DRIVE SYSTEM FOR TURNING A SWIVEL

Abstract: A system for turning a swivel or swivels aboard a vessel for oil extraction at sea, consisting of a stationary swivel part connected to a rotary drilling rig on a vessel, and one or more rotating parts connected to the vessel. The rotating swivel parts are connected to a torsionally rigid frame structure (8) via a drive mechanism which transmits the rotary motion between the vessel and the swivel without angular displacement or significant reactive forces in the frame structure (8). The vertical frame structure (8) consists of four walls where one of the walls forms a gate (20) for the insertion and removal of a whole swivel or parts of a swivel. The frame structure (8) is attached to an overhead frame (7) which extends over the whole diameter of the rotary drilling rig and is secured to the hull of the vessel.

Description: DRIVE SYSTEM FOR TURNING A SWIVEL The present invention concerns a system for turning a swivel, the said swivel representing a rotating connection between one or more risers and a piping system on a production vessel, a platform or the like for the production of oil or gas, and consisting of a stationary part connected with a rotary drilling rig or the like on the vessel and one or more parts pivotally mounted in relation to the stationary part and connected to the vessel. Systems for turning such a swivel aboard a production vessel for oil extraction at sea are known, but are of relatively small dimensions and weights, and have low operating pressures. The conventional systems are furnished with a single drive arm attached to the lower part of the swivel and controlling the rotary motion between the stationary part and the lower, rotating part of the swivel, and transmit motion to the other parts of the swivel by means of shear stress connections. The systems work well at relatively low production pressures and fluid volumes, in calm waters and at shallow-to-medium sea depths, but have disadvantages at high production pressures, high fluid volumes and in turbulent waters. In such conditions the swivel weight may be 100-150 tonnes and the operational safety requirements are very high. For these large, heavy swivel systems the conventional turning systems are not very suitable, because the dimensions of the drive arm and the shear stress connections are very large, and get in the way of other equipment on the rotary drilling rig. One object with the present invention is to create a system for turning heavy swivels aboard oil extraction vessels at sea, such that even at high production pressures in turbulent waters, the handling risks involved in replacing such a swivel will be substantially reduced. A further aim has been to obtain stable, direct transmission of the rotary motion of the vessel ("yawing" movements) to the various rotating parts of such a swivel in order to reduce the load on rigid pipe connections between the swivel parts and the frame, but at the same time retaining flexibility with respect to the relative movements in the x and y axes. A further object has been to create a drive solution which will permit sideways replacement of a swivel without affecting rotational stability during normal operations. In accordance with the invention, a solution has been devised which is characterized in that the rotating part or parts of the swivel are connected to a frame structure via a drive mechanism, the said frame structure being fixed to a rigid overhead frame which extends over the rotary drilling rig and is fixed to the vessel as defined in Claim 1. The subsidiary Claims 2-7 define advantageous features of the invention. The following will describe the invention by means of an example and with reference to the drawings, which show: Fig. 1 part of a ship with a rotary drilling rig with overhead frame and frame structure in accordance with the invention. Fig. 2 the principle for the arrangement of the frame struc¬ ture in relation to the arrangement of the various rotating parts in a swivel. Fig. 3 perspective view of the construction of the frame structure with the placement of the swivel in it. Fig. 4 plan of the frame structure at the lower edge of the overhead frame. Fig. 5 section of a gate in the frame structure in the closed state. Fig. 6 details of a connection (hinge and lock) between the gate and the frame structure. Fig. 7 longitudinal section of the arrangement of a swivel lifting device. Fig. 8 a drive mechanism with the connection between the outer, rotating part of the swivel and the frame structure. Figure 1 shows a rotary drilling rig 3 stored in the hull 17 of a production vessel, and a lifting device 