AU2007306160A1

AU2007306160A1 - Method and apparatus for running tubulars

Info

Publication number: AU2007306160A1
Application number: AU2007306160A
Authority: AU
Inventors: Paul Howlett; Mike Wardley
Original assignee: Caledus Ltd
Current assignee: Caledus Ltd
Priority date: 2006-10-13
Filing date: 2007-10-04
Publication date: 2008-04-17
Also published as: GB0620272D0; WO2008043985A3; WO2008043985A2; GB0901454D0; NO20091850L; GB2454836A; US20100032170A1; CA2666465A1

Description

WO 2008/043985 PCT/GB2007/003769 1 1 Method and apparatus for running tubulars 2 3 The present invention relates to the drilling and 4 completion of wellbores. In particular, the present 5 invention in one of its aspects relates to a method for 6 running a completion string, such as casing, into a 7 predrilled hole. In another of its aspects, the 8 invention relates to apparatus for allowing rotation of a 9 downhole component with respect to a completion string. 10 In another of its aspects, the invention relates to a 11 drillable or millable drive assembly and applications 12 thereof. 13 14 Casing is steel pipe cemented in place during the 15 wellbore construction in order to stabilise the wellbore. 16 The casing string is made up of a plurality of casing 17 sections, usually threaded together, each run from the 18 surface to a casing point at the bottom of an open hole 19 at a specific diameter. The wellbore is extended by 20 drilling beyond the casing at a smaller inner diameter, 21 and a second casing string is run from the bottom of that 22 open hole back to the surface. The wellbore thus 23 comprises a series of concentric casing strings, with the WO 2008/043985 PCT/GB2007/003769 2 1 inner most strings extending to a greater depth in the 2 wellbore. 3 4 When the casing is run into the wellbore, it is desirable 5 to use casing that is a close fit to the open hole 6 diameter. A float shoe may be used to guide the casing 7 toward the centre of the hole and minimise the impact of 8 the casing with rock ledges or washouts as the casing is 9 run into the wellbore. The float shoe is typically made 10 from a drillable material, since the float shoe must be 11 drilled through if the well is to be deepened beyond the 12 casing point. 13 14 When running casing using conventional float shoes, the 15 casing string can still have a propensity to stand up on 16 ledges and washouts. Casing reaming shoes attached to 17 the lower end of the casing have an abrasive surface for 18 enlarging the open hole size and assisting in deployment 19 of the casing. During casing reaming, the entire casing 20 string will be rotated, and the reaming shoe smoothes the 21 run-in of the casing. However, the frictional forces of 22 the casing string against the open bore reduce the torque 23 transferable to the casing reaming shoe. The forces can 24 be significant as the casing string may extend over 25 considerable distances. In addition, rotation of the 26 casing string in the open bore can cause wear and damage 27 to the casing string. 28 29 Casing drilling techniques have also been developed, in 30 which the casing is run into the hole as it is being 31 drilled. In most cases, it would be necessary to drill 32 beyond the casing point. One solution to this is to 33 divert a drill string around the drill bit used for the WO 2008/043985 PCT/GB2007/003769 3 1 casing drilling operation, using a whipstock provided in 2 the casing section. Alternatively, the drill bit can be 3 retrieved from the wellbore using a specialised fishing 4 tool in a dedicated run. Alternatively, it may be 5 possible to use a drillable bit that can be drilled 6 through in a subsequent drilling operation. All of these 7 solutions are specialised operations requiring dedicated 8 equipment and procedures, and present significant 9 technical challenges in some drilling environments. 10 11 Similar challenges apply to the running of completion 12 strings such as including liners, sand control screens, 13 slotted liners, expandable tubulars, sometimes referred 14 to as lower completion strings or openhole completion 15 strings. 16 17 It is 'one object of the invention to provide a method and 18 apparatus for casing the running that at least mitigate 19 one or more disadvantages of conventional casing running 20 methods and apparatus. 21 22 It is an aim of at least one aspect of the invention to 23 provide a method and apparatus for allowing selectable 24 rotation of downhole equipment mounted at the bottom of 25 the casing string. 26 27 It is a further aim of an embodiment of the invention to 28 provide a method and apparatus for rotating a portion of 29 a completion string by controlled pumping of circulation 30 fluid. 31 32 It is a further aim of at least one aspect of the 33 invention to provide a drive assembly for downhole WO 2008/043985 PCT/GB2007/003769 4 1 equipment that is drillable or millable by conventional 2 downhole drilling equipment. 3 4 According to a first aspect of the invention there is 5 provided a method of running a casing string in a 6 wellbore, the method comprising the steps of: 7 - providing a casing string assembly in a wellbore, 8 the casing string assembly having a first portion 9 and a second portion; and 10 - rotating a first portion of the casing string 11 assembly relative to a second portion of the 12 casing string assembly while running the casing 13 string. 14 15 It should be understood that the term casing string 16 assembly includes any casing sections along with 17 apparatus associated with the casing sections, including 18 a drill shoe, or reaming shoe located at the lower end of 19 the casing string. 20 21 Preferably, the casing string assembly includes a swivel, 22 and the first portion of the casing string assembly is a 23 lower portion located below the swivel, and the second 24 portion of the casing string assembly is an upper portion 25 located above the swivel. 