Assembly for use in abandoning a wellbore

Abstract

An assembly 2 for use in abandoning a wellbore comprises at least one perforating apparatus 4 operable to mechanically cut perforations in a wellbore casing and a cement retainer deployment assembly 6

Description

The present disclosure relates to an assembly for use in abandoning a wellbore, and relates particularly, but not 5 exclusively to an assembly for use in abandoning a wellbore using a perforating apparatus operable to mechanically cut perforations in a wellbore casing and a cement retainer deployment assembly configured to place a cement retainer assembly or bridge plug in a wellbore, in which the assembly 10 can be used repeatedly downhole to abandon multiple sections of a wellbore by perforating and cementing without retrieval to the surface. The present disclosure also relates to a method for abandoning a wellbore. 15 The procedure to safely abandon a wellbore to prevent for example hydrocarbons polluting ground water is best conducted by perforating the wellbore casing and then filling the wellbore with cement, BiSN, resin or resolute material. The perforations in the casing enable the cement to access the 20 formation to ensure that the annulus behind the casing is filled with cement and properly sealed off. It is known to therefore run wire line perforating explosive guns downhole to perforate the wellbore, and after the 25 explosive perforating operation is conducted, pull the explosive guns out from the wellbore. Tubing can then be run into the wellbore to set a cement retainer. After this operation, cementing and pressure testing can be conducted below and above the cement retainer. 30 This procedure suffers from the drawback that it is costly and time consuming. Multiple different operations must be conducted in the wellbore and each time the equipment needs to be changed, the work string must be retrieved to the surface for the next tool to be run into the wellbore. Preferred embodiments of the present disclosure seek to 5 overcome the above disadvantages of the prior art. According to an aspect of the present disclosure, there is provided an assembly for use in abandoning a wellbore, the assembly comprising: 10 at least one perforating apparatus operable to mechanically cut perforations in a wellbore casing; a cement retainer deployment assembly comprising a mandrel 15 configured to slidably receive at least one cement retainer assembly, wherein said mandrel is configured to deploy said at least one cement retainer assembly in the wellbore and wherein said mandrel also comprises a longitudinal bore to enable cement or another sealing material to be pumped 20 through said at least one cement retainer assembly; and wherein said mandrel is configured to be pulled through said at least one cement retainer assembly to release said at least one cement retainer assembly to enable re-use of said 25 at least one perforating apparatus and said cement retainer deployment assembly at a different location in the wellbore or retrieval of the assembly to the surface for re-use. This provides the advantage of a work string assembly that 30 can conduct a multi-zone perforating and cementing operation to safely abandon a wellbore in a single downhole operation without retrieval to the surface. Using a perforating apparatus operable to mechanically cut perforations in a wellbore casing removes the need for explosive charges to be first deployed in the wellbore and then retrieved to the surface to perforate the wellbore 5 casing. It has been found that a cement retainer deployment assembly can be placed in the assembly below the perforating tool to enable the one or more cement retainers or bridge plugs to be deployed in a single operation after perforating. 10 In a preferred embodiment, said mandrel is configured to selectively permit or prevent relative rotation between said mandrel and a cement retainer assembly disposed thereon. In a preferred embodiment, said mandrel has a non-circular 15 portion formed along part of the length of the mandrel, wherein when a first part of said at least one cement retainer assembly is located on said non-circular portion, relative rotation is prevented between the mandrel and said first part of said at least one cement retainer assembly and 20 when a second part of said at least one cement retainer is not located on said non-circular portion, relative rotation is permitted between the mandrel and said second part of said at least one cement retainer assembly. 