System and method for performing well operations

Abstract

System and associated method for performing well operations in a plurality of hydrocarbon wells (120a, 120b, 120c) of a wellhead cluster (104), has a main drilling rig (106) with a main drilling unit (107) displaying a drill floor (108) and having a drilling and hoisting system (109) arranged to operate on the drill floor about a well center (110), wherein the main drilling unit is positioned at least partially vertically above the wellhead cluster enabling the drilling and hoisting system to perform well operations in the plurality of hydrocarbon wells. A plurality of secondary drilling units (105a, 105b), each having its own drilling equipment for performing drilling operations, are positioned on the wellhead cluster below the main drilling unit for performing well operations in the plurality of hydrocarbon wells, wherein the main drilling unit and at least one of the plurality of secondary drilling units are arranged for performing alternating well operations in at least one of the plurality of hydrocarbon wells.

Claims

1. A system for performing well operations in a plurality of hydrocarbon wells of a wellhead cluster, which system comprises a main drilling rig comprising a main drilling unit displaying a drill floor and comprising a drilling and hoisting system arranged to operate on the drill floor about a well center, wherein the main drilling unit is positioned at least partially vertically above the wellhead cluster enabling the drilling and hoisting system to perform well operations in the plurality of hydrocarbon wells, wherein a plurality of secondary drilling units, each comprising its own drilling equipment for performing drilling operations, are positioned on the wellhead cluster below the main drilling unit for performing well operations in the plurality of hydrocarbon wells, wherein the main drilling unit and at least one of the plurality of secondary drilling units are arranged for performing alternating well operations in at least one of the plurality of hydrocarbon wells.

2. The system according to claim 1, wherein the main drilling unit has a well operations capacity in at least one of said well operations which is higher than the well operations capacity of said at least one of the plurality of secondary drilling units.

3. The system according to claim 1, further comprising at least one umbilical running from the main drilling unit to the wellhead cluster for providing drilling support to said plurality of secondary drilling units and/or for allowing control and operation of the plurality of secondary drilling units from the main drilling unit.

4. The system according to claim 3, wherein the main drilling unit provides at least one of mud control, power supply, hydraulics supply to the wellhead cluster.

5. The system according to claim 1, wherein the main drilling unit is movable in a plane above the wellhead cluster.

6. The system according to claim 1, wherein the main drilling rig is any one of a jack-up rig, a drilling module, a drillship, a tension leg platform, a jacket, a land rig or a semi-submersible platform.

7. The system according to claim 1, wherein said plurality of hydrocarbon wells comprise distributed well activities.

8. The system according to claim 1, wherein said main drilling rig comprises a skiddable cantilever comprising a drilling mast and drilling machinery, wherein said main drilling unit is placed on the skiddable cantilever, wherein the wellhead spread is placed adjacent and below the cantilever of the main drilling unit, said wellhead spread comprising said secondary drilling units, where each secondary drilling unit has its own drilling equipment for performing drilling operations, and each secondary drilling unit is being arranged for simultaneously well operations in separate wells while being supported by the main drilling unit.

9. The system according to claim 8, wherein the wellhead spread comprises distributed well centers comprising said secondary drilling units.

10. The system according to claim 8, wherein the main drilling rig is a jack-up rig standing on support legs and comprising a barge that can be raised or lowered, the jack-up rig being further equipped with the cantilever supporting the main drilling unit, where the cantilever can be driven or skidded out over water, such that the main drilling unit is above an operational area to perform desired drilling operations.

11. The system according to claim 8, wherein the secondary drilling units each comprises a mast, drill floor and BOP, which mast comprises a rotary drilling machine which is adapted to drive a tubular through the BOP and into a desired wellhead.

12. The system according to claim 8, wherein the main drilling unit comprises a driller's cabin/control station connected by at least one umbilical to the equipment on the wellhead spread for control and operations of the secondary drilling units and equipment on the wellhead spread.