26 27 Preferably, the first portion of the casing string 28 assembly includes a shoe. More preferably, the shoe 29 includes an abrasive or cutting surface. The shoe may be 30 a casing reaming shoe. 31 32 The second portion of the casing string assembly may 33 include a plurality of casing sections. Preferably, the WO 2008/043985 PCT/GB2007/003769 5 1 second portion of the casing string assembly provides the 2 majority of the length of the casing string assembly. 3 More preferably, the second portion of the casing 4 assembly provides greater than 70% of the length of the 5 casing string assembly. More preferably greater than 6 80%. More preferably, at least 90%. 7 8 Preferably, the casing string is run while the second 9 portion of the casing string assembly is substantially 10 not rotated with respect to the wellbore. 11 12 In this manner, the invention allows for a reduction to 13 the length of tubular that is rotated with respect to the 14 wellbore, reducing frictional forces and wear to the 15 casing string. 16 17 Preferably, all casing sections in the casing string 18 assembly are provided in the second portion. 19 20 The method may include the step of driving rotation of 21 the first portion of the casing string assembly by 22 circulation of fluid through the casing string. The 23 rotation of the first portion of the casing string 24 assembly may be driven by a drive assembly, which may 25 comprise a mud motor. In this way, pumping of fluid 26 controls the rotation and reaming function. 27 28 The method may include the step of locating a drive 29 assembly with respect to the casing string assembly. The 30 drive assembly may be run in hole with the casing string 31 assembly. Where this is the case, the drive assembly may 32 be located in the casing string assembly at surface. 33 WO 2008/043985 PCT/GB2007/003769 6 1 The method may include the step of retrieving the drive 2 assembly from the casing string assembly. In this way, 3 after the reaming operation is complete, for example when 4 no further reaming is required due to formation 5 conditions or because the casing string has reached its 6 casing point, the drive assembly can be retrieved to 7 surface. 8 9 The drive assembly may be retrieved using a wireline 10 fishing tool. Alternatively, the drive assembly may be 11 retrieved using drill pipe. In a further alternative, 12 the drive assembly may be retrieved by reverse 13 circulation of the fluid in the wellbore to pump the 14 drive assembly upward in the well. 15 16 In a preferred embodiment, the method includes the step 17 of locating the drive assembly with respect to the casing 18 string when the casing string has been at least partially 19 run into the wellbore. 20 21 In this way, initial running of the casing could be by 22 floating the casing string into the wellbore. If 23 difficulties are experienced while running the casing in 24 this fashion, for example, if the casing string stands up 25 on a rock ledge or a washout, the drive assembly can be 26 deployed through the casing string to locate with respect 27 to the swivel components. 28 29 The method may include the step of pumping the drive 30 assembly through the casing string. The drive assembly 31 may comprise a swab cup or wiper. In an alternative 32 embodiment, the drive assembly is run on drill pipe. 33 WO 2008/043985 PCT/GB2007/003769 7 1 The method may include the additional step of engaging 2 first and second portions of the casing string assembly 3 with the driving assembly. The first and second portions 4 of the casing string assembly may be rotationally keyed 5 with corresponding portions of the drive assembly. 6 7 The method may include the additional step of rotating 8 the casing string during running. That is, the casing 9 string could be run as a conventional casing reamer over 10 distances or through formation for which casing reaming 11 is achievable and desirable. If difficulties are 12 encountered, for example, if the reaming shoe stands up 13 on a ledge or washout and sufficient torque is not 14 available to continue the casing reaming operation, or 15 alternatively, if the frictional wear on the casing 16 string poses a risk of damage to the string, the 17 equipment could then perform in its swivel mode, with 18 just a portion of the casing string being rotated. 19 20 In an alternative embodiment, the first portion includes 21 a drill shoe or drill bit, and the method is implemented 22 as a casing-while-drilling operation. 23 24 The method may include the additional step of preventing 25 rotation of the first portion of the casing string 26 assembly with respect to the second portion. Preferably, 27 the first portion of the casing string assembly is locked 28 with respect to the second portion. 29 30 The method may include the additional step of cementing 31 the casing. The cementing of the casing may prevent 32 rotation of the first portion of the casing string 33 assembly with respect to the second portion. The first WO 2008/043985 PCT/GB2007/003769 8 1 and second portions of the casing string assembly may 2 thereby be locked by a cementing operation. 3 4 The method may include the additional step of drilling 5 beyond the casing string assembly. 6 7 Advantageously, all components of the casing string 8 assembly left downhole are drillable or millable by 9 conventional drilling apparatus. 10 11 The method may include the additional step of drilling 12 through the drive assembly. The drive assembly may be a 13 drillable or millable downhole motor. The drive assembly 14 may be integral with the casing string assembly. 15 16 The method may include the steps of: 17 - running the drive assembly with the casing; and 18 - cementing the casing with the drive assembly 19 downhole. 20 21 The method may include the steps of running a float 22 collar with the casing, above the drive assembly. 23 24 According to a second aspect of the invention, there is 25 provided a method of running a completion string in a 26 wellbore, the method comprising the steps of: 27 - providing a completion string assembly in a 28 wellbore, the completion string assembly having a 29 first portion and a second portion; and 30 - rotating a first portion of the completion string 31 assembly relative to a second portion of the 32 completion string assembly while running the 33 completion string.

