NO20190742A1

NO20190742A1 - System and method for handling a pipe string

Info

Publication number: NO20190742A1
Application number: NO20190742A
Authority: NO
Inventors: Bernt Olav Holen
Original assignee: Mhwirth As
Priority date: 2016-12-21
Filing date: 2019-06-17
Publication date: 2019-06-17
Also published as: WO2018117853A1; GB2573412A; NO343305B1; NO20162037A1; GB201908673D0

Description

SYSTEM AND METHOD FOR HANDLING A PIPE STRING

The present invention relates to a system and method for handling pipe, and particularly a system and method suitable for insertion and/or withdrawal of a drill pipe string or the like to or from a wellbore.

BACKGROUND

In offshore petroleum exploration, various operations need to be carried out. One key operation is the drilling of the well. Such drilling is usually carried out by specialized vessels. The operation of such vessels can be very costly and make up a substantial part of the cost of a petroleum well. Similarly, completion, work-over and plug-and-abandonment operations are also usually carried out with the same or similar vessels. Due to the high cost for such vessels, operational efficiency and reliability during these processes is of great importance.

Traditionally, offshore wellbores are formed (e.g. drilled, completed) using a single load path (e.g. derrick, rig, drilling assembly), thus requiring all wellbore tasks (e.g. drilling, completion, simulations, workovers etc.) to be performed sequentially from a single assembly. In order to improve efficiency, various efforts have been made to decrease the time required to drill wells offshore by performing some tasks simultaneously. Examples of such efforts include US 6,085,851, US 6,056,071 and US 5,762,279. Nevertheless, there remains a need for further optimization and for systems and methods which further improve operational efficiency.

Other prior art useful for understanding the background includes US 4023449 A; US 2008/0307930 A1 ; CA 2207832 C; US 3760658 A; US 3,194,313; WO 01/33034 A1; US 3,158,212; US 6,581 ,698; US 3,533,516; WO 2010/098672 A1 ; SE 450144 B; WO 2013/125961 A1 and NO 171233 B.

The present invention has the objective to provide an improved system and method for handling a pipe string. Some embodiments may provide advantages in terms of efficiency, reliability, operational simplicity, or other advantages compared to known systems and techniques.

SUMMARY

In an embodiment, there is provided a system for handling a pipe string formed by a series of aligned pipe sections having facing threaded upper and lower end portions directly connected together and defining a releasable joint between each pair of pipe section, the system comprising

a drill floor having a well centre opening,

a first lifting unit and a second lifting unit,

each lifting unit having a respective pipe handling unit,

each pipe handling unit being vertically movable in relation to the drill floor and comprising

a gripping device configured for selective engagement with an upper end portion of a pipe section such as to, when engaged, hold the pipe section fixed and carry the weight of the pipe section, and

a motor configured for threaded engagement with an upper end portion of the pipe section and for rotating the pipe section.

In an embodiment, each pipe handling unit has an advanced position, in which the pipe handling unit is aligned vertically above the well centre opening in the drill floor, and a retracted position, in which the pipe handling unit is spaced horizontally from a vertical axis extending through the well centre.

In an embodiment, each motor has an advanced position, in which the motor is aligned vertically above the gripping device, and a retracted position, in which the motor is spaced horizontally from a vertical axis extending through the gripping device.

In an embodiment, each lifting unit comprises

a vertically arranged hoisting cylinder assembly,

a yoke fixed in an upper section of the hoisting cylinder assembly, at least one sheave arranged on the yoke,

a wire,

wherein the pipe handling unit is suspended by the wire, the wire running from the pipe handling unit, via the at least one sheave and to an anchor.

In an embodiment, in each lifting unit the pipe handling unit and the at least one sheave is arranged such that in the advanced position of the pipe handling unit, the wire extends vertically between the pipe handling unit and the at least one sheave.

In an embodiment, in each lifting unit the anchor and the at least one sheave is arranged such that the wire extends vertically between the anchor and the at least one sheave.

In an embodiment, the wire extends between the pipe handling unit and the at least one sheave at a first side of the vertically arranged hoisting cylinder assembly and

the wire extends between the between the anchor and the at least one sheave at a second side of the vertically arranged hoisting cylinder assembly, and the distance between the wire and the vertically arranged hoisting cylinder assembly is the same on the first side and the second side.

In an embodiment, the wire suspending the first pipe handling unit and the wire suspending the second pipe handling unit intersect an axis which is perpendicular to and intersects a vertical axis extending through the well centre.

