WO2016118714A1

WO2016118714A1 - Wellhead-mounted hydraulic workover unit

Info

Publication number: WO2016118714A1
Application number: PCT/US2016/014268
Authority: WO
Inventors: Richard J. Segura; Steven A. CANNY; Keith J. WICKER; Delaney Michael Olstad
Original assignee: Weatherford Technology Holdings, Llc
Priority date: 2015-01-21
Filing date: 2016-01-21
Publication date: 2016-07-28

Abstract

The present disclosure generally relates to a workover unit (100) that is efficient, light weight and with a small footprint, and methods for performing well intervention using the work unit (100). A workover unit (100) according to the present disclosure includes a work floor (114), a first mast tower (116A) and a second mast tower (116B) mounted on the work floor (114), and a drill line assembly connecting the first and second mast towers (116A,116B). The workover unit (100) may be mounted on a wellhead (104).

Description

WELLHEAD-MOUNTED HYDRAULIC WORKOVER UNIT

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

[0001] The present disclosure generally relates to a workover unit for offshore platforms.

Description of the Related Art

[0002] Workover units are well service tools used to perform intervention, well abandonment, and other well control functions against well pressure. Traditional workover units, such as snubbing units, generally include stationary slips, and travelling slips mounted on a hydraulic jack. The stationary slips and the travelling slips work together to perform the function of gripping, pulling and inserting a drill pipe string. Traditional workover units also include a work basket, which is usually located above the stationary slips, to provide space for operation. A gin pole, a tong carrier, and other equipment are also mounted on the work basket.

[0003] Traditional workover units are usually cumbersome and cannot be rigged up on small platforms, such as mono-pod platforms, tri-pod platforms, or platforms that do not have a deck with enough area or weight bearing. Additionally, traditional workover units are also slow in performing well intervention tasks as it takes multiple exchanges of gripping between the stationary slips and the travelling slips to insert or pull one link of drill pipe.

[0004] Therefore, there is a need for a workover unit that is efficient, light weight and with a small footprint.

SUMMARY OF THE DISCLOSURE

[0005] The present disclosure generally relates to a workover unit that is efficient, light weight and with a small footprint, and methods for performing well intervention using the work unit.

[0006] One embodiment of the present disclosure provides a workover unit. The work unit includes a work floor, a first mast tower and a second mast tower mounted on the work floor, a drill line assembly coupled to the two mast towers, and a tool connected to the drill line assembly between the first and second mast towers, wherein stroking up or stroking down of the first and second mast towers moves the tool up or down.

[0007] Another embodiment provides a method for well intervention. The method comprises gripping a drill pipe string using a gripping assembly suspended from a drill line assembly between a first and second mast towers, and stroking up or stroking down the first and second mast towers to raise or lower down the drill pipe string.

[0008] Another embodiment provides a workover unit. The work unit includes a work floor, a first mast tower and a second mast tower mounted on the work floor, a drill line assembly coupled to the two mast towers, and a tool connected to the drill line assembly between the first and second mast towers, wherein extending or retracting at least one of the first mast tower and the second mast tower moves the tool up and down relative to the work floor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

[0010] Figure 1 A is a schematic side view of a workover unit according to one embodiment of the present disclosure.

[0011] Figure 1 B is the workover unit of Figure 1 A in a raised position.

[0012] Figure 1 C is a schematic side view of a workover unit without an optional casing jack and an optional load distributing assembly. [0013] Figure 2 is a schematic side view of a workover unit according to another embodiment of the present disclosure.

[0014] Figure 3 is a schematic partial side view of a workover unit according to another embodiment of the present disclosure.

[0015] Figure 4 is a schematic view of a workover unit mounted on a moored vessel.

[0016] Figure 5 is a schematic view of a workover unit mounted on a cantilever of a lift boat.

[0017] Figure 6A is a schematic side view of a workover unit according to another embodiment of the present disclosure.

[0018] Figure 6B is another schematic side view of the workover unit of Figure 6A.

[0019] Figure 6C is a schematic top view of the workover unit of Figure 6A.

[0020] Figure 6D is a schematic side view of the workover unit of Figure 6A in an extended position.

[0021] Figure 7A is a schematic top view of a spreader bar according to one embodiment of the present disclosure.

[0022] Figure 7B is a schematic side view of the spreader bar of Figure 7A connected to a power swivel.

[0023] Figure 7C is a schematic side view of the spreader bar of Figure 7A connected to an elevator.

[0024] Figure 8A is a schematic side view of a telescope cylinder used in workover units according to embodiments of the present disclosure.

[0025] Figure 8B is a schematic side view of the telescope cylinder in an extended position. [0026] Figure 9 schematically illustrates a layout of a workover unit deployed on a single well according to one embodiment of the present disclosure.

[0027] Figure 10 schematically illustrates a layout of a workover unit deployed on multiple wells according to one embodiment of the present disclosure.

[0028] Figure 1 1 schematically illustrates a layout of a workover unit deployed on multiple wells according to another embodiment of the present disclosure.

[0029] Figure 12 schematically illustrates a layout of a workover unit deployed on a single well caisson according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

[0030] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope of the present invention is determined by the claims that follow.

[0031] Embodiments of the present disclosure relate to a light weight and small footprint workover unit to perform well intervention or abandonment on offshore platforms. The workover unit is able to pick up joints of drill pipe or tubing as well as completion BHA's (bottomhole assemblies). The workover unit may be rigged up on small platforms such as mono-pod platforms, tri-pod platforms, and platforms that do not have a deck that has enough space or weight bearing capacity to support the traditional units.