WO 2008/043985 PCT/GB2007/003769 9 1 2 The completion string may be tubular including liners, 3 sand control screens, slotted liners, expandable tubulars 4 or casing. These strings may be referred to as lower 5 completion strings or openhole completion strings. 6 Embodiments of the second aspect of the invention are as 7 embodiments of the first aspect, with references to 8 casing string changed to completion string accordingly. 9 10 According to a third aspect of the invention, there is 11 provided apparatus for connection to a tubular forming 12 part of a completion string, the apparatus comprising an 13 upper section adapted to be coupled to the completion 14 string; a lower section rotatable with respect to the 15 upper section and adapted to be coupled to equipment 16 located below the tubular; and engaging means 17 corresponding to engaging means provided on a drive 18 assembly adapted to be coupled to the apparatus to allow 19 rotation to be imparted to the lower section, wherein the 20 apparatus is operable to be engaged or disengaged with 21 the drive assembly in the wellbore. 22 23 Preferably, the apparatus is operable to be engaged or 24 disengaged with the drive assembly in the wellbore to 25 allow the drive assembly to be run into the wellbore or 26 retrieved from the wellbore separately from the 27 apparatus. 28 29 Preferably, the engaging means arranged to be 30 rotationally keyed on engagement with the corresponding 31 engaging means. Preferably, the engaging means comprises 32 a plurality of splines. 33 WO 2008/043985 . PCT/GB2007/003769 10 1 Preferably, the apparatus includes an upper spline 2 section, a lower spline section, and a bearing portion. 3 4 Preferably, the apparatus is adapted to have a rotating 5 mode and a non-rotating mode. The bearing portion may be 6 operable to rotate under load or under pressure. In one 7 embodiment, the apparatus is provided with means for 8 preventing rotation of the upper portion with respect to 9 the lower portion. Preferably, the upper and lower 10 portions of are provided with formations which are 11 lockable by a cementing operation. 12 13 The apparatus may be adapted to be coupled to a shoe, 14 such as a casing reamer shoe or drill shoe. 15 16 According to a fourth aspect of the invention, there is 17 provided a drive assembly for a downhole apparatus, the 18 drive assembly comprising a main body portion and a 19 rotating portion and a motor for effecting rotation of 20 the rotating portion with respect to the main body 21 portion; wherein the drive assembly comprises engaging 22 means for engagement of the main body portion and the 23 rotating portion with corresponding engaging means 24 provided on the downhole apparatus to allow rotation to 25 be imparted to the downhole apparatus, and the drive 26 assembly is operable to be engaged or disengaged with the 27 downhole apparatus in the wellbore. 28 29 Preferably, the drive assembly is operable to be engaged 30 or disengaged with the downhole apparatus in the wellbore 31 to allow the drive assembly to be run into the wellbore 32 or retrieved from the wellbore separately from the 33 downhole apparatus.

WO 2008/043985 PCT/GB2007/003769 11 2 Preferably, the engaging means arranged to be 3 rotationally keyed on engagement with the corresponding 4 engaging means. Preferably, the engaging means comprise 5 a plurality of splines. 6 7 In one embodiment, the drive assembly comprises a fluid 8 circulation path therethrough. Preferably, the motor is 9 a positive displacement motor or mud motor. 10 11 The drive assembly may be adapted to be run in and/or 12 retrieved from a completion string, such as a casing 13 string. The drive assembly may be adapted to be received 14 in a shoe assembly of a completion string. Preferably, 15 the drive assembly is adapted to be received in a shoe 16 assembly to allow rotation of the shoe to be driven by 17 the drive assembly. 18 19 In one embodiment, the drive assembly is adapted to be 20 pumped downhole. Preferably, the drive assembly 21 comprises a resilient member for providing a seal with a 22 completion string, against which the drive assembly is 23 pumped. Preferably, the drive assembly comprises a swab 24 cup or wiper. 25 26 The drive assembly may be provided with means for 27 preventing fluid flow through its circulation path. Such 28 means may be a rupture disc assembly. In this way, a 29 sufficient increase in pressure will rupture the disc and 30 open the circulation path, and allow the motor to be 31 activated. 32 33 The drive assembly may comprise a wireline fishing neck.