In an embodiment, a plurality of wires suspend the first pipe handling unit and a plurality of wires suspend the second pipe handing unit, and wherein the plurality of wires intersect the axis.

In an embodiment, wires suspending the first pipe handling unit are arranged on opposite sides of the vertical axis extending through the well centre, and wires suspending the second pipe handing unit are arranged on opposite sides of the vertical axis extending through the well centre.

In an embodiment, the system comprises a derrick, and each lifting unit comprises

a sheave arranged in an upper section of the derrick,

a wire,

wherein the pipe handling unit is suspended by the wire, the wire running via the sheave to a winch.

In one embodiment, there is provided a system according to any of the embodiments described above, where the motor is a drilling machine.

In one embodiment, there is provided a system according to any of the embodiments described above, where the pipe handling units are arranged on opposite sides of the vertical axis extending through the well centre.

In one embodiment, there is provided a system according to any of the embodiments described above, wherein the pipe string is a drill pipe.

In one embodiment, there is provided a system according to any of the embodiments described above, further comprising a roughneck machine arranged on the drill floor.

In one embodiment, there is provided a drilling rig comprising a system according to any of the embodiments described above.

In an embodiment, there is provided a method of running a pipe string into a borehole, comprising the steps

(i) providing a system according to any preceding claim,

(ii) suspending the pipe string from the first pipe handling unit,

(iii) operating the first lifting unit to lower the pipe string,

(iv) suspending a pipe section from the second pipe handling unit, (v) operating the second lifting unit to lift the pipe section,

(vi) connecting an upper end of the pipe section to the motor of the second pipe handling unit,

(vii) operating the motor of the second pipe handling unit to threadedly connect a lower end of the pipe section to the pipe string while the pipe string is suspended by the first pipe handling unit whereby the pipe section becomes part of the pipe string,

(viii) suspending the pipe string from the second pipe handling unit, (ix) operating the second lifting unit to lower the pipe string.

In an embodiment, the method includes the step of operating the gripping device of the second pipe handling unit prior to the step of suspending the pipe string from the second pipe handling unit, such as to hold the pipe section fixed with the gripping device of the second pipe handling unit.

In an embodiment, the step of suspending the pipe string from the second pipe handling unit includes suspending the pipe string from the motor of the second pipe handling unit.

In an embodiment, the method includes the step of rotating the motor of the second pipe handling unit while carrying out the step of operating the second lifting unit to lower the pipe string.

In an embodiment, the method includes the steps:

(x) suspending a pipe section from the first pipe handling unit,

(xi) operating the first lifting unit to lift the pipe section,

(xii) connecting an upper end of the pipe section to the motor of the first pipe handling unit,

(xiii) operating the motor of the first pipe handling unit to threadedly connect a lower end of the pipe section to the pipe string while the pipe string is suspended by the second pipe handling unit whereby the pipe section becomes part of the pipe string.

In an embodiment, there is provided a method according to any of the embodiments described above, further comprising repeating steps (ii) to (xiii) for a plurality of further pipe sections.

In an embodiment, there is provided a method according to any of the embodiments described above, further comprising carrying out step (vii) simultaneously with step (iii).

In an embodiment, there is provided a method according to any of the embodiments described above, further comprising carrying out step (xiii) simultaneously with step (ix).

In an embodiment, there is provided a system for handling a pipe string, the system comprising: a drill floor having a well centre opening, a first lifting unit and a second lifting unit, each lifting unit having a respective pipe handling unit, each pipe handling unit being vertically movable in relation to the drill floor.

In an embodiment, each pipe handling unit comprises a first pipe handling device and a second pipe handling device.

In an embodiment, the first and second pipe handling devices are vertically spaced on the respective pipe handling unit.

In an embodiment, in at least one of the first and second pipe handling unit the first pipe handling device is located above the second pipe handling device and the first pipe handling device has an advanced position, in which the first pipe handling device is aligned vertically above the second pipe handling device, and a retracted position, in which the first pipe handling device is spaced horizontally from a vertical axis extending through the second pipe handling device.

In an embodiment, the first pipe handling device is a gripping device, and the second pipe handling device is a gripping device or a motor.

In an embodiment, the gripping device is configured for selective engagement with an upper end portion of a pipe section such as to, when engaged, hold the pipe section fixed and/or carry the weight of the pipe section.

In an embodiment, each pipe handling unit has an advanced position, in which the pipe handling unit is aligned vertically above the well centre opening, and a retracted position, in which the pipe handling unit is spaced horizontally from a vertical axis extending through the well centre opening.

