There is provided a method for operations on, in or through a tubular structure. More precisely there is provided a method for operations in or through a tubular structure passing through a wellhead. The invention also includes machinery for operations in or through a tubular structure.

When wells associated with the production of hydrocarbons are permanently plugged and abandoned, well completions such as production tubing and/or casing, may have to be removed from the well prior to permanent abandonment.

Performing downhole operations, especially related to the removal of tubular structures from a well which are to be permanent plugged and abandoned, a compression force in the tubular structures may be disadvantageous.

Often, cutting attempts are made in a tubular structure such as production tubing that is "at rest". The phrase "at rest" typically indicates that the production tubing is landed in its respective tubing hanger at surface level . When at rest, the tubing is often in a state of compression in its deeper parts. The reason may for example be anchoring by means of a production packer, or because of friction forces relative the casing.

Prior art downhole cutting tools are generally run on wireline or coiled tubing and are based on several cutting principles using for instance explosives, chemicals, mechanical cutting blades or thermal cutting.

Because of potential leakage of dangerous or hazardous materials, for example explosives or chemicals, mechanical cutting tools are preferred.

There are some disadvantages of using prior art mechanical downhole cutting tools for cutting a tubular structure that is in a state of compression. The blades of the cutting tool might for instance be clamped and destroyed during the cutting process because of a collapsing cut or gap, whilst cutting the tubular structure. Traditionally, for pulling completions such as production tubing, prior to permanent plugging and abandonment, drilling rigs have been utilized to perform these operations.

The purpose of the invention is to overcome or reduce at least one of the disadvantages of the prior art.

The purpose is achieved according to the invention by the features as disclosed in the description below and in the following patent claims.

According to a first aspect of the present invention there is provided a method for operations on, in or through a tubular structure passing through a wellhead wherein the method includes:

- positioning a hollow lifting apparatus at the wellhead or at a structure above the wellhead;

- engaging a releasable lifting frame of the lifting apparatus to the tubular structure; and

- lifting the tubular structure to provide tension in the tubular structure, at least within the relevant portion where the cut is to be made, while operating a bottom hole assembly, hereinafter referred to as well intervention assembly, in or through the tubular structure.

Thus, the method for creating relative vertical movement between a tubular structure and a wellhead and/or other well structures which may be used as reference on or in a well, is provided. The method is applicable on onshore as well as offshore well sites. Due to the mass of the tubular structure and/or if it has been attached to, for example, a downhole packer, the relative vertical movement will create a tensile load inside the tubular structure.

The method also prevents unintentional relative vertical movement between a tubular structure and the wellhead of onshore or offshore well sites. Preferably, a gripper design is chosen where the gripper also causes a certain kinematic behaviour, the axial load, applied by the mass of the tubular structure increases the compressive force acting on the tubular structure and thereby the friction between the tubular structure and the gripper. Thus, the risk for an unintentional relative vertical movement of the tubular structure is largely overcome.

On a platform, a vessel or similar, the lifting apparatus may be arranged above or on top of the wellhead. Depending on the barrier status of the well, required well barrier elements, typical a drilling blowout preventer, have to be placed in between wellhead and the lifting apparatus. If necessary, such pressure control equipment may also be positioned inside or on top of the pulled tubular structure. A known wireline blowout preventer or coiled tubing blowout preventer or a wireline stuffing box or grease injection head, may thus be placed on top of an upper end of the hollow shaft.

The method may further include operating the well intervention assembly by using wireline or coiled tubing. The lifting apparatus provides a hollow shaft which allows passing of a wireline or a coiled tubing well intervention assembly. The hollow shaft may also be used to engage tubular structures, for example, tubing hanger or production tubing. Typically the hollow shaft together with a downhole pipe and equipment above the hollow shaft constitute the tubular structure.

The method may include at least perforating or cutting the tubular structure while keeping the tubular structure in tension. The problem of a cutting tool's blade being clamped and destroyed during the cutting process because of the collapsing cut or gap, whilst cutting the tubular structure, is thus largely avoided.

