The invention relates to an offshore wellhead supported by a foundation provided with a cluster pile provided with at least two or three suction piles (also called: "suction bucket" or "bucket" or "pile") embedded or penetrated into the sea bottom by generating an underpressure within the bucket during installation. The wellhead is for oil or gas application. Sea depth typically will be at least 10 or 20 or 50 or 60 metres.

A cluster pile is provided with at least two or three self contained buckets mutually parallel and spaced, that are fastened to each other in a rigid manner, wherein preferably their mutual spacing is less than a bucket diameter. The suction level within the suction space of each individual suction pile can be controlled independently of the other suction piles of the cluster pile.

A prior art is disclosed in US4830541 (Shell Offshore Inc.).

OBJECT OF THE INVENTION

The object of the invention is versatile.By way of example, the object is one or more of:the combination of improved control during installation of the cluster pile (especially enhanced stability during sinking towards the sea bottom); low costs; improved reliability/durability/service life (especially fatigue and cracking corrosion are less severe); damage tolerant; ease of damage repair of the completely installed structure; ease of tilting correction during installation to secure accurate verticality. The object can also be learned from the information disclosed in the application documents.

According to the invention, the cluster pile is centrally provided with a conductor head catcher spaced from and axially parallel to the buckets, wherein the conductor head catcher is rigidly fastened to each of the buckets of the cluster pile by a radially extending, spaced, preferably hollow and/or box like, supporting structure provided by a rigid top panel (e.g. 46) and a rigid bottom panel (e.g. 24), mutually parallel and mutually spaced, axially, at least 200 millimetre, e.g. 465 millimetre, and located near the top bulkhead (e.g. 27) of the buckets, the top panel (e.g. 46) axially spaced not more than 50 or 100 centimetre from said top bulkheads, the top panel (e.g. 46) and bottom panel (e.g. 24) mutually fastened by an axially extending rigid first bridging panel (e.g.39) radially remote from the conductor head catcher at least 300 millimeter, said first bridging panel (e.g. 39) also fastened to and bridging the axial external wall of two adjacent buckets, and the top panel (e.g. 46) radially extending at least 300 millimetre beyond the bottom panel (e.g. 24) towards and fastened to a rigid second bridging panel (e.g.4) which extends parallel to the first bridging panel (e.g. 39) and is radially outwardly spaced therefrom at least 300 millimetre and is also fastened to and bridging the axial external wall of two adjacent buckets.

The, e.g. box like, supporting structure allows ease of damage repair of the area of the conductor head catcher while the structure is completely installed (i.e. the buckets have penetrated the sea bottom to the desired final depth by suction), by supplying to said supporting structure from a remote source, preferably into the space delimited by the above mentioned panels, initially fluid and/or form or shape free material that cures or becomes less fluid or becomes rigid or stiff or shape retaining after being supplied, e.g. grout or mineral concrete or similar material, preferably of stone/rock or stone/rock like type, wherein the supply is carried out by using a tube like supply channel connected to the source and debouching at or adjacent or near or into the supporting structure.

Preferably inside each bucket, at a distance of less than 700 millimetre below the top bulkhead (e.g. 27) a panel (e.g. 33) extends parallel to the top bulkhead and preferably keeps a gap of at least 50 or 100 millimetre with the radial outer wall (e.g. 52) of the bucket. Such panel (e.g. 33) enhances the contribution of the above mentioned panels to the object of the invention.

Suction buckets and how to install them are a.o. known from GB-B-2300661 and EP-B-0011894, which are enclosed in here by reference. Briefly, a suction bucket is a thin walled steel or reinforced mineral cement concrete sleeve or pipe or cylinder, which cylinder is closed at its longitudinal top end by a bulkhead (also called top plate) or different sealing means of steel or reinforced mineral cement concrete and which cylinder is sealingly located on the subsea bottom with the open end opposite the bulkhead since this open end penetrates the subsea bottom due to the weight of the suction bucket. Thus the cavity, also called suction space,delimited by the cylinder and the bulkhead is sealed by the subsea floor such that vacuum or suction can be generated by removing water from within the suction space such that a resulting force tends to force the suction bucket deeper into the subsea floor. The creation of the suction can be with the aid of a suction source, such as a fluid pump, being on, or close to or at a distance from the suction bucket and connected to the suction space. The applied level of the suction can be e.g. at least substantially constant, smoothly increase or decrease or else pulsate, for which there are convenient means. After use, the suction bucket can easily be removed by creating an overpressure within the suction space, e.g. by pumping in (sea) water. The fluid pump is preferably designed to pump liquid, e.g. water.