In an embodiment, each lifting unit comprises: a vertically arranged hoisting cylinder assembly, a yoke fixed in an upper section of the hoisting cylinder assembly, at least one sheave arranged on the yoke, and a wire, wherein the pipe handling unit is suspended by the wire, the wire running from the pipe handling unit, via the at least one sheave and to an anchor.

In an embodiment, in each lifting unit, the pipe handling unit and the at least one sheave is arranged such that the wire extends vertically between the pipe handling unit and the at least one sheave.

In an embodiment, the wire extends vertically between the pipe handling unit and the at least one sheave in the advanced position of the pipe handling unit and not in the retracted position.

In an embodiment, in each lifting unit, the anchor and the at least one sheave is arranged such that the wire extends vertically between the anchor and the at least one sheave.

In an embodiment, the wire extends between the pipe handling unit and the at least one sheave at a first side of the vertically arranged hoisting cylinder assembly and between the between the anchor and the at least one sheave at a second side of the vertically arranged hoisting cylinder assembly.

In an embodiment, the distance between the wire and the vertically arranged hoisting cylinder assembly is the same on the first side and the second side.

In an embodiment, a plurality of wires suspend the first pipe handling unit and a plurality of wires suspend the second pipe handing unit, and the plurality of wires intersect the axis.

In an embodiment, the wires suspending the first pipe handling unit are arranged on opposite sides of the vertical axis extending through the well centre, and wires suspending the second pipe handing unit are arranged on opposite sides of the vertical axis extending through the well centre.

In an embodiment, the system further comprises a derrick and each lifting unit comprises a sheave arranged in an upper section of the derrick, a wire, and the pipe handling unit is suspended by the wire, the wire running via the sheave to a winch.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments of the present invention will now be described with reference to the appended drawings, in which:

Figures 1-6 illustrate a system for handling a pipe string according to an embodiment, in various operational states.

Figure 7 illustrates a system for handling a pipe string according to an embodiment.

Figure 8 illustrates a drilling rig comprising a system for handling a pipe string. Figure 9 illustrates a top view of aspects of the system shown in Fig. 1-6.

DETAILED DESCRIPTION

Figures 1-6 shows an embodiment of a system 100 for handling a pipe string 5 on a drilling rig 102 (see Fig. 8), the system being illustrated in various operational states. The pipe string is formed by a series of aligned pipe sections having facing threaded upper and lower end portions directly connected together and defining a releasable joint between each pair of pipe section. The system comprises a drill floor 10 having a well centre opening 11, a first lifting unit 1a and a second lifting unit 1b. Each lifting unit 1a, 1b have a respective pipe handling unit 2a, 2b. Each pipe handling unit 2a, 2b is vertically movable in relation to the drill floor 10 by means of the respective lifting unit 1a, 1b.

The lifting units 1a, 1b each comprise at least one vertically arranged cylinder. In the embodiments shown, the first lifting unit 1a has two cylinders 6a and 6b, and the second lifting unit 1b has two cylinders 6c and 6d. Each cylinder assembly has a yoke 7a and 7b fixed in its upper section 6’ and 6”. On each yoke 7a and 7b there are arranged sheaves 8a-h. The first yoke 7a is fixed to the cylinders 6a and 6b and comprises four sheaves 8a-d. The second yoke 7b is fixed to the cylinders 6c and 6d, and comprises four sheaves 8e-h. The cylinders 6a-d and yokes 7 a and 7b may be provided within a derrick structure (not shown) or another type of support frame on the drill floor 10 in the conventional manner, in order to support these components and guide the yokes 7a and 7b. Similarly, the pipe handling units 2a and 2b are guided by the cylinders 6a-d or by the derrick stricture or support frame.

The lifting units 1 a and 1 b further comprise a set of wires 9a-h, where each wire 9a-h extend from an anchor 12a-d, via two sheaves 8a-h and to one of the pipe handling units 2a and 2b. The anchors 12a-d can be any type of fixation structure, and may be provided on the drill floor 10, or on a different structure, for example a different part of the drilling rig 102 (see Fig. 8). Each wire 9a-h may have one anchor, or one anchor may fix two or more wires. The pipe handling unit 2a, 2b are thereby suspended by the wires 9a-h. In an alternative embodiment, a single sheave for each wire may be used in the upper section 6’, 6”, for example by using one large-diameter sheave instead of the two sheaves as shown in this embodiment.

