GUIDE POST

Guide post

The present invention relates to a guide post for use in the final part of a guided lowering of equipment toward a predetermined point, or location, on the seabed, where the guide post is continued in a guide wire extending towards a structure on the sea surface.

Guiding of subsea equipment down towards and onto well heads by use of guide wires, normally wire rope, and a guide post structure is commonly known. Such guide posts are often used to locate components on subsea bases during oil drilling or oil production, or to locate modules on top of each other. In drilling of a subsea well, for example, a guide base is normally placed around the conductor housing of a well to be drilled. The guide base has guide posts and these are used to position a blow out preventer BOP on top of the well head. Guide posts can also be used to install and position other modules, for example to guide and position a lower marine riser package LMRP onto a blow out preventer, or an emergency disconnect package on a well workover preventer.

Such guide posts create a coarse alignment between the equipment and the well head and provides vertical stability in the system in order to be able to make connection to the wellhead. Final alignment is performed by the connector itself. Normally four guide wires and four guide posts will be used during a lowering operation.

One object with the present invention has been to reduce risk for rupture or damage on the guide posts placed on top of a BOP. The guide posts are normally used to guide in place a LMRP down onto the BOP. In an emergency situation, a connector between the BOP and LMRP is opened and the LMRP is elevated off from the end piece on top of the BOP. One requirement to the current equipment is that this can take place within 5 degrees of angular difference between the riser and the LMRP. Thus it is to be understood that in such a situation there is a danger for breaking/damaging the guide posts. By the present invention, it is secured that the guide posts can flex 5 degrees such that LMPR easily comes free. By reinstallation, the drilling rig is positioned directly above the well, and guide wires are secured and tensioned by 40kN, for example, such that LMPvP can be set down and securely landed.

This is solved by guide post of the introductory said kind which is distinguished in that a joint is introduced between the very guide post and a fixation foot designed for fixed attachment to a subsea construction, which joint is able to transfer axially acting forces simultaneously with suspending, or annulling, bending moments.

Preferably the joint forms a support element that includes an elastomeric matrix located at the interface between the guide post and the fixation foot.

Further, the elastomeric matrix may include at least one embedded armoring lamella, such as a steel plate.

Typically, the elastomeric matrix will be in the form of a rubber material, natural or synthetic, alternatively a polymeric material. Suitably, the elastomeric matrix is vulcanized, glued or similar to a metal plate which in turn is secured to the fixation foot.

The elastomeric matrix may also be loosely located within the fixation foot and be in the form of an insert element.

In a preferred embodiment, the fixation foot includes a lower radially outwards directed flange plate, an upper radially outwards directed flange plate having upwards projecting hat shape for receipt of the elastomeric matrix and an anchor sub, with flange portion, secured to the guide post, which flange portion being designed to be clamped between the upper and lower flange plate via the elastomeric matrix.

Normally, the respective flange plates will be secured to each other by means of bolt connections. If desired or necessary, at least one sealing ring can, in addition, be included in the joint construction. A clearance can be present between the flange portion of the anchor sub and the lower flange plate, more precisely the more peripheral circumference of the flange portion and a radially inner portion of the lower flange plate.

Further, a clearance can be present between the circumferential area of the anchor sub and the inner radius of the upper flange plate.

Other and further objects, features and advantages will appear from the following description of preferred embodiments of the invention, which are given for the purpose of description, and given in context with the appended drawings where:

Fig. 1 shows in perspective view a guide post according to the invention,

Fig. 2 shows in perspective view, the guide post according to fig. 1 with the parts taken apart,

Fig. 3 shows somewhat exaggerated the lower part of the guide post shown in fig. 2, Fig. 4 shows in longitudinal cross section the lower part of the guide post according to fig. 3 in assembled state such as this part is shown in fig.1 ,

Fig. 5A shows an elevational view of the guide post according to the invention having indicating arrows, in addition to a top view and bottom view,

Fig. 5B shows a side view and a section line A-A,

Fig. 5C shows a longitudinal section along the line A-A in fig. 5B, and

Fig. 6 shows a subsea equipment when it is about to be elevated off from a subsea structure and performs a tilting motion.