WO 2008/043985 PCT/GB2007/003769 12 1 2 According to a fifth aspect of the invention, there is 3 provided an assembly comprising the apparatus of the 4 third aspect of the invention, and the drive assembly of 5 the fourth aspect of the invention. 6 7 According to a sixth aspect of the invention, there is 8 provided apparatus for running a casing string, the 9 apparatus comprising an upper section adapted to be 10 coupled to the casing string; a lower section rotatable 11 with respect to the upper section and including a shoe 12 located below the tubular; and engagement means for 13 engaging a drive assembly adapted to rotate the shoe with 14 respect to the upper section. 15 16 According to a seventh aspect of the invention there is 17 provided a drive assembly for a downhole apparatus 18 comprising an upper section adapted to be coupled to a 19 tubular; a lower section rotatable with respect to the 20 upper section; and a motor for imparting rotation to the 21 lower section; wherein the drive assembly is drillable or 22 millable by conventional downhole drilling equipment. 23 24 Preferably, the motor is a positive displacement motor 25 such as a mud motor. More preferably, the motor 26 comprises a drillable or millable rotator. The rotator 27 may be made from a drillable alloy. The motor may 28 comprise a stator formed from a rubber or nitrile rubber 29 material. 30 31 The drive assembly may be provided with a fluid 32 circulating path for actuating the motor and a fluid 33 bypass path. The fluid bypass path may be provided with WO 2008/043985 PCT/GB2007/003769 13 1 a rupture disc. In this way, the rupture disc prevents 2 fluid flow through the bypass channel until pressure 3 behind the disc is sufficient to break the disc. 4 5 Preferably, the lower section is connected to a shoe, 6 such as a casing reamer shoe or a drill shoe. More 7 preferably, the show is drillable or millable by 8 conventional downhole drilling equipment. The shoe may 9 include a non-return valve to prevent fluid flow into the 10 shoe from the wellbore. 11 12 In one embodiment, the drive assembly is adapted to have 13 a rotating mode and a non-rotating mode. A bearing 14 portion may be operable to rotate under load or under 15 pressure. In one embodiment, the drive assembly is 16 provided with means for preventing rotation of the upper 17 portion with respect to the lower portion. Preferably, 18 the upper and lower portions of are provided with 19 formations which are lockable by a cementing operation. 20 21 It will be appreciated that where the terms 'up' and 22 'down' are used in this specification, they are used in a 23 relative sense and the invention could equally apply to 24 deviated or horizontal wellbores, in which case the 25 references would convert accordingly. 26 27 There will now be described by way of example only, 28 various embodiments of the invention with reference to 29 the following drawings, of which: 30 31 Figure 1 is a schematic representation of a shoe assembly 32 according to an embodiment of the invention; 33 WO 2008/043985 PCT/GB2007/003769 14 1 Figures 2A and 2B are schematic representations of a 2 drive assembly, used in accordance with the apparatus of 3 Figure 1; 4 5 Figures 3A, 3B, and 3C show the apparatus of Figures 1 6 and 2 at different stages of running; 7 8 Figure 4 is a schematic representation of a shoe assembly 9 in accordance with a second embodiment of the invention; 10 11 Figure 5 is a schematic representation of a casing string 12 comprising the shoe assembly of Figure 4. 13 14 Referring firstly to Figure 1, there is shown in 15 schematic form a shoe assembly, generally depicted at 10, 16 at its downhole end. The apparatus is shown in half 17 section in order to reveal internal components. At an 18 upper end 12, the apparatus 10 is connected to a casing 19 string (not shown). The apparatus includes an upper 20 spline section 16, which comprises longitudinally 21 oriented internal splines 17, protruding radially inward 22 from the inner wall of the section, and spaced 23 circumferentially around the inner bore 34 of the 24 apparatus. Bearing assembly 18 is coupled to the upper 25 spline section 16, in this case via an optional spacer 26 section 20, and provides a downhole swivel. The bearing 27 assembly comprises upper and lower bearing portions, 28 respectively 22a and 22b, and a bearing housing 24 29 functioning to keep the bearing assembly together. Upper 30 and lower bearing portions 22a and 22b are rotated with 31 respect to one another. 32 WO 2008/043985 PCT/GB2007/003769 15 1 Coupled to the lower bearing portion is a lower spline 2 section 26, which in turn is coupled to shoe 28. The 3 lower spline section 26 comprises longitudinally oriented 4 internal splines 27, protruding radially inward from the 5 inner wall of the section, and spaced circumferentially 6 around the inner bore 34 of the apparatus. The shoe 28 7 in this example is a casing reaming shoe, having abrasive 8 portions 30 on its out surface. Internal to the shoe is 9 a dual non-return valve arrangement 32 allowing one-way 10 flow of circulating fluid from the internal bore 34 of 11 the apparatus through the shoe 28 and out through the 12 jets 36. 13 14 Referring now to Figures 2A and 2B, there is shown a 15 drive assembly, generally depicted at 50, for use with 16 the apparatus of Figure 1. Figure 2B shows a 17 continuation of the same of the drive assembly 50, in 18 half section to show internal components. 