DEVICE OF A DERRICK The present invention relates to a device of a derrick, comprising of lifting-and lowering equipment for movement of a drill string/pipe string in an axial direction in a derrick and gripping-and holding equipment ( « slips »), which is arranged at the upper and lower end of the lifting-and lowering equipment, to individually, in turn, grip and release respectively, the string in connection with lifting and lowering same.

The present invention is particularly intended for use in drilling operations at sea, such as on drilling platforms or drilling ships, but can also be used during drilling operations ashore. An aim is the application of the device in connection with, for one thing, hydraulic overhauls of wells, so called « slime hole drilling », drilling of multilateral completions, side track drilling, underbalanced drilling, etc.

During lowering of the string in a well, during drilling operations, and also at maintenance of a well (« work-over »), or during other topical operations, it is common to join together, in turn, a succession of pipe sections in the derrick in the extension of the string and also, in turn, to dismantle in the derrick, a series of pipe sections from the string. The joining together occurs with the pipe sections being placed in turn in the derrick and with the lower end of the pipe section being joined to

the string by a rotation of the pipe section with respect to the string. The joining together itself occurs via equivalent thread parts in two mutually adjoining pipe sections, and the joining together is followed by a lowering of the joined string towards the bottom of the well.

Correspondingly, during lifting of the string from the well, it is common to dismantle the string in the opposite sequence by removing the pipe sections individually in turn, after a preceding step-wise lifting of the string.

Generally, the lifting and lowering of the string has hitherto occurred with a combination of, for example, four pressure-medium cylinders, arranged side by side and acting in unison, which are placed at a suitable mutual distance around a centrally arranged string. In certain phases of the lowering, this may be effected by means of the weight of the string. In other phases of the lowering of the string, there is a need for extra pushing force on the string in addition to its weight.

With the present invention, one aims for a solution which gives a much simpler construction than previously known, but which nevertheless has a lightweight and robust design.

As mentioned above, the movement of a string in an axial direction in the derrick has presently occurred by means of several pressure-medium cylinders arranged around a central string and acting in unison. In an initial phase of the lowering of the string or during the displacement of the string in lateral drilling at levels below the sea bottom, respectively, it is common to exert an axial pressure ( « snubbing ») against the string to exert sufficient pushing force in the string in addition to the weight load of same.

One aims specifically with the present invention, in relation to the above, to combine the lifting-and lowering operations in one and the same appliance, that means to replace a group of several pressure-medium cylinders with one single pressure-medium cylinder.

The device according to the invention is characterised in that the lifting-and lowering equipment is comprised of a single pressure-medium cylinder with a hollow (pipe- shaped) piston rod, and that the string is adapted to extend through the piston rod and an associated cylinder part in a free-moving way, and that the pressure-medium chamber of the cylinder part, which is arranged to take up the piston associated with the cylinder and associated hollow piston rod, is limited in the cylinder part between an outer wall and an inner wall.

Preferred embodiments of the device according to the invention are described in the dependent claims 2-4.

According to the invention, by letting the string pass centrally through the cylinder part of the cylinder and hollow piston rod, one achieves a particularly simple and robust construction, which is not space demanding and which can be given a lightweight embodiment. This makes it possible to replace the device in a simple way when required.

It is possible in this connection, to fasten slips directly to the lower end of the cylinder part, and directly to the upper end of the piston rod, respectively, as integrated parts. This particularly simple construction makes it possible to fit and dismantle the complete lifting-and lowering equipment and associated slips in a particularly simple and easy way, especially as a consequence of the minimal space requirement for this embodiment and its relatively low weight.

By using a pressure-medium cylinder with double-walled cylinder, one can, furthermore, with a relatively low weight obtain considerable stiffness and strength. In addition, one can use limited amount of pressure-medium in the working chamber between the outer-and inner walls of the pressure-medium cylinder.

Further features of the invention will become apparent in the subsequent description with reference to the enclosed drawings, in which:

Figures 1-3 show a side diagram, according to a known embodiment, a group of pressure-medium cylinders, which are arranged in a ring-shape around a central pipe string/drill string, shown in three different user positions in connection with a derrick on an oil platform.

Figures 4-5 show the device, partly in a side diagram and partly in vertical section, according to the invention, shown in two different user positions in a derrick on an oil platform.

Figures 6,7 and 8 show vertically in section and a diagram, details in the transition between cylinder part and piston rod (figure 6), and the extreme positions of the piston rod (the figures 6 and 8) and in an intermediate position (figure 7).

Fig. 9 shows schematically a derrick on a platform with the previously known equipment for fitting/dismantling of a drill string.

Figures 10 and 11 show a corresponding derrick in the drilling rig, with the new appliance according to the invention for fitting/dismantling of a drill string.

In the known embodiment of figures 1-3, a combination of four pressure-medium cylinders 10a, lOb, lOc, 10d is illustrated, each with a lower cylinder part 11 and an upper piston rod 12. The unit is fitted at a level level with, or associated to, a working deck or drilling deck 14.

