Mill assembly

Abstract

A mill assembly (1) for milling a well casing, comprising a mill (5) with a mill body (9) The mill body (9) has a socket (15) and a locking member (17) that is arranged at least partially inside the socket and that is movable between an engaged position and a retracted position. The mill assembly further has a biasing member (31) biasing the locking member towards the retracted position. The locking member (17) comprises a shear element bore (37) receiving a shear element (39), and a whipstock engagement portion (17a) with a whipstock engagement profile (19). A method is also disclosed.

Description

MILL ASSEMBLYTechnical Field

[0001] The present disclosure relates to a mill assembly for use in a drilled well, for instance a subsea well.Background Art

[0002] Mill assemblies have been applied for a long time in wells to drill deviated bores. A whipstock is installed in the well, and the milling tool is used to drill through the casing as the whipstock causes the mill to deviate from the original wellbore.

[0003] It has become common to connect the whipstock to the mill in a detachable manner, so that they can both be run into the well with one single trip. Once the whipstock is installed, the mill must be disconnected from the whipstock before the milling can commence. There are several ways to obtain this disconnection function. Some solutions apply use of hydraulic pressure to actuate a disconnection actuator. Other solutions use one or more shear elements that are shorn off by applying sufficient force to the mill when the whipstock is securely anchored in the wellbore.

[0004] Since the cost of rig time is significant, focus on fast installation of the whipstock has increased. The operator wishes to run the assembly down into the well with significant speed to save time. However, excessive speed puts high demands on the connection between the whipstock and the mill. One cannot risk the connection to disconnect before the whipstock has been run to the desired position and anchored.

[0005] US10871034 discloses a whipstock assembly where the mill is disconnected from the whipstock by shearing off a shear bolt. Furthermore, an additional support member is arranged for transferring torsion forces between the mill and the whipstock.

[0006] A similar solution is disclosed in US11142996, where a shear bolt is shorn off when disconnecting.

[0007] A solution which applies a hydraulic actuator is described in US11519234 B2. In this solution, the mill connects to the whipstock with a retractable pin which is biased to move into the mill body. A hydraulic release mechanism maintains theretractable pin in a connecting state until the release mechanism is operated to release the pin and hence disconnect the mill from the whipstock. A similar solution is shown in US10704328 B2.Summary of invention

[0008] There is disclosed a mill assembly for milling a well casing, the assembly comprising a mill with a mill body. The mill body has a socket and a locking member that is arranged at least partially inside the socket and is movable between an engaged position and a retracted position. The mill assembly further comprises a biasing member biasing the locking member towards the retracted position. The locking member comprises a shear element bore receiving a shear element, and a whipstock engagement portion with a whipstock engagement profile.

[0009] When the locking member is in its engaged position, it is in an outer position, wherein it can be in engagement with a mill engagement profile of a whipstock, such as for connecting the mill to the whipstock. When in the retracted position, it has been moved further into the socket.

[0010] By having one or more biasing members, for instance one or more retraction springs, that bias the locking member towards the retracted position, the locking member will be moved into the mill body when the mill is disconnected from the whipstock.

[0011] The locking member may further comprise a shear element spring biasing the shear element outwardly of the shear element bore. As will be discussed further below, this facilitates connection of the mill assembly to a whipstock.

[0012] The mill assembly may further comprise a mounting bore that extends between an outer face of the mill body and the socket. The mill assembly further comprises a mounting bolt retaining means configured to releasably retain a mounting bolt that engages the locking member.

[0013] The term bolt shall be broadly construed, as it can be a screw or a pin, or another element that is received in the bolt bore and connects the locking member to the mill body. The mounting bolt retaining means can advantageously be in the form of threads inside the mounting bore. The threads can engage with the mounting bolt.

[0014] In some embodiments, the locking member comprises a bolt bore with a bolt that connects the locking member to the mill body, and the biasing member.

[0015] In some embodiments, the mill body can comprise the biasing member. For instance, the biasing member can be arranged inside a bolt bore of the mill body.

