot axis of the second arm assembly, and the second pair of diametrically opposite arm assemblies comprises a third arm assembly and a fourth arm assembly, and the first pivot axis of the third arm assembly is colinear with the first pivot axis of the fourth arm assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An example embodiment of the invention is now discussed with reference to the Figures.

(2) FIG. 1 is a schematic representation of a well site and a tool string descending a wellbore in a wireline logging operation.

(3) FIGS. 2A to 2F provide schematic representations of a centralising device (a centraliser) according to one example of the present invention. FIG. 2A is a side view of the centraliser with arm assemblies of the centraliser in a radially outward position corresponding with a larger wellbore diameter. FIG. 2B is a side view with the arm assemblies in a radially inward position corresponding with a smaller wellbore diameter. FIG. 2C is an end view of the centraliser in the radially outward position. FIG. 2D is an end view of the centraliser in the radially inward position. FIGS. 2E and 2F are isometric views again showing the arm assemblies in the radially outward and radially inward positions.

(4) FIGS. 3A to 3F provide schematic representations of a centralising device according to another example of the present invention. FIG. 3A is a side view of the centraliser with arm assemblies of the centraliser in a radially outward position corresponding with a larger wellbore diameter. FIG. 3B is a side view with the arm assemblies in a radially inward position corresponding with a smaller wellbore diameter. FIG. 3C is an end view of the centraliser in the radially outward position. FIG. 3D is an end view of the centraliser in the radially inward position.

(5) FIGS. 3E and 3F are isometric views again showing the arm assemblies in the radially outward and radially inward positions.

(6) FIGS. 4A to 4C show a sliding support member and two pivotally attached first arms of the centralisers of FIGS. 2A to 2F and 3A to 3F. FIG. 4A is a sectional view on line A-A in FIG. 4B, FIG. 4B is a side view, and FIG. 4C is an exploded trimetric view. The first arms are pivoted to a position intermediate the radially inward and radially outward positions.

(7) FIGS. 5A to 5F provide schematic representations of a centralising device according to another example of the present invention. FIG. 5A is a side view of the centraliser with arm assemblies of the centraliser in a radially outward position corresponding with a larger wellbore diameter. FIG. 5B is a side view with the arm assemblies in a radially inward position corresponding with a smaller wellbore diameter. FIG. 5C is an end view of the centraliser in the radially outward position. FIG. 5D is an end view of the centraliser in the radially inward position.

(8) FIGS. 5E and 5F are isometric views again showing the arm assemblies in the radially outward and radially inward positions.

(9) FIGS. 6A and 6B FIG. 6A is a side view of a sliding support member and two pivotally attached first arms of the centraliser of FIG. 5A to 5F, and FIG. 6B a trimetric view of the arms with the support member and pivot pins of first pivot joints omitted.

BEST MODES FOR CARRYING OUT THE INVENTION

(10) FIG. 1 provides a schematic representation of a well site 100. A logging tool string 101 is lowered down the wellbore 102 on a wireline 103. Wellsite surface equipment includes sheave wheels 104 typically suspended from a derrick and a winch unit 105 for uncoiling and coiling the wireline to and from the wellbore, to deploy and retrieve the logging tool 101 to and from the wellbore to perform a wellbore wireline logging operation. The logging tool string 101 may include one or more logging tools each carrying one or more sensors 106 coupled together to form the logging tool string 101. The wireline 102 includes a number of wires or cables to provide electrical power to the one or more sensors 106 and transmit sensor data to the wellsite surface. One or more centralising devices 1 are provided to the logging tool 101 to centralise the logging tool 101 in the wellbore 102.

(11) FIGS. 2A to 2F illustrate a centralising device 1 to be provided with or as part of the tool string 101. The centralising device (or centraliser) comprises a coupling 2 or interface (illustrated schematically) at each end to connect the centraliser 1 to other components of the tool string 101. The couplings may include electrical or hydraulic connections to provide electrical and hydraulic communication from the wireline to the wireline logging tool and/or between wireline tools. Alternatively, the centraliser device may be integral with the wireline logging tool, e.g. the outer housing of the logging tool may form a central mandrel of the centraliser. Alternatively, the centraliser device may slip over the outside of the wireline logging tool (housing) thereby avoiding any electrical or hydraulic connections with the tool string and wireline. The couplings or interfaces may be any suitable coupling or interface known in the art.