The method may include operating the well intervention assembly separately from the lifting apparatus. The lifting apparatus may be active or inactive while the well intervention assembly is operational.

The method may include removing the tubular structure from the well after cutting.

The lifting apparatus is typically provided with one or more vertically moving lifting frame(s) positioned above each other in the longitudinal direction of the well. If two lifting frames are present, they may be referenced to as the lower first lifting frame and the upper second lifting frame. The first and second lifting frames are most conveniently provided with at least self-activating or activatable locking means which are designed to engage with the tubular structure. The first and second lifting frames and locking means may be moved simultaneously, separately or in a sequence in order to create a relative vertical movement between the tubular structure and a base of the lifting apparatus. The first and second lifting frames may also simultaneously be moved in opposite directions.

Moreover, the engagement of the locking means with the tubular structure will overlap in time, with the result that the locking means of the first lifting frame engages with the tubular structure before the locking means of the second lifting frame engages with the tubular structure. After both of the locking means of the lifting frames are in engagement, the locking means of the first lifting frame will disengage from the tubular structure; thereby ensuring that at least one locking means is engaged with the tubular structure at any time. When the second lifting frame first is applied, the procedure is similar.

The lifting frames are configured to be controlled in various ways where the lifting frames may be individually movable or they may be controlled by a common control system.

The locking means may be activated by different factors such as, for example, where the activation of the locking means is coordinated with the actual movement of the lifting frame. Furthermore, the activation of the locking means may be coordinated with the position of the lifting frame or in relation to the positions of the lifting frame relative to the tubular structure. The looking means may be especially activated simultaneously, whilst all movements of the lifting frames are also locked, to carry out other activities/operations, for example cutting the tubular structure.

The locking means may be designed so that the locking means on the first lifting frame may become engaged before the locking means in the second frame are disengaged while the two lifting frames are still moving relative to each other.

The locking means are typically provided with a plurality of opposing grippers. The grippers are at least self-activating or activatable, and are designed to engage with the tubular structure. The grippers are also de-activatable. The grippers may be activated or moved simultaneously, separately or in a sequence in order to engage with the tubular structure and prevent an unintentional relative vertical movement between the tubular structure and the wellhead. At least simultaneous activation of the grippers may be utilized for securing and aligning the tubular structure within the plurality of opposing grippers. In some cases the grippers may also be moved simultaneously in opposite directions to balance radial misalignment of tubular structure and ambient structure, for instance a rotary table equipped such locking means.

Moreover, the engagement of the locking mean with the tubular structure will overlap in time with other activities such as disconnecting a top drive from a drill string.

Such a locking means may include a plurality of opposing cam lobe-shaped grippers which are independently coupled to one or more actuators. Examples of such actuators are a combination of springs and hydraulics to actuate and pre-load each cam lobe and to de-active each cam lobe. A de-activation may be necessary to run in hole tubular structures or if the tubular structure has to be released immediately, for instance. The locking means may be activated by different factors such as where activation of the locking means is coordinated with other activities. Such other activities may include the disconnection of a top drive from a drill string.

In a preferred embodiment the activated cam lobes have not to be de-activated while pulling tubular structures, for instance a drill pipe or a production tubing, out of the well. Due to shape and kinematic behaviour of the cam lobes, different diameters of tubing and tubing coupling may pass the locking means without manually adjustment.

According to a second aspect of the present invention there is provided machinery for operations on, in or through a tubular structure passing through a wellhead, wherein a lifting apparatus, having an axially through-going opening for the tubular structure, is fixed to the wellhead or to a structure above the wellhead, and where the lifting apparatus includes at least one actuator operated lifting frame having at least one locking means designed for releasably engaging the tubular structure, and where the tubular structure is designed for simultaneously performing well intervention operations.

The stroke of the at least one actuator, which actuates a lifting frame, may be equal or longer than the length of an individual coupling of the tubular structure. In this way, gripping on the coupling itself may be avoided.