25 This provides the advantage of enabling the cement retainer assembly to be set in the wellbore by rotation only in most circumstances. The parts of a cement retainer requiring rotation to set such a slips can be accommodated in the same work string as for example a no-turn tool to provide drag for 30 setting. In a preferred embodiment, said cement retainer assembly further comprises a tensioning and release apparatus disposed on the end of said mandrel to enable the mandrel to be pulled to put said cement retainer assembly into tension, and wherein said cement retainer assembly tensioning and release apparatus is inwardly deformable to enable said mandrel to be 5 pulled through said cement retainer assembly to release said cement retainer assembly from said mandrel. This provides the advantage of both a means to release the mandrel from a set cement retainer and a means of setting 10 cement retainers or bridge plugs that are set by tension and compression only. Said cement retainer assembly tensioning and release apparatus may comprise a deformable collet disposed on an end 15 of said mandrel, wherein once a cement retainer assembly has been set in position in a wellbore casing, pulling the mandrel with a predetermined level of force deforms said deformable collet and enables the mandrel to be pulled through the cement retainer assembly to release said cement 20 retainer assembly from the mandrel. This provides the advantage of a straightforward means of releasing a cement retainer once set in a wellbore. 25 In a preferred embodiment, said at least one perforating apparatus comprises at least one hydraulic cylinder operable to move said and at least one perforating element between the inwardly retracted condition and outwardly deployed condition in response to actuation of said at least one hydraulic 30 cylinder. This provides the advantage that the perforating apparatus can be actuated by use of pressurised fluid pumped from the surface to deploy the perforating elements. This is advantageous because it means that the same longitudinal bore used to increase fluid pressure in the assembly can also be used to pump cement into the portion of the wellbore below 5 the set retainer after the perforating operation is completed. In a preferred embodiment, said at least one perforating apparatus further comprises a deformable ball seat arranged 10 to catch a deformable ball dropped through a longitudinal bore of said at least one perforating apparatus to cause a blockage to enable fluid pressure to be increased in said at least one perforating apparatus to enable said at least one perforating element to move between the inwardly retracted 15 condition and outwardly deployed condition. This provides the advantage of a straightforward means of activating and deactivating the perforating apparatus. 20 In a preferred embodiment, increasing fluid pressure in the longitudinal bore above a predetermined level deforms said deformable ball to enable said deformable ball to move past the deformable ball seat to permit cement to be pumped into a longitudinal bore of the mandrel. 25 This provides the advantage that the act of deactivating the perforating tool clears the obstruction of the deformable ball in the longitudinal bore of assembly to clear a path for cement to flow through the mandrel after the perforating 30 operation is completed. In a preferred embodiment, the assembly further comprises a cement retainer assembly which comprises: a cement retainer comprising at least one gripping element, wherein the gripping element is moved from an inwardly retracted condition to an outwardly deployed condition in 5 which said at least one gripping element grips a wellbore casing by rotation of the mandrel relative to said at least one gripping element; a valve apparatus configured to close when said mandrel is 10 removed from the cement retainer assembly to retain cement below the cement retainer assembly in the wellbore; and a rotation prevention apparatus configured to engage a wellbore casing to prevent rotation of the cement retainer 15 assembly to enable relative rotation between the cement retainer assembly and the mandrel. This provides the advantage of a cement retainer assembly that can be deployed on an assembly for abandoning a wellbore 20 comprising a mechanical perforating apparatus and a rotatable mandrel. The rotation prevention apparatus commonly known as a no-turn tool in downhole operations creates drag against the wellbore 25 to enable the mandrel to rotate and deploy the various elements of the assembly. In a preferred embodiment, said cement retainer assembly further comprises a first elastomeric sealing element 30 deformable to seal against a wellbore casing by rotation of the mandrel relative to said first elastomeric sealing element. In a preferred embodiment, said cement retainer assembly further comprises a ratchet sleeve configured to prevent movement of said cement retainer assembly along said mandrel in a first direction, but permit movement of said cement 5 retainer assembly along said mandrel in a second direction, opposite to said first direction. This provides the advantage of both preventing the cement retainer moving up the mandrel during setting which could 10 result in the cement retainer being partially un-set as well as providing the advantage that weight can be set down on the assembly to ensure full setting of the cement retainer. In a preferred embodiment, said cement retainer assembly 15 further comprises an internal sealing apparatus comprising a second elastomeric sealing element deformable to form a seal between said mandrel and an inner diameter of the assembly by rotation of the mandrel relative to said second elastomeric sealing element. 