[0016] As will be discussed further below, the locking member may have two bolt bores and two biasing members, typically in the form of retraction springs. It may, however, also have more than two bolt bores and more than two biasing members.

[0017] The locking member has an axial dimension, a radial dimension, and a crosswise dimension being crosswise to the axial and radial dimensions.Advantageously, the locking member may extend longer in the axial and radial dimensions than in the crosswise dimension.

[0018] This shape enables transfer of large axial forces between the mill onto the whipstock into the well, i.e. axially forward. Furthermore, it enables a sufficient pulling force to shear off the shear element.

[0019] Moreover, the shape enables the mill to accommodate the locking member without impacting the milling function of the mill when the locking member is in the retracted position.

[0020] The locking member may comprise two side-faces that are parallel and that face in the crosswise direction. In other embodiments, the two side-faces may exhibit an angle with respect to the axial direction, while extending along the radial direction.

[0021] In some embodiments, the mill assembly further comprises a whipstock with a mill engagement profile, wherein the whipstock engagement profile of the locking member is in engagement with the mill engagement profile of the whipstock. The mill engagement profile can advantageously be an axially extending mill engagement profile.

[0022] There is thus provided a mill assembly with a quick-connection between the mill and the whipstock.

[0023] In such embodiments, the whipstock may comprise a whipstock recess and the shear element can advantageously be in engagement with the whipstock recess.

[0024] The term whipstock recess shall be understood to mean an arrangement with an edge or groove that will halt the movement of the shear element towards the well surface (axially rearwards) when the shear element engages with or abuts against the whipstock recess. The whipstock recess can thus for instance be a hole, a shoulder, a step, or an edge that can abut against the shear element when in the engaged state.

[0025] Thus, when the mill is connected to the whipstock, the engagement between the locking member and the mill engagement profile prevents mutual movement in a radial direction and an axial forward movement of the mill with respect to the whipstock. Furthermore, the engagement between the shear element and the whipstock recess prevents axial rearward movement of the mill with respect to the whipstock. However, since it is a shear element, it can be shorn off to allow such axial rearward mutual movement if sufficient force is applied. Typically, the operator will anchor the whipstock in the well to enable a sufficient pulling force for shearing off the shear element.

[0026] In some embodiments, the whipstock engagement profile can comprise a collar and the mill engagement profile can comprise a shoulder that engages the collar. The shoulder can advantageously be an axially extending shoulder.

[0027] The whipstock engagement profile can comprise a U-shaped collar. The collar will fit below the shoulder of the mill engagement profile. In other embodiments, the whipstock engagement profile can comprise a first collar and a second collar, arranged on respective sides of the locking member. Only one collar on one side of the locking member may also suffice in some embodiments.

[0028] The whipstock can advantageously comprise a guide face that is inclined with respect to the axial direction of the mill assembly.

[0029] The guide face can move the shear element, such as a shear bolt, into the shear element bore during connection of the mill to the whipstock. Once the shear element reaches the whipstock recess, the shear element can snap into the whipstock recess.

[0030] With such a mill assembly, the operator is enabled to run the assembly down the well with significant speed and force without unintentionally detaching the millfrom the whipstock. Once the whipstock is anchored in the well, the operator can disconnect the mill from the whipstock with a pull that shears off the shear element.

[0031] Also disclosed herein is a method of connecting a mill, of a mill assembly as presented above to a whipstock. The method comprisesb) sliding the whipstock engagement profile in an axial direction along an axially extending mill engagement profile of a whipstock until the shear element aligns with a whipstock recess of the whipstock and moves crosswise to the axial direction into engagement with the whipstock recess.

[0032] In some embodiments of the method, it further comprises, before step b), a) retaining the locking member in the engaged position by fixing a mounting bolt to the mill body and in engagement with the locking member. Furthermore, the method can comprise, after step b),c) removing the mounting bolt.

[0033] Removal of the mounting bolt enables the locking member to retract into the mill body when the mill is disconnected from the whipstock.