[0032] In one embodiment, the workover unit is designed to have the pull force directly applied over the wellhead. In one embodiment, the workover unit includes two mast towers positioned symmetrically about a well center. Each mast tower includes a hydraulic cylinder and one or more sheaves, and a drill line assembly connects the two mast towers. The drill line assembly may include a spreader bar or a travelling block with a pulley or pulleys. The spreader bar or the travelling block may be attached to either a set tubular elevators or a power swivel. The cylinder stroke of the mast towers provides the lifting power to the elevators or the power swivel through the drill line assembly.

[0033] In one embodiment, a casing jack may be used to provide additional lifting power. The casing jack can also be used as a work window for running ESP cables (Electrical Submersible Pump cables), control lines or intelligent completion cables, thus preventing any damage to the cables on the rig floor without using special handling equipment, such as slotted bowls.

[0034] The workover unit may be rigged up on a wellhead and the wellhead provides support of the entire weight of the workover unit as well as the over pull needed. In some embodiments, the workover unit may have an option of distributing the weight and load between a wellhead and a platform. The distribution may be achieved by I-beams installed across platform legs to transfer the load from the work floor to the platform legs.

[0035] In one embodiment, auxiliary equipment, such as work strings, completion strings, completion equipment, pumps, tanks, generators, HPU's (Hydraulic Power Units), and the like, may be located on a vessel or a lift boat. In another embodiment, the auxiliary equipment may be rigged up on the platform.

[0036] In one embodiment, the workover unit may be rigged up on a lift boat with a cantilever system that extends over the platform. The lift boat can position the workover unit over the well center. Mounting the workover unit on the lift boat can be used to limit the weight on small or downgrade platforms.

[0037] Figure 1 A is a schematic side view of a workover unit 100 according to one embodiment of the present disclosure. The workover unit 100 is shown mounted on a platform wellhead 104 of a platform 102. An assembly of valves, spools, pressure gauges and chokes, also known as the Christmas tree, typically fitted to the platform wellhead 104 for controlling production, is removed from the platform wellhead 104 to allow mounting of the workover unit 100. In one embodiment, the workover unit 100 may be mounted on a flange 106 of the platform wellhead 104.

[0038] Optionally, a BOP (blowout preventer) stack 108 may be disposed between the workover unit 100 and the platform wellhead 104. The BOP stack 108 functions to restrain the pressure in the wellbore during the operation of the workover unit 100. In one embodiment, the BOP stack 108 may include a lower annular BOP 108a, an upper annular BOP 108b, and a ram BOP 108c.

[0039] An adaptor 1 10 may be mounted on the BOP stack 108 as shown in Figure 1A, or directly on the flange 106 of the platform wellhead 104 when the BOP stack 108 is not present. The adaptor 1 10 may have a shoulder 1 1 1 to receive and support of the workover unit 100. In Figure 1A, the shoulder 1 1 1 receives a unit floor 1 12 and provides support to the workover unit 100. Columns 1 13 may extend from the unit floor 1 12. A work floor 1 14 may be supported by the columns 1 14. Handrails 1 15 may be installed at a perimeter of the work floor 1 14.

[0040] An optional casing jack 130 may be mounted over the adaptor 1 10. The casing jack 130 may be used to provide additional pulling capacity to the workover unit 100. Slips in the casing jack 130 may be used to support a drill pipe string 101 , thus eliminating a need of slips on the work floor 1 14. In one embodiment, the casing jack 130 may include a lower casing bowl 132 attached to the adaptor 1 10, one or more hydraulic cylinders 134 extending vertically from the lower casing bowl 132, and an upper casing bowl 136 attached to the hydraulic cylinders 134. The hydraulic cylinders 134 may be activated to raise and/or lower the upper casing bowl 136. The upper casing bowl 136 may be raised above the work floor 1 14 through an opening 1 14a on the work floor 1 14. The upper casing bowl 136 includes slips 138. The slips 138 may be manual or air slips. The drill pipe string 101 may be set on the slips 138 during operation. When additional pulling force is needed, the drill pipe string 101 may be set on the slips 138 and the hydraulic cylinders 134 may be activated to provide pulling power in addition to the pulling power provided by the workover unit 100. Additionally, spacing between the hydraulic cylinders 134 may be used as work window(s) to allow cables, such as ESP power cables, control lines, intelligent completion, and the like, to be run or pulled from the wellbore. This configuration keeps all the standard drill pipe handlings on the work floor 1 14. [0041] Alternatively, the casing jack 130 may be mounted on the unit floor 1 12. Alternatively, slips may be installed on the work floor 1 14 to support the drill pipe string 101 during operation when the casing jack 130 is not used.

[0042] Two mast towers 1 16A, 1 16B may be mounted vertically on the work floor 1 14 for pulling the drill pipe string 101 . The mast towers 1 16A, 1 16B may be positioned symmetrically about a central axis 105 of the platform wellhead 104. The symmetrical positioning of the mast towers 1 16A, 1 16B enables a balanced load distribution on the platform wellhead 104.

[0043] Each mast tower 1 16A, 1 16B may include an outer frame 1 18A, 1 18B, a hydraulic cylinder 1 17A, 1 17B disposed in the outer frame 1 18A, 1 18B, and one or more sheaves 122A, 122B mounted on an upper end of the hydraulic cylinder 1 17A, 1 17B. Each of the sheaves 122A, 122B may be a single sheave or a double sheave. A drill line assembly may be coupled to the mast towers 1 16A, 1 16B to pull a tool using the mast towers 1 16A, 1 16B. The drill line assembly may include a spreader bar 126 suspended between the mast towers 1 16A, 1 16B by drill lines 124A, 124B. The drill lines 124A, 124B may be threaded through the sheaves 122A, 122B and connected to line holders 123A, 123B. The line holders 123A, 123B may be fixedly disposed on the work floor 1 14. In one embodiment, each of the line holders 123A, 123B may include a spool for adjusting lengths of the drill line 124A, 124B. In one embodiment, a top frame 120 may be coupled between the mast towers 1 16A, 1 16B near the upper ends of the mast towers 1 16A, 1 16B. The top frame 120 insures that the mast towers 1 16A, 1 16B maintain parallel to each other under load.