20 This provides the advantage of preventing fluid leakage through the elements of the assembly during a pressure test of the set cement retainer. 25 According to another aspect of the present disclosure, there is provided a cement retainer assembly, wherein the cement retainer assembly is slidably mountable on a mandrel of an assembly for use in abandoning a wellbore, the cement retainer assembly comprising: 30 a cement retainer comprising at least one gripping element, wherein the gripping element is moved from an inwardly retracted condition to an outwardly deployed condition in which said at least one gripping element grips a wellbore casing by rotation of the mandrel relative to said at least one gripping element; 5 a valve apparatus configured to close when said mandrel is removed from the cement retainer assembly to retain cement below the cement retainer assembly in the wellbore; and a rotation prevention apparatus configured to engage a 10 wellbore casing to prevent rotation of the cement retainer assembly to enable relative rotation between the cement retainer assembly and the mandrel. This provides the advantage of a cement retainer assembly 15 that can be deployed on an assembly for abandoning a wellbore comprising a mechanical perforating apparatus and a rotatable 1— mandrel. 00 The rotation prevention apparatus commonly known as a no-turn 20 tool in wellbore operations creates drag against the wellbore to enable the mandrel to rotate and deploy the various elements of the assembly. According to a further aspect of the present disclosure, 25 there is provided a method of abandoning a wellbore, the method comprising deploying into a wellbore an assembly as defined above on which at least one cement retainer assembly is slidably mounted on the mandrel of the assembly; 30 operating said at least one perforating apparatus to cut perforations in the wellbore casing; moving the assembly to a position in which said at least cement retainer assembly is positioned above the perforations cut into the wellbore casing; and 5 operating the cement retainer deployment assembly to place a cement retainer assembly in the wellbore; pumping cement through the mandrel of the assembly to fill the portion of the wellbore below said cement retainer 10 assembly with cement; and removing the cement retainer deployment assembly from the cement retainer assembly. 15 This provides the advantage of a method of conducting a multiple-zone perforating and cementing operation to safely abandon a wellbore in a single downhole operation without retrieval to the surface. 20 Using a perforating apparatus operable to mechanically cut perforations in a wellbore casing removes the need for explosive charges to be first deployed in the wellbore and then retrieved to the surface to perforate the wellbore casing. It has been found that a cement retainer deployment 25 assembly can be placed in the assembly below the perforating tool to enable the one or more cement retainers or bridge plugs to be deployed in a single operation after perforating. Said at least one cement retainer assembly may be a cement 30 retainer assembly as defined above. In a preferred embodiment, the step of removing the cement retainer deployment assembly from the cement retainer assembly comprises operating a cement retainer assembly tensioning and release apparatus to deform inwardly to enable said mandrel to be pulled through said cement retainer assembly to release said cement retainer assembly from said 5 mandrel. In a preferred embodiment, the step of operating said at least one perforating apparatus includes dropping a deformable ball into the longitudinal bore of the assembly. 10 This provides the advantage of a straightforward means of activating and deactivating the perforating apparatus. This also provides the advantage that the act of deactivating 15 the perforating tool clears the obstruction of the deformable ball in the longitudinal bore of assembly to clear a path for cement to flow through the mandrel after the perforating operation is completed. 20 In a preferred embodiment, the step of operating the cement retainer deployment assembly includes rotating said cement retainer deployment assembly to cause said rotation prevention apparatus to engage the wellbore and create drag which causes said mandrel to rotate relative to said at least 25 one gripping element to cause the gripping element to move from the inwardly retracted condition to the outwardly deployed condition to set the cement retainer in the wellbore . 