13. A method of performing well operations in a plurality of hydrocarbon wells of a wellhead cluster, comprising the steps of: positioning a main drilling unit displaying a drill floor and comprising a drilling and hoisting system operating on the drill floor above the wellhead cluster, positioning a plurality of secondary drilling units at wellheads on the wellhead cluster, and alternatingly or simultaneously performing well operations in the hydrocarbon wells using the main drilling unit and at least one of said secondary drilling units.

14. The method according to claim 13, comprising the steps of: positioning the main drilling unit above the wellhead cluster such that a well center of the drilling unit becomes positioned vertically above a first wellhead of a first hydrocarbon well of the wellhead cluster, performing a well operation in the first hydrocarbon well using the main drilling unit, repositioning the main drilling unit such that the well center of the drilling unit becomes positioned vertically above a second wellhead of a second hydrocarbon well of the wellhead cluster, performing a well operation in the second hydrocarbon well using the main drilling unit and simultaneously performing a well operation in the first hydrocarbon well using a first secondary drilling unit positioned on the wellhead spread at the first wellhead.

15. The method according to claim 13, wherein the step of positioning a plurality of secondary drilling units at wellheads on the wellhead cluster comprises deploying the plurality of secondary drilling units from a main drilling rig carrying the main drilling unit.

16. The method according to claim 13, wherein the method is realised using a system comprising a main drilling rig comprising an elevated main drilling unit comprising a drill floor positioned on a skiddable cantilever, equipped with at least one main well center, and a wellhead spread placed adjacent and below the cantilever of the main drilling rig, wherein the method comprises the steps of: (a) deploying, from the main drilling rig, several secondary drilling units onto a well deck of the wellhead spread, (b) running well operations in a first well from the main well center through a first secondary drilling unit on the wellhead spread, (c) breaking the connection between the main well center and the first secondary drilling unit, (d) proceeding with drilling operations in the first well using the first secondary drilling unit, (e) moving the main drilling rig to a position above a second secondary drilling unit on the wellhead spread, (f) running well operations in a second well from the main well center through the second secondary drilling unit on the wellhead spread, (g) breaking the connection between the main well center and the second secondary drilling unit , and (h) proceeding with well operations in the second well using the second secondary drilling unit.

17. The method according to claim 16, wherein the main drilling unit performs preparations for the next activity, such as making up bottom hole assembly or rack up or down casing, while not supporting one of the secondary drilling units.

18. The method according to claim 16, wherein the main drilling unit in step (b) is tripping in with bottom-hole assembly through the first secondary drilling unit's rotary bushing and BOP, and when reaching TD the drill string is landed in said secondary drilling unit's rotary bushing and an iron roughneck machine on the secondary drilling unit breaks the connection freeing the main drilling unit for other operations.

19. The method according to claim 16, wherein the main drilling unit moves over immediately to the second secondary drilling unit, after breaking the connection between the main well center and the first secondary drilling unit, to assist the second secondary drilling unit while the first secondary drilling unit is drilling ahead using local pipe storage.

20. The method according to claim 16, wherein the main drilling unit in step (f) is tripping in with the bottom hole assembly to TD through the second secondary drilling unit, and when reaching TD the string is landed out in the rotary bushing on the second secondary drilling unit and an iron roughneck breaks the connection releasing the drill string from the main well center, while the second secondary drilling unit starts drilling using its own local drill pipe storage.

21. The method according to claim 16, wherein the main drilling rig prepares the casing section for the first secondary drilling unit, moves over and when ready pulls out the drill string from the first secondary drilling unit and then run in the casing section through the secondary drilling unit's rotary bushing and BOP.

22. The method according to claim 21, wherein when the run is close to be completed, the casing landing string is transferred to the secondary drilling unit which is landing out the casing.

Description

DRAWINGS

[0077] FIGS. 1 and 2 disclose schematic top-views of a plurality of wellheads 101 of wells on which the operational principle of the present invention can be employed.

[0078] FIG. 3 discloses a top view of a main drilling rig comprising a main drilling unit.

[0079] FIGS. 4 and 5 disclose a system for performing well operations in a plurality of wells according to the invention.

[0080] FIG. 6 illustrates a secondary drilling unit or pod for use in the invention.

[0081] FIG. 7 illustrates a jack-up drilling rig for use in the invention.