The pipe handling units 2a and 2b are in this embodiment substantially identical in design. Each pipe handling unit 2a and 2b comprises a gripping device 20a, 20b configured for selective engagement with an upper end portion of a pipe section 5’, 5” such as to, when engaged, hold the pipe section 5’, 5” fixed. The gripping devices 20a and 20b may be conventional tongs, such as those known from roughneck machines, which grip from the side around the outside of the pipe section end. This permits access to the pipe section end from above the gripping device 20a or 20b, also while the pipe section 5’, 5” is held. The gripping device 20a, 20b may be arranged to both hold the weight of the pipe section 5’, 5” and hold the pipe section 5’, 5” rotationally fixed. A single pair of tongs may be used for this purpose, or separate tongs or holding units within the gripping device 20a, 20b to carry out the different functions of holding the weight and lock / prevent rotation.

Each pipe handling unit further comprises a motor 3a, 3b configured for threaded engagement with an upper end portion of the pipe section 5’, 5” and for rotating the pipe section 5’, 5”. The connection may be similar to those used in conventional top drives or DDMs, i.e. a threaded subs arranged on the motor 3a and 3b which extends downwards and to which the pipe section 5’, 5” can be connected.

Each pipe handling unit 2a and 2b has an advanced position, in which the respective pipe handling unit 2a, 2b is aligned vertically above the well centre opening 11 in the drill floor 10, and a retracted position, in which the pipe handling unit 2a, 2b is spaced horizontally from a vertical axis 11’ extending through the well centre 11. In Fig. 1 , the first pipe handling unit 2a is shown in the retracted position and the second pipe handling unit 2b is shown in the advanced position. This can, for example, be achieved by means of a guide frame, as illustrated. The position of the guide frame may be controlled by, for example, hydraulic cylinders, in order to move the pipe handling units between the advanced and retracted positions. In the retracted position, the first pipe handling unit 2a can be moved out of the way, as shown in Fig. 1 , such as to not interfere with the pipe string 5 extending down into the well and being handled by the second pipe handling unit 2b, and vice versa.

In its advanced position, each pipe handling unit 2a, 2b is suspended by the wire 9a-h with the wire 9a-h running vertically between the pipe handling unit 2a, 2b and the respective sheave 8a-h. The sheaves are also arranged such that the wire 9a-h extends vertically between the anchor 12a-d and the sheaves 8a-h. The distance between the wires 9a-h and the hoisting cylinder assembly 6a-d is the same on both sides.

Figure 9 illustrates schematically a top view of the system and the arrangement of the sheaves 8c-f and wires 9a-h in relation to the well centre 11. The sheaves are arranged such that the wires 9a-h are aligned along an axis 66 which is perpendicular to and intersects a vertical axis 11’ (see Fig. 1) extending through the well centre 11.

This eliminates a moment force acting on the lifting units 1a, 1b when the pipe handling units 2a, 2b are carrying a load. Such moment forces need to be compensated for, thus requiring a stronger support structure, and may be also be damaging to the hoisting cylinders, which have low tolerance for side forces. This embodiment moreover permits a larger drill floor space, since the hoisting cylinder assemblies can be positioned farther apart, without experiencing excessive moments acting on the lifting units 1a, 1b. In the retracted position, the pipe handling units 2a and 2b may pass each other in their vertical movement during operations. As can be seen from Figs 1-6 and 9, the sheaves 8c-f may be spaced sideways in relation to each other such that they may also pass each other when moving vertically during operations.

Each motor 3a and 3b has an advanced position, in which the motor 3a, 3b is aligned vertically above the respective gripping device 20a, 20b, and a retracted position, in which the motor 3a, 3b is spaced horizontally from a vertical axis extending through the gripping device 20a, 20b. In an embodiment, each motor 3a and 3b in the advanced position is aligned vertically above a pipe handling area of the respective gripping device 20a, 20b, and a retracted position, in which the motor 3a, 3b is spaced horizontally from a vertical axis extending through the pipe handling area. The pipe handling area means an area occupied by a pipe section 5’, 5” or pipe string 5, when that pipe section or pipe string is held by the gripping device 20a, 20b. In the case of a tong, the pipe handling area may be the area between the jaws.

By providing each motor 3a and 3b with an advanced an a retracted position, access to the pipe section 5’, 5” or pipe string 5 from above may be permitted, when that pipe section or pipe string is held by the gripping device 20a, 20b. This allows, for example, a new pipe section to be connected to the pipe string 5, while the pipe string 5 is suspended by a gripping device.