19 20 The drive assembly 50 comprises a main cylindrical body 21 52, shown predominantly in Figure 2A, and an upper end 22 54, shown in Figure 2B. The drive assembly is 23 dimensioned to fit inside the internal bore of the 24 apparatus 10. The upper end 54 comprises a wireline 25 fishing neck 56, but could be provided with any other 26 suitable retrieval means. Provided in the body 52 at the 27 upper end 54 are inlet ports for entry of circulating 28 fluid. In this embodiment, a rupture disc assembly 58 is 29 provided internal to the body 52. The drive assembly 50 30 is also provided with a swab cup 59 made of resilient 31 material to form a seal with the inner wall of the 32 casing. 33 WO 2008/043985 PCT/GB2007/003769 16 1 The drive assembly further comprises an upper spline sub 2 60, comprising a plurality of longitudinally oriented 3 splines 62, extending radially from the outer surface of 4 the upper spline sub. The splines 62 are distributed 5 circumferentially around the upper spline sub 60, and are 6 arranged to complement and engage with the splines 17 of 7 the upper spline section 16. 8 9 Beneath the upper spline sub 60 is a housing 64 for a mud 10 motor, rotationally coupled to a lower spline sub 66 via 11 a bearing assembly 68. The spline sub 66 comprises 12 splines 70, distributed circumferentially around the 13 lower spline sub 66, and arranged to complement and 14 engage with the splines 27 of the lower spline section 15 16. 16 17 At the lower end 72 of the drive assembly 50 there are 18 provided a plurality of outlet ports for circulating 19 fluid. 20 21 In use, the drive assembly 50 fits inside of the 22 apparatus 10, such that the upper spline sub 60 is 23 rotationally keyed with the upper spline section 16, and 24 the lower spline sub 66 is rotationally keyed with the 25 lower spline section 26. When fluid is circulated in the 26 mud motor 64 by pumping from surface, the lower spline 27 sub 66 is rotated with respect to the main body 52. The 28 upper spline sub 60 becomes a reactive torque sub with 29 the upper spline section 16 acting as a reactive torque 30 section of the apparatus 10, against which the lower 31 spline sub 66 rotates. The rotation of the sub 66 causes 32 rotation of the casing reaming shoe 28. 33 WO 2008/043985 PCT/GB2007/003769 17 1 In the embodiment of Figures 1, 2A and 2B, the apparatus 2 is adapted to be run into the casing to the apparatus 10 3 in a subsequent run, when the apparatus 10 is already 4 downhole. The running method will be described with 5 reference to Figures 3A to 3C, each of which shows 6 schematically the apparatus 10, 50 at a different stage 7 of running in a pre-drilled bore 100. 8 9 In Figure 3A, the apparatus 10 has been run into bore 100 10 on the downhole end of a casing string 110. The 11 apparatus 10 is connected to the casing string 110 via an 12 optional spacer section 120. The casing string is 13 provided with a landing collar 122 for landing a 14 cementing plug, which is a non-float collar. 15 16 The casing string and apparatus 10 has been run to a 17 first depth A conventionally. During this stage of 18 running, the casing string might not be rotated in the 19 bore, or the casing string could be run as a conventional 20 casing reamer over distances or through formation for 21 which casing reaming is achievable and desirable. At 22 depth A, difficulties are encountered, for example, the 23 reaming shoe has stood up on a ledge or washout and 24 sufficient torque is not available to continue the casing 25 reaming operation. Alternatively, the operator may 26 decide that frictional wear on the casing string poses a 27 risk of damage to the string. The operator elects to run 28 the drive assembly 50. 29 30 As shown in Figure 3B, the drive assembly 50 into the 31 casing. The swab cup 59 provides a seal with the casing 32 wall and along with the resistance provided by the 33 rupture disc assembly 58, allows the drive assembly 50 to WO 2008/043985 PCT/GB2007/003769 18 1 be pumped downhole in the direction of arrow B. The 2 drive assembly 50 and landing collar 122 are selected to 3 allow the drive assembly to pass the collar. When the 4 drive assembly 50 locates in the apparatus, the splines 5 of the respective spline subs 60, 66 and spline sections 6 16, 26 are rotationally keyed, and the lower end 72 abuts 7 a formation in the apparatus 10. The pump pressure 8 breaks the rupture disc assembly 58 and fluid circulates 9 in the drive assembly. The mud motor 64 causes the lower 10 spline sub 66, the lower spline section 26, and shoe 28 11 to rotate against the portions of the apparatus above the 12 bearing portions. Downweight on the casing string 110 13 allows the depth of the casing to be increased to the 14 casing point while reaming the bore 100, as indicated by 15 arrow C. 16 17 When the reaming operation is complete, the pump pressure 18 is bled off and the wireline fishing neck 56 allows the 19 drive assembly 50 to be retrieved from the casing prior 20 to cementing. 21 22 The above-described method and apparatus allows casing 23 reaming without rotating the entire casing string, and in 24 a manner in which the only components left downhole may 25 be drilled through if the wellbore is to be drilled 26 beyond the casing point. In addition, the method and 27 apparatus provides for elective deployment and/or 28 retrieval of the driving assembly. 29 30 To assist in drilling out the apparatus, an alternative, 31 non-illustrated embodiment of the invention provides a 32 bearing assembly that has rotating and non-rotating 33 states. For example, the bearing assembly may include a WO 2008/043985 PCT/GB2007/003769 19 1 mechanism that is configured such that it only allows 2 rotation when under a load or under pressure. In an 3 alternative embodiment, portions of the apparatus 4 attached to the upper and lower bearing portions are 5 profiled or ribbed such that after the cement job has 6 been carried out, relative rotation of the components is 7 prevented or mitigated. 