(12) A plurality of arm assemblies (linkages) 3 are spaced circumferentially apart around a longitudinal axis 4 of the device 1. The arm assemblies 3 are configured to move axially and radially to engage the wellbore wall 102a to provide a centering force to maintain the tool string 101 in the centre of the wellbore 102.

(13) The arm assemblies 3 are pivotally coupled between two support members, a first support member 7 and a second support member 8. Each arm assembly or linkage comprises a first arm or link 5 pivotally connected to one of the support members 7, 8 by a first pivot joint 11 having a first pivot axis 11a, and a second arm or link 6 pivotally connected to the other one of the support members 7, 8 by a second pivot joint 12 having a second pivot axis 12a. The first and second arms 5, 6 a pivotally attached via a third pivot joint 13 having a third pivot axis 13a. One or both of the support members 7, 8 are configured to move axially along a longitudinal axis 4 of the device 1 to cause the arm assemblies to move radially to engage the wellbore wall by pivoting of the first and second arms 5, 6 about the respective first 11a, second 12a and third 13a pivot axes. One or both support members 7, 8 may slide axially on a central member or mandrel 10 of the centraliser or on a body of the tool string. The support members may comprise a collar or annular member colinear with and received on the mandrel 10 to slide thereon. The support members 7, 8 may be keyed to the mandrel to rotationally fix the support members to the mandrel so that the support members move axially on the mandrel without relative rotation between the support members and the mandrel.

(14) Each arm assembly 3 carries a roller or wheel 14 (herein wheel) to contact the wellbore wall to reduce friction between the wellbore wall 102a and the tool string 101 as the tool string 101 traverses the well bore 102. The wheel 14 is located at or adjacent the third pivot joint 13. The wheel 14 may have a rotational axis colinear with the pivot axis 13a of the third pivot joint 13 as shown in FIG. 2A or may be located adjacent the third pivot joint 13, for example the wheel may be rotationally mounted to the first arm 5 or the second arm 6 adjacent the third pivot joint 13. Springs 9 (most visible in FIG. 2A) are provided to bias the arm assemblies 3 radially outwards against the wellbore wall 102a, to center the centraliser 1 and connected tool string in the wellbore.

(15) A mechanical stop 15 may be provided on the mandrel to set a maximum diameter for the centraliser 1. Each stop 15 limits axial movement of the respective support member 7, 8 to limit the radial outward movement of the arm assemblies 3 and therefore the outer diameter of the device 1. The radial extremities of the centraliser provided by the wheels 14 together present or define the outer diameter of the centraliser. The springs 9 provide a radial force to the arm assemblies 3 with the wheels 14 at the maximum outer diameter so that the centraliser supports the sensor assembly at the maximum outer diameter as it traverses along a bore. Prior to running the centraliser into a bore or where the centraliser 1 enters a large diameter section in the wellbore, the mechanical stops 15 prevent the arm assemblies 3 extending radially outside a desired diameter range, to avoid for example difficulties with inserting the device 1 into a bore or passing from a larger diameter to a smaller diameter section of the wellbore or passing through a wellhead control assembly.

(16) The first arm 5 of each arm assembly 3 comprises a fork section comprising two limbs 16, 17. The fork section extends around opposite sides of the corresponding or respective support member 7, 8 relative to a plane in which the arm assembly moves radially between radially inward and radially outward positions. The limbs 16, 17 of the fork of the first arm 5 extend on opposed sides of the support member 7, 8. By extending around opposed sides of the support member 7, 8, the fork section positions the first pivot axis 11a further from the third pivot axis 13a, thereby increasing the effective length of the first arm 5 compared to an arm comprising a first pivot axis on a side of the support member 7, 8 facing the third pivot joint. Positioning the first pivot axis 11a further from the third pivot joint via the fork section extending around opposed sides of the support member also increases an angle of the first arm relative to the longitudinal axis 4 of the device 1.