The cylinder part 11 in each of the four cylinders lOa-lOd is rigidly connected at the upper area of the cylinder part to a common upper bridge part or platform 13a and at the central area of the cylinder part 11, to a common lower bridge part or platform 13b on an intermediate deck 15. On the underside of the combination of the pressure-medium cylinders lOa-lOd, a stationary lower set of gripping-and holding bodies, herein called « slips », is arranged for local, intermittent retention of a pipe string/drill string 17, which is axially movable in a passage between the mentioned four pressure-medium cylinders lOa-lOd. The upper parts (pistons) of the four pressure-medium cylinders lOa- lOb are rigidly connected to a third bridge part or

platform 13c which supports an upper set of gripping-and holding bodies, herein denoted « slips », 18 for local, intermittent retention of the string 17.

In fig. 1, the grip between the lower slips 16 is released from the string 17, whilst the upper slips 18 of the string 17 has a firm grip on the string 17, such that the weight of the string 17 is relieved in same.

By pressure setting of the cylinders lOa-lOd (by feeding pressure oil inwards to/outwards from the working chamber 25 through the inlet 29 in figure 6), the string 17 can be lowered down and alternatively be pushed (« snubbed ») down with an extra pushing force with respect to the drilling platform. In fig. 2, the arrangement is shown in a half lowered pushing phase and in fig. 3 in a fully lowered pushing phase. In fig. 3, the arrangement is shown ready for the attachment of a new pipe section in connection to the string 17.

After the mentioned new pipe section is fitted, the lower slips 16 is activated and the upper slips 18 is deactivated, whereupon the bridge part 13c with associated slips 18 is lifted upwards to an upper position as shown in fig. 1. Thereafter, the functions are repeated as described above in turn with subsequent lifting-and lowering movements.

By dismantling of pipe sections from the string 17 the functions take place in the opposite order.

In the embodiment of the invention which is shown in the figures 4 and 5, the functions take place in an equivalent way as described above.

An essential difference with the embodiment according to the invention in comparison to the known embodiment, consists of the four pressure-medium cylinders lOa-lOd mentioned above being replaced by one single pressure- medium cylinder 20.

In fig. 4, the cylinder 20 is shown in fully extended position and in fig. 5 it is shown in a fully collapsed position.

As shown in figures 4 and 5, a lower slip 16 is fastened directly to the bottom part of the pressure-medium cylinder 20. The cylinder part 21 of the cylinder 20 has its upper end secured to a bridge part/platform 22, which is placed in a level below the working deck or drilling deck 14. An upper slips 18 is fastened to the upper end of the piston rod 23 of the cylinder 20. When the cylinder 20 takes up a fully collapsed position, as can be seen in figure 5, the slips 18 is taken up in a recessed level, i. e. in a housing part 24 (technically called « diverter housing ») which is recessed with regard to the working deck 14. The upper end of the string 17 is shown in this last mentioned position with a socket end 17a extending upwards over the working deck and the slips 18. The socket end is made ready for the fitting of a new pipe section 17b from the upper side. The new pipe section 17b is manoeuvred in place, coupled together and screwed together with the upwardly extending part of the string 17 with the aid of an appliance 40 running on wheels and moving horizontally.

The cylinder part 21 is shown double-walled, i. e. with an extended, but relatively narrow, working chamber 25 limited between an outer wall 26 and an inner wall 27. In the working chamber 25, a piston 28, which can be moved axially, is secured to the lower end of the piston rod 23.

The piston rod 23 is shown in a hollow form, i. e. pipe formed, so that the string 17 can freely, that is with free play, extend through the internal hollow space 23a of the piston rod 23 and the essentially aligned internal hollow space 21a of the cylinder part 21.

With the double arrows 29 and 30 in figures 6,7 and 8 there are shown tubes which feed pressure-oil inwards to/outwards from the working chamber 25 at its opposite ends, respectively so that one can carry out the subsequent lifting-and lowering movements which are described in detail in connection with the figures 1-3.

In connection with the figures 6,7 and 8, there is shown at the upper end of the cylinder part 21 a sealing/gasket arrangement 31a between cylinder part 21 and

piston rod 23. A sealing and gasket arrangement 31b is shown between piston 28 and cylinder part.

In figure 6 there is, in addition, shown a wedge 32 which extends inwards in a longitudinal wedge-groove on the outer side of the piston rod 23 to ensure that the piston rod 23 is prevented from rotating with respect to the cylinder part 21. The wedge is connected to the upper part of the cylinder part 21. Thus, the cylinder part 21 and the piston rod 23 comprise, according to the invention, mutually corresponding male/female bodies to prevent the hollow piston rod 23 from being able to rotate with respect to the cylinder part 21. To give an even better stability, the unit can include upper and lower sets of such male/female bodies to prevent the mentioned rotation.

In figures 4 and 5, and in the figures 9,10 and 11, an appliance 40 is shown which is used to couple together and screw together new pipe units in the string.

In figure 9 is shown schematically the deck 52 on a drilling rig 50 with derrick 54, and the previously known appliance 56 on top of the deck, which is used to extend/ dismantle drill strings/pipe strings.

In figures 10 and 11, the new embodiment according to the invention is shown, in which the drive means is placed in a recess 24 down in the deck-construction itself. The lower 16 and upper 18 slips are also shown in the figures 8 and 9. The figures 8 and 9 illustrate clearly how much less space-demanding the appliance according to the invention is, compared to the known method. It can be seen that with the invention, the space-demanding appliance in the derrick 54 itself and which is shown in figure 9, is removed completely. This is due to the lifting-and lowering equipment for drill strings and drill pipes according to the invention can be placed in or under the deck level itself.

Thus, the embodiment according to the invention represents a big step forward in this area.