[0082] FIG. 8 illustrates a jack-up drilling rig comprising a main drilling unit and a wellhead platform comprising secondary drilling units or pods for use in the invention.

[0083] FIG. 9 illustrates a drill floor on a main drilling rig.

[0084] FIG. 10 shows a comparison between the operation of a standard drilling unit and the distributed well concept according to the invention.

DETAILED DESCRIPTION

[0085] In the following, the basic principles of the present invention will be discussed in more detail with reference to FIGS. 1 to 5.

[0086] FIGS. 1 and 2 disclose schematic top-views of a plurality of wellheads 101 of wells on which the operational principle of the present invention can be employed.

[0087] FIG. 1 discloses a plurality of wellheads 101 which are positioned in a grid pattern on a wellhead template 102, as is common for offshore applications where the wellhead template 102 is usually located on a wellhead platform.

[0088] FIG. 2 discloses a plurality of wellheads 101 which are locate within a limited geographical area 103 but which are not positioned on a common wellhead template. Such a wellhead configuration is sometimes used in land-based or subsea application instead of positioning the wellheads on a common wellhead template, although wellhead templates are sometimes used in land-based or subsea applications as well.

[0089] The inventive concept of the present invention is equally applicable to both of the above-described wellhead configurations, and for the purpose of this specification the term wellhead cluster 104 will be used to comprise any one of a plurality of wellheads which are located on a common wellhead template, e.g. on a wellhead jacket platform or a wellhead spread, or within a limited geographical area without necessarily being located on a common wellhead template.

[0090] A plurality of drilling units, or drilling pods 105, is associated with the wellhead cluster 104. Each drilling unit 105 comprises equipment for performing well operations or well activities, e.g. drilling, milling and jarring, pumping and cementing and wireline operations. Such equipment are known in the art and will not be descried in any detail here, but may typically include a rotary support table, a drilling mast or derrick and a rotary drilling and hoisting machine.

[0091] At least one of the drilling units 105 may be movable between different wellheads 101 of the wellhead cluster 104. If the wellheads 101 are located on a wellhead template 102, it may be advantageous to position the drilling units 105 on an x-y skid (not indicated in the drawings).

[0092] FIG. 3 discloses a schematic top-view of a drilling rig or support structure 106 which forms part of the system according to the invention. The drilling rig 106 comprises a drilling unit 107 which is movably mounted on the drilling rig 106 and which comprises a drilling floor or deck 108 on which a drilling and hoisting system 109 is located. The drilling floor 108 displays a well center or well center position 110 from which the drilling and hoisting system can perform well operations or activities.

[0093] The drilling unit 107 is movably mounted on the drilling rig 106 such that it can be moved or repositioned along the plane of the drilling floor or deck 108. Such movement or repositioning can be achieved by skidding the drilling unit 107 in orthogonal x and y directions, as is indicated by reference characters X and Y in FIG. 3. However, the repositioning can alternatively be achieved by other movement patterns, e.g. angular rotation and radial skidding.

[0094] The drilling unit 107 comprises the equipment and facilities necessary for the drilling and hoisting system 109 to perform the well operations or activities. Within the art, such equipment is known as such and will not be discussed in any detail here. However, the equipment and facilities may advantageously comprise a stand building area or position 111 where operations can be performed to prepare the drilling and hoisting system 109 for a subsequent well operation, a rail system 112 for catwalk machinery, a set back or racking area 113, a racking machine 114, iron roughnecks 115 and a driver's cabin or control station 116. To implement the actual well operation or activity, the drilling and hoisting system 109 comprises a support table 117, a guide structure 118 and a rotary drilling and hoisting machine 119 (cf. FIG. 4).

[0095] FIG. 4 is a schematic disclosure of the system according to the invention. The system comprises a main drilling unit 107 which is movably mounted on a drilling rig or support structure 106, e.g. a jack-up rig or an offshore platform. The main drilling unit 107 comprises a drilling floor 108 on which a drilling and hoisting system 109 is arranged to operate centered about a well center 110.