At least one actuator, which actuates a lifting frame, may be hydraulically, pneumatically, electrically or mechanically driven. In the case of the actuator being a ram type actuator, the piston may be ring-formed, possibly encircling the tubular structure.

In an embodiment the cam lobe-shaped grippers are each hinged about an off- centered placed pivot point that is fixed to a structural frame, such that a simultaneous pivoting movement of the grippers results in a change of an enclosure defined by an innermost edge of each of the plurality of the opposing grippers. The enclosure may be circular shaped. With "innermost edge" is meant the portion of the cam lobe being closest to the centre of the enclosure defined by the plurality of opposing gri ppers. When the diameter of the tubular structure is larger than the minimum circular enclosure formed by the grippers within the structural frame, this may be advantageously used to establish a locking grip when the grippers engage with the tubular structure while the tubular structure is subject to a force downward with respect to the locking means. Nevertheless, the locking means of the invention is conveniently suitable for a range of diameters of the tubular structure.

The grippers may be adjusted to the actual tubular outer dimension by the shape of cam lobes, and by use of a connected preload device. The preload device may be in the form of a spring or an actuator. The grippers may be separately movable or movable in groups. Due to the adjustment to the actual tubular outer dimension, for instance, tubing couplings may also pass the locking means without changing or deactivating the grippers.

The shape of cam lobes may enable camming functionality for one-directional movement. Therefor the grippers may be activated and engaged to a tubular structure, which may also be connected to hoisting equipment capable of moving the tubular structure in one direction. Due to the design and kinematic behaviour of the cam lobes, a movement in one certain direction may not energise the compressive force in between the grippers and the tubular structure. Thereby the tubular structure may be moved in this direction by a force overcoming the friction force cause by a preload of the gripper.

In a preferred embodiment an upwards oriented relative vertical movement between a tubular structure and a wellhead may be enabled by the activated grippers, thus preventing an unintentional downwards oriented relative vertical movement between a tubular structure and a wellhead.

In another embodiment the machinery itself may be designed to meet well barrier acceptance criteria and be provided with a common coupling. Thus the lifting apparatus can be placed directly on top of the wellhead or in any order to complement the pressure control equipment.

The method and machinery according to the present invention renders it possible to undertake well intervention operations while keeping the tubular structure, also in the lower parts of the well, in tension. This may be achieved without the heavy lifting equipment associated with a drilling rig. The problems experienced with clamped cutting blades by a collapsing cut or gap during cutting of the tubular structure, are thus largely overcome.

The method and machinery according to the present invention renders it possible to undertake operations related to tubular structures while keeping them attached to at least one locking means during an entire operation of pulling a tubular structure such as production tubing. The problems experienced with common slip design are thus largely overcome.

Below, an example of a preferred method and machinery is explained under reference to the enclosed drawings, where: Fig. 1 shows schematically machinery according to the invention in position on a platform;

Fig. 2 shows schematically in a larger scale a lifting apparatus of the machinery in fig. 1 with related components;

Fig. 3 shows a principal sketch of a lifting apparatus in its initial position with both a first lifting frame and a second lifting frame in their respective lower positions;

Fig. 4 shows substantially the same as in fig. 3, but where the first lifting frame, which locking means are engaged with a tubular structure, has lifted the tubular structure, and where also the locking means of the second lifting frame are engaged to the tubular structure;

Fig. 5 shows substantially the same as in fig. 3, but where the second lifting frame, which locking means are engaged with the tubular structure, is lifting the tubular structure, and where the first lifting frame, which locking means remain activated but enabling one-directional movement of the tubular structure, has returned to its initial position;

Fig. 6 shows substantially the same as in fig. 3, but where the second lifting frame is extended to its upper position and released from the tubular structure after the locking means of the first lifting frame have been engaged to the tubular structure;

Fig. 7 shows in a larger scale a plane view from the downward facing side of a

locking means;

Fig. 8 shows a cross section VII-VII of the locking means in fig. 7;

Fig. 9 shows substantially the same as in fig. 8, but with the tubular structure

passing through; and.