8 9 In an alternative, non-illustrated embodiment, the drive 10 assembly is run in with the casing string 110, and not 11 pumped down in a separate operation. In this embodiment, 12 the drive assembly is substantially identical to that of 13 Figures 2A and 2B, but the swab cup 59 and rupture disc 14 assembly 58 will not be required and may be omitted. The 15 drive assembly is located with respect to the spline 16 sections at surface, and run into the bore together with 17 the casing. If reaming is required, circulating fluid is 18 pumped down from surface and the mud motor effects 19 rotation of the shoe to ream the hole. Subsequent to the 20 reaming operation the drive assembly can be retrieved 21 from the casing, although it could be left downhole. 22 However, it is preferable in most casing running 23 applications to avoid leaving equipment downhole that is 24 difficult to drill out, should the depth of the bore be 25 increased beyond the casing point. 26 27 In a further embodiment of the invention the driving 28 assembly is run on a wireline subsequent to running of 29 the casing section. 30 31 In a further, non-illustrated embodiment of the 32 invention, the landing collar 122 is modified to provide 33 a profile that maximises its contact area for landing a WO 2008/043985 PCT/GB2007/003769 20 1 cementing plug, but allows passage of the driving 2 assembly. The landing collar could for example comprise 3 portions of increased inner diameter to allow passage of 4 the splines of the driving assembly. In a further 5 alternative embodiment, the reduced inner diameter of the 6 upper spline section functions as a landing collar for a 7 cementing plug. 8 9 Referring now to Figure 4, there is shown in schematic 10 form a shoe and motor assembly in accordance with an 11 alternative embodiment of the invention, generally 12 depicted at 200. The apparatus is shown in half section 13 in order to reveal internal components. At an upper end 14 212, the apparatus 200 is connected to a casing string 15 (not shown). The apparatus includes an upper section 216 16 and a lower section 226 via a bearing assembly 218 to 17 provide a downhole swivel. The bearing assembly 218 18 comprises upper and lower bearing portions, respectively 19 222a and 222b, and a bearing housing 224 functioning to 20 keep the bearing assembly together. Upper and lower 21 bearing portions 222a and 222b are rotatable with respect 22 to one another. 23 24 The lower portion 226 is connected to shoe, in this case 25 a standard reamer shoe 228 having tungsten carbide 26 reaming portions 230 and stabilising portions 234. The 27 shoe 228 includes a non-return valve 232 to prevent 28 backflow of circulation fluid. 29 30 The upper section 216 houses a drillable or millable 31 motor 240. The motor 240 includes a stator 242 coupled 32 to, and static in relation to, the upper portion 216. 33 The stator is made from a rubber or nitrile rubber WO 2008/043985 PCT/GB2007/003769 21 1 material, having the properties of being elastically 2 deformable, but resistant to wellbore and circulation 3 fluids. The motor also comprises a rotator 244, 4 concentric with the stator 242, and formed from a 5 drillable or millable alloy. The rotator 244 comprises a 6 main body portion 246 and a lower body portion 248, 7 coupled to the lower portion 226 of the assembly by a 8 threaded connection. Fluid ports 250 are provided in the 9 lower body portion 248. As is understood in the art, the 10 stator and rotator are profiled on their inner and outer 11 surfaces respectively, such that fluid pumped through the 12 motor causes rotation of the rotator with respect to the 13 stator. Such rotation is transferred to the lower 14 portion of the assembly and the shoe. 15 16 The assembly is also provided with a bypass bore 252 and 17 a rupture disc 254. Should the motor block or jam, the 18 pressure build up behind the motor will cause the disc to 19 rupture and open the bore 252 for passage of fluid. 20 21 The components of the drive assembly are selected to be 22 readily drillable or millable using conventional drilling 23 equipment. Similarly, the components of the show 228 are 24 readily drillable or millable. This allows the apparatus 25 to be left downhole, even in applications where 26 subsequent drill-out, for example to extend the wellbore 27 beyond the casing point, is required. This arrangement 28 also allows the drive assembly to be integral with the 29 shoe assembly. 30 31 To assist in drilling out the apparatus, an alternative, 32 non-illustrated embodiment of the invention provides a 33 bearing assembly that has rotating and non-rotating WO 2008/043985 PCT/GB2007/003769 22 1 states, as described with reference to Figure 1. For 2 example, the bearing assembly may include a mechanism 3 that is configured such that it only allows rotation when 4 under a load or under pressure. In, an alternative 5 embodiment, portions of the apparatus attached to the 6 upper and lower bearing portions are profiled or ribbed 7 such that after the cement job has been carried out, 8 relative rotation of the components is prevented or 9 mitigated. 10 11 Figure 5 shows schematically a representation of a casing 12 string 308 comprising the shoe assembly of Figure 4 in a 13 bore 300. In this arrangement, the drive assembly 240 is 14 integral with the casing string assembly on run in, and 15 is coupled at its upper end to a casing section 302. 16 Further casing section 304 is provided with a float 17- collar 306 for catching a cementing plug and providing a 18 non-return valve. The use of the float collar is made 19 possible because the drive assembly does not require 20 separate deployment or retrieval. 21 22 Various modifications and improvements could be made to 23 the above-described embodiments of the invention within 24 the scope of the invention herein defined.