[0044] The hydraulic cylinders 1 17A, 1 17B stroke up and down to move the sheaves 122A, 122B vertically. The hydraulic cylinders 1 17A, 1 17B may be configured to stroke up and down in synchronization. When the hydraulic cylinders 1 17A, 1 17B stroke up causing the sheaves 122A, 122B to move up, the drill line 124A, 124A pull the spreader bar 126. The spreader bar 126 moves at a ratio of 2 to 1 over stroke of the hydraulic cylinders 1 17A, 1 17B. When the hydraulic cylinders 1 17A, 1 17B stroke down causing the sheaves 122A, 122B to move down, the spreader bar 126 pulls down the drill lines 124A, 124B down at a rate of 2 to 1

[0045] The workover unit 100 may further include a power swivel 128 suspended below the spreader bar 126. In one embodiment, the power swivel 128 may be suspended from the spreader bar 126 by cables 127. The power swivel 128 may include a gripping tool 140 extending towards the platform wellhead 104. The gripping tool 140 is configured to grip and rotate the drill pipe string 101 . The power swivel 128 transfers the up and down movements of the spreader bar 126 to the drill pipe string 101 . The power swivel 128 may also rotate the drill pipe string 101 , for example while fluid is being circulated through the holes and down the drip pipe string 101 .

[0046] Optionally, the workover unit 100 may include torque arms 142 as an anti-rotation device for the power swivel 128. Each torque arm 142 may have a first end coupled to the power swivel 128 and a second end movably connected a track 144A, 144B attached to the mast tower 1 16A, 1 16B. When the power swivel 128 moves vertically, the torque arms 142 may slide vertically within the tracks 144A, 144B. When the gripping tool 140 rotates the drill pipe string 101 , the torque arms 142, secured in the tracks 144A, 144B, stop any reactive torque from turning the power swivel 128. Therefore, all rotation is below the power swivel 128.

[0047] The symmetrical configuration of the mast towers 1 16A, 1 16B allow the platform wellhead 104 to bear the weight and load of the workover unit 100 in a stable and balanced manner. Additional features may be used to increase stability and/or adjust load distribution.

[0048] In one embodiment, optional guy wires 146 may be used to increase stability of the workover unit 100. The guy wires 146 may be fixed from the mast towers 1 16A, 1 16B to the platform 102 or outriggers.

[0049] In another embodiment, an optional load distributing assembly 148 may be used to support a portion of the weight and load of the workover unit 100. The load distribution assembly 148 may include I-beams 150 installed between the unit floor 1 12 and the platform 102. The I-beams 150 may be arranged in parallel above and secured to platform beams through support risers 152. The I-beams 150 are positioned below the unit floor 1 12. The support risers 152 may be adjusted to divide a portion of the weight and load from the platform wellhead 104 to the platform 102. For example, the support risers 152 may raise the l-Beams 150 to lift the unit floor 1 12 from the adaptor 1 10 so that the weight and load from the mast towers 1 16A, 1 16B are transferred to the platform 102 through the I- Beams 150 and the platform wellhead 104 only needs to support the weight of the drill pipe string 101 and the weight of the casing jack 130.

[0050] The hydraulic cylinders 1 17A, 1 17B in the mast towers 1 16A, 1 16B stroke up and down to move the workover unit 100 between a lowered position, shown in Figure 1 A, and a raised position, shown in Figure 1 B. The workover unit

100 moves between the lowered position and the raised position to pull or insert the drill pipe string 101 or other type of strings.

[0051] To pull the drill pipe string 101 from a well bore using the workover unit

100, first set the drill pipe string 101 on the slips on the work floor 1 14 or the slips 138 in the upper casing bowl 136 of the casing jack 130. The hydraulic cylinders 1 17A, 1 17B may stroke down to lower the spreader bar 126 and the power swivel 128 towards the work floor 1 14 so that the gripping tool 140 can grip the top of the drill pipe string 101 . Once the gripping tool 140 takes hold of the drill pipe string

101 , the slips 138 may be released to allow vertical movement of the drill pipe string 101 .

[0052] The hydraulic cylinders 1 17A, 1 17B may then stroke up to move the sheaves 122A, 122B up. As the sheaves 122A, 122B move up, the drill lines 124A, 124B pull up the spreader bar 126, the power swivel 128, and the drill pipe string 101 . In one embodiment, the hydraulic cylinders 1 17A, 1 17B may be moved in synchronization so that the load from the weight of the drill pipe string

101 is evenly distributed between the mast towers 1 16A, 1 16B. In one embodiment, a controller may be used to coordinate the movements of the hydraulic cylinders 1 17A, 1 17B.

