GB2245923A

GB2245923A - Sea bed frame for oil wells

Info

Publication number: GB2245923A
Application number: GB9112702A
Authority: GB
Inventors: Kerel Karal
Original assignee: Norwegian Contractors AS
Current assignee: Norwegian Contractors AS
Priority date: 1990-06-15
Filing date: 1991-06-13
Publication date: 1992-01-15
Anticipated expiration: 2011-06-13
Also published as: NO170992B; NO902673L; NO902673D0; GB9112702D0; GB2245923B; NO170992C

Abstract

A sea bed frame for support and protection of equipment, e.g. a drilling template, for drilling subsea wells comprises one single or several joined hollow bodies 1 anchored to the sea bed. Elongated, circumferentially arranged, hollow bodies 1 form a polygonal, preferably quadratic, frame. The hollow bodies form a monolith, or are joined together by elements allowing rotation between adjacent bodies (Figs. 12 and 13). The hollow bodies 1 may be of concrete, may be buoyant to allow submersion without a crane, may be ballasted or may store materials. The bodies may be shaped, e.g. have a triangular cross-section, to allow overtrawling and to allow local access and the running of pipes. The frame may include a drilling template, and may have a lid, e.g. a grating. For frame levelling, material may be injected between the frame and a support (Fig. 11). The frame may have skirts for penetrating the sea bed. <IMAGE>

Description

Bottom well base frame" The present invention relates to a structure and a method for support and protection of equipment for drilling sea bottom based wells and the like.

A known method in connection with drilling of subsea wells is to provide a bottom based frame which is defining a drilling template for the wells which shall be drilled, and which provides space for necessary equipment for completing the wells including valves, pipe couplings etc. The bottom frame is usually made as a steel construction, and is prefabricated and installed on the sea bottom prior to initiating the piling operation. The bottom frame is being correctly levelled and secured by piling.

The necessary equipment for security and protection is mounted on the bottom frame successively with the drillig operation. Equipment for protection against falling bodies and trawling are being mounted in necessary and possible extent.

such bottom frames are heavy and requires substantial crane capasity during the submersion and installation of the equipment. Ramming of the piles implies extensive work and heavy equipmentg. Foundamentation and levelling utilizing piles is a difficult task especially in connection with difficult sea bed conditions, for instance if the sea bed presents large stones which also complicates the piling work. The problems will not be less when the pile diving equipment and the piles shall be removed when the operations shall cease and the field shall be abolished.

The present invention solves the above.mentioned problems in that the bottom frame is realized as a system of circumscribing or bottom based hollow bodies which are adapted to an installation method which is independent utilization of crane equipment, and is suitable for so called direct foundamentation, i.e. without the use of piles. The bottom frame and the hollow bodies can be built or be together either monolithically or by joining together prefabricated separate sections prior to the transport to the installation site.

The construction in accordance with the invention is well suited to be made in concrete. The hollow bodies, which are situated along the side or the underside of the bottom frame (all or some of these), shall, prior to the installation work, and also several times during the installation work, function as buoyancy and ballast vessels.

The entire structure can (on this basis) be towed out to the installation site and the sinking operation can be carried out and controlled by ballasting. The installation can thus be carried out without use of any cranes. The hollow bodies are equipped with skirts designed for penetration of the sea bed, and the construction can in simple fashion be levelled by controlled penetration, and, if required, by injection of concrete in separate chambers or spaces formed by these skirts.

In connections with difficult bottom conditions, for instance large permeability in the ground, and or presenting a risk for local disintegration of the bottom ground due to water pressure in the separate hollow spaces which are formed by the skirts, a levelling is carried out in that the hollow bodies (one or several of the same) are equipped with a foundament which is moveably connected with the hollow body. Levelling can be carried out by injection between the fundament and the hollow body.

The structure can with advantage be installed utilizing of a surface vessel system as described in Applicant's U.S. Patent No. 4909671. This system can be used if the hollow bodies are pressure resistent. Hollow bodies which are not pressure resistent can be submerged or lowered into correct position, for instance by means of firmly attached pressure resistent vessels of the type described in Applicant's copending U.K.

Patent Application No. 8915021.3. Use of this method may lead to a more reasonable construction, and is particularly economical in connection with large depths.

The hollow bodies can be given a configuration which in addition to providing a terminating wall for the bottom frame simultaneously can offer a construction which can be cover trawled".