(17) Extending the arm length increases a bore diameter range over which the centraliser 1 can operate. Furthermore, increasing the minimum arm angle improves the coupling of the arm assemblies 3 together, since a larger arm angle results in a greater axial displacement of the support member 7, 8 for a given radial displacement of the arm assembly 3. Effective coupling the radial movement of the plurality of arm assemblies 3 is critical to ensure the arm assemblies act together in unison to accurately centralise the device and tool string in the bore. To ensure effective coupling between the arm assemblies 3, the arm angle (angle A, FIG. 4B) between at least one of the arms in the arm assemblies should not be less than about 10 degrees. Preferably the minimum angle of at least one of the two arms 5, 6 should be at least 10 degrees, or at least 15 degrees, or at least 20 degrees, or at least 25 degrees. In the illustrated embodiment, the minimum angle of the first arm when the arm assemblies are in the radially inwards position is 25 degrees.

(18) It is to be understood that the angle between an arm and the central axis is an angle between a line extending through the pivot axes at respective ends of the arm and the longitudinal axis of the device 1. For example, with reference to FIG. 4B, the angle between the first arm 5 and the longitudinal axis 4 is the angle A between a line extending through the first and third pivot axes 11a, 13a and the longitudinal axis 4. It is to be understood that the effective length of the arm is the distance between the pivot axes at respective ends of the arm. For example, the length of the first arm 5 is the distance between the first and third pivot axes 11a, 13a.

(19) In the illustrated example device 1, the fork section extends around opposed sides of the support member 7, 8 so that the first pivot axis 11a is coincident with the longitudinal axis 4 of the device 1. Alternatively, as described below with reference to FIGS. 5A to 5F, the fork section may extend around opposed sides of the support member 7, 8 so that the first pivot axis 11a is on an opposite side of a plane 4A, 4B coincident with the longitudinal axis 4 of the device 1 to the third pivot axis 13a, in other words, the first 11a and third 13a pivot axes are on opposite sides of the plane 4A, 4B. The fork section may extend around opposed sides of the support member 7, 8 so that the first pivot axis 11a is located radially within an outer diameter of the mandrel 10 on which one or both support members move. For example, in a further alternative embodiment, the first pivot 11a and third pivot 13a axes may be located on the same side of the plane 4A, 4B, with the first pivot axis 11a located radially within the OD of the mandrel 10. However, such an arrangement is less preferred as not extending the length of the arm 5 or increasing the arm angle A to such an extent as achieved by moving the first pivot axis further from the third pivot axis 13a. In the illustrated example, the second pivot axis 12a is on the same side of the plane 4A, 4B to the third pivot axis 13a.

(20) The arm assemblies 3 must be located within a limited annular space between the mandrel 10 and the inner diameter of the bore 102. The forked arm arrangement achieves a compact configuration for efficient utilisation of the available annular space.

(21) A compact arm assembly arrangement is further achieved by arranging the arm assemblies 3 in two diametrically opposite pairs—a first pair 3a of diametrically opposite arm assemblies and a second pair 3a of diametrically opposite arm assemblies, as illustrated in the example of FIGS. 2A to 2F, such that the centraliser 1 has four arm assemblies 3. A diametrically opposite pair of arm assemblies means the two arm assemblies of the pair are positioned on opposite sides of the central mandrel 10 to be azimuthally misaligned by 180 degrees with respect to the central longitudinal axis 4 of the device 1. With the arm assemblies diametrically opposite, the wheels 14 of the pair of arm assemblies are azimuthally misaligned by 180 degrees to contact the wellbore wall on opposite sides of the well bore. The second pair 3b of arm assemblies is orthogonal to the first pair 3a of arm assemblies, such that the arm assemblies 3 (and wheels 14 of the device 1) are azimuthally spaced apart by 90 degrees. Thus, the pivot axes 11a, 12a, 13a of the pivot joints 11, 12, 13 of the arm assemblies in the first pair 3a are orthogonal to the pivot axes 11a, 12a, 13a of the pivot joints 11, 12, 13 of the arm assemblies in the second pair 3b.

(22) The two pairs of arm assemblies 3 are arranged so that the first arms 5 of the arm assemblies 3 in the first pair are pivotally coupled to the first support member 7, and the first arms 5 of the arm assemblies 3 in the second pair are pivotally coupled to the second support member 8. This arrangement provides for two diametrically opposite forked arm connections at each support member 7, 8 and avoids interference between the forked arms at each support member as the arms pivot between radially inward and radially outward positions.