[0053] If the load from the drill pipe string 101 is larger than the maximum pull of the hydraulic cylinders 1 17A, 1 17B, the casing jack 130 may be used to provide additional power to pull up the drill pipe string 101 . To pull the drill pipe string 101 with the casing jack 130, the hydraulic cylinders 134 first stroke down to lower the upper casing bowl 136 while the drill pipe string 101 is set on the gripping tool 140. The slips 138 are then set to grip the drill pipe string 101 . The hydraulic cylinders 134 then stroke up with the drill pipe string 101 set on the slips 138 to pull the drill pipe string 101 upward. The casing jack 130 may be activated alone to pull up the drill pipe string 101 , and once the hydraulic cylinders 134 reach their upper position, the hydraulic cylinders 1 17A, 1 17B move up to hold the drill pipe string 101 at the raised position. The slips 138 may then be released and the upper casing bowl 136 lowered to repeat the pulling process. Alternatively, the casing jack 130 may be used in conjunction with hydraulic cylinders 1 17A, 1 17B of the mast towers 1 16A, 1 16B. The hydraulic cylinders 1 17A, 1 17B, and 134 may be activated at the same time to achieve maximum pulling capacity.

[0054] Figure 1 B is a schematic sectional view of the workover unit 100 at a raised position. In Figure 1 B, the optional load distributing assembly 148 is not shown. The workover unit 100 is configured to raise the drill pipe string 101 for a length twice as long as the stroke range of the hydraulic cylinder 1 17A or 1 17B, thus allowing one or more lengths of a drill pipe to be raised from the wellbore during each stroke up. In the raised position shown in Figure 1 B, each of the hydraulic cylinders 1 17A, 1 17B has raised a distance 154 from the lowered position shown Figure 1 A while the power swivel 128 has raised a distance 156. The distance 156 is twice as long as the distance 154. From the lower position of Figure 1 A to the raised position of Figure 1 B, one drill pipe is raised from the wellbore. In Figure 1 B, a drill pipe joint 101 a is raised above the work floor 1 14 allowing the top most drill pipe to be removed.

[0055] At the raised position shown in Figure 1 B, the drill pipe string 101 may be again set on the slips 138 so that the top most drill pipe may be removed. For example, the power swivel 128 may rotate the top most drill pipe to undo to the joint 101 a. The gripping tool 140 may then release the drip pipe allowing it to be removed from the drill pipe string 101 . The hydraulic cylinders 1 17A, 1 17B may then stroke down to repeat the same process.

[0056] Similarly, the workover unit 100 may be used to insert the drill pipe string 101 down the wellbore. In a raised position, the grill tool 140 may grip a new drill pipe, the power swivel 128 may then rotate to join the new drill pipe to the drill pipe string 101 set on the slips 138. The slips 138 are then released, the hydraulic cylinders 1 17A, 1 17B then stroke down together to insert the drill pipe string 101 down the wellbore under the combination of the weight of the drill pipe string 101 and the lift force of the hydraulic cylinders 1 17A, 1 17B. When the hydraulic cylinders 1 17A, 1 17B are at the lower position, the drill pipe string 101 is again set on the slips 138 and ready for a new drill pipe. The gripping tool 140 may release the drill pipe string 101 , and the hydraulic cylinders 1 17A, 1 17B may grip a new drill pipe and stroke up to repeat the process.

[0057] Even though, Figure 1 B shows that the workover unit 100 strokes up to pull up one drill pipe, multiple drill pipes, for example three drill pipes, may be pulled up in one stroke.

[0058] Figure 1 C is a schematic side view of a workover unit 100C according to the present disclosure. The workover unit 100C is similar to the workover unit 100 except the workover unit 100C does not have the optional casing jack 130 and the optional load distributing assembly 148. Slips 160 may be mounted on the work floor 1 14 for supporting the drill pipe string 101 during operation.

[0059] Figure 2 is a schematic side view of a workover unit 200 according to another embodiment of the present disclosure. The workover unit 200 is similar to the workover unit 100 except the workover unit 200 includes an elevator 228 in place of the power swivel 128 of the workover unit 100. Tongs 229 may be disposed on the work floor 1 14 to rotate the drill pipes during operation. In one embodiment, the tongs 229 may be hydraulic tongs. In one embodiment, a tong carrier 227 may be used to transfer the tongs 229 back and forth. The tong carrier 227 may be disposed on the platform 102.

[0060] Figure 3 is a schematic partial side view of a workover unit 300 according to another embodiment of the present disclosure. The workover unit 300 is similar to the workover unit 100 except the workover unit 300 includes a travelling block 326 in place of the spreader bar 126 of the workover unit 100. The workover unit 300 includes a pulley 360 rotatably attached to the travelling block 326. Even though one pulley 360 is shown, multiple pulleys or a pulley system may be used. A single drill line 324 is connected between the line holders 123A, 123B through the sheaves 122A, the pulley 360 and the sheaves 122B. In one embodiment, optional stabilizing arms 362 may extend from the traveling block 326 to the tracks 144A, 144B. The stabilizing arms 362 may move vertically along the tracks 144A, 144B. The tracks 144A, 144B prevent the traveling block 326 from rotating through the stabilizing arms 362. The power swivel 128 is attached to the traveling block 326 through cables 327. Alternatively, an elevator instead of a power swivel may be attached to the traveling block 326.

[0061] During operation, the drill line 324 transfers the up and down movement of the mast towers 1 16A, 1 16B to the pulley 360 and the travelling block 326, which in turn raises and lowers the drill pipe string 101 . The rotation of the pulley 360 adjusts lengths of the drill line 324 on opposite sides of the pulley 360, thus correcting any imbalance of load when the movements of the mast towers 1 16A, 1 16B are not in synchronization.

[0062] The workover units according to the present disclosure have small footprints and may be set up at various locations. As described in Figures 1 A-1 C and Figure 2, the workover units may be set on a wellhead. For example, the workover units may be directly set up on a wellhead without a BOP stack. Alternatively, the workover units may be set up on a BOP stack that is attached to a wellhead.