The hollow bodies can be made with accesses and the like providing space for positioning piping extending along the sea botton, and for lateral access to the bottom frame including equipment for divers or ROV.

The hollow spaces may as mentioned function as ballast chambers during launching, towing and installation further to providing lateral protection and support for the bottom frame including equipment therefore. In addition the hollow spaces can be used for storage and degrading of the drill chips produced by the drilling operations and later during the operational life time of the installation, or these bodies can be utilized for storage of hydrocarbons during the production phase.

In order to offer best possible protection against falling objects and in order to improve trawling override properties one may position a lid across the bottom frame including the equipment mounted on the same. The lid or cover may be realized in the shape of a grating or a number of generally plane elements, such as concrete beams, with suitable size in order to simplifye handling, and having the necessary recesses, openings necessary for the operation. The hollow bodies will offer a good basis for a such lid. The hollow bodies may be joined together to frame elements along the sides and the underside of the bottom frame. The frame elements may be terminated with monolithical or solid corner transitions if such with advantage can be made utiliing slip casting.

Otherwise it will be better to terminate each frame element with a prefabricated corner element. Smaller bottom frames can with advantage be made monolithical.

The joints between the elements will be exposed to large stresses due to wave actions during the towing operation. This may also be the case during the penetration phase and during the levelling operation.

In order to reduce or limit prevailing stresses and injurious effects of such stresses the connection between the elements may with advantage be provided with a limited movement of freedom, more particularly a limited freedom of rotation about an horizontal axis in the joint between the frame elements.

Subject to particularly severe bottom conditions requiring very large skirts and which therefore may lead to an economically unattractive construction and in order to limit ground settings to acceptable magnitudes, one can utilize a conventional topart splitting of the elements, wherein - the drilling template or frame as such constitutes one element, which during transport and installation is supported by - the support- and protection structure positioned around and partly below said drilling template, which during the installation shall be attached to the drill piping in connection with the well drilling, such that the support and protection structure during installation is given a downwardly directed movement of freedom relative to the drilling template.

The levelling of the drill template and the frame is carried out in conventional manner, i.e. by means of hydraulic and/or mechanical jacks.

The invention shall in the following be further described in connection with some practical embodiments in connection with the accompanying drawings wherein: Fig. 1 is showing a large bottom frame including a drill template seen in a plane view, Fig. 2 is showing the sae bottom frame in two vertical sections, Fig. 3 is showing a monolithical bottom frame with an integral drill template, seen in a plane view, Fig. 4 is showing two sections through a monolithical bottom frame which may be supported in floating position, Figs. 5 and 6 is showing a frame element which is suitable for slip casting.

Fig. 7 is showing a frame element having a lateral opening, Pigs. 8a, b, c and d are showing some combinations of frame elements adapted to various special needs, Figs. 9a, b, c and d is showing various solutions for covering, Fig. 10 is showing a preferred embodiment of a grate element of concrete, Fig. 11 is showing in section a bottom frame provided with possibilities for levelling, and Pigs. 12 and 13 are illustrating various joining systems for frame elements.

Fig. 1 is showing a large bottom frame provided with a drilling template seen in a plane view.

It is composed of prefabricated elements 1 on three sides, and joined together with special corner elements 4.

One of the frame elements 2 has a recess 3 to offer space for a pipe coupling and/or give access to the drilling template 6. The drilling template or grating is here shown as a conventional construction made by steel piping.

Fig. 2 is showing the same along two vertical sectional planes, namely plane A-A and plane B-B respectively. The shown frame elements 1 are given a triangular shape to offer best possible trawling override properties. At the bottom the frame elements 1 are terminated with skirts 5 for penetrating the sea bottom, and is equipped with support knobs 7, see section A-A.

The drilling template 6 is attached to the knobs 7. The concrete surfaces may easily be given a contour conformed to the present needs, Per example, the surface 8 in the frame element 2 is given a contour to offering a practical support for piping and cables which is coupled to the equipment positioned on the grating 6, such as illustrated schematically in section B-B.

Fig. 3 is showing a monolithical bottom frame of concrete seen in a plan view, wherein the drilling template forms an integrated part of the structure. The positioning and design of the piping 9 and attachements for the equipment (not shown) is assumed to be of conventional type. The bottom frame is also in this embodiment given a shape to sustain trawling overriding. The short sides are equipped with openings 10 for easy access and in order to provide space for pipe couplings. Also the lower sides of the structure may be provided with such openings.