The motor 3a, 3b may be a drilling machine. This allows the system to perform drilling operations. Alternatively, the motor 3a, 3b may be configured only for making up and connecting a new pipe section to the pipe string 5.

Alternatively, the pipe handling units 2a, 2b may be provided with a second gripping device, which can be similar to the gripping devices 20a, 20b, in place of the motors 3a, 3b.

The pipe handling units 2a, 2b may be arranged on opposite sides of the well centre opening 11.

The pipe string may be a drill pipe. The drill pipe may be used for drilling, for well intervention operations, for installing equipment subsea, or other operations. Alternatively, the pipe string may be a casing string. Alternatively, the pipe string may be a different type of elongate pipe.

Figure 7 shows one embodiment of a system 101 for handling a pipe string 5, employing a conventional, drawworks-based hoisting system. In this embodiment, the system comprises a derrick 31 arranged on a drill floor 10. Each lifting unit 1a, 1b comprises a sheave 32a, b arranged in an upper section 31 ’ of the derrick 31 and a wire 34a, b. The pipe handling unit 2a, 2b is suspended by the wire 34a, b, which runs via the sheave 32a, b to a winch 35a, b. Other components operate similarly as described above. The winch 35a, b can thus be operated to lift and lower the pipe handling units 2a and 2b.

The system 100 or 101 according to any of the embodiments described above may comprise a roughneck machine 36 (illustrated in Fig. 7) arranged on the drill floor 10. The roughneck machine 36 may be used, for example, for breaking out stands when tripping out a drill string using the system 100 or 101.

With reference to Figs 1-6, a method of operation of the system will now be described. The system is used to run a pipe string 5 into a borehole (not shown) via the well centre opening 11. Building and running the pipe string 5 is carried out by the first and second pipe handling units 2a and 2b in cooperation.

As shown in Fig. 1 , the pipe string 5 extending into the borehole is suspended from the second pipe handling unit 2b. The second pipe handling unit 2b is then lowered by the second lifting unit 1b, as shown in Fig. 2 (the side arrows illustrate the direction of motion of the lifting units 1a and 1b). The second pipe handling unit 2b thus carries the weight of the pipe string 5; this is done by the second gripping device 20b and the second motor 3b is placed in its retracted position during this process. This permits tripping in of the pipe string 5, i.e. simply lowering it into an existing borehole. In such a case, the second gripping device 20b can be operated and maintained in engagement to hold the pipe string 5 and carry its weight through the entire process of lowering the pipe string 5 until the second lifting system 1b is in its lowermost position.

Alternatively, the pipe string 5 may be suspended from the second motor 3b during the lowering of the second pipe handling unit 2b. In this case the second gripping device 20b can release the pipe string 5. The second motor 3b can then be rotated to drill while the pipe string 5 is being lowered. This permits drilling or reaming to be carried out by the system while tripping in.

Simultaneously, the first pipe handling unit 2a can be lowered to its lowermost position and operated to engage a pipe section 5” which is to be connected to the pipe string 5. This may be done with the first gripping device 3a. The first pipe handing unit 2a is then lifted by the first lifting unit 1a, as shown in Fig. 2. This process can be carried out simultaneously with the operation of the second lifting unit 1b, or, alternatively, the processes can be carried out sequentially.

When the second pipe handling unit 2b is near its lowermost position and the first pipe handling unit 2a is near its uppermost position, the pipe section 5” can be brought into alignment with the pipe string 5 by moving the first pipe handling unit 2a into its advanced position, whereby the pipe section 5” is aligned directly above the well centre opening 11 and the pipe string 5, and can be connected to the pipe string 5. This is illustrated in Fig. 3. A pipe guide machine 40a may be provided for this purpose. The second motor 3b is in its retracted position such that the pipe section 5” can be connected to the pipe string 5 while the pipe string is held in place by the second gripping device 20b. The first motor 3a is then brought into its advanced position, threadedly connects to the upper end of the pipe section 5”, and rotates the pipe section 5” to connect it at its lower end to the pipe string 5. The second gripping device 20b is released, and the pipe section 5” is now part of the pipe string 5, carried by the first pipe handling unit 2a. The first lifting unit 1a can immediately continue lowering the pipe string 5 into the wellbore.

The first gripping device 20a can then be engaged to carry the weight of the pipe string 5 such that the first motor 3a can be retracted (in a tripping in operation, as is illustrated here). Alternatively, if drilling, the first motor 3a will remain connected to the pipe string 5 such as to carry the weight of the pipe string 5 and rotate it while it is being lowered by the first lifting unit 1a, with the first gripping device 20a not engaged.