[0034] The method may further comprised) running the mill assembly into a well;e) anchoring the whipstock inside the well; andf) pulling the mill, thereby shearing off the shear element and moving the whipstock engagement profile out of its engagement with the mill engagement profile.Detailed description

[0035] While various features have been discussed in general terms above, some more detailed and non-limiting examples of embodiment will be presented in the following with reference to the drawings, in whichFig. 1 is a perspective view of a mill assembly comprising a mill and a whipstock; Fig. 2 depicts a perspective cross-section view through a mill assembly with a connection assembly that connects the mill to the whipstock;Fig. 3 is a cross-section sideview of the connection assembly shown in Fig. 2;Fig. 4 is a perspective view of an end portion of the whipstock comprising a mill engagement profile;Fig. 5 is a perspective view of a locking member;Fig. 6 is an enlarged cross-section sideview of the end portion of the whipstock; Fig. 7 is a cross-section sideview of the connection assembly before the mill connects to the whipstock;Fig. 8 is a cross-section sideview of the connection assembly during disconnection of the mill from the whipstock;Fig. 9 is a cross-section sideview of the connection assembly after complete disconnection of the mill from the whipstock;Fig. 9a is a cross-section side-view of an alternative embodiment of the mill assembly;Fig. 10 is a perspective view of an alternative embodiment of the whipstock;Fig. 11 is a perspective view of an alternative embodiment of the locking member; Fig. 12 is a perspective view of an alternative embodiment of the locking member; Fig. 13 is a top-view of the locking member shown in Fig. 12;Fig. 14 is a perspective view of a slot configured to receive the locking member shown in Fig. 12; andFig. 15 is a top-view of the slot shown in Fig. 14.

[0036] Fig. 1 depicts a mill assembly 1. It comprises a whipstock 3 and a mill 5. The mill 5 is connected to the whipstock in a detachable manner.

[0037] As the mill assembly 1 is configured for being used inside a cased well (not shown), it has a longitudinal shape extending along an axial direction.

[0038] Fig. 2 depicts a part of a mill assembly 1. The whipstock 3 has an end portion 7, to which the mill 5 connects. The mill 5 has a mill body 9 with an axial bore 11. The axial bore 11 communicates with an outlet bore 13. During milling, the operator will flush liquid out of the outlet bore 13 for cooling and flushing away debris.

[0039] The mill 5 connects to the whipstock 3 with a connection assembly 10, which will be discussed in the following.

[0040] Fig. 3 depicts, with an enlarged cross section side view, the connection assembly 10 when in a connected state, i.e. when the mill 5 is connected to the whipstock 3. The connection assembly 10 comprises a socket 15 which is formed as a recess extending into the mill body 9. The socket 15 receives a locking member 17 that fits snugly inside the socket 15 and is configured to move in a direction crosswise to the axial direction of the mill 5.

[0041] The locking member 17 extends out from the socket 15 with a whipstock engagement portion 17a. The whipstock engagement portion 17a comprises a whipstock engagement profile 19, which in the shown embodiment is in the form of a collar.

[0042] The whipstock 3 comprises, at its end portion 7, a mill engagement profile 21 , which in the shown embodiment is in the form of a slot. The mill engagement profile, i.e. the slot 21 , receives the collar 19 (whipstock engagement profile) of the locking member 17. The shape of the locking member 17 is shown in better detail with the perspective view of Fig. 5. The collar 19 extends along a lower perimeter of the locking member 17, having a U-shape. The whipstock engagement portion 17a is indicated being at the lower part of the locking member 17. It further has a mill engagement portion 17b. The mill engagement portion 17b is the part that is received in the socket 15 when the locking member 17 is engaged with the mill engagement portion 21 of the whipstock 3. The peripheral cross section is constant along at least a portion of the mill engagement portion 17b. This cross section can advantageously correspond to the cross section of the socket 15. This enables the locking member 17 to move radially inside the socket 15.

[0043] The locking member 17 can move between an engaged position, wherein it is in engagement with the whipstock 3, and a retracted position, wherein it is moved further into the socket 15.