12 for removing a swivel 1 which normally stands on the base 6 of the rotary drilling rig, or for placing a spare swivel 13 on the base 6. The lifting device 12 for the swivel runs on rails 10 which are mounted on the underside of an overhead frame 7 such that the swivel lifting device 12 can move between a first position, the centre of the rotary drilling rig 3, and a second position, the backup swivel 13, which is stored on a base 2 outside the rotary table. This solution is shown and described in more detail in the applicant's Norwegian Patent Application No. 921102 and will not be described in any more detail here. The overhead frame 7 is three-dimensional and consists of a virtually horizontal lattice framework which is rigidly fixed to the hull of the vessel and spans the whole diameter of the rotary drilling rig 3. This overhead frame 7 and the frame structure 8, which is attached to the frame 7, constitute the drive structure of the invention. The frame structure 8 is vertical, and is built with substantial strength and torsional rigidity such that it can transmit torsi- onal forces without angular displacement between the pipe coup¬ ling l and the horizontal frame 7. Figure 2 shows, on a larger scale, the frame structure 8 and the placing of the individual parts of the swivel (41', 42''...). Figure 3 further shows the frame structure 8 in perspective. It has four "walls" 20, 21, 22, 23 and a bottom 34, and at its upper part is rigidly connected with the frame 7. It surrounds the swivel 1 and extends towards the base 6 on the rotary drilling Three of the walls are built as two-dimensional latticework and consist of chords 41, 42, 43, 44, horizontal stays 51, 52, 53 etc. and diagonal stays 55, 56 etc. The bottom 33 consists of a frame 34 with an aperture 35 for the swivel 1 which is mounted on the base 6 at the centre. There is a clearance between the bottom 33 and the swivel base 6 and swivel 1, such that the drive structure can rotate freely in relation to the swivel base. The fourth wall (20 in Fig. 4) consists of the gate 20', which is built as a plane frame, with hinges and locks connecting important structural elements in the gate 20' and the frame 8. Figure 4 shows a plane section (section C-C in Fig. 7) of the frame 8 at the underside of the overhead frame 7. This shows the craneway with the rails 10 for the swivel lifting device 12 which runs into the centre for the swivel 1 such that the swivel can be taken in and out of the frame 8 through the gate 20'. Figure 5 shows a section of the gate 20' which constitutes an independent plane frame with horizontal stays 26, vertical stays 27 and diagonal stays 28. The gate 20' forms a side of the frame 8 when it is closed during operations, and can be swung out to the side (Figs. 4 and 7) to create free access to the swivel 1 for the swivel lifting device 12. The gate 20' is suspended in the chords 42 with hinges 25, and locks 30 against the chord 45. These can easily be opened such that the gate 20' can be swung out to the side and simply closed to obtain structural continuity. The structural continuity between the latticework in the gate 20' and in the other walls 21 and 23 in the frame 8 is achieved inasmuch as: The hinges are mainly mounted level with both the horizontal stays 50, 51, 52, 53 etc. in the frame 8 and the horizontal stays 26 in the gate 20' . The hinges and locks are strong and rigid, since in principle they are built in the same way as an ordinary pipe junction. The pipes 81 and 83 constitute a part of the hinges 25 and the closing mechanism 30, and are attached directly to the horizontal stays 26 in the gate 20' in the same way as a stay is attached at a pipe junction. The hinges 25 shown in Fig. 6 consist of solid pipe sections 81 which are pivotally mounted about the chord 80, and thus at the same time function as a reinforcement of the pipe junction. The hinge 25 and the lock 30 are held axially in position inasmuch as the pipe sections 81, 84 are flush with the pipe 45, 42, such that they have a substantial resistance to axial forces. The advantage of the lock 30 and the hinge 25 is that they also function as structural elements, and that they mainly take the form of standard pipe junctions with known strength characteris¬ tics. The swivel lifting device 12 shown in Fig. 7 indicates how the swivel 1 is carried over the bottom frame 34 in the frame struc¬ ture 8. Fig. 8 shows the drive mechanism 60, which consists of: Four hydraulic cylinders 61, 62, 63 and 64, which are secured by pins 40 on the outer ring 41 of the swivel, or on each of the outer rings of the swivel where the swivel consists of several swivel