Figure 4 illustrates the first lifting unit 1a lowering the pipe string 5 while the second pipe handling unit 2b has engaged a new pipe section 5’ which is suspended by the second gripping device 20b, with the assistance of a pipe guide machine 40b, and is being lifted. When the first lifting unit 1a is near its lowermost position and the second lifting unit 1b is near its uppermost position, the second pipe handling unit 2b can be brought to its advanced position and the pipe section 5’ can be connected to the pipe string 5 in a manner equivalently to that described above. This is illustrated in Figs 5 and 6. The first pipe handling unit 2a will release the pipe string 5 and be retracted, and the operation continues as described above in relation to Figs 1 and 2. These steps can be repeated multiple times, until a desired length of pipe string 5 has been run into the wellbore.

In an embodiment, a new pipe section 5’, 5” is connected to the pipe string 5 by one pipe handling unit, while the pipe string 5 is being lowered by the other pipe handling unit. This can be achieved by operating one pipe handling unit to bring a new pipe section into alignment with the pipe string 5 and connecting the new pipe section to the pipe string 5 during a downwards motion of both lifting units 1a and 1b. This permits a substantially continuous tripping in motion of the pipe string 5 into the wellbore, i.e. without having to stop the motion during the connection phase. This reduces the overall time required to trip in a given length of pipe string 5 into the wellbore.

During tripping out, substantially the reverse processes of the above may be carried out. A roughneck machine 36 (see Fig. 7) may, for example, be employed to break out pipe sections during tripping out.

The invention is not restricted to the embodiments described herein; reference should be had to the appended claims.

Claims

1. A system (100, 101 ) for handling a pipe string (5) formed by a series of aligned pipe sections (5’, 5”) having facing threaded upper and lower end portions directly connected together and defining a releasable joint between each pair of pipe section (5’, 5”), the system comprising a drill floor (10) having a well centre opening (11 ),

a first lifting unit (1a) and a second lifting unit (1b),

each lifting unit (1a, 1b) having a respective pipe handling unit (2a, 2b), each pipe handling unit (2a, 2b) being vertically movable in relation to the drill floor (10) and comprising

a gripping device (20a, 20b) configured for selective engagement with an upper end portion of a pipe section (5’, 5”) such as to, when engaged, hold the pipe section (5’, 5”) fixed and carry the weight of the pipe section (5’, 5”), and

a motor (3a, 3b) configured for threaded engagement with an upper end portion of the pipe section (5’, 5”) and for rotating the pipe section (5’, 5”).

2. A system according to claim 1 , wherein each pipe handling unit (2a, 2b) has an advanced position, in which the pipe handling unit (2a, 2b) is aligned vertically above the well centre opening (11 ) in the drill floor (10), and a retracted position, in which the pipe handling unit (2a, 2b) is spaced horizontally from a vertical axis (11’) extending through the well centre (11).

3. A system according to claim 1 or 2, wherein each motor (3a, 3b) has an advanced position, in which the motor (3a, 3b) is aligned vertically above the gripping device (20a, 20b), and a retracted position, in which the motor (3a, 3b) is spaced horizontally from a vertical axis extending through the gripping device (20a, 20b).

4. A system according to any preceding claim, wherein each lifting unit (1a, 1b) comprises

a vertically arranged hoisting cylinder assembly (6a-d),

a yoke (7a, 7b) fixed in an upper section (6’, 6”) of the hoisting cylinder assembly (6a-d),

at least one sheave (8a-h) arranged on the yoke,

a wire (9a-h),

wherein the pipe handling unit (2a, 2b) is suspended by the wire (9a-h), the wire (9a-h) running from the pipe handling unit (2a, 2b), via the at least one sheave (8a-h) and to an anchor (12a-d).

5. A system according to claim 4, wherein in each lifting unit (1a, 1b) the pipe handling unit (2a, 2b) and the at least one sheave (8a-h) is arranged such that in the advanced position of the pipe handling unit (2a, 2b), the wire (9a-h) extends vertically between the pipe handling unit (2a, 2b) and the at least one sheave (8a-h).

6. A system according to claim 4 or 5, wherein in each lifting unit (1a, 1b) the anchor (12a-d) and the at least one sheave (8a-h) is arranged such that the wire (9a-h) extends vertically between the anchor (12a-d) and the at least one sheave (8a-h).

