System and Method for Foundation of Wellheads

Abstract

A wellhead foundation is for one or more subsea wells. The wellhead foundation has a suction foundation provided with a housing with an open bottom and a top which is closable with a top cover, and one or more pipes being attached to the housing and extending from the top of the housing and at least over a substantial part of the vertical extent of the housing towards or beyond the open bottom of the housing inside or outside of the periphery of the housing, and a straight upper portion of each pipe projecting up above the top of the housing and forming an upper well-pipe portion which forms part of a high-pressure barrier in the well. The straight upper pipe portion of each pipe is arranged parallel to the center axis of the housing. A method of establishing a subsea wellhead foundation is described as well.

Claims

1. A wellhead foundation for one or more subsea wells, the wellhead foundation comprising: a suction foundation provided with a housing with an open bottom and a top which is closable with a top cover, and one or more pipes being attached to the housing and extending from the top of the housing and at least over a substantial part of the vertical extent of the housing towards or beyond the open bottom of the housing at least one of inside and outside the periphery of the housing, wherein a straight upper portion of each pipe projects up above the top of the housing and forms an upper well-pipe portion which forms part of a high-pressure barrier in the well, and wherein the straight upper pipe portion of each pipe is arranged parallel to the center axis of the housing.

2. The wellhead foundation according to claim 1, wherein the straight upper pipe portion of said pipe is arranged eccentrically in the suction foundation.

3. The wellhead foundation according to claim 1, wherein a deflected pipe extends through the top cover and through a wall opening in the housing, and wherein the wall opening fits tightly against the periphery of the deflected pipe.

4. The wellhead foundation according to claim 1, wherein a deflected pipe extends through the top cover and beyond a skirt edge of the housing.

5. The wellhead foundation according to claim 1, wherein the pipe is lengthenable.

6. The wellhead foundation according to claim 5, wherein the pipe is telescopingly lengthenable by means of one or more telescope sections.

7. The wellhead foundation according to claim 5, wherein the pipe is joinably lengthenable by means of one or more pipe sections.

8. The wellhead foundation according to claim 1, wherein several pipes are distributed at least one of inside and outside the periphery of the housing.

9. The wellhead foundation according to claim 1, wherein at least one straight pipe or deflected pipe is arranged outside the periphery of the housing.

10. The wellhead foundation according to claim 1, wherein the housing is provided with several internal walls forming several separate chambers which are each provided with a suction-line connection.

11. A method of establishing a subsea wellhead foundation, the method comprising: providing a suction foundation with a housing with an open bottom and a top which is closable with a top cover, and one or more pipes being attached to the housing and extending from the top of the housing and at least over a substantial part of the vertical extent of the housing towards or beyond the open bottom of the housing at least one of inside and outside the periphery of the housing, wherein a straight upper portion of each pipe projects up above the top of the housing and forms an upper well-pipe portion which forms part of a high-pressure barrier in the well, and wherein the straight upper pipe portion of each pipe is arranged parallel to the center axis of the housing; placing the suction foundation in an upright position over a location on a seabed for the establishment of one or more subsea wells; bringing a skirt edge of the suction foundation into abutment on the seabed; and driving one or more pipes attached to a suction-foundation housing and a skirt of the suction-foundation housing down into an unconsolidated mass, said pipes projecting up above the top of the housing and forming an upper well-pipe portion which forms part of a high-pressure barrier in the wells.

12. The method according to claim 11, further comprising: before the suction foundation is brought into abutment on the seabed, lengthening at least one of the pipes.

13. The method according to claim 11, further comprising: before the suction foundation is driven down into the unconsolidated mass, forming one or more boreholes in the unconsolidated mass, corresponding to one or more straight pipes integrated in the suction foundation; placing the suction foundation on the seabed in such an orientation that the straight pipe or pipes are arranged over the respective boreholes; and moving the straight pipes down into the respective boreholes by driving the skirt of the housing down into the unconsolidated mass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In what follows, examples of preferred embodiments are described, which are illustrated in the accompanying drawings, in which:

[0042] FIG. 1 shows an axial section through a cylinder-shaped suction foundation, in which several pipes in the form of the upper portions of well pipes are attached to the suction foundation, a straight well pipe being attached to the outside of the suction foundation, a slightly deflected well pipe being attached internally in the suction foundation and extending to the lower skirt edge of the suction foundation, whereas a greatly deflected well pipe is attached in the side wall of the suction foundation;