parts, in the drive frame 8. Hydraulic pipes 65 which couple the cylinders 61 and 64 in one system. Hydraulic pipes 66 which couple the cylinders 62 and 63 in one system. Filling valves 69, 72 located in each of the pipes 65 and 66. Accumulator containers 67, 68 each coupled with its own pair of hydraulic systems 65, 66. The drive system is designed to transmit rotary motion of the frame 8 to the outer ring 41 of the swivel, but at the same time to permit changes in the lateral position of the swivel 1 in relation to the frame structure 8. More precisely, the response of the hydraulic system to relative movements between the frame structure 8 and the swivel 1 will be as follows: A movement of the swivel along the x axis will cause the hydraulic fluid in the cylinders 64 and 62 to be pressed out into the piping systems 65 and 66 respectively. At the same time hydraulic fluid will be sucked in on the opposite side into the cylinders 61 and 62 respectively in corresponding amounts, so there will be no resistance to this motion. In the event of torsion on the drive frame 8 when the vessel turns, on the other hand, there will be resistance, because hydraulic fluid from the cylinders 62 and 63 will be pressed through the piping systems 66 and 65 respectively against corresponding pressure in the cylinders 63 and 61 respectively. In the first case, in the event of motion in the x or y axis, the two pairwise mounted cylinder arrangements will thus be in phase (pressure against suction) such that there will be no resistance to movement; while in the second case, i.e. rotation, the two cylinders will be in phase opposition (pressure against pressure) and there will be no relative movement between the structural frame 8 and the swivel. In this connection it should be noted that the invention is not restricted to the example cited here. Thus, instead of piston/ cylinder devices, shock-absorber/spring devices could be used, in which case however there would be a certain amount of angular movement between the frame 8 and the swivel l when the latter is rotated.

Claims: Patent claims A system for turning a swivel or swivels aboard a production vessel or the like for oil extraction at sea, the said swivel consisting of a stationary part which is connected with a rotary drilling rig or the like on the vessel and one or more parts pivotally mounted in relation to the stationary part and connected with the vessel, c h a r a c t e r i z e d in that the rotating part or parts (46) of the swivel are connected to a frame structure (8) via a drive mechanism (61, 62, 63, 64) , the said frame structure being attached to a rigid overhead frame (7) which extends over the rotary drilling rig and is secured to the vessel. System in accordance with Claim 1, c h a r a c t e r i z e d in that the drive mechanism consists of hydraulic piston/cylinder devices (61, 62, 63, 64), attached at one end to the frame structure (8) and attached at the other end to the rotating parts (46) of the swivel. System in accordance with Claims 1 and 2, c h a r a c t e r i z e d in that the drive system consists of at least two pairs of piston/ cylinder devices, the pairs being coupled in parallel such that the hydraulic fluid is conveyed through pipes (65, 66) to the opposite end of the pressure direction of the swivel or swivels, and that accumulator containers (67, 68) and valves (69, 72) are mounted for purposes of fluid equaliza¬ tion. SUBSTITUTESHEET 4. System in accordance with Claim 1, c h a r a c t e r i z e d in that the drive mechanism (60) consists of spring/shock-absorber devices attached at one end to the frame structure (8) and at the other end to the rotating parts (46) of the swivel. 5. System in accordance with Claims 1-4, c h a r a c t e r i z e d in that the frame structure (8) is embodied as a latticework structure with four sides and a bottom surrounding the swivel with an opening and clearance to the stationary swivel base. 6. System in accordance with Claim 5, c h a r a c t e r i z e d in that one side consists of a gate (20) which can be opened for insertion or removal of a swivel or parts of a swivel, and closed such that the framework is given a firmness and rigidity approximating to that of a welded continuous frame. 7. System in accordance with Claims 1-6, c h a r a c t e r i z e d in that the overhead frame (7) extends over the whole diameter of the rotary drilling rig (3) with one leg on each side secured to the vessel. SUBSTITUTESHEET

Inventors: ASKESTAD SIGMUND, ASKESTAD, SIGMUND
Applicants: ASKESTAD SIGMUND, NORSK HYDRO AS, NORSK HYDRO A.S
Application year: 1993
Main classification: E21B43
IPC codes: E21B43