[0096] The system also comprises a wellhead cluster 104 which comprises first, second and third wellheads 101a, 101b, 101c of first, second and third hydrocarbon wells 120a, 120b, 120c. First and second secondary drilling units 105a, 105b are positioned over the first and second wellheads 101a and 101b, respectively. Each secondary drilling unit 105a, 105b comprises a support table 121 and may advantageously also comprise a drilling mast or derrick 122 and a rotary drilling and hoisting machine 123.

[0097] The main drilling unit 107 is positioned above the wellhead cluster 104 and is movably mounted onto the drilling rig 106 such that the well center 110 can be positioned vertically above any of the wellheads 101a, 101b, 101c, allowing the drilling and hoisting system 109 to perform well operations and activities in the hydrocarbon wells 120a, 120b, 120c. In other words, the main drilling unit 107 is arranged such that the drilling floor 108 can be moved above the wellhead cluster 104. If the wellheads 101a, 101b, 101c are arranged on a wellhead template, it may be advantageous if the main drilling unit 107 is arranged such that the plane defined by the drilling floor 108 is parallel to the plane defined by the wellhead template, i.e. the plane in which the wellheads are arranged.

[0098] The drilling and hoisting system 109 is supported by the apparatuses, sub-systems and equipment of the main drilling unit 107. Consequently, the main drilling unit 107 will have a well operations capacity which is higher than the well operations capacity of the secondary drilling units 105a, 105b. In other words, the drilling and hoisting system 109 can perform well operations faster and more efficiently than the secondary drilling units 105a, 105b. There may also be some well operations which the main drilling unit 107 but not the secondary drilling units 105a, 105b can perform.

[0099] According to the method of the invention, each hydrocarbon well 120a, 120b, 120c can be operated on alternatingly by the main drilling unit 107 and a secondary drilling unit 105a, 105b. This will allow well operations to be allocated to the main drilling unit 107 and the secondary drilling units 105a, 105b in an efficient manner. It will also allow the main drilling unit 107 to perform well operations in one hydrocarbon well at the same time as at least one of the secondary drilling unit 105a, 105b performs well operations in another hydrocarbon well, thus allowing well operations to be performed on at least two wells at the same time.

[0100] A typical sequence of operations according to the inventive method will now be disclosed in more detail with reference to FIGS. 4 and 5.

[0101] The main drilling unit 107 is positioned above the wellhead cluster 104 such that the well center 110 becomes positioned vertically above the first wellhead 101a allowing the drilling and hoisting system 109 to perform a first well operation in the first hydrocarbon well 120a. In the illustrated embodiment, the drilling and hoisting system 109 performs the first well operation through the support table 121 of the first secondary drilling unit 105a.

[0102] When the first well operation is completed, the connection between the drilling and hoisting system 109 and the first secondary drilling units 105a is broken and the main drilling unit 107 is repositioned such that the well center 110 becomes positioned vertically above the second wellhead 101b of the wellhead cluster 104.

[0103] Once the connection between the drilling and hoisting system 109 and the first drilling units 105a is broken, the first secondary drilling unit 105a is free to perform a second well operation in the first hydrocarbon well 120a, and once the drilling and hoisting system 109 is in position above the second wellhead 101b, and the drilling and hoisting system 109 is free to perform a first well operation in the second hydrocarbon well 120b, as is disclosed in FIG. 5.

[0104] Once the first well operation in the second hydrocarbon well 120b is completed, the main drilling unit 107 can be repositioned to another well, or back to the first well 120a, to perform further well operations, and the second secondary drilling unit 105b can proceed with a second well operation in the second well 120b.

[0105] As discussed above, demanding well operations are advantageously allocated to the main drilling unit 107 while less demanding well operations are allocated to the secondary drilling units 105a, 105b.

[0106] It may be advantageous if at least one of the secondary drilling units 105a, 105b can be repositioned between the wellheads such that all hydrocarbon wells on the wellhead cluster can be reached by at least one secondary drilling unit even if the number of secondary drilling units is less than the number of wellheads.