[0063] In one embodiment, the workover units of the present disclosure may be set on a platform deck. For example, instead of being supported by the wellhead 104 through the adaptor 1 10, the workover unit 100 of Figures 1A-1 B may be set on the platform 102 directly.

[0064] In one embodiment, when there are two or more wellheads in a platform, the workover unit may be set up on a transfer structure, such as tracks, on the platform, and then move among the wellheads using the transfer structure.

[0065] In another embodiment, the workover units may be partially set on a platform and partially set on a wellhead by using a load distributing assembly, such as the load distributing assembly 148 in the workover unit 100. This configuration allows distribution of the load from the workover unit and the string plus over pull between the wellhead and platform legs.

[0066] When a platform cannot support the weight or doesn't have enough area of all the necessary auxiliary equipment and/or living quarters of the operators, a dynamic positioning vessel or moored vessel may be used to support all the necessary auxiliary equipment and provide living quarters for operators.

[0067] When a wellhead or a platform could not support the workover units or the pipeline string, the workover units of the present disclosure may be mounted on a vessel. Figure 4 is a schematic view of the workover unit 100 mounted on a vessel 400. The vessel 400 includes an opening 402 on the deck 404 to allow access to a well 406. The vessel 400 may be a moored vessel having a motion compensator or a dynamic positioning vessel. The vessel 400 may be positioned to align the opening 402 with the well 406. The workover unit 100 is mounted on the deck 404. The unit floor 1 12 is supported by the deck 404. In one embodiment, the casing jack 130 is also mounted on the deck 404. Other than providing additionally pulling power, the casing jack 130 may also be used to provide motion compensation during operation.

[0068] Even though the workover unit 100 is shown mounted on the vessel 400, all workover units according to the present disclosure may be mounted on a vessel in similar manner.

[0069] In another embodiment, the workover units of the present disclosure may be mounted on a cantilever of a lift boat. Figure 5 is a schematic view of a workover unit 100 mounted a lift boat 500. The lift boat 500 has a cantilever system 506 extending from the deck 502. The workover unit 100 is mounted on the cantilever system 506. Risers 504 of the lift boat 500 may be raised to position the cantilever system 506 over above a wellhead 508 to be worked over. The lift boat 500 may be positioned so that the workover unit 100 is aligned with the wellhead 508.

[0070] Even though the workover unit 100 is shown mounted on the lift boat 500, all workover units according to the present disclosure may be mounted on a lift boat in similar manner.

[0071] Figure 6A is a schematic side view of a workover unit 600 according to another embodiment of the present disclosure. Figure 6B is another schematic side view of the workover unit 600. The workover unit 600 is shown at a retracted position in Figures 6A and 6B. Figure 6C is a schematic top view of the workover unit 600. Figure 6D is a schematic side view of the workover unit 600 in an extended position.

[0072] The workover unit 600 is shown mounted on a wellhead 104. The workover unit 600 includes a unit base 612. The unit base 612 is configured to be mounted on a wellhead, such as the wellhead 104. In one embodiment, the unit base 612 may have a flange which is secured to a flange on the wellhead 104. Columns 613 may extend from the unit base 612. A work floor 614 may be supported by the columns 613. Handrails 615 may be installed at a perimeter of the work floor 614. In one embodiment, the work floor 614 may be larger in size than the unit base 612. In one embodiment, an optional casing jack 630 may be mounted on the unit base 612. Alternatively, the casing jack 630 may be mounted on the adaptor of the wellhead 104. Alternatively, slips may be installed on the work floor 614 to support a drill pipe string during operation when the casing jack 630 is not used.

[0073] Two mast towers 616A, 616B may be mounted vertically on the unit base 612 for pulling the drill pipe string. The mast towers 616A, 616B may be positioned symmetrically about a central axis of the wellhead 104. The symmetrical positioning of the mast towers 616A, 616B enables a balanced load distribution on the wellhead 104.

[0074] Each mast tower 616A, 616B may include a telescope frame 618A, 618B, a hydraulic cylinder 617A, 617B disposed in the telescope frames 618A, 618B, and one or more sheaves 622A, 622B mounted on an upper end of the hydraulic cylinder 617A, 617B. Each of the telescope frames 618A, 618B may include an inner frame 618i and an outer frame 618o. The outer frame 618o is stationary relative to the unit base 612. The inner frame 618i is coupled to the mobile end of the hydraulic cylinder 617A, 617B and movable relative to the outer frame 618o.

[0075] A stability frame 620 may be connected between the inner frame 618i of the two mast towers 616A, 616B to prevent relative movement between the mast towers 616A, 616B.

[0076] The sheaves 622A, 622B may be attached to an upper end of the inner frame 618i in each mast tower 616A, 616B. In one embodiment, each mast tower 616A, 616B may include two sets of sheaves 622A, 622B positioned on a front side and a back side of the mast tower 616A, 616B. As shown in Figure 6B, the two sets of sheaves 622A may be symmetrically position about a central axis 617a of the hydraulic cylinder 617A.

[0077] A drill line 624 is threaded on each set of sheaves 622A, 622B between the unit base 612 and a spreader bar 626. As shown in Figure 6C, the spreader bar 626 is carried by four drill lines 624. The four drill lines 624 may be symmetrically connected to the spreader bar 626. The symmetrical configuration of the drill lines 624 about two axis allow the platform wellhead 104 to bear the weight and load of the workover unit 100 in a stable and balanced manner.