(23) In the illustrated example, to accommodate the first 11 and second 12 pivot joints at each support member 7, 8, the first pair of diametrically opposite arm assemblies is axially offset from the second pair of diametrically opposite arm assemblies, with the second pivot joints 12 located towards an axially inward side of the first pivot joints 11, i.e. the second pivot joints 12 of the first (or second) pair of arm assemblies are located axially between the first pivot joints 11 of the first (or second) pair of arm assemblies and the first pivot joints 11 of the second (or first) pair of arm assemblies. This results in the first arms being at distal ends of the device 1 such that when the device 1 passes from a larger bore diameter to a smaller bore diameter, a step in the bore diameter impacts the first arm. This may achieve a benefit whereby a lower force is required to move the centraliser 1 into the smaller diameter bore section of the bore since the impact is applied to a longer moment arm provided by the positioning of the first pivot axis 11a away from the third pivot axis 13a, increasing a torque applied to deflect the spring elements 9 to move the arm assemblies radially inwards.

(24) In the illustrated example of FIGS. 2A to 2F, the first pivot axes 11a are coincident with (i.e. intersecting) the central longitudinal axis 4 of the device 1. With the arm assemblies 3 arranged in two orthogonal diametrically opposite pairs, the first pivot axes 11a in the first pair of arm assemblies 3 are coincident with a first plane 4A (refer FIG. 2C) coincident with the central longitudinal axis 4 of the device 1, and the first pivot axes 11a in the second pair of arm assemblies are coincident with a second plane 4B (refer FIG. 2C) coincident with the central longitudinal axis 4 of the device 1, with the second plane 4B orthogonal to the first plane 4A. In the first pair, the second pivot axis 12a is on the same side of the plane 4A to the third pivot axis 13a, and in the second pair, the second pivot axis 12a is on the same side of the plane 4B to the third pivot axis 13a.

(25) The first pivot joints 11 in each pair of arm assemblies 3 may be axially offset at each support member, by axially offsetting the two arm assemblies in each pair of arm assemblies. Alternatively, and as illustrated by the example of FIGS. 2A to 2F, in each pair of diametrically opposite arm assemblies, the first pivot axes 11a of the pair of arm assemblies 3 are colinear, such that the first arms 5 pivot on the respective first or second support member 7, 8 on a common pivot axis 11a. Such an arrangement makes for efficient use of the annular space between the mandrel 10 and the bore wall, achieves a shorter length device 1 and/or reduces complexity.

(26) To achieve colinear first pivot axes at the support member, with reference to FIGS. 4A to 4C, in each pair of arm assemblies 3, one of the first arms 5a comprises a pair of colinear pivot pins 18 spaced apart by the fork section of the first arm 5a. The pins 18 are received in corresponding bearing portions 20 on opposed sides of the support member 7, 8 to pivotally connect the first arm 5a to the support member 7, 8. The other one of the first arms 5b in the pair of arm assemblies 3 comprises a pair of colinear eyes 19 spaced apart by the fork section of the first arm 5b. The eyes 19 are received on the pins 18, such that the pair of first arms 5a, 5b are pivotally connected to pivot on the support member 7, 8 on a common pivot axis 11a. In this example, the first pivot joint 11 for one arm 5a comprises the two pivot pins 18 and the corresponding bearing portions 20, and the first pivot joint for the other arm comprises the two eyes 19, the two pins 18 and the two bearing portions 20.

(27) As best shown in FIG. 4C, the first arm 5a comprising the pivot pins 18 is provided in two parts, each part providing one limb 16, 17 of the fork section with a corresponding pin 18. The two parts are assembled on the support member 7, 8 with the pins 18 received in the bearing portions 20 and the eyes 19 of the fork section of the other first arm 5b received on the pins 18, to retain and pivotally connect both first arms 5a, 5b to the support member 7, 8. Thus, the first arm 5b comprising a fork section with eyes 19 is captured between the support member 7, 8 and the first arm 5a comprising a fork section with pins 18. The first arm comprising eyes may be formed as a single unitary member, i.e. not assembled from more than one part. The limbs of the fork section of one first arm 5b are received radially inside the limbs of the fork section of the other first arm 5a.