In order to facilitate fundamentation and levelling of the bottom frame is utilized circular skirts 11. For monolithical bottom frames are used 3-4 such skirts. In order to secure best possible a trawling override properties and also easy axcess can be used gates 12 as indicated in Fig. 4.

Fig. 4 is showing two sectional views seen along planes A A and B-B along in rig. 3, respectively, through a monolithical bottom frame forming a hollow structure which can be transported in floating state. The structure has a bottom plate 14, a top plate 14, strengthening walls 15, tilted walls 16 in order to provide trawling override properties, and a recess or shoulder 17 for receiving a lid or cover (not shown).Neither in this or in any other figures are details for transport, submersion and levelling of the bottom frame, included, since these technique belong to conventional technique and form no part of this invention, such as piping for ballasting, attachement for installation equipment, piping for the skirt chambers for controlling the water pressure during penetration and levelling, piping for injecting materials into the hollow spaces which may be created below the bottom frame. etc.

Fig. 5 is showing an embodiment of the frame element 18 which is suitable for slip casting. It can be made pressure resistent and is suitable for installation and removal without the use of cranes or a separate external buoyancy vessel, and wherein also the skirt 5 has been made by slip casting.

otherwise is shown knobs 7 for reception of a drilling template or grating, and ribs or walls 19 which shall secure trawling overrideness, and spaces 20 which may be divided with bulk heads (not shown).

Fig. 6 is showing a frame element 21 which is suitable for slip casting. The element can be made watertight for floating and towing, but there is not pressure resistent. Submersion must therefore be carried out with oscillary buoyancy equipment or cranes. The hollow space is opened to the ambient sea for equalizing the pressure on the inside and the outside of the frame element, respectively, during the submersion and sinking operation. The configuration of the element as shown offers good over-trawling properties.

Fig. 7 is showing a frame element 22 having a lateral opening for access and pipe couplings. It is suitable for making by means of slip casting and can be used in combination with element 18 as shown in Fig. 5, or element 21, shown in Fig. 6, and it has buoyancy space 20 and a curved surface 13 for pipe couplings, end plates 23 for a possible corner connections or attachements and a top element or beam 24 for strengthening the entire element and for support of a lid (not shown) and for supporting trussers 25. Tilted beams are utilized if these spacings between the end plates 23 are large, and if trawling override properties are desirable. Such tilted beams are mounted subsequent to that the slip casting has been finalized.

The frame elements can be given a configuration to conform to specific needs.

Fig. 8a-d are showing a selection of combination possibilities: a) Not for trawling overriding, and without access from the sides, b) Made for trawling overriding, access from the side, and being pressure resistent.

c) Made for trading overriding, no access from the sides.

d) Made for trawling overriding, has axcess from the long sides.

When the installation is finalized it can be equipped with some kinds of covering 3, such as shown in Figs. 9a, b, c, d, respectively, supported in recesses 13 provided in the frame elements. The cover or lid can be plane such as shown in Fig.

9a or curved as shown in Fig. 9b, or it can be made as an open trusswork as shown in Fig. 9c or having circular holes as shown in Fig. 9d.

Fig. 10 is showing a preferred embodiment of the grating element 9 made by concrete and having a lining 10 for the planned or selected drilling wells. The drilling template is equipped with spacings 11 which also can be utilized for ballasting purposes during the assembly of the grating element into the frame and the same is floating at the sea surface.

Subject to special sea bed conditions making difficult to obtain sufficient sealing towards the bottom, for instance due to large permeability and/or a danger for local ground disintegration, it may be necessary to provide a further possibility for levelling.

Fig. 11 is showing a section through a bottom frame providing possibility for carrying out levelling independent of the bottom conditions. The bottom frame 13 rests without further support on a foundament 14, having skirts 15 penetrating the sea bottom 16. The foundment 14 is provided in a upwardly directed edge 17 circumscribing the lower part of the frame element 13, which is provided with'a knob 18 with a small clearence against the edge 17 on the foundament which edge is provided with a stopper 19. The bottom frame 13 is supported by the foundament in guided fashion, but with a possibility for a limited vertical movement relative to the foundament.During transport and submersion the two parts are loosely interconnected, but relative movements are hindered by the stopper 19. Through passages 20 material 21 can be injected into the space between the foundament 14 and the bottom 13 in order to level the bottom frame.