Fig. 10 shows substantially the same as in fig. 2, but in another embodiment.

In the drawings the reference number 1 denotes a platform that is equipped with machinery 2 according to the invention for well intervention. The platform 1 includes a wellhead area 4 where a wellhead 6 of a well 8 is positioned. Surface pressure control equipment 10 in the form of a BOP (blowout preventer) is connected to the wellhead The machinery 2 includes a lifting apparatus 12 that is positioned on a floor structure 14 above the wellhead area 4 of the platform 1. A hollow shaft 16, which may consist of several coupled hollow sub shafts connected by couplings 17, see fig. 2, extends through the lifting apparatus 12 and is connected to the tubular 18 that extends into the well 8 in a tubing hanger 22 of the wellhead 6. In the drawings, the well 8 is equipped with a well completion. For illustration purposes the well completion is reduced to one casing 20 and one additional tubular 18, for instance in the form of a casing or production tubing.

In this preferred embodiment a well intervention assembly 24 that includes a down- hole cutting device 26 is moved into the well 8 by the use of a wireline 28. The wireline 28 extends through a wireline surface pressure control equipment 29 and/or a grease injection head 30, both optionally positioned on the upper end portion of the hollow shaft 16, to a winch 32 on the floor structure 14. Generally, the machinery 2 includes the lifting apparatus 12 and the wireline 28. In another embodiment, not shown, a coiled tubing setup may take the place of the wireline 28.

The hollow shaft 16, the grease injection head 30 and the tubular 18, for instance in the form of a casing or production tubing, are parts of a tubular structure 34.

The lifting apparatus 12, which is connected to the floor structure 14, includes a main frame 36, a first lifting frame 38 and a second lifting frame 40, as shown in figs 2-6. The lifting apparatus 12 has a through going opening 41 for the tubular structure 34. At least one first actuator 42, herein shown in the form of a hydraulic ram, is fixed to the main frame 36 and designed to move the first lifting frame 38 in the longitudinal direction of the hollow shaft 16. A locking means 44, see below, is designed to releas- ably engage with the hollow shaft 16 and thus connecting the first lifting frame 38 to the hollow shaft 16.

Similarly, at least one second actuator 46 is fixed to the main frame 36 and designed to move the second lifting frame 40 in the longitudinal direction of the hollow shaft 16. The second lifting frame 40 is also equipped with a locking means 44.

Preferably, the lifting apparatus 12 is directly connected to the surface pressure control equipment 10 or by a riser 48 that may be a high pressure riser.

An example of a locking means 44 is shown in figs. 7 to 9. A plurality of opposing grippers 50 (six are shown in the embodiment of fig. 7) with the shape of cam lobes are distributed around a centre axis 52 in a structural frame 54 of the locking means 44. Even though the gripping technique of the invention works already for one gripper, it is still preferred to place a plurality of grippers (preferably three or more) distributed (preferably evenly) along the circumference of the structural frame. Each gripper 50 has a curved gripping surface 56, and is hinged about a pin 58 that is fixed to the structural frame 54. The design of the cam lobe-shaped grippers 50 and the (off- centered) placement of the pin 58 around which the grippers 50 pivot is such that a simultaneous pivoting movement of the grippers 50 results in a change of the circular- shaped enclosure 55 (see fig. 7) defined by the innermost edges of the grippers 50. When the diameter of the tubular structure 16 is larger than the minimum circular- shaped enclosure 55 formed by the grippers 50 within the structural frame 54, this may be advantageously used to establish a locking grip when the grippers 50 engage with the tubular structure 16 while the tubular structure 16 is subjected to a downward force. This is evident from fig. 9; a downward force in the tubular structure 16 will urge the grippers 50 to increase the grip due to the geometry of the gripping surface 56 relative the position of a pin 58 being arranged off-centered as discussed above and shown in fig. 9. This is evident from fig. 9; a downward force in the hollow shaft 16 will urge the grippers 50 to increase the grip due to the geometry of the gri ping surface 56 relative the position of the pin 58 being arranged off-centered as discussed above and shown in fig. 9.