30 This provides the advantage that the cement retainer can be set by rotation alone. In a preferred embodiment, rotation of the cement retainer deployment assembly also deforms said first elastomeric sealing element against the wellbore. 5 In a preferred embodiment, rotation of the cement retainer deployment assembly causes said second elastomeric sealing element to be deformed to form a seal between said mandrel and an inner diameter of the assembly. 10 Preferred embodiments of the present disclosure will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which: Figure la is a truncated elevation view of a work string 15 bottom hole assembly (BHA) comprising an assembly in accordance with the present disclosure for abandoning a wellbore; Figure lb is a longitudinal cross-section corresponding to 20 Figure la; Figure 2 is a perspective view of the mandrel of the assembly of Figure la; 25 Figure 3 is a radial cross-section of the mandrel of Figure 2; Figure 4a is an end view of a cement retainer assembly for use on the assembly of Figures la and lb; Figure 4b is a longitudinal cross-sectional view of the cement retainer assembly taken along line D-D of Figure 4a; Figure 5a is an end view of the cement retainer assembly of Figures 4a and 4b shown with the cement retainer in the set position; 5 Figure 5b is a longitudinal cross-section of the cement retainer assembly taken along line Dl-Dl of Figure 5a; Figure 6a is an end view of a cement retainer of the cement retainer assembly of Figures 4a to 5b; 10 Figure 6b is a longitudinal cross-section of the cement retainer of Figure 6a taken along line B-B of Figure 6a; Figure 7a is an end view of an internal sealing apparatus of 15 the cement retainer assembly of Figures 4a to 5b shown in the unset position; Figure 7b is a longitudinal cross-sectional view taken along line C-C of Figure 7a; 20 Figure 8a is an end view of the internal sealing element of Figures 7a and 7b shown in the set position; Figure 8b is a longitudinal cross-sectional view of the 25 internal sealing element taken along line Cl-Cl of Figure 8a; Figure 9a is a truncated elevation view of the assembly of Figures la and lb shown with the cement retainer assembly set in a wellbore and the mandrel being separated from the cement 30 retainer assembly above perforations; Figure 9b is a longitudinal cross-sectional view of the assembly of Figure 9a; and Figure 10 is a truncated elevation view of a wellbore in which multiple retainers are set above perforations. 5 Referring to Figures la and lb, an assembly 2 for use in abandoning a wellbore comprises at least one perforating apparatus 4 operable to mechanically cut perforations in a wellbore casing and a cement retainer deployment assembly 6 comprising a mandrel 10 configured to slidably receive at 10 least one cement retainer assembly 8, wherein said mandrel 10 is configured to deploy the cement retainer assembly 8 in the wellbore and wherein said mandrel 10 also comprises a longitudinal bore 16 to enable cement or another sealing material to be pumped through the cement retainer assembly 8. 15 Referring to Figure 2, mandrel 10 is configured to selectively permit or prevent relative rotation between the mandrel 10 and a cement retainer assembly 8 disposed thereon. Mandrel 10 has a non-circular portion 10a formed along a part 20 of its length and a circular portion 10b at its end. The non-circular portion 10a is formed by a pair of splines 12a and 12b diametrically opposed and machined into the surface of the mandrel 10. 25 Parts of cement retainer assembly 2 disposed on the non-circular portion 10a of the mandrel 10 are not permitted to rotate relative to the mandrel 10, whilst parts of the cement retainer assembly 8 disposed on the circular portion 10b of mandrel 10 are permitted to rotate relative to the mandrel 30 10. Whilst a pair of diametrically opposed splines are used to make the mandrel non-circular, any means of preventing rotation can be used, such as stick-slip mechanisms, clutches or ratchets. Referring to Figures la, lb, 9a and 9b, a cement retainer assembly tensioning and release apparatus in the form of a deformable collet 56 is formed on the end of the mandrel 5 having collet fingers 58 and inclined surfaces 60. When the operator pulls the assembly 2 upwardly with sufficient force, inclined surfaces 60 push against the bottom of rotation prevention apparatus 38 to deform fingers 58 inwardly enabling the mandrel 10 to be pulled through cement retainer 10 assembly 8 to release the cement retainer 8. An alternative embodiment of cement retainer assembly tensioning and release apparatus would be a collet having an indexing mechanism which is indexed by tensioning and 15 releasing