(28) In the illustrated embodiment of FIGS. 2A to 2F, each first arm comprises the forked section and an elongate section (a single elongate section) extending between the fork section and the third pivot joint 13, i.e. the arm comprises an elongate section extending from the third pivot joint 13 and divides into the two limbs 16, 17 of the fork section to extend around the respective support member 7, 8. The elongate section pivots in a plane coincident with the central longitudinal axis 4 of the device, e.g. as shown by arm 5b in FIG. 2A. Again, with reference to FIGS. 4A to 4C, in the illustrated example, the two parts of the first arm 5a with pivot pins 18 each comprise a fork limb 16 or 17 and a portion of the elongate section of the arm 5a. The two parts of the arm 5a are clamped or held together at the elongate section of the arm by fasteners.

(29) The example device of FIGS. 2A to 2F comprises leaf springs to bias the arms assemblies 3 radially outwards. A spring 9 is provided to each arm assembly. The leaf spring 9 is mounted to a support member 7, 8 to act between the support member 8 and the arm assembly 3 to provide a radial outward force to the arm assembly 3. The illustrated example, each spring 9 is mounted to the second support member 8. Each spring 9 acts against a corresponding second arm 6, to bias the arm assemblies 3 radially outwards. The illustrated example comprises a spring 9 per arm assembly, however, a device may comprise one or more springs acting on one arm assembly, or two arm assemblies, or all of the arm assemblies as illustrated. Alternatively, one or more springs may act between the mandrel 10 and the arm assembly 3 or assemblies 3.

(30) In the alternative example of FIGS. 3A to 3F, the centraliser 201 has an axial spring 209 acting on each support member 207, 208 to bias the support members 207, 208 axially together to thereby bias the arm assemblies 203 radially outwards against the wellbore wall 102a. Where one of the support members 207, 208 is fixed against axial movement, the centraliser 201 is without a spring acting on the fixed support member. The axial spring(s) 209 may be coil springs that are colinear with the mandrel 210 as shown in the illustrated embodiment or may include a plurality of coil springs arranged circumferentially (azimuthally spaced apart) around the mandrel.

(31) Those skilled in the art will understand that other types of springs and spring configurations may be used to power the centraliser such as torsion springs and Belleville Washers for example. A combination of two or more spring devices may also be used, for example one or more springs may be provided end-to-end to impart a combined non-linear spring rate. Alternatively, the pitch of the coil spring may vary over its length to provide a non-linear spring rate. A centraliser according to the present invention may have only axial springs, only radial springs, or a combination of both axial and radial springs. A combination of both axial and radially acting springs may be used to provide a relatively constant radial force.

(32) Device 201 has many of the same or similar parts/features as described above with reference to the example device of FIGS. 2A to 2F. Same or similar parts/features already described above with reference to FIGS. 2A to 2F are identified by the same reference numerals in FIGS. 3A to 3F but with an added prefix of ‘2’ or ‘20’. The device of FIGS. 3A to 3F is therefore not described for brevity, other than noting the difference in spring configuration between the two example devices 1, 201 described in the above preceding paragraphs. It is also noted that the incorporation of axial springs may achieve a reduction in overall length of the device 1, 201. Leaf springs 9 may require longer arm assemblies 3 to incorporate the leaf springs acting on one of the arms in one or more arm assemblies. Axial springs 221 arranged as shown in FIGS. 3A to 3F add length to the device 201 beyond the support members 207, 208, however, a length reduction may be achieved by having a spring 221 acting on one support member 207, 208 only, or by incorporating axial springs arranged circumferentially (azimuthally spaced apart) around the mandrel interposed between adjacent arm assemblies 203, as described in U.S. Pat. No. 11,136,880, the contents of which are incorporated herein by reference.