As previously mentioned it is not desirable to provide completely stiff connection' between the various frame elements due to the very large loads and stresses, which the structure may be exposed to during towing, penetration of the sea bottom, and during the levelling operation. Figs. 12 and 13 are showing two preferred joining systems which are different in regard the access possibilities to the active part 100 of the joining cables or wire 30. It is no access to the 'passive" part 101 during the joining operation. Two frame elements, respectively, are joined together with a number of tension legs or cable 30 or the like, positioned in ridgefying pipes 27.

Stoppers 29, 29' are casted into the frame element 21a in order to limit mutual movements between the various elements, and buoyancying plates 26 having a curved terminating surface are provided in order to facilitate a certain rotational movement between the elements until the stoppers 29, 29' enter into active function. The bolt or anchor is tightened from the outside.

Fig. 13 is showing a joining system providing access on the element 21b which has a side opening into the joining point.

Claims

Patent claims

1. Bottom frame foundament structure for support and protection of equipment for drilling subsea wells and the like of the kind, comprising one single or several mutually joined hollow bodies which are anchored to the sea bed, which structure consists of a number of elongated circumferentially arranged, mutually joined hollow bodies which together form a substantially polygonal, preferably quadratic frame.

2. Structure in accordance with claim 1, wherein said hollow bodies are joined monolithically together.

3. Structure in accordance with claim 1, wherein the structure comprises a number of separate, in connection with the installation, ridgedly interconnected hollow bodies, and in that special corner elements are positioned in at least some of the corners of the frame.

4. Foundament structure in accordance w5th claim 3, wherein at least some of said hollow bodies are joined together in couples by means of coupling elements, for instance at least one rod, and which coupling elements, enabling a rotational movement to take place between adjacent hollow bodies about the longitudinal axis of said bodies.

5. Foundament structure in accordance with claim 4, wherein said coupling element in the form of a cable or a rod is combined with a buoyancing plate establishing a certain space between adjacent hollow bodies and thereby render it possible for adjacent hollow bodies to accomplish a pivoting and rotational movement with the joint between the bodies to act as pivot point.

6. Structure in accordance with claim 5, wherein between adjacent hollow bodies is arranged stoppers limiting the rotational movement.

7. Structure in accordance with claim 3, wherein said frame confines and supports a grating or trusswork serving as drilling template for mounting and passing through drilling equipment.

8. Structure in accordance with claim 7, wherein said drilling template is supported on extremeties or knobs located on the inside of the frame elements.

9. Structure in accordance with claim 7, wherein said drilling template constitutes an integral part of the circumscribing claim.

10. Structure in accordance with claim 7, wherein a lid or cover is arranged and resting on the bottom frame.

11. Lid in accordance with claim 10, wherein said lid is configurated as an upwardly convex shell.

12. Bottom frame as defined in claim 4, wherein said hollow bodies are realized with a substantially triangular cross sectional shape.

13. Bottom frame in accordance with claim 1, wherein said frame including a drilling template constitute a unitary monolithical structure, and in that said drilling template comprises a bottom plate element, a top plate element and vertical webbed walls.

14. A bottom frame in accordance with claim 1, wherein said bottom frame is configurated as a pan-shaped vessel or foundament with upwardly directed edges or walls which uppermost have an inwardly pointing part and in that the hollow bodies of the bottom frame are provided with a foot on the underside, positioned on the foundament on the inside of said walls such that the bottom frame may undergo limited vertical movements in mounted and installed position.

15. Bottom frame in accordance with claim 14, c h a r a c t e r i z e d i n that said foundament and/or said foot is provided with passages for injecting mass in order to effect a levelling of the bottom frame installed position.

16. Bottom frame in accordance with claim 7, wherein said drilling template or gating is provided with throughgoing openings adaptable to be covered with a lid, except for openings for passing through of piping, cables and the like.

17. Bottom frame in accordance with claim 7, wherein said hollow bodies are provided with lateral reccesses and/or openings for passing through of piping, cables and the like.

18. Bottom frame in accordance with claim 7, wherein said hollow bodies, are provided with means in order to be loaded with ballast and be utilized as a storage for petroleum products.