[0078] In one embodiment, the drill lines 624 may be secured to the unit base 612 by a rocker assembly 650. The rocker assembly 650 may include an anchor 652 bolted to the unit base 612 and a pivot arm 654 pivotably connected to the anchor 652. Two drill lines 624 are connected at opposite sides of the pivot arm 654. The pivot arm 654 allows adjustment of the drill lines 624 to adjust or distribute loads between the drill lines 624. In one embodiment, a sensor 656 may be disposed between the pivot arm 654 and the drill line 624 to measure tension on the drill line 624. Tensions on the drill lines 624 may be adjusted according to measurements of the sensor 656. [0079] In one embodiment, each of the inner frames 618i includes a guide rail 644A, 644B. The spreader bar 626 may include wheels 648 to couple with the guide rails 644A, 644B. The wheels 646 and the guide rails 644A, 644B movably couple the spreader bar 626 to the mast towers 616A, 616B preventing the spreader bar 626 from rotating.

[0080] The hydraulic cylinders 617A, 617B stroke up and down to move the sheaves 622A, 622B vertically. The hydraulic cylinders 617A, 617B may be configured to stroke up and down in synchronization. An elevator 628 may be attached to the spreader bar 626 to operate the drill line. Alternatively, a power swivel may be attached to the spreader bar 626.

[0081] In one embodiment, guy wires 646 may be used to increase stability of the workover unit 600. The guy wires 646 may be fixed from a top of the outer frame 618o of the mast towers 616A, 616B to a platform or outriggers attached to the unit base 612. In one embodiment, a tong carrier 660 may be movably disposed on the work floor 614. The tong carrier 660 may be used to operating the drill string.

[0082] Figure 7A is a schematic top view of the spreader bar 626 according to one embodiment of the present disclosure. The spreader bar 626 may include wheels 648 to allow the spreader bar 626 to slide along guide rails 644A, 644B of the mast towers 616A, 616B. Figure 7B is a schematic side view of the spreader bar 626 connected to a power swivel 702. Drill lines 624 may be connected to the spreader bar 626 symmetrically about the power swivel 702. Figure 7C is a schematic side view of the spreader bar 626 connected to an elevator 704 through a beckett 706.

[0083] Figure 8A is a schematic side view of the telescope cylinder 617 used in workover units 600. In Figure 8A, the telescope cylinder 617 is in a retracted position and in Figure 8B the telescope cylinder 617 is in an extended position.

[0084] Figure 9 schematically illustrates a layout of a workover unit deployed on a single well according to one embodiment of the present disclosure. In Figure 9, the workover unit 600 is shown to be deployed on an offshore platform 902 having a single well 904 disposed on a platform deck 920. In one embodiment, an outrigger assembly 912 may be attached to the unit base 612 of the workover unit 600. The outrigger assembly 912 may include two or more beams extending out radially from the unit base 612 to improve stability of the workover unit 600. In one embodiment, the outrigger assembly 912 may include at least three beams attached to the unit base 612. The three or more beams may be evenly disposed around a perimeter of the workover unit 600. In one embodiment, a V-door 926 may be attached to the workover unit 600 for temporarily holding a pipe 922 during operation.

[0085] Guy wires may be used to improve stability of the workover unit 600, particularly to improve the stability of the workover unit 600 over wind load. In one embodiment, guy wires 914 may be connected between an outer edge of the outrigger assembly 912 and a top of the mast 618. In one embodiment, two or more guy wires 914 may be connected to two or more beams of the outrigger assembly 912. In another embodiment, optional guy wires 916 may be applied between an adaptor 918 attached to the well 904 and outer edges of the outrigger assembly 912. The adaptor 918 may be a clamp fixed or welded to the well. In one embodiment, the guy wires 916 may be symmetrical to the guy wires 914 about the outrigger assembly 912. Alternatively, the guy wires 916 may be secured between the outrigger assembly 912 and the platform deck 920.

[0086] In one embodiment, sensors 924 may be connected to the guy wires 914 to monitor the load on the corresponding guy wires 914. The sensors 924 may be attached to upper ends and/or lower ends of the guy wires 914. In one embodiment, the sensors 924 may be load cells or other suitable sensors.

[0087] The workover unit 600 may be installed over the offshore platform 902 by a crane 910 on a boat 908 positioned near the offshore platform 902. In one embodiment, the workover unit 600 may be installed by first hoist the unit base 612 over the wellhead assembly 906 and secured thereon. The unit base 612 may be secured to the wellhead assembly 906 through flanges using bolts. The outrigger assembly 912 may then be installed on the unit base 612. If the workover unit 600 includes a casing jack, the casing jack may then be hoisted and installed over the unit base 612. The masts 618A, 618B may then be installed on the unit base 612 one by one. The work floor 614 may be installed on the unit base 612. Sheaves 622 and drill lines 624 may then be installed. The spreader bar 626 may then be installed to the drill lines 624. The workover unit 600 is supported only by the wellhead assembly 906 after installation. Alternatively, the workover unit 600 may be preassembled and installed a wellhead assembly 906 of the well 904.

[0088] Even though the workover unit 600 is shown in Figure 9, other workover units according to the present disclosure may be used in the layout of Figure 9.

[0089] Figure 10 schematically illustrates a layout of the workover unit 600 deployed on an offshore platform 1002 according to one embodiment of the present disclosure. The offshore platform 1002 may include multiple wells, such as wells 1004, 1006, 1008. The workover unit 600 may be installed over one of the wells 1004, 1006, 1008 using the crane 910 on the boat 908. The workover unit 600 may be installed on the offshore platform 1002 in a similar manner as shown in Figure 9. The workover unit 600 may be supported by a wellhead assembly 1010 of one of the wells 1004, 1006, 1008. In one embodiment, guy wires 1012 may be applied between a deck 1014 of the offshore platform 1002 and the base 912. In one embodiment, the workover unit 600 may be transferred among the wells 1004, 1006, 1008 using the crane 910.