7. A system according to claim 6 in combination with claim 5, wherein the wire (9a-h) extends between the pipe handling unit (2a, 2b) and the at least one sheave (8a-h) at a first side of the vertically arranged hoisting cylinder assembly (6a-d) and

the wire (9a-h) extends between the between the anchor (12a-d) and the at least one sheave (8a-h) at a second side of the vertically arranged hoisting cylinder assembly (6a-d), and wherein

the distance between the wire (9a-h) and the vertically arranged hoisting cylinder assembly (6a-d) is the same on the first side and the second side.

8. A system according to any one of claims 4-7, wherein the wire (9a-d) suspending the first pipe handling unit (2a) and the wire (9e-h) suspending the second pipe handling unit (2b) intersect an axis (66) which is perpendicular to and intersects a vertical axis (11’) extending through the well centre (11 ).

9. A system according to claim 8, wherein a plurality of wires (9a-d) suspend the first pipe handling unit (2a) and a plurality of wires (9e-h) suspend the second pipe handing unit (2b), and wherein the plurality of wires (9a-h) intersect the axis (66).

10. A system according to claim 9, wherein wires (9a-d) suspending the first pipe handling unit (2a) are arranged on opposite sides of the vertical axis (11’) extending through the well centre (11), and wires (9e-h) suspending the second pipe handing unit (2b) are arranged on opposite sides of the vertical axis (11 ’) extending through the well centre (11 ).

11. A system according to any one of claims 1 -3, further comprising a derrick (31), and wherein each lifting unit (1a, 1b) comprises

a sheave (32a, b) arranged in an upper section (31’) of the derrick (31), a wire (34a, b),

wherein the pipe handling unit (2a, 2b) is suspended by the wire (34a, b), the wire running via the sheave (32a, b) to a winch (35a, b).

12. A method of running a pipe string (5) into a borehole, comprising the steps

(i) providing a system according to any preceding claim,

(ii) suspending the pipe string (5) from the first pipe handling unit (2a), (iii) operating the first lifting unit (1a) to lower the pipe string (5),

(iv) suspending a pipe section (5’) from the second pipe handling unit (2b),

(v) operating the second lifting unit (1b) to lift the pipe section (5’), (vi) connecting an upper end of the pipe section (5’) to the motor (3b) of the second pipe handling unit (2b),

(vii) operating the motor (3b) of the second pipe handling unit (2b) to threadedly connect a lower end of the pipe section (5’) to the pipe string (5) while the pipe string (5) is suspended by the first pipe handling unit (2a) whereby the pipe section (5’) becomes part of the pipe string (5), (viii) suspending the pipe string (5) from the second pipe handling unit (2b),

(ix) operating the second lifting unit (1 b) to lower the pipe string (5).

13. A method according to claim 12, further including the step of operating the gripping device (20b) of the second pipe handling unit (2b) prior to the step of suspending the pipe string (5) from the second pipe handling unit (2b), such as to hold the pipe section (5) fixed with the gripping device (20b) of the second pipe handling unit (2b).

14. A method according to claim 12, wherein the step of suspending the pipe string (5) from the second pipe handling unit (2b) includes suspending the pipe string (5) from the motor (3b) of the second pipe handling unit (2b).

15. A method according to claim 14, further comprising the step of rotating the motor (3b) of the second pipe handling unit (2b) while carrying out the step of operating the second lifting unit (1 b) to lower the pipe string (5).

16. A method according to any one of claims 12-15, further comprising the steps:

(x) suspending a pipe section (5”) from the first pipe handling unit (2a), (xi) operating the first lifting unit (1a) to lift the pipe section (5”),

(xii) connecting an upper end of the pipe section (5”) to the motor (3a) of the first pipe handling unit (2a),

(xiii) operating the motor (3a) of the first pipe handling unit (2a) to threadedly connect a lower end of the pipe section (5”) to the pipe string (5) while the pipe string (5) is suspended by the second pipe handling unit (2b) whereby the pipe section (5”) becomes part of the pipe string (5).

17. A system (100, 101) for handling a pipe string (5), the system comprising:

a drill floor (10) having a well centre opening (11 ),

a first lifting unit (1a) and a second lifting unit (1b),

each lifting unit (1a, 1b) having a respective pipe handling unit (2a, 2b), each pipe handling unit (2a, 2b) being vertically movable in relation to the drill floor (10).