[0044] Furthermore, the locking member 17 has an elongated form. Its dimensions in the axial direction X and in the radial direction Y are larger than its dimension in the crosswise direction Z (i.e. crosswise to both the axial and radial direction). Theaxial direction X, the radial direction Y, and the crosswise direction Z are indicated in Fig. 5.

[0045] In the embodiment shown in Fig. 5, the locking member 17 has two parallel side-faces 17c that face in the crosswise direction Z. Furthermore, the two parallel side-faces 17c extend along the plane defined by the axial direction X and the radial direction Y.

[0046] The slot 21 is shown with the perspective view of Fig. 4 and the cross-section side view of Fig. 6. The slot 21 comprises a recessed groove 23 configured to receive the collar 19 of the locking member 17. The collar 19 and the recessed groove 23 extend along a plane that is parallel to the axial direction of the mill assembly 1. The recessed groove 23 comprises a slot shoulder 21 b that prevents mutual radial movement between the locking member 17 and the whipstock 3 when in the engaged state. The slot shoulder 21b is indicated in Fig. 6. When the collar 19 of the locking member 17 enters or leaves the recessed groove 23, it moves in an axial direction.

[0047] Reference is again made to Fig. 3, which depicts the connection assembly 10 when in the connected mode. Due to the engagement between the collar 19 of the locking member 17 and the recessed groove 23 of the slot 21, a mutual radial movement of the locking member 17 and the whipstock 3 is not possible.

[0048] The locking member 17 comprises two bolt bores 25 that extend through the locking member 17. The bolt bores 25 receive bolts 27 that connect the locking member 17 to the mill body 9 at an inner end of the socket 15. The bolts 27 can advantageously connect to threaded bores 29 provided at the inner end of the socket 15.

[0049] Compressed biasing members, which in the shown embodiment are in the form of retraction springs 31 , are arranged inside the bolt bores 25 of the locking member 17 and extend along a portion of the stem of the bolts 27. The retraction springs 31 are compressed between a washer 33 at the heads of the bolts 27 and a bolt bore edge 35. The function of the retraction springs 31 will appear further below.

[0050] The locking member 17 further comprises a shear element bore 37. A shear element, which in the shown embodiment is in the form of a shear bolt 39, issupported in the shear element bore 37. Instead of a shear bolt, the shear element could also be for instance a shear screw or a pin.

[0051] The shear bolt 39 extends from the shear element bore 37 and into a whipstock recess 41 arranged in the end portion 7 of the whipstock. In the shown embodiment, the whipstock recess 41 is arranged as a recess in the slot 21. This is shown also in Fig. 4 and in Fig. 6.

[0052] Inside the shear element bore 37, a shear element spring 43 is compressed to bias the shear bolt 39 outwardly from the shear element bore 37 and into the whipstock recess 41. A nut 45 is arranged in association with the shear element bore 37 to retain the shear element spring 43 in the compressed state.

[0053] Before the mill assembly 1 is run into the well, the whipstock 3 is connected to the mill 5. This will now be discussed with reference to Fig. 7.

[0054] In the situation shown in Fig. 7, the locking member 17 is being moved into the slot 21 (thus moving towards the right in the shown image). To prevent the compressed retraction springs 31 inside the bolt bores 25 to move the locking member 17 further into the socket 15 before the collar 19 engages the recessed groove 23 of the slot 21 , a mounting bolt 47 is installed in a mounting bore 49 which is arranged in the mill body 9. As shown in Fig. 7, the mounting bolt 47 fixes the locking member 17 in an outer position.

[0055] Advantageously, the mounting bore 49 comprises a mounting bolt retaining means for securing the mounting bolt 47. In the shown embodiment, the mounting bolt retaining means is in the form of threads 49a that engage with threads of the mounting bolt 47. The mounting bolt retaining means can, however, also be of another design. For instance, a rotating lever (not shown) can be arranged to lock the mounting bolt 47 in its inserted position. Once the shear bolt 39 has been moved into engagement with the whipstock recess 41 , the rotating lever can be rotated back to allow pulling out of the mounting bolt 47. Correspondingly, if the mounting bolt retaining means are in the form of threads 49a, as in the shown example, the mounting bolt 47 is screwed out of engagement once the shear bolt 39 engages with the whipstock recess 41.