index fingers inwardly with a clutch system, barrel cam or other mechanism. However, the objective of the cement retainer assembly tensioning and release apparatus is to enable inward deformation to reduce the outer end diameter of mandrel 10 to enable the mandrel to be pulled through cement 20 retainer assembly 8. The perforating apparatus 4 comprises at least one hydraulic cylinder 14 arranged to be filled with pressurised fluid flowing along longitudinal bore 16 to move perforating 25 elements 18 from the inwardly retracted condition as shown in Figure lb to an outwardly deployed condition to cut perforations in a wellbore. The perforating apparatus described herein is the Gator Perforator ® of Lee Energy Systems of Calgary, Canada as disclosed in EP2616625B and its 30 corresponding family of patents, the contents of which are incorporated herein by reference. This apparatus operates by using differential pressure between the longitudinal bore 16 and the annulus outside of the tool to create a linear force to deploy perforating elements 18. However, other apparatuses that mechanically perforate casing could also be used in assembly 2. 5 Perforating apparatus 4 is activated by dropping a deformable ball down longitudinal bore 16. The deformable ball lodges in deformable ball seat 20 and the operator can then pressure up the longitudinal bore 16 to deploy perforating elements 18 to cut perforations 52. By reducing and increasing pressure 10 and moving the assembly 2 along the wellbore, as many perforations 52 can be cut as required. In an alternative embodiment, perforating apparatus 4 could be activated by using a velocity control valve (not shown). 15 The velocity control valve would be configured to close at a higher flow rate to enable the perforating apparatus 4 to be pressured up for perforating. At lower flow rates, the velocity control valve would be open to permit cement or other sealing agents to be pumped through the longitudinal 20 bore without activating the perforating apparatus 2. Referring to Figures la through 8b, cement retainer assembly 8 comprises a cement retainer 22 having a lower slip cone 24 which forms a gripping element, a further gripping element in 25 the form of an upper slip cone 26 and an elastomeric deformable element 28. When the mandrel 10 (Figure lb) is rotated, splines 12a and 12b (Figures 2 and 3) engage corresponding splines (not shown) machined into the cement retainer 22. This rotational movement rotation causes lower 30 slip cone 24 to ride upwardly along a machined thread (not shown) to upwardly compress the retainer 22 which causes slips 30 and 32 to ride outwardly to grip the wellbore and elastomeric sealing element 28 to be compressed to seal in the wellbore. This rotational movement is enabled by rotation prevention 5 apparatus 38 engaging the casing to cause drag and a reaction force to enable splines 12a and 12b to rotate the inner components of the assembly. Rotation prevention apparatus 38 comprises spring loaded drag elements 40 configured to cause drag against rotation in the wellbore. Rotation prevention 10 apparatus 38 is mounted on the circular portion 10b of mandrel 10 such that mandrel 10 freely rotates inside of rotation prevention apparatus 38. However, since the rotation prevention apparatus 38 is rotationally fixed to the cement retainer 22, the splined section of mandrel 10b can rotate 15 inner components of cement retainer 22. Such rotation prevention apparatuses 38 are generally known as no-turn tools. Any means of engaging the wellbore casing to create drag may be used rather than spring loaded elements 20 40. A valve apparatus 34 comprises a flapper element 36 configured to spring closed from the open position shown in Figure 4b to the closed position of Figure 5b when the 25 mandrel 10 is withdrawn from the cement retainer assembly 8. This ensures that cement pumped into the wellbore below flapper element 36 cannot move back up the wellbore. Cement retainer assembly 8 also includes an inner diameter 30 sealing assembly 42. When the cement retainer assembly 8 is set, a seal must be made on the mandrel 10 to enable a pressure test of the assembly to be conducted. This is where fluid is pumped into the annulus outside of the assembly 2 to test that the cement retainer 22 is set and seals against the wellbore. The first elastomeric sealing element 44 of inner diameter sealing assembly 42 is splined to engage splines 12a and 12b of mandrel 10 such that rotation of the mandrel 10 5 moves lower sleeve 46 upwardly along a machined thread (not shown) to compress first elastomeric sealing element 44. A ratchet sleeve 48, also known as a slip set, has teeth 50 which can slip downwardly (to the right in Figure 4b) but 10 when teeth 50 attempt to move upwardly (to the left in Figure 4b) the teeth 50 bite into a profile to prevent the ratchet sleeve