[0043] FIG. 2 shows an axial section corresponding to FIG. 1, but the straight well pipe attached to the outside of the suction foundation has been lengthened and extends way down below the skirt edge of the suction foundation through a pre-drilled hole in an unconsolidated mass, and the greatly deflected well pipe extends out from the side wall of the suction foundation;

[0044] FIG. 3 shows a simplified plan view, on a smaller scale, of a cylinder-shaped suction foundation with pipes arranged inside the periphery of the suction foundation;

[0045] FIGS. 4 and 5 show simplified plan views of a cylinder-shaped suction foundation with pipes arranged inside and outside the periphery of the suction foundation;

[0046] FIG. 6 shows a simplified plan view of an oval suction foundation with pipes arranged inside the periphery of the suction foundation, the housing being divided into several chambers;

[0047] FIG. 7 shows a simplified plan view of a triangle-shaped suction foundation with pipes arranged near the corners of the suction foundation and inside the periphery of the suction foundation;

[0048] FIGS. 8a-c show principle drawings, in side views, of the deployment of a suction foundation with a projecting portion of a well pipe, FIG. 8a showing the suction foundation in a horizontal position during transport on a vessel, FIG. 8b showing the suction foundation in an upright position on a framework projecting from the vessel, and FIG. 8c showing the suction foundation hanging from a lifting device, in the process of being lowered into a water mass;

[0049] FIGS. 9a-c show principle drawings, in side views, of the deployment of a suction foundation with a telescopically lengthenable portion of the well pipe, FIG. 9a showing the suction foundation with a retracted well pipe during transport on the vessel, FIG. 9b showing the suction foundation hanging from the lifting device before the well pipe has been extended, and FIG. 9c showing the suction foundation after the well pipe has been extended and the suction foundation is in the process of being lowered into the water mass; and

[0050] FIGS. 10a-c show principle drawings, in side views, of the deployment of a suction foundation with a portion of the well pipe which is lengthened by joining before the suction foundation is lowered into the water mass, FIG. 10a showing a pipe section lying on the vessel and the suction foundation standing on a framework projecting from the vessel, FIG. 10b showings the suction foundation standing on the framework and being connected to the lifting device prepared for lowering into the water mass, the well pipe having been lengthened with the pipe section, and FIG. 10c showing the suction foundation in the process of being lowered into the water mass.

DETAILED DESCRIPTION OF THE DRAWINGS

[0051] Reference is first made to FIG. 1, in which the reference numeral 1 indicates a suction foundation provided with a cylindrical housing 11 forming a wall 111, also called a skirt. The housing 11 has an open bottom 114 defined by a lower wall edge 111a, also called a skirt edge. The housing 11 has a top, which is closed by means of a top cover 112. Several well pipes 14, 14a, 14b extend downwards from above the top of the suction foundation 1. A straight first well pipe 14 is attached to the outside of the housing 11; a slightly deflected second well pipe 14a extends through an opening 112a in the top cover 112 and through the housing 11 and has its mouth at the skirt edge 111a. Said second well pipe 14a is supported against the wall 111 by means of a pipe mount 15. A greatly deflected third well pipe 14b extends through the housing 11 to an opening 111b in the wall 111 where said well pipe 14b is attached and fits tightly against the periphery of the wall opening 111b. The top cover 112 fits tightly against the second and third well pipes 14a, 14b. All the well pipes 14, 14a, 14b have a straight upper well-pipe portion 141 arranged parallel to the center axis of the housing 11. The deflected well pipes 14a, 14b include a curved lower well-pipe portion 142.

[0052] The skirt 111 and well pipes 14, 14a, 14b of the suction foundation 1 have substantially been driven down into an unconsolidated mass 4 forming a seabed 31.

[0053] In a manner known per se, a negative pressure may be created inside the housing 11 when the suction foundation 1 is standing on the seabed 31 by the housing 11 being evacuated of water through one or more suction-line connections 113. Thereby the suction foundation 1 is driven down into the unconsolidated mass 4 by the pressure from an overlying water mass.