[0056] When the locking member 17 has been moved further, i.e. towards the right in Fig. 7, the shear element spring 43 will push the shear bolt 39 into the whipstock recess 41. In this position, the engagement between the collar 19 and the recessed groove 23 prevents mutual movement in the axial direction. Furthermore, the engagement between the shear bolt 39 and the whipstock recess 41 prevents movement in the axial direction. When in this connected position, which is shown in Fig. 3, the mounting bolt 47 can be removed. The mill assembly 1 can now be run into the well.

[0057] When in the position shown in Fig. 7, when the mill body 9 is being moved towards the right to move the locking member 17 into engagement with the slot 21 , the shear bolt 39 slides against a guide face 21a. The guide face 21a is inclined with respect to the axial direction. The engagement between the shear bolt 39 and the guide face 21a pushes the shear bolt 39 into the shear element bore 37, against the force from the shear element spring 43.

[0058] Once the whipstock 3 has been anchored at its desired location in the well, the operator can disconnect the mill 5 from the whipstock 3 by pulling the mill 5 rearwards (i.e. upwards in the well). The pull in the mill 5 will shear off the shear bolt 39. This is shown in Fig. 8. A shorn off part 39a of the shear bolt 39 remains at the whipstock recess 41 , while the other part may remain in the shear element bore 37.

[0059] The rearward movement of the mill 5 moves the locking member 17 out of its engagement with the slot 21. The mill 5 is now thus totally disconnected from the whipstock 3 in both axial and radial directions. The operator may thus commence the milling process by moving the mill 5 forward against the anchored whipstock 3 while rotating the mill 5.

[0060] When the mill 5 is disengaged from the whipstock 3, the compressed retraction springs 31 move the locking member 17 further into the socket 15. In this manner, the locking member 17 will be retained inside the mill body 9 during the milling process, as shown in Fig. 9.

[0061] The connection assembly 10 shown and discussed with reference to Fig. 2 to Fig. 9 above, allows large axial forces from the mill 5 against the whipstock 3 in the axial direction into the well. Large radial forces are also tolerated, due to the engagement between the collar 19 and the recessed groove 23 of the slot 21.

[0062] Fig. 9a depicts an alternative embodiment. In this embodiment, the mill body 9 comprises the bolt bores 25a. Furthermore, the retraction springs 31 are arranged inside the bolt bores 25a. The bolts 27 are thus fixed to the locking member 17.

[0063] To prevent debris from entering the bolt bores 25a and prevent retraction of the locking member 17, protective nuts 26 are installed inside the bolt bores 25a. The protective nuts 26 can advantageously be vented to allow liquid to exit the bolt bores 25a.

[0064] The skilled reader will appreciate that the shear bolt 39, in the shown situation, would move to protrude out of the locking member 17, but would be forced into the locking member 17 if for instance sliding against a guide face 21a as shown in Fig. 7.

[0065] Fig. 10 and Fig. 11 illustrate an alternative embodiment. Instead of forming the whipstock engagement profile 19 as a collar, as discussed above, it is shaped as a locking groove, cf. Fig. 11. The locking groove is configured to engage with the mill engagement profile 21 of the whipstock 3, which in this embodiment is formed as a rail, cf. Fig. 10. The rail can slide axially into and out of the locking groove. When in the engaged state, the engagement will prevent radial mutual movement of the mill 5 and the whipstock 3. Depending on the specific design, after disengaging the mill 5 from the whipstock 3 downhole, the operator may have to mill away at least parts of the rail to enable milling through a casing.