(33) For an axial spring configuration, the arm angle may be maintained within a range to achieve a relatively constant radial force. The arm assemblies provide a mechanical advantage (mechanical leverage) between the axial displacement and the radial displacement to provide, in combination with the axial spring elements 221, a radial force to the bore wall 102a. The mechanical advantage changes with the axial and radial position of the arm assemblies 203. The mechanical advantage of each arm assembly 203 may be expressed as Fr/Fa, where Fa is the axial force provided by the axial spring element(s) 221 on the arm assembly and Fr is the resulting radial force applied to the wellbore wall 102a. As the mechanical advantage increases, the radial force, transferred from the axial spring force to the wellbore wall increases. The mechanical advantage is dependent on the angle between each arm and the centreline of the device and increases as the angle increases. Thus, the mechanical advantage of the arm assembly 203 increases with increasing well bore diameter. In balance with the mechanical advantage, the spring(s) 221 provide(s) a force that decreases with increasing wellbore diameter, since the support members 207, 208 slide axially to decompress the spring. Conversely, as the wellbore diameter decreases, the mechanical advantage decreases and the axial spring force increases as the spring is further compressed by the sliding support member 207, 208. To achieve a relatively constant force, the arm angle of at least one of the arms 5, 6 should be much greater than 10 degrees and much less than 75 degrees. The angle is preferably maintained in a range of 20 to 70 degrees, or more preferably 25 to 65 degrees. In the illustrated embodiment, the arm angle for the first arm 205 is in the range of 25 degrees to 60 degrees as the arm assemblies move from the radially inwards position to the radially outwards position.

(34) FIGS. 5A to 5F illustrate a further example of a centralising device 301 with arm assemblies 303 each comprising an arm 305 with a fork section extending around opposed sides of a corresponding or respective support member 307, 308. Parts/features in the example of FIGS. 5A to 5F that are the same as or similar to parts/features in the example of FIGS. 2A to 2F and already described above are identified by the same reference numerals appearing in FIGS. 2A to 2F but with an added prefix of ‘3’ or ‘30’. The same or similar features or configurations are not described again for brevity.

(35) In each arm assembly 303, limbs 316, 317 (refer FIG. 6B) of the fork section of the first arms 305 extend around opposed sides of the support member 307, 308. As briefly mentioned above, in the example of FIGS. 5A to 5F, for each arm assembly 303, the fork section extends on opposed sides of the respective support member 307, 308 so that the first pivot axis 311a is on an opposite side of a plane 4A, 4B coincident with the longitudinal axis 4 of the device 301 to the third pivot axis 313a, or in other words, the first pivot axis 311a and the third pivot axis 313a are positioned on opposite sides of the plane 4A, 4B.

(36) Like the configuration described above for the example of FIGS. 2A to 2F, in the example of FIGS. 3A to 3F, the arm assemblies 303 are arranged in two diametrically opposite pairs 303a, 303b. The two pairs 303a, 303b of arm assemblies 303 are arranged so that the first arms 305 of the arm assemblies 303 in one pair (first pair 303a) are pivotally coupled to the first support member 307, and the first arms 305 of the arm assemblies 303 in the other pair (second pair 303b) are pivotally coupled to the second support member 308. This provides for two diametrically opposite forked arm connections at each support member 307, 308 and avoids interference between the forked arms at each support member as the arms pivot between radially inward and radially outward positions.

(37) With the arm assemblies 303 arranged in two orthogonal diametrically opposite pairs, in each arm assembly 303 in the first pair of diametrically opposite arm assemblies, the first pivot axis 311a and the third pivot axis 313a are positioned on opposite sides of the first plane 4A (ref FIG. 5C) coincident with the central axis 4 of the device 301, and for each arm assembly in the second pair of diametrically opposite arm assemblies 303, the first pivot axis 311a and the third pivot axis 313a are positioned on opposite sides of a second plane 4B (refer FIG. 5C) coincident with the central longitudinal axis of the device, with the second plane orthogonal to the first plane. In the first pair, the second pivot axis 312a is on the same side of the plane 4A to the third pivot axis 313a, and in the second pair, the second pivot axis 312a is on the same side of the plane 4B to the third pivot axis 313a.

(38) With reference to FIGS. 6A and 6B, in the example of FIGS. 5A to 5F, to accommodate the two first arms 305 of the diametrically opposite arm assemblies 303 at the respective support member 307, 308, the fork section of one of the first arms 305a laterally crosses over the fork section of the other one of the first arms 305b, as shown in the side view of FIG. 6A, i.e. the limbs of one fork section cross the limbs of the other fork section. The fork sections are laterally offset, with each fork section having one limb laterally outside and one limb laterally inside the fork section of the other first arm, as shown in FIG. 6B, such that the fork sections laterally cross over without interference between the arms. In the illustrated embodiments, the two first arms 305a, 305b are identical, with one arm 305a rotated 180 degrees relative to the other arm 305b. Alternatively, the fork section of one first arm 305a may be received radially inside (with respect to the central axis of the device) the fork section of the other first arm 305b, i.e. the limbs 316, 317 of the forked section of one first arm 305b may be received radially inside the limbs 316, 317 of the fork section of the other first arm 305a. In each pair of arm assemblies, the first pivot axes 311a of the two arm assemblies (at the respective support member 307, 308) are axially aligned.