18. A system according to the preceding claim, wherein each pipe handling unit (2a, 2b) comprises a first pipe handling device (3a, 3b, 20a, 20b) and a second pipe handling device (3a, 3b, 20a, 20b).

19. A system according to the preceding claim, wherein the first and second pipe handling devices (3a, 3b, 20a, 20b) are vertically spaced on the respective pipe handling unit (2a, 2b).

20. A system according to the preceding claim, wherein, in at least one of the first and second pipe handling unit (2a, 2b), the first pipe handling device (3a, 3b, 20a, 20b) is located above the second pipe handling device (3a, 3b, 20a, 20b) and the first pipe handling device (3a, 3b, 20a, 20b) has an advanced position, in which the first pipe handling device

(3a, 3b, 20a, 20b) is aligned vertically above the second pipe handling device (3a, 3b, 20a, 20b), and a retracted position, in which the first pipe handling device (3a, 3b, 20a, 20b) is spaced horizontally from a vertical axis extending through the second pipe handling device (3a, 3b, 20a, 20b).

21.A system according to any of the three preceding claims, wherein

the first pipe handling device (3a, 3b, 20a, 20b) is a gripping device (20a, 20b), and

the second pipe handling device (3a, 3b, 20a, 20b) is a gripping device (20a, 20b) or a motor (3a, 3b).

22. A system according to the preceding claim, wherein the gripping device (20a, 20b) is configured for selective engagement with an upper end portion of a pipe section (5’, 5”) such as to, when engaged, hold the pipe section (5’, 5”) fixed and/or carry the weight of the pipe section (5’, 5”).

23. A system according to any of claims 17-22, wherein each pipe handling unit (2a, 2b) has an advanced position, in which the pipe handling unit (2a, 2b) is aligned vertically above the well centre opening (11), and a retracted position, in which the pipe handling unit (2a, 2b) is spaced horizontally from a vertical axis (11’) extending through the well centre opening (11).

24. A system according to any preceding claim, wherein each lifting unit (1a, 1b) comprises:

a vertically arranged hoisting cylinder assembly (6a-d), a yoke (7a, 7b) fixed in an upper section (6’, 6”) of the hoisting cylinder assembly (6a-d),

at least one sheave (8a-h) arranged on the yoke (7a, 7b), a wire (9a-h),

25. A system according to the preceding claim, wherein, in each lifting unit (1a, 1b), the pipe handling unit (2a, 2b) and the at least one sheave (8a-h) is arranged such that the wire (9a-h) extends vertically between the pipe handling unit (2a, 2b) and the at least one sheave (8a-h).

26. A system according to the preceding claim in combination with claim 23, wherein the wire (9a-h) extends vertically between the pipe handling unit (2a, 2b) and the at least one sheave (8a-h) in the advanced position of the pipe handling unit (2a, 2b) and not in the retracted position.

27. A system according to any of the three preceding claims, wherein, in each lifting unit (1a, 1b), the anchor (12a-d) and the at least one sheave (8a-h) is arranged such that the wire (9a-h) extends vertically between the anchor (12a-d) and the at least one sheave (8a-h).

28. A system according to any of the four preceding claims, wherein

the wire (9a-h) extends between the pipe handling unit (2a, 2b) and the at least one sheave (8a-h) at a first side of the vertically arranged hoisting cylinder assembly (6a-d) and

the wire (9a-h) extends between the between the anchor (12a-d) and the at least one sheave (8a-h) at a second side of the vertically arranged hoisting cylinder assembly (6a-d).

29. A system according to the preceding claim, wherein

30. A system according to any of the six preceding claims, wherein the wire (9a-d) suspending the first pipe handling unit (2a) and the wire (9e-h) suspending the second pipe handling unit (2b) intersect an axis (66) which is perpendicular to and intersects a vertical axis (11’) extending through the well centre (11 ).

31. A system according to the preceding claim, wherein a plurality of wires (9a-d) suspend the first pipe handling unit (2a) and a plurality of wires (9e-h) suspend the second pipe handing unit (2b), and wherein the plurality of wires (9a-h) intersect the axis (66).

32. A system according to the preceding claim, wherein wires (9a-d) suspending the first pipe handling unit (2a) are arranged on opposite sides of the vertical axis (11 ’) extending through the well centre (11 ), and wires (9e-h) suspending the second pipe handing unit (2b) are arranged on opposite sides of the vertical axis (11’) extending through the well centre (11).

33. A system according to any one of claims 17-32, further comprising a derrick (31), and wherein each lifting unit (1a, 1b) comprises