Claims

1. A method of running a casing string in a wellbore, the method comprising the steps of:

a. providing a casing string assembly in a wellbore, the casing string assembly having a first portion and a second portion; and

b. rotating a first portion of the casing string assembly relative to a second portion of the casing string assembly while running the casing string.

2. A method as claimed in claim 1 wherein the casing string assembly includes a swivel, and the first portion of the casing string assembly is a lower portion located below the swivel, and the second portion of the casing string assembly is an upper portion located above the swivel.

3. A method as claimed in Claim 1 or claim 2 wherein the first portion of the casing string assembly includes a shoe.

4. A method as claimed in Claim 3 wherein the shoe includes an abrasive or cutting surface.

5. A method as claimed in any one of claims 2 to 4 wherein the shoe is a casing reaming shoe.

6. A method as claimed in any one of the preceding claims wherein the second portion of the casing string assembly includes a plurality of casing sections.

7. A method as claimed in any one of the preceding claims wherein the casing string is run while the second portion of the casing string assembly is substantially not rotated with respect to the wellbore.

8. A method as claimed in any one of the preceding claims including the step of driving rotation of the first portion of the casing string assembly by circulation of fluid through the casing string.

9. A method as claimed in Claim 8 wherein the rotation of the first portion of the casing string assembly is driven by a drive assembly, comprising a mud motor.

10. A method as claimed in any one of the preceding claims including the step of locating a drive assembly with respect to the casing string assembly.

11. A method as claimed in claim 10 including the step of running the drive assembly in hole with the casing string assembly.

12. The method as claimed in Claim 10 or 11 further including the step of retrieving the drive assembly from the casing string assembly.

13. A method as claimed in claim 12 wherein the drive assembly is retrieved using a wireline fishing tool.

14. A method as claimed in claim 12 wherein the drive assembly is retrieved using drill pipe.

15. A method as claimed in claim 12 wherein the drive assembly is retrieved by reverse circulation of the fluid in the wellbore to pump the drive assembly upward in the well.

16. A method as claimed in claim 10 wherein the drive assembly is located with respect to the casing string when the casing string has been at least partially run into the wellbore.

17. A method as claimed in claim 16 including the step of pumping the drive assembly through the casing string.

18. A method as claimed in claim 17 wherein the drive assembly comprises a swab cup or wiper.

19. A method as claimed in claim 16 including the step of running the drive assembly on drill pipe.

20. A method as claimed in any one of claims 10 to 19 including the additional step of engaging first and second portions of the casing string assembly with the driving assembly.

21. A method as claimed in any one of the preceding claims including the additional step of rotating the casing string during running.

22. A method as claimed in any one of the preceding claims wherein the first portion includes a drill shoe or drill bit, and the method is implemented as a casing-while-drilling operation.

23. A method as claimed in any one of the preceding claims including the additional step of preventing rotation of the first portion of the casing string assembly with respect to the second portion.

24. A method as claimed in any one of the preceding claims including the additional step of cementing the casing.

25. A method as claimed in any one of the preceding claims including the additional step of drilling beyond the casing string assembly.

26. A method of running a casing string in a wellbore, the method comprising the steps of:

a. providing a casing string assembly in a wellbore, the casing string assembly having a first portion and a second portion; b. rotating a first portion of the casing string assembly relative to a second portion of the casing string assembly while running the casing string;

c. locating a drive assembly with respect to the casing string assembly; and

d. drilling through the drive assembly.