(39) In each pair of arm assemblies 303, the fork section of each of the first arms 305a, 305b is pivotally connected to the support member by a pivot pin extending through the support member and eyes 319 (FIG. 6B) of the fork section. Alternatively, the pivot joint may comprise pins (stub axles) on the support member or the fork section of one or both first arms may comprise a pair of colinear pivot pins spaced apart by the fork section of the first arm, the pins received in corresponding bearing portions on opposed sides of the support member 307, 308.

(40) In the illustrated example, the first arms 305 are each provided as single unitary members. Alternatively, one or both first arms may be provided in two parts, e.g. each part providing one limb 316, 317 of the fork section, e.g. in a similar assembly to the arm of the earlier example device 1. As described for the example of FIGS. 2A to 2F, each first arm comprises the fork section and a single elongate section extending between the fork section and the third pivot joint 313.

(41) The example device of FIGS. 5A to 5F comprises axial springs 321 acting on the support members 307, 308, like in the example of the device of FIGS. 3A to 3F. However, the device of FIGS. 5A to 5F may include alternative spring arrangements as described earlier, such as radial springs acting on the arm assemblies, like the leaf spring arrangement in the example embodiment of FIGS. 2A to 2F.

(42) The relative positioning of the pivot axes is achieved by the first arms having fork sections. However, the relative positioning of the pivot axes may be achieved by an arm without a fork section, the arm extending on one side of the support member only, by for example an arm extending approximately helically around the mandrel. However, such an arrangement is less preferred as the centering force applied by the arm assemblies against the wellbore wall may result in a torque applied to the support member and pivot joints.

(43) A centraliser according to one or more aspects of the present invention as described above provides one or more of the following benefits. The relative positioning of the arm assembly pivot points effectively increases the length of the arm of the arm assemblies for a given diameter and length centraliser, improving the bore diameter range over which the centraliser can operate. Furthermore, the minimum arm angle is increased which improves the coupling between the plurality of arm assemblies to ensure the arms act together to effectively centralise the device in the bore. An increase in minimum arm angle is also beneficial for ensuring a satisfactory mechanical advantage particularly important where axial spring(s) acting on the support member(s) are utilised.

(44) Further, increasing the minimum arm angle can assist in achieving a constant radial centering force. The disclosed arm arrangements can also present a longer moment arm to reduce the force required to collapse the centraliser when moving into a bore or lower diameter section of a bore. The described arm arrangements achieve compact arm configurations for efficient utilisation of the available annual space between the mandrel or sensor assembly and the ID of the wellbore, may achieve a shorter length device, and reduce complexity. Furthermore, the centraliser is a passive device, with energisation being provided by the mechanical spring components 9, 221, 321 only. No other power input, such as electrical or hydraulic power provided from service located power units is required. The invention therefore provides a lower cost, effective, and simplified device that provides improved operational reliability and accuracy of logged data.

(45) The invention has been described with reference to centering a tool string in a wellbore during a wireline logging operation. However, a centralising device according to the present invention may be used for centering a sensor assembly in a bore in other applications, for example to center a camera in a pipe for inspection purposes.

(46) Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the spirit or scope of the appended claims. 1 Centraliser 2 Coupling 3 Arm assembly 3a a first pair of diametrically opposite arm assemblies 3 3b a second pair of diametrically opposite arm assemblies 3, orthogonal to the first pair 3a 4 Central axis 4A plane coincident with the central axis 4 4B plane coincident with the central axis 4 orthogonal to plane 4A 5 First Arm 5a and 5b first arms 6 Second Arm 7 First support member 8 Second support member 9 Spring 10 Mandrel 11 First pivot joint 12 Second pivot joint 13 Third pivot joint 14 Wheel 15 stops on the mandrel 16 limb of fork 17 limb of fork 18 pivot pins 19 eyes 20 bearing portions 221 spring 321 spring