The invention concerns a skidding system intended for use when moving equipment horizontally in connection with oil and gas recovery. More specifically, the invention concerns a skidding system meant for use when moving equipment horizontally in connection with oil and gas recovery, for instance during well interventions, where the skidding system comprises a skid frame displaceably arranged on a traverse and wherein the traverse is rotatably connected to a curved skid rail. The invention also concerns a method for use of a skidding system.

The English word "skid" is within the petroleum industry also used in Norwegian, and is conjugated according to Norwegian grammar. This word has got a more defined meaning within the industry than the Norwegian words "skliramme" and the verb "a skli". The Norwegianized word is used in this document.

During petroleum recovery it is usual to arrange access from a common installation to a plurality of wells rising above the surface. It is usual to arrange the wells such that there is access to them from an intervention deck on an installation offshore. Similarly there is access to the wells from an intervention floor on land based installations.

When work has to be carried out in a well relatively heavy equipment has to be brought into position over the relevant well. Since the same equipment over time will be used for work in different wells, it is appropriate to arrange the equipment on a skid frame connected to a traverse. By moving the skid frame on the traverse and moving the traverse over the intervention deck, it is possible to position the skid frame and thereby the relevant equipment over any one of the wells on the intervention deck or intervention floor.

From time to time it might happen that for instance a riser rises up from one of the wells and prevents the traverse from being able to be moved to the opposite side of the riser relative to where the traverse is located. This problem is solved by lifting equipment and possibly also the traverse over to the desired position, which is time consuming and requires caution since relatively heavy weights are involved.

It is known to rotatably arrange heavy items on petroleum installations. US 4065934 shows a skidding system on a jackup platform wherein the skidding system comprises a skid rail and a traverse which is displacably connected to the skid rail by means of a skid shoe. US 2012/0067642 describes an offshore rig comprising a skidding system wherein the skidding system includes a circular, peripheral skid rail and skid beam, traverse and skid frame, wherein both the traverse and the skid frame are displacea- ble. Both documents describe embodiments wherein the traverse is rotatable around the centre of the skid rail, but otherwise fixed.

The invention has for its object to remedy or reduce at least one of the drawbacks of prior art, or at least to provide a useful alternative to the prior art.

The object is obtained by features given in the following description and in the subsequent claims.

In a first aspect the invention concerns a skidding system intended for use when moving equipment horizontally in connection with oil and gas recovery, for instance during well interventions, wherein the skidding system comprises a skid frame displaceably arranged on a traverse and wherein the traverse is rotatably connected to a curved skid rail, and wherein the traverse beam is displaceable in the radial direction relative to the skid rail.

Therewith, it is possible to rotate the traverse around an obstacle, for example by displacing the traverse radially relative to the skid rail such that the traverse, when it thereafter is rotated on the curved skid rail, does not get into conflict with the obstacle.

The skid rail may be continuous so that the traverse, if desired, may be rotated 360 degrees around the obstacle.

The skid rail may be circular. A circular skid rail is often appropriate in order to provide the simplest solution possible, both when it comes to design and manufacturing. However, certain conditions may require the skid rail to be non-circular. The skid rail may for example be oval or elliptic. The traverse may be connected to the skid rail by means of a skid shoe which is displaceable along the skid rail, and a seat which is displaceable along the traverse in the longitudinal direction of the traverse, and wherein the skid shoe and the seat are mutually rotatable around a vertical axis.

The seat may also be displaceable along the skid shoe in order to be able to adjust for changes in the distance between two seats connected to the same skid shoe.

In a second aspect, the invention concerns a method at a skidding system intended for use when moving equipment horizontally in connection with oil and gas recovery, for instance during well interventions, wherein the skidding system comprises a skid frame displaceably arranged on a traverse and wherein the traverse is rotatably connected to a curved skid rail, wherein the method comprises:

- to arrange the traverse with the skid frame on the curved skid rail;

- to connect the traverse to the skid rail by means of a skid shoe which is displaceable along the skid rail, and a seat which is displaceable along the traverse, as the skid shoe and the seat are mutually rotatable around the vertical axis; and

- to displace the traverse radially on the skid rail.

As with the first aspect of the invention the skid rail may be continuous, circular or non-circular.

The system and the method in accordance with the invention make possible a considerable improvement with regards to equipment and work on the installation, since an obstacle which rises up from one well no longer is a problem for the moving of equipment between two wells.

In the following an example of a preferred embodiment is described, which is illustrated in the accompanying drawings, wherein :

Fig. 1 shows a perspective view of a skidding system according to prior art

mounted on an intervention deck;

Fig. 2 shows a perspective view of a skidding system according to the invention wherein the skidding system comprises a skid rail and a traverse;

Fig. 3 shows at a larger scale a section from Figure 2;

Fig. 4 shows at a smaller scale a plan view of the skidding system of Figure 2, wherein the skid rail is circular; and Fig. 5 shows a plan view similar to Figure 4, but wherein the traverse is in another radial position on the skid rail and where the skid rail is non-circular.

On the drawings the reference numeral 1 denotes a skidding system according to prior art which comprises a skid frame 2 which is displaceably mounted on a traverse 4. The traverse 4 which at least spans over parts of an intervention deck 6, see Figure 1, is displaceable on rails 8 in a direction perpendicular to the displacement direction of the skid frame 2 on the traverse 4. In the drawings, an intervention deck 6 is shown, but the invention may also be used on an intervention floor.

A number of well openings 10 open to the intervention deck 6. The skid frame 2 constitutes a mounting table for not shown equipment which has to be able to be arranged over any one of the well openings 10.

In Figure 1 a riser 12 rises above one of the well openings 10. The riser 12 is an obstacle for displacement of the traverse 4 such that the skid frame 2 may get into position over all of the well openings 10.

In Figure 2 which shows a skidding system 14 in accordance with the invention, the traverse 4 is arranged on a circular, endless skid rail 16. A skid shoe 18 is by means of a skid tractor 20 displaceable along the skid rail 16, also see Figure 3.

In the shown preferred embodiment the skid shoe 18 is provided with a first seat mounting 22 wherein a seat 24 which is displaceable along the traverse 4 in the longitudinal direction of the traverse 4, is rotatably connected to the skid shoe 18. A second seat mounting 26 comprises a seat 24'. The seat 24' is rotatably connected to the skid shoe 18 and is displaceable along the skid shoe 18 along a guide 19.

The traverse 4 is connected to the skid rail 16 at both its end portions 28 by means of a skid shoe 18 and seats 24, 24' .

Since the skid shoes 18 are mutually independently displaceable, the traverse 4 may, in addition to being rotated on the skid rail 16, also be displaced radially on the skid rail 16, see Figures 4 and 5.

In an alternative embodiment shown in Figure 5, the skidding system 14 is provided with a non-circular but oval skid rail 16. As the radius of the curve changes along the oval, the skid shoes 18 cannot have a set arc. The example embodiment in Figure 5 thus shows that there are four skid shoes 18 arranged each with a first seat mounting 22 and each with a skid tractor 20. Alternatively, two skid shoes 18 can be jointly connected in order to be able to follow the radius of the curve along the oval skid rail