[0107] It may be advantageous if the power and utilities necessary to operate the secondary drilling units 105a, 105b are provided from the drilling rig 106 or the main drilling unit 107. For example, it may be advantageous if such power and utilities are provided via umbilicals and service loops 124 running from the main drilling unit 107 to the wellhead cluster 104.

[0108] In offshore applications, where the wellhead cluster 104 is typically arranged on a wellhead template located on a wellhead platform, the drilling rig 106 may typically be a jack-up rig, a drillship, a semi-submersible platform or a tension leg platform. However, the drilling structure may be any type of structure which is capable of movably supporting a main drilling unit over a wellhead cluster. The main drilling unit 107 may typically be mounted on a skiddable cantilever, allowing the main drilling unit to be moved between different hydrocarbon wells of the wellhead cluster.

[0109] According to one embodiment of the invention, the drilling structure 106 is a jack-up rig.

[0110] A jack-up rig or a self-elevating unit is a type of mobile platform that consists of a buoyant hull fitted with a number of movable legs, capable of raising its hull over the surface of the sea. The buoyant hull enables transportation of the unit and all attached machinery to a desired location. Once on location the hull is raised to the required elevation above the sea surface supported by the sea bed. The legs of such units may be designed to penetrate the sea bed, may be fitted with enlarged sections or footings, or may be attached to a bottom mat. A jack-up rig is regarded as well known to a skilled person and is therefore not described in detail, but a typical jack-up rig is in general discussed later in the description.

[0111] A jack-up is a floating barge fitted with long support legs that can be raised or lowered. The jack-up is maneuvered (self-propelled or by towing) into location with its legs up and the hull floating on the water. Upon arrival at the work location, the legs are jacked down onto the seafloor. Then preloading takes place, where the weight of the barge and additional ballast water are used to drive the legs securely into the sea bottom so they will not penetrate further while operations are carried out. After preloading, the jacking system is used to raise the entire barge above the water to a predetermined height or air gap, so that wave, tidal and current loading acts only on the relatively slender legs and not on the barge hull.

[0112] Modern jacking systems use a rack and pinion gear arrangement where the pinion gears are driven by hydraulic or electric motors and the rack is affixed to the legs.

[0113] Jack-up rigs can only be placed in relatively shallow waters, generally less than 120 meters (390 ft) of water. However, specialized classes of jack-up rigs known as premium or ultra-premium jack-ups are known to have operational capability in water depths ranging from 150 to 190 meters (500 to 625 feet).

[0114] FIG. 7 is a drawing of a typical jack-up drilling rig 10 suitable for use together with the distributed well concept to perform effective tubular operations through a secondary drilling unit or pod and then transfer the operation back to the secondary drilling unit for performing slower drilling, milling or similar operations. The jack-up rig comprises a barge 12 fitted with long support legs 14 that can be raised or lowered, wherein said support legs 14 are placed on the sea floor 18. As shown, the barge 12 is located above the sea level 16 at a desired level. The jack-up rig 10 is further equipped with a cantilever 20 with a main drilling unit 22, and where the cantilever can be driven or skidded out over the water, such that the main drilling unit 22 is above an operational area to perform the desired drilling operations. The operational area is indicated by the two vertical dotted lines running down from the cantilever 20. The main drilling unit 22 is equipped in a normal manner with a drilling mast/derrick 24 and drilling machinery 26. The main drilling unit 22 is operable on a drilling floor 28.

[0115] FIG. 6 shows a drawing of a typical secondary drilling unit, or drilling pod, 30 with mast 32, drill floor 34 and BOP 36. The BOP is located above the wellhead 42. In the mast 32 of the secondary drilling unit 30 a rotary drilling and hoisting machine 38 is fitted which is adapted to drive a tubular 40 through the BOP 36 and into a desired wellhead 42. Simple secondary drilling units or drilling pods like this are suitable for use in the distributed well activity concepts. The secondary drilling units can also be more advanced if the well operations so require.