Preferably each suction bucket has one or more of:a diameter of at least 5 metres, typically between 7 or 10 and 15 metre or even more; a height of at least 5 metres, typically between 10 and 15 metre or even more and/or less than 20 or 30 metre, subject to the soil conditions; a wall thickness of at least 1 centimetre, typically at least 3 or 5 centimetre and/or below 10 or 15 or 20 centimetre.

Preferably, the design of the suction bucket is such that fluid from a source, e.g. pressure pump, flows from the source through a sealed channel, terminating below the top bulkhead and within the suction space. During sucking in the pressure is typically at least 0.1 or 0.25 or 0.5 or 1 bars below the local water pressure external from the suction bucket. During pressing out (correction operation or decommissioning) the pressure is typically at least 0.25 or 0.5 or 1 or 2 bars above the local water pressure external from the suction bucket. The suction bucket is also preferably provided with known as such valves and/or hatches adjacent or at its top bulkhead for selectively allowing water and air to enter or exit the suction space through the top side of the suction bucket.

The top bulkhead of the suction pile is provided with an interface means, e.g. upward projecting tube stud, providing the suction pile interface to connect the fluid pump to the suction space. Preferably this means is provided with one or more of: a valve to selectively seal the suction space; a seat, e.g. a flange, at its end remote from the top bulkhead, onto which the corresponding interface means at the pump system, e.g. downward directed pipe stud, becomes seated, e.g. a corresponding seat, e.g. a flange; a coupling member for releasable and/or temporary engagement with the corresponding member at the pump system interface.

By way of non-limiting example, a presently preferred embodiment is disclosed in the attached drawing, in particular fig. 5 + 6 + 15. Fig. 14 shows panel 33. Shown is in:

Fig. 1 a cluster pile in perspective view;

Fig. 2 a top view of the Fig. 1 pile;

Fig. 3 a side view of the Fig. 1 pile;

Fig. 4 section C-C (viz. Fig. 3);

Fig. 5 section D-D (viz. Fig. 3);

Fig. 6 the area within circle Z in Fig. 5, enlarged;

Fig. 7 section E-E (viz. Fig. 3);

Fig. 8 section F-F (viz. Fig. 3);

Fig. 9 the area within circle Z in Fig. 7, enlarged;

Fig. 10 section G-G (viz. Fig. 3);

Fig. 11 section Q-Q (viz. Fig. 10);

Fig. 12 a detail of the top of the Fig. 1 pile;

Fig. 13 section C-C (viz. Fig. 12);

Fig. 14 section M-M (viz. Fig. 13);

Fig. 15 section N-N (viz. Fig. 13);

Fig. 16 section P-P (viz. Fig. 13);

Fig. 17 an offshore, floating drilling configuration;

Fig. 18 an offshore, floating drilling configuration. The bulkhead 27 of each of the three suction piles of the cluster pile has a pipe 10 to connect the suction space below the bulkhead 27 with a suction source, e.g. pump, to lower the pressure within the suction space to penetrate the suction pile into the sea bottom by suction action. In particular Fig. 15 and 16 show the conductor head catcher X. Fig. 18 shows the drill floor F (above the water level), the submerged blow out preventer B (above the sea floor), conductor C and casing Y (below the sea floor).

The invention is not limited to the above described and in the drawings illustrated embodiments. The drawing, the specification and claims contain many features in combination. The skilled person will consider these also individually and combine them to further embodiments. Features of different in here disclosed embodiments can in different manners be combined and different aspects of some features are regarded mutually exchangeable. All described or in the drawing disclosed features provide as such or in arbitrary combination the subject matter of the invention, also independent from their arrangement in the claims or their referral.

Orientations, e.g. "up", "down", "top", "aside", "upright", "vertical", "above", "level" are in this document related to the situation that the bucket is oriented vertically upright, top bulkhead above and open underside below, longitudinal axis vertical.