[0066] An alternative design of the locking member 17 is shown in Fig. 12 and Fig.13. As appears best from the top-view of Fig. 13, the locking member 17 has a conical or wedge-shaped design. It thus differs from the design shown in Fig. 5, wherein the locking member 17 has two parallel side-faces 17c that face in the crosswise direction Z. The locking member 17 shown in Fig. 12 and Fig. 13 instead have two side-faces 17c that both have an angle with respect to the axial direction X. Furthermore, the side-faces 17c face in a direction that has an angle with respect to the crosswise direction Z.

[0067] This provides a wedge shape. Consequently, the slot 21 , which is depicted in Fig. 14 and Fig. 15, and which is configured to receive the locking member 17 shown in Fig. 12 and Fig. 13, is also designed with a wedge-shape.

[0068] The wedge shape of the locking member facilitates the insertion of the locking member 17 into the slot 21 when the operator shall connect the mill 5 to the whipstock 3.

Claims

Claims1. A mill assembly (1 ) for milling a well casing, comprising a mill (5) with a mill body (9),wherein the mill body (9) comprises a socket (15) and a locking member (17) that is arranged at least partially inside the socket and is movable between an engaged position and a retracted position,wherein the mill assembly (1 ) further comprises a biasing member (31 ) biasing the locking member towards the retracted position,wherein the locking member (17) comprises- a shear element bore (37) receiving a shear element (39); and- a whipstock engagement portion (17a) with a whipstock engagement profile (19).

2. A mill assembly (1) according to claim 1, wherein the locking member (17) further comprises a shear element spring (43) biasing the shear element (39) outwardly of the shear element bore (37).

3. A mill assembly (1) according to claim 1 or claim 2, further comprising a mounting bore (49) extending between an outer face of the mill body (9) and the socket (15), and a mounting bolt retaining means (49a) configured to releasably retain a mounting bolt (47) engaging the locking member (17).

4. A mill assembly (1) according to one of the preceding claims, wherein the locking member (17) further comprises a bolt bore (25) with- a bolt (27) that connects the locking member (17) to the mill body (9); and - the biasing member (31 ).

5. A mill assembly (1) according to one of the preceding claims, wherein the locking member (17) has an axial dimension (X), a radial dimension (Y), and a crosswise dimension (Z) being crosswise to the axial and radial dimensions, wherein locking member (17) extends longer in the axial and radial dimensions than in the said crosswise dimension.

6. A mill assembly (1) according to one of the preceding claims, further comprising a whipstock (3) with a mill engagement profile (21), wherein the whipstock engagement profile (19) of the locking member (17) is in engagement with the mill engagement profile (21).

7. A mill assembly (1) according to claim 6, wherein the whipstock (3) comprises a whipstock recess (41) and wherein the shear element (39) is in engagement with the whipstock recess.

8. A mill assembly (1) according to claim 6 or claim 7, wherein the whipstock engagement profile (19) comprises a collar and wherein the mill engagement profile (21) comprises an axially extending shoulder (21b) that engages the collar.

9. A mill assembly (1) according to one of claims 6 to 8, wherein the whipstock (3) comprises a guide face (21a) that is inclined with respect to the axial direction of the mill assembly.

10. A method of connecting a mill (5), of a mill assembly (1) according to one of the preceding claims, to a whipstock (3), comprisingb) sliding the whipstock engagement profile (19) in an axial direction along an axially extending mill engagement profile (21) of a whipstock (3) until the shear element (39) aligns with a whipstock recess (41 ) of the whipstock (3) and moves crosswise to the axial direction into engagement with the whipstock recess (41).

11. A method according to claim 10, further comprising, before step b), a) retaining the locking member (17) in the engaged position by fixing a mounting bolt (47) to the mill body (9) and in engagement with the locking member;and after step b),c) removing the mounting bolt (47).

12. A method according to claim 10 or claim 11 , further comprisingd) running the mill assembly (1 ) into a well;e) anchoring the whipstock (3) inside the well;f) pulling the mill (5), thereby shearing off the shear element (39) and moving the whipstock engagement profile (19) out of its engagement with the mill engagement profile (21 ).

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