moving up and therefore prevent the other elements of the cement retainer assembly 8 moving upwardly. This enables the operator to put set down weight on to the cement retainer 15 22 to ensure full pack-off if rotation has not completely set the retainer. With reference to Figures la, lb, 4a, 4b, 5a, 5b, 9a and 9b, the operation of the assembly 2 to abandon a wellbore will be 20 described. A bottom hole assembly 2 for abandoning a wellbore is assembled by first sliding plurality of cement retainer assemblies 8 on to mandrel 8. Perforating apparatus 4 is then 25 connected to mandrel 10 and the assembly 2 deployed in a wellbore to a position in which perforations 52 are to be cut in casing 53 to allow fluid communication between the inside of the casing 53 and the annulus 55 outside of the casing. 30 The perforating operation is conducted by dropping a deformable ball down longitudinal bore 16. The deformable ball lodges in deformable ball seat 20 and the operator can then pressure up the longitudinal bore 16 to deploy perforating elements 18 to cut perforations 52. By reducing and increasing pressure and moving the assembly 2 along the wellbore, as many perforations 52 can be cut as required. 5 Once the perforating operation is conducted, the lower most cement retainer assembly is positioned above the perforations and the longitudinal bore 16 is pressurised to blow deformable ball through deformable ball seat 20. The assembly 2 is then rotated. This rotation causes splines 12a 10 and 12b of mandrel 10 to rotate corresponding splines (not shown) in cement retainer 22 and corresponding screw threads (not shown) cause the slips 32 and 30 to be deployed outwardly to grip the wellbore. 15 This relative rotation is permitted because the rotation prevention apparatus 38 is located on the circular part 10b of mandrel 10 such that relative rotation is permitted between the mandrel 10 and rotation prevention apparatus 38. However, drag elements 40 create drag against the casing and 20 because all of the parts of the cement retainer assembly 8 are rotationally fixed together, the cement retainer assembly 8 is held rotationally static in the wellbore by rotation prevention apparatus 38 meaning that mandrel 10 can rotate and move the inner components of the cement retainer assembly 25 8 to cause both the cement retainer slips 30 and 32 to set as well as deploy the elastomeric sealing element 28. This rotation also causes the inner diameter sealing apparatus 42 to set and form a seal 44 against the mandrel. 30 A pressure test can then be conducted to ensure that the cement retainer assembly is set. The operator has the option of setting down weight on the assembly to complete the setting of the cement retainer 22. All of the elements of the cement retainer 78 are prevented from moving up the wellbore by ratchet sleeve 48. Once the operator is satisfied that the cement retainer 22 is 5 set and forms a seal in the wellbore, cement can be pumped along longitudinal bore 16 to fill the area 54 below the wellbore. In some wellbore conditions, in order to prevent perforating elements 18 deploying during the cementing operation, there may be a hydrostatic imbalance which 10 requires the operators to apply pressurised fluid down the annulus to offset imbalance in order to prevent the perforating tool 4 actuating during cementing. Referring to Figures 9a and 9b, a deformable collet 56 is 15 formed on the end of the mandrel having collet fingers 58 and inclined surfaces 60. When the operator pulls the assembly 2 upwardly with sufficient force, inclined surfaces 60 push against the bottom of rotation prevention apparatus 38 to deform fingers 58 inwardly enabling the mandrel 10 to be 20 pulled through cement retainer assembly 8 to release the cement retainer 8 as shown in Figures 9a and 9b. The act of doing this causes spring loaded flapper 36 to spring shut into the condition shown in Figure 9b to trap cement, wellbore fluid and / or hydrocarbons in the wellbore. The perforating and cementing operation can then be repeated again in a location in the wellbore above the cement retainer assembly 8 has been set. A further cement retainer assembly 8 will slide down the mandrel 10 to engage collet 56 such 30 that once perforation has been conducted, a further cement retainer assembly 8 can be set. Referring to Figure 10, which is a truncated view of a wellbore in which multiple retainers are set, it can be seen that each cement retainer assembly 8 is set in position above wellbore perforations 52 which shows what can be achieved by 5 assembly 2 without having to retrieve the assembly 2 to the surface. All this is accomplished in a single downhole operation and the number of cement retainer assemblies 8 able to be placed in a wellbore is only limited by the length of mandrel 10. 