27. A method as claimed in any one of claims 10 to 26 where the drive assembly is a drillable or millable downhole motor.

28. A method as claimed in any one of the preceding claims including:

a. running the drive assembly with the casing; and

b. cementing the casing with the drive assembly downhole.

29. A method as claimed in any one of claims 10 to 28 including the step of running a float collar with the casing, above the drive assembly.

30. A method of running a completion string in a wellbore, the method comprising the steps of:

a. providing a completion string assembly in a wellbore, the completion string assembly having a first portion and a second portion; and

b. rotating a first portion of the completion string assembly relative to a second portion of the completion string assembly while running the completion string.

31. Apparatus for connection to a tubular forming part of a completion string, the apparatus comprising an upper section adapted to be coupled to the completion string; a lower section rotatable with respect to the upper section and adapted to be coupled to equipment located below the tubular; and engaging means corresponding to engaging means provided on a drive assembly adapted to be coupled to the apparatus to allow rotation to be imparted to the lower section, wherein the apparatus is operable to be engaged or disengaged with the drive assembly in the wellbore.

32. The apparatus as claimed in claim 31 operable to be engaged or disengaged with the drive assembly in the wellbore to allow the drive assembly to be run into the wellbore or retrieved from the wellbore separately from the apparatus.

33. The apparatus as claimed in claim 31 or 32 including an upper spline section, a lower spline section, and a bearing portion.

34. The apparatus as claimed in any one of claims 31 to 33 adapted to have a rotating mode and a non- rotating mode.

35. The apparatus as claimed in any one of claims 31 to 34 wherein the upper and lower portions are provided with formations which are lockable by a cementing operation.

36. The apparatus as claimed in any one of claims 31 to 35 adapted to be coupled to a shoe, such as a casing reamer shoe or drill shoe.

37. A drive assembly for a downhole apparatus, the drive assembly comprising a main body portion and a rotating portion and a motor for effecting rotation of the rotating portion with respect to the main body portion; wherein the drive assembly comprises engaging means for engagement of the main body portion and the rotating portion with corresponding engaging means provided on the downhole apparatus to allow rotation to be imparted to the downhole apparatus, and the drive assembly is operable to be engaged or disengaged with the downhole apparatus in the wellbore.

38. A drive assembly as claimed in claim 37 operable to be engaged or disengaged with downhole apparatus in the wellbore to allow the drive assembly to be run into the wellbore or retrieved from the wellbore separately from the downhole apparatus.

39. A drive assembly as claimed in claim 37 or 38 wherein the engaging means is arranged to be rotationally keyed on engagement with the corresponding engaging means.

40. A drive assembly as claimed in any one of claims 37 to 39 comprising a fluid circulation path therethrough.

41. A drive assembly as claimed in any one of claims 37 to 40 wherein the motor is a positive displacement motor or mud motor.

42. A drive assembly as claimed in any one of claims 37 to 41 adapted to be run in and/or retrieved from a completion string, such as a casing string.

43. A drive assembly as claimed in any one of claims 37 to 42 adapted to be received in a shoe assembly of a completion string.

44. A drive assembly as claimed in any one of claims 37 to 43 adapted to be pumped downhole.

45. A drive assembly as claimed in claim 44 comprising a resilient member for providing a seal with a completion string, against which the drive assembly is pumped.

46. A drive assembly as claimed in any one of claims 44 or 45 provided with means for preventing fluid flow through its circulation path.

47. A drive assembly as claimed in any one of claims 37 to 46 comprising a wireline fishing neck.

48. An assembly comprising the apparatus of claim 31 and the drive assembly of claim 37.

49. Apparatus for running a casing string, the apparatus comprising an upper section adapted to be coupled to the casing string; a lower section rotatable with respect to the upper section and including a shoe located below the tubular; and engagement means for engaging a drive assembly adapted to rotate the shoe with respect to the upper section.

50. A drive assembly for a downhole apparatus comprising an upper section adapted to be coupled to a tubular; a lower section rotatable with respect to the upper section; and a motor for imparting rotation to the lower section; wherein the drive assembly is drillable or millable by conventional downhole drilling equipment.

51. A drive assembly as claimed in claim 50 wherein the motor is a positive displacement motor.

52. A drive assembly as claimed in claim 50 or 51 wherein the motor comprises a drillable or millable rotator.

53. A drive assembly as claimed in any one of claims 50 to 52 provided with a fluid circulating path for actuating the motor and a fluid bypass path.

54. A drive assembly as claimed in any one of claims 50 to 53 wherein the lower section is connected to a shoe, such as a casing reamer shoe or a drill shoe.

55. A drive assembly as claimed in claim 54 wherein the shoe includes a non-return valve to prevent fluid flow into the shoe from the wellbore.

56. A drive assembly as claimed in any one of claims 50 to 55 adapted to have a rotating mode and a non- rotating mode.