The structural frame 54 is connected to the first and second lifting frame 38, 40 respectively.

Nevertheless, the locking means 44 of the invention is conveniently suitable for a range of diameters of the tubular structure 16.

The gripping surface 56 is provided with friction increasing means. In fig. 8 the friction increasing means is shown as a toothed surface. However, any known means that will increase the friction between the gripping surface and the tubular structure may be utilized.

A preloaded device 60 for instance in the form of a spring 59 or an actuator 61 may be used for the individual or joint operation of the cam lobe formed grippers 50. The same actuators 61 may be utilized as a release device 63, see figs. 8 and 9.

Necessary cables, pipes or control equipment for the machine are not shown.

When, for instance the tubular structure 18, more precisely the tubing 18 is to be cut by utilizing the cutting device 26, the lifting apparatus 12 is engaged to the tubular structure 34 in order to apply tension to the tubular 18 at the position of cutting. A sequence of lifting and thus stretching the tubular structure 34 while running the wireline 28 through the lifting apparatus 12, is shown in figs. 3 to 6.

In fig. 3, both lifting frames 38, 40 are at their lower position and the locking means 44 of the first lifting frame 38 is engaged to the hollow shaft 16. In fig. 4, the first lifting frame 38 has been lifted to its upper position bringing the hollow shaft 16 with it. Some additional tension is thus induced to the tubing 18.

As the tubing 18 might be fairly long, they stretch accordingly, and additional lifting at the lifting apparatus 12 may be necessary. In fig. 4, the locking means 44 of the second lifting frame 40 engages the hollow shaft 16 prior to the release of the locking means 44 of the first lifting frame 38. The release of the locking means 44 of the first lifting frame 40 may be automatic as a downward movement of the first lifting frame will release it.

In fig. 5, the second lifting frame 40 is lifting the hollow shaft 16, while the first lifting frame 38 has returned to its lower position. When the second lifting frame 40 has reached its upper position as indicated in fig. 6, the procedure is repeated in order to further stretch the tubular structure 18. The procedure may also be repeated by engaging the tubing 18 itself, instead of the hollow shaft 16. Therefore the hollow shaft 16 has to be coupled to an appropriate fishing device, for instance a fishing spear or an overshot fishing tool not shown.

In a different embodiment, for instance if the tubing hanger 22 has a significant larger outer dimension as the tubing 18, the lifting apparatus 12 may be positioned on a floor structure 14 above the wellhead and an additional locking means not shown may be located on top of the surface pressure control equipment 10. This additional locking means may provide an axially through-going opening for the tubing hanger 22 and secure the tubing 18 after the tubing hanger 22 has been lifted to a position above this locking means. Thus lifting apparatus 12 can be rigged down to disassemble tubing hanger 22 and tubing 18, while tubing 18 is secured . After disassembling the tubing hanger 22 the lifting apparatus 12 may be rigged up again and the procedure, described in fig. 3 to fig. 5 repeated.

When the cutting of the tubular 18 is finished, the tubular 18 may be lowered by a similar sequence, then in the opposite direction.

Although the actuators 42 and 46 in the principal sketches are shown as single hydraulic rams, there may be more than one actuator at each lifting frame 38, 40 and the actuators 42, 46 may for instance be pneumatically, electrically or mechanically operated.

As mentioned above, in another embodiment the wireline 28 may be replaced by a coiled tubing 62.

Necessary cables, pipes or control equipment for the locking mean are not shown.

In yet another embodiment, see fig. 10, the machinery 2 itself is designed to meet well barrier acceptance criteria and is provided with common couplings incl uding seal ing 64 and 65 at top and bottom end to be connected to any standard surface pressure control equipment or wellhead. Thereby the lifting apparatus 12 can be placed directly on top of the wellhead 6 or in any order to complement pressure control equipment. In this embodiment, the wireline surface pressure control equipment 29 i connected to lifting apparatus 12 by a riser 49.