[0090] Even though the workover unit 600 is shown in Figure 10, other workover units according to the present disclosure may be used in the layout of Figure 10.

[0091] Figure 1 1 schematically illustrates a layout of the workover unit 600 deployed on an offshore platform 1 102 according to another embodiment of the present disclosure. The offshore platform 1 102 may have multiple wells 1 104, 1 106, 1 108. The workover unit 600 may disposed over a wellhead assembly 1 1 16 of the well 1 104. The load of the workover unit 600 may be supported on a deck 1 1 10 of the offshore platform 1 102, the wellhead assembly 1 1 16 of the well 1 104, or both. In one embodiment, support raisers 1 1 12 may be disposed between the workover unit 600 and the deck 1 1 10. The raiser 1 1 12 may be adjusted to balance the load of the workover unit 600 between the deck 1 1 10 and the wellhead assembly 1 1 16.

[0092] In one embodiment, the workover unit 600 may be disposed over a track 1 1 14 on the deck 1 1 10. The workover unit 600 may be movably disposed on a track 1 1 14 so that the workover unit 600 may be transferred among the wells 1 104, 1 106, and 1 108 along the track 1 1 14 without requiring disassemble and reassemble.

[0093] Even though the workover unit 600 is shown in Figure 1 1 , other workover units according to the present disclosure may be used in the layout of Figure 1 1 .

[0094] Figure 12 schematically illustrates a layout of the workover unit 600 deployed on a single well caisson 1202 according to one embodiment of the present disclosure. The single well caisson 1202 includes a well 1204 but does not have a platform or a deck. The workover unit 600 is supported by a wellhead 1206 of the well 1204. Guy wires 914, 916 are secured between the outrigger assembly 912 and masts and between the outrigger assembly 912 and the well 1204 to provide stability.

[0095] Even though the workover unit 600 is shown in Figure 12, other workover units according to the present disclosure may be used in the layout of Figure 12.

[0096] Workover units according to the present disclosure may be used for application of upper and lower completion, removal and re-completion along with well clean up and simulation operations. When the platform structure is small and has limited load bearing capacity, the workover units of the present disclosure may be at least partially deployed on the wellhead to transmit pulling and jacking loads into the wellhead. A guy wire system with sensors may be used to perform active tension monitoring to achieve stability.

[0097] For small platforms with limited structural capacity that can accommodate small capping beams between structural hard points, capping beams may be used in conjunction with the BOP interface to allow the pulling and jacking loads to be transmitted into both the wellhead and the platform structure.

[0098] Workover units according to the present disclosure may also be mounted on platform. For example, the workover units of the present disclosure may be installed on platforms with existing capping beams and risers with a casing jack change, jack conductors.

[0099] Even though drill pipe strings are described with the Figures, the workover units according to the present disclosure may be used to handle other strings, such as casing strings.

[0100] One embodiment of the present disclosure includes a workover unit, comprising a frame having a work floor, wherein the frame is configured to mount on a wellhead, a first mast tower and a second mast tower mounted on the work floor, and a drill line assembly coupled to the two mast towers to move a tool.

[0101] In one or more embodiments, each of the first and second mast towers comprises a hydraulic cylinder, and one or more sheaves attached on an upper end of the hydraulic cylinder, wherein a drill line of the drill line assembly is supported by the one or more sheaves.

[0102] In one or more embodiment, the workover unit further includes a gripping assembly suspended from the drill line assembly between the first and second mast towers, wherein stroke up and stroke downs of the hydraulic cylinders move the gripping assembly up and down between the first and second mast towers.

[0103] In one or more embodiment, the gripping assembly comprises a power swivel.

[0104] In one or more embodiment, the gripping assembly further comprises two torque arms extending between the power swivel and tracks attached the first and second mast towers. [0105] In one or more embodiment, the gripping tool comprises an elevator.

[0106] In one or more embodiment, the drill line assembly comprises a travelling block having one or more pulleys, and a drill line coupling the one or more sheaves of the first mast tower, the one or pulleys of the travelling block, and the one or more sheaves of the second mast tower, wherein the travelling block is positioned between the first and second mast towers by the drill line.

[0107] In one or more embodiment, the drill line assembly further comprises two anti-rotation arms extending between the sliding block and tracks attached to the first and second mast towers.

[0108] In one or more embodiment, the drill line assembly comprises a first drill line coupled to the one or more sheaves of the first mast tower, a second drill line coupled to the one or more sheaves of the second mast tower, and a spreader bar connecting the first drill line and the second drill line, wherein the spreader bar is positioned between the first and second mast towers by the first and second drill lines.

[0109] In one or more embodiment, the workover unit further includes slips disposed on the work floor.

[0110] In one or more embodiment, the workover unit further includes an adaptor configured to mount the frame on a wellhead.

[0111] In one or more embodiment, the workover unit further includes a casing jack.

[0112] In one or more embodiment, the workover unit further includes an adaptor configured to mount on a wellhead, wherein the casing jack is mounted on the adaptor.

[0113] In one or more embodiment, the workover unit further includes a load distributing assembly attached to the frame, wherein the load distributing assembly is configured to mount on a platform. [0114] In one or more embodiment, the workover unit further includes guy wires coupled to the first and second mast towers.

[0115] In one or more embodiment, the workover unit further includes tongs disposed on the work floor.