10 Assembly 2 is also able to deploy cement retainers, bridge plugs and other sealing tools which do not require rotation to set. Many such tools are released by rotation but are then set by applying tension and compression on the tools to 15 lock the slips and sealing elements in place. This can be accomplished with assembly 2 because assembly 2 enables tensioning and compression on cement retainers or bridge plugs of any configuration as set out above. Assembly 2 can therefore be used with other cement retainers and bridge 20 plugs aside from cement retainer assembly 8 as described. Any reference to 'cement' in the present disclosure should be construed to also cover other types of sealing agents such as BiSN, resin or resolute material. 25 Any reference to 'cement retainer' in the present disclosure should be construed to also cover other types of sealing apparatuses such as bridge plugs that can be used to retain fluids in wellbores. 30 It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of protection as defined by the appended claims. 20 05 25

Claims

1. An assembly for use in abandoning a wellbore, the5 assembly comprising:at least one perforating apparatus operable to mechanically cut perforations in a wellbore casing;10 a cement retainer deployment assembly comprising a mandrel configured to slidably receive at least one cement retainer assembly, wherein said mandrel is configured to deploy said at least one cement retainer assembly in the wellbore and wherein said mandrel also comprises a longitudinal bore to15 enable cement or another sealing material to be pumped through said at least one cement retainer assembly; andwherein said mandrel is configured to be pulled through said at least one cement retainer assembly to release said at20 least one cement retainer assembly to enable re-use of said at least one perforating apparatus and said cement retainer deployment assembly at a different location in the wellbore or retrieval of the assembly to the surface for re-use.25 2. An assembly according to claim 1, wherein said mandrelis configured to selectively permit or prevent relative rotation between said mandrel and a cement retainer assembly disposed thereon.30 3. An assembly according to claim 2, wherein said mandrelhas a non-circular portion formed along part of the length of the mandrel, wherein when a first part of said at least one cement retainer assembly is located on said non-circular20 05 25portion, relative rotation is prevented between the mandrel and said first part of said at least one cement retainer assembly and when a second part of said at least one cement retainer is not located on said non-circular portion,5 relative rotation is permitted between the mandrel and said second part of said at least one cement retainer assembly.

4. An assembly according to any one of the preceding claims, further comprising a cement retainer assembly10 tensioning and release apparatus disposed on the end of said mandrel to enable the mandrel to be pulled to put said cement retainer assembly into tension, and wherein said cement retainer assembly tensioning and release apparatus is able to be pulled through said cement retainer assembly to release15 said cement retainer assembly from said mandrel when a predetermined tension is applied to the cement retainer assembly tensioning and release apparatus.

5. An assembly according to claim 4, wherein said cement 20 retainer assembly tensioning and release apparatus is inwardly deformable to enable said mandrel to be pulled through said cement retainer assembly to release said cement retainer assembly from said mandrel.25 6. An assembly according to claim 4 or 5, wherein saidcement retainer assembly tensioning and release apparatus comprises a deformable collet disposed on an end of said mandrel, wherein once a cement retainer assembly has been set in position in a wellbore casing, pulling the mandrel with a 30 predetermined level of force deforms said deformable collet and enables the mandrel to be pulled through the cement retainer assembly to release said cement retainer assembly from the mandrel.20 05 257. An assembly according to any one of the preceding claims, wherein said at least one perforating apparatus comprises at least one hydraulic cylinder operable to move 5 said and at least one perforating element between theinwardly retracted condition and outwardly deployed condition in response to actuation of said at least one hydraulic cylinder .10 8. An assembly according to claim 7, wherein said at leastone perforating apparatus further comprises a deformable ball seat arranged to catch a deformable ball dropped through a longitudinal bore of said at least one perforating apparatus to cause a blockage to enable fluid pressure to be increased15 in said at least one perforating apparatus to enable said at least one perforating element to move between the inwardly retracted condition and outwardly deployed condition.