With reference to fig. 1 , a guide post generally given the reference number 1 , is shown. The guide post 1 is assembled of several parts, a lower (when in use) fixation foot 2, a joint means 3 and the post part 4 itself. The post part 4 has in turn an upper end piece 4a and a lower end piece 4b, which in a position of use is fixedly secured to the post part 4. In a position of use, a guide wire (not shown) is attached to the upper end piece 4a of the guide post 1 and extends upwards to the surface, normally to a surface vessel, for connection thereto. Subsequent to mounting of the fixation foot 2, the lower end piece 4b is welded or by other means fixedly secured to the post part 4.

Reference is now made to fig. 2 and 3 which more clearly show that the fixation foot 2 is assembled by several parts. These parts are a lower radially outwards directed flange plate 2a having a series of holes around the perimeter thereof, an upper radially outwards directed flange plate 2b having corresponding holes and having an upwardly directed hat profile 2c forming a cavity for receipt of an elastomeric matrix 5, or elastomeric element 5, and one to the post part 4 fixed anchor pin 4c that is provided with a flange portion 4d. It is otherwise to be noted, with reference to fig. 2 and 3, that by assembling the guide post 1 , the anchor pin 4c with its flange part 4d firstly needs to be put down into a recess 2a' in the lower flange plate 2a, then the elastomeric element 5 is placed over the anchor pin 4c and down to abutment against the top surface of the flange part 4d before the upper flange part 2b is thread over the anchor pin 4c and laid by its hat profile 2c down against the top surface of the elastomeric element 5. This is clearly shown in figure 4 which will be described below. Then the lower end piece 4b of the post part 4is threaded over the anchor pin 4c before the elongated post part 4 is placed against the lower end piece 4b and welded thereto or fixed in another suitable way. Fig. 4 shows in closer detail that the flange portion 4d is designed to be clamped between the upper and lower flange plate 2b, 2a via the elastomeric element 5. The element 5 is normally located, and acts, between the flange portion 4d and the internal top surface 2c' of the hat profile 2c. Notice that the make up (clamping) between the upper and lower flange plate 2b, 2a via the elastomeric element 5, normally results in pretension in the elastomeric element 5. This therefore provides a self aligning moment in the guide post 1 if the post is subjected to contemporary lateral forces. As an alternative to an elastomeric element, it is also possible to vulcanize an elastomeric matrix 5 to one of the parts, either it be the flange part 4d, the internals of the hat part 2c, or to both parts.

The element or the matrix can have armors 5a in the form of steel plates or other suitable material, in order to further reinforce or stiffening the matrix. This also increases the self restoring moment of the guide post 1.

As it appears from fig. 4, a clearance d_\ between the flange portion 4d of the anchor pin 4c and the lower flange plate 2a, is deliberately provided. More precisely, this is at the more peripheral circumferential surface of the flange portion 4d and a radially inner portion of the lower flange plate 2a. The clearance d] decreases towards the central axis of the anchor pin 4c. This clearance enables the entire post part 4 to kink or tilt relative to the fixation foot 2 if the post part 4 is subjected to laterally acting forces. The element or matrix 5 enables such tilting motion to provide resistance, and more resistance the more the guide post 1 is kinked laterally. However, a limit at about 5 degrees of angular deflection is set, without this being considered as an absolute limit or restriction.

Another clearance d₂ is provided between the circumferential surface 4c' of the anchor pin 4c and the internal radius 2b' of the upper flange plate 2b. This clearance d₂ is contributing to limit the angle that the post part 4 can adopt relative to the fixation foot 2.

With such a design of the guide post 1 as above described, a joint is introduced between the post part 4 and the fixation foot 2. As mentioned, the fixation foot 2 is designed for fixed attachment to a subsea structure. The introduced joint is able to transfer axially acting forces at the same time as the joint annuls or suspends bending moments.

Fig. 6 illustrates a situation where the guide post according to the present invention becomes particularly useful. When subsea equipment LMRP 20 is to be lifted from a subsea structure BOP 30, and the LMRP 20 is subjected to a bias, the situation shown in fig. 6 will arise. In the illustrated situation, the subsea equipment LMRP 20 is oriented relative to the subsea structure BOP 30 by means of four guide posts 1. The bias arises if a lifting crane for the subsea equipment LMRP 20, in addition to the vertical