[0116] Another embodiment provides a method for well intervention. The method includes gripping a drill pipe string using a gripping assembly suspended from a drill line assembly between a first and second mast towers, and stroking up or stroking down the first and second mast towers to pull up or lower down the drill pipe string.

[0117] In one or more embodiment, stroking up or stroking down comprises controlling hydraulic cylinders of the first and second mast towers to move the first and second mast towers in synchronization.

[0118] In one or more embodiment, stroking up or stroking down comprises raising or lowering one or more drill pipe in a single journey of stroke up or stroke down.

[0119] In one or more embodiment, the method further includes mounting a workover unit comprising the first and second mast towers on a wellhead.

[0120] In one or more embodiment, the method further includes mounting a workover unit comprising the first and second mast towers on a BOP stack on a wellhead.

[0121] In one or more embodiment, the method further includes mounting a workover unit comprising the first and second mast towers on a platform.

[0122] In one or more embodiment, the method further includes mounting a workover unit comprising the first and second mast towers on a cantilever system of a lift boat.

[0123] In one or more embodiment, the method further includes mounting a workover unit comprising the first and second mast towers on a deck of a vessel. [0124] In one or more embodiment, the method further includes distributing a load of a workover unit comprising the first and second mast towers between a platform and a wellhead.

[0125] In one or more embodiment, the method further includes pulling the drill pipe string with a casing jack.

[0126] Another embodiment provides a workover unit, comprising a frame having a work floor, a first mast tower and a second mast tower mounted on the work floor, a drill line assembly coupled to the two mast towers to move a tool, and a casing jack configured to mount on a wellhead.

[0127] In one or more embodiment, the workover unit further includes an adaptor configured to mount on a flange of a wellhead, wherein the frame and the casing jack are mounted on the adaptor.

[0128] In one or more embodiment, the workover unit further includes an adaptor configured to mount on a flange of a wellhead, wherein the casing jack is mounted on the adaptor.

[0129] In one or more embodiment, the workover unit further includes a load distributing assembly configured to mount on a platform, and the frame is attached to the load distributing assembly.

[0130] Another embodiment provides a workover unit, comprising a unit base configured to mount on a wellhead, a first mast tower and a second mast tower mounted on the unit base, and a spreader bar slidingly disposed between the first mast tower and the second mast tower to move a tool.

[0131] In one or more embodiment, each of the first mast tower and second mast tower comprises two sets of sheaves each operating a drill line, wherein the spreader bar connected with four drill lines.

[0132] In one or more embodiment, the workover unit further includes sensors coupled to at least one of the four drill lines, wherein the sensors are configured to measure tension in the corresponding drill line. [0133] In one or more embodiment, the workover unit further includes two or more guy wires connecting the first and second mast towers to a platform deck or outriggers secured to the unit base.

[0134] In one or more embodiment, each of the two or more guy wires comprises a sensor configured to measure tension in the corresponding guy wire.

[0135] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1 . A workover unit, comprising:

a work floor;

a first mast tower and a second mast tower mounted on the work floor; a drill line assembly coupled to the two mast towers; and

a tool connected to the drill line assembly between the first and second mast towers, wherein stroking up or stroking down of the first and second mast towers moves the tool up or down.

2. The workover unit of claim 1 , wherein each of the first and second mast towers comprises:

a hydraulic cylinder; and

one or more sheaves attached on an upper end of the hydraulic cylinder, wherein a drill line of the drill line assembly is supported by the one or more sheaves.

3. The workover unit of claim 1 , wherein the drill line assembly comprises: a travelling block having one or more pulleys, wherein the tool is attached to the travelling block; and

a drill line coupling the one or more sheaves of the first mast tower, the one or pulleys of the travelling block, and the one or more sheaves of the second mast tower, wherein the travelling block is positioned between the first and second mast towers by the drill line.

4. The workover unit of claim 1 , wherein the drill line assembly comprises: a first drill line coupled to the one or more sheaves of the first mast tower; a second drill line coupled to the one or more sheaves of the second mast tower; and

a spreader bar connecting the first drill line and the second drill line, wherein the spreader bar is positioned between the first and second mast towers by the first and second drill lines, and the tool is connected to the spread bar.

5. The workover unit of claim 3 or 4, wherein the tool comprises a power swivel.

6. The work over unit of claim 3 or 4, wherein the gripping tool comprises an elevator.

7. The work over unit of claim 3 or 5, further comprising two torque arms extending from the power swivel or the travelling block to tracks attached the first and second mast towers.

8. The workover unit of claim 1 , further comprising an adaptor configured to mount the workover unit on a wellhead.

9. The workover unit of claim 1 , further comprising a casing jack mounted on the adaptor.

10. The workover unit of claim 1 , further comprising a load distributing assembly configured to mount on a platform.

1 1 . The workover unit of claim 1 , further comprising two or more guy wires connecting the first and second mast towers to a platform deck or outriggers secured to the work floor.

12. A method for well intervention, comprising:

gripping a tubular string using a tool connected to a drill line assembly between a first mast tower and a second mast tower of a workover unit; and

stroking up or stroking down the first and second mast towers to raise or lower the tubular string.

13. The method of claim 12, further comprising mounting the workover unit on a wellhead.

14. The method of claim 12, further comprising mounting the workover unit on a platform.

15. The method of claim 17, further comprising mounting the workover unit on a vessel.

16. A workover unit, comprising:

a work floor;

a tool connected to the drill line assembly between the first and second mast towers, wherein extending or retracting at least one of the first mast tower and the second mast tower moves the tool up and down relative to the work floor.

17. The unit of claim 16, wherein extending the first mast tower moves the tool up.