9. An assembly according to claim 8, wherein increasing20 fluid pressure in the longitudinal bore above a predetermined level deforms said deformable ball to enable said deformable ball to move past the deformable ball seat to permit cement to be pumped into a longitudinal bore of the mandrel.25 10. An assembly according to any one of the precedingclaims, further comprising at least one cement retainer assembly which comprises:a cement retainer comprising at least one gripping30 element, wherein the gripping element is moved from an inwardly retracted condition to an outwardly deployed condition in which said at least one gripping element grips a20 05 25wellbore casing by rotation of the mandrel relative to said at least one gripping element;a valve apparatus configured to close when said mandrel5 is removed from the cement retainer assembly to retain cement below the cement retainer assembly in the wellbore; anda rotation prevention apparatus configured to engage a wellbore casing to prevent rotation of the cement retainer10 assembly to enable relative rotation between the cement retainer assembly and the mandrel.

11. An assembly according to claim 10, wherein said cement retainer assembly further comprises a first elastomeric15 sealing element deformable to seal against a wellbore casing by rotation of the mandrel relative to said first elastomeric sealing element.

12. An assembly according to claim 10 or 11, wherein said20 cement retainer assembly further comprises a ratchet sleeve configured to prevent movement of said cement retainer assembly along said mandrel in a first direction, but permit movement of said cement retainer assembly along said mandrel in a second direction, opposite to said first direction.2513. An assembly according to any one of claims 10 to 12, wherein said cement retainer assembly further comprises an internal sealing apparatus comprising a second elastomeric sealing element deformable to form a seal between said30 mandrel and an inner diameter of the assembly by rotation of the mandrel relative to said second elastomeric sealing element.20 05 2514. A method of abandoning a wellbore, the method comprising deploying into a wellbore an assembly according to any one of the preceding claims on which at least one cement 5 retainer assembly is slidably mounted on the mandrel of the assembly;operating said at least one perforating apparatus to cut perforations in the wellbore casing;10moving the assembly to a position in which said at least cement retainer assembly is positioned above the perforations cut into the wellbore casing; and15 operating the cement retainer deployment assembly to place a cement retainer assembly in the wellbore;pumping cement through the mandrel of the assembly to fill the portion of the wellbore below said cement retainer20 assembly with cement; andremoving the cement retainer deployment assembly from the cement retainer assembly.25 15. A method according to claim 14, wherein the step ofremoving the cement retainer deployment assembly from the cement retainer assembly comprises operating a cement retainer assembly tensioning and release apparatus to deform inwardly to enable said mandrel to be pulled through said30 cement retainer assembly to release said cement retainer assembly from said mandrel.20 05 2516. A method according to claim 14 or 15, wherein the step of operating said at least one perforating apparatus includes dropping a deformable ball into the longitudinal bore of the assembly.

517. A method according to any one of claims 14 to 16 wherein the step of operating the cement retainer deployment assembly includes rotating said cement retainer deployment assembly to cause said rotation prevention apparatus to10 engage the wellbore and create drag which causes said mandrel to rotate relative to said at least one gripping element to cause the gripping element to move from the inwardly retracted condition to the outwardly deployed condition to set the cement retainer in the wellbore.1518. A method according to claim 17, in which rotation of the cement retainer deployment assembly also deforms said first elastomeric sealing element against the wellbore.20 19. A method according to claim 17 or 18, wherein rotationof the cement retainer deployment assembly causes said second elastomeric sealing element to be deformed to form a seal between said mandrel and an inner diameter of the assembly.

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