[0116] FIG. 8 is a typical setup for the distributed well center operation with two secondary drilling units, or drilling pods, 30 assisted by a jack-up rig 10. As shown the secondary drilling units 30 are placed on a separate platform 50 standing on its own legs 54 on the sea floor 18, such as a wellhead platform (wellhead spread). Several secondary drilling units, or pods, 30, at least two, are placed on the drill floor 34 of the auxiliary wellhead platform 50, and can be skidded around for placement above a desired wellhead 42. A riser 44 can be placed between the BOP 36 and the wellhead 42. From the wellheads 42 several tubulars 56 run down into the water and down into hydrocarbon well bores at the sea floor 18. Umbilicals 58 and service loops run from the main drilling unit 22 in order to provide the necessary power and utilities from the main drilling unit to the distributed well centers on the wellhead platform 50.

[0117] FIG. 9 is a typical layout of a drill floor 28 on a jack-up rig 10 capable of efficient tubular handling and offline stand building. As shown, in the upper left corner of the drill floor 28 is a driller's cabin/control station 60 connected to the equipment on the drill floor 28 on the cantilever 20. The driller's cabin/control station 60 is also connected by the umbilicals 58 to the equipment on the wellhead platform 50, for control and operations of the equipment and the secondary drilling units 30.

[0118] Further, the drill floor 28 is equipped with a set back/racking area 62 and, as shown, with two racking machines 64 placed in front of the set back/racking area 62. Running longitudinal on the drill floor 28 are two rails 66 for catwalk machinery. Between the rails 66 is a main well center 68, to the right in the drawing, and an auxiliary stand building area 70, to the left in the drawing, each equipped with an iron roughneck 72. At the end of the rails, the drilling machine 26 of the main drilling unit 22 is shown.

[0119] Consequently, the drill floor 28 and the equipment thereon form an elevated main drilling unit 22 which is carried by the cantilever 20, which main drilling unit 22 generally has the same configuration and the same equipment as the main drilling unit 107 disclosed in FIG. 3.

SEQUENCE OF OPERATION

[0120] The sequence of operation and distribution of tasks between the elevated main drilling unit 22 and the distributed well centers on the wellhead platform 50 is set up so that any tripping activities or similar where there is a significant efficiency gain to have a tall derrick and large setback area is performed by the elevated main drilling unit 22. All slow progressing activities such as drilling ahead, milling, circulating and so on where there is little difference between a high spec and a low spec unit can be carried out in the distributed well centers. A typical sequence is illustrated in FIGS. 8 and 10. Initially the secondary drilling units 30 are deployed from the main drilling unit 22 and rigged on the well deck of the wellhead platform 50. The operation proceeds by the main elevated drilling unit 22 tripping in with bottom-hole assembly through a first secondary drilling unit's 30 rotary bushing and BOP. When reaching TD the drill string is landed in the secondary drilling unit's rotary bushing and the iron roughneck machine on the first secondary drilling unit breaks the connection freeing the main well center 68 of the main drilling unit 22 for other operations. The elevated drilling unit 22 will then immediately move over to a position above the second secondary drilling unit 30 to assist the second secondary drilling unit while the first secondary drilling unit 30 is drilling ahead using local pipe storage. The elevated main drilling unit 22 will perform preparations for the next activity such as making up bottom hole assembly or rack up or down casing. The elevated main drilling unit will trip in with the bottom hole assembly to TD through the second distributed well center. When reaching TD the string is landed out in the rotary bushing on the second secondary drilling unit and the iron roughneck breaks the connection releasing the drill string from the elevated main drilling unit. The second secondary drilling unit can then start drilling using its own local drill pipe storage. The elevated main drilling unit will prepare the casing section for the first secondary drilling unit, move over and when ready pull out the drill string from the first secondary drilling unit and then run in the casing section through the secondary drilling unit's rotary bushing and BOP. When the run is close to completed the casing landing string is transferred to the secondary drilling unit, which can land out the casing.

[0121] By using this principle two or more wells can be drilled simultaneously from one main drilling unit by use of two or more distributed well centers keeping the well control for the well at all times. The size of the distributed well centers can be kept small as the main drilling unit is supplying services including mud, power, hydraulics and so on. Furthermore the main drilling unit can be utilized to time optimize operations or operations requiring increased capabilities such as tripping in and out of the hole and running or pulling casings.