[0054] Each of the well pipes 14, 14a, 14b as shown in FIG. 1 are arranged to be lengthened so that a high-pressure barrier is formed down through the unconsolidated masses from an upper well pipe portion 141 projecting up above the suction foundation 1 in order to form a high-pressure wellhead housing in a manner known per se.

[0055] The well pipe 14 forms a stable boundary of a borehole in the unconsolidated mass 4 in a manner known per se. In FIG. 2, the different well pipes 14, 14a, 14b are shown with different lengths downwards in the unconsolidated mass 4.

[0056] The invention enables an optimization of the wellhead foundation by the good carrying capacity of the suction foundation 1 being turned to account, and conductor casings (not shown) of a prior art known per se may be omitted as supporting elements.

[0057] It may be an advantage to form a borehole 41 (see FIG. 2) that can accommodate a lengthened well pipe 14, before the suction foundation 1 is put down on the seabed 31.

[0058] When there is a need to lengthen the well pipes 14 further, this may happen by telescopic well-pipe sections (not shown) being driven down through the integrated portions of the well pipes 14, 14a, 14b, for example. The establishing of the complete wellbore by drilling and installing further well pipes 14, 14a, 14b happens in the ordinary way through the integrated portions of the well pipes 14, 14a, 14b.

[0059] The installation of a suction foundation 1 with well pipes 14, 14a, 14b may be carried out in the ways shown in FIGS. 8a-8c, 9a-9c and 10a-10c.

[0060] FIG. 8a shows a suction foundation 1 with a well pipe 14 that extends out of the suction foundation 1. Because of that, it is transported in a lying position on a shiftable framework 21 on a vessel 2. When the suction foundation 1 is to be put down on the seabed 31, the suction foundation 1 is put into the upright position by means of the framework 21, see FIG. 8b. Then the suction foundation 1 is connected to a lifting device 22, typically a crane, and lowered through a water mass 3 to the seabed 31 (see FIG. 8c) where the suction foundation 1 with the well pipe 14 is driven down into the unconsolidated mass 4, after which the well is established through the suction foundation 1.

[0061] FIGS. 9a-9c correspondingly show a suction foundation 1 with a telescopic well pipe 14 which is retracted during the transport of the suction foundation 1, but which is lengthened, after the suction foundation 1 has been lifted up from the vessel 2, by a telescope section 143 being released from its retracted position and then secured to the well pipe 14 in its extended position. Alternatively, the telescopic well pipe 14 may be lengthened while the suction foundation 1 is standing on a framework 21 as shown in FIGS. 10a-10c.

[0062] FIGS. 10a-10c show an embodiment in which the well pipe 14 is having a pipe section 144 joined to it, which, during transport of the suction foundation 1, is separate from the suction foundation 1, indicated in FIG. 10a as lying on the vessel 2. The joining takes place while the suction foundation 1 is standing on a framework 21 projecting from the vessel 2.

[0063] FIGS. 3-7 show examples of suction foundations 1 having different ground plans and positionings of integrated well pipes 14 inside and outside the periphery of the housing 11. In FIG. 4, several pipes 14, 14a, 14 having different deflections outwards from the center axis of the suction foundation 1 are indicated. In FIG. 6, the housing is divided into several chambers 11a-11f by means of internal walls 111c-111j. Each chamber is preferably provided with a suction-line connection 113 (see FIG. 1) for the negative pressure of each chamber 11a-11f to be adjustable independently of the negative pressures of the other chambers 11a-11f. At least some of the chambers may be provided with means not shown, typically sensors that can be connected to a remote control system not shown, for recording pressures and the occurrence of gases.

[0064] The suction foundation 1 may be provided with means not shown for registering verticality.

[0065] The suction foundation 1 may also be provided with arrangements not shown, typically guiding elements, for receiving equipment that is to be connected to the suction foundation 1 during well establishment, well maintenance or well shut-down.

[0066] It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative embodiments without departing from the scope of the attached claims. In the claims, reference numbers in parentheses are not to be regarded as restrictive.

[0067] The use of the verb to comprise and its different forms does not exclude the presence of elements or steps that are not mentioned in the claims. The indefinite article a or an before an element does not exclude the presence of several such elements.

[0068] The fact that some features are indicated in mutually different dependent claims does not indicate that a combination of these features cannot be used with advantage.