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 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 and away from the housing at least in a vertical direction. A straight upper part of each pipe projects up above the top of the housing and forms an upper conductor-casing portion which is arranged to receive the upper well-pipe portion and forms part of a low-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 and away from the housing at least in a vertical direction, wherein a straight upper portion of each pipe projects up above the top of the housing and forms an upper conductor-casing portion which is arranged to receive an upper well-pipe portion and forms part of a low-pressure barrier in the well, wherein the straight upper pipe portion of each pipe is arranged parallel to the center axis of the housing; and 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.

2. The wellhead foundation according to claim 1, wherein the straight upper pipe portion of said pipe is arranged eccentrically in the suction foundation with respect to a center axis of the housing.

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

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

5. The wellhead foundation according to claim 4, wherein the pipe is telescopingly lengthenable via one or more telescope sections.

6. The wellhead foundation according to claim 4, wherein the pipe is joinably lengthenable via one or more pipe sections.

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

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

9. 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 and away from the housing at least in a vertical direction, wherein a straight upper portion of each pipe projects up above the top of the housing and forms an upper conductor-casing portion which is arranged to receive an upper well-pipe portion and forms part of a low-pressure barrier in the well, wherein the straight upper pipe portion of each pipe is arranged parallel to the center axis of the housing; and wherein the housing is provided with several internal walls forming several separate chambers which are each provided with a suction-line connection.

10. The wellhead foundation according to claim 9, wherein the straight upper pipe portion of said pipe is arranged eccentrically in the suction foundation with respect to a center axis of the housing.

11. The wellhead foundation according to claim 9, wherein a deflected pipe extends through the top cover and beyond a skirt edge of the housing.

12. The wellhead foundation according to claim 9, wherein the pipe is lengthenable.

13. The wellhead foundation according to claim 9, wherein the pipe is telescopingly lengthenable via one or more telescope sections.

14. The wellhead foundation according to claim 9, wherein the pipe is joinably lengthenable via one or more pipe sections.

15. The wellhead foundation according to claim 9, wherein several pipes are distributed at least one of inside and outside the periphery of the housing.

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

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In what follows, examples of preferred embodiments are described, which are illustrated in the accompanying drawings, in which:

(2) FIG. 1 shows an axial section through a cylinder-shaped suction foundation, in which several pipes in the form of the upper portions of conductor casings are attached to the suction foundation, a straight conductor casing being attached to the outside of the suction foundation and extending down below the skirt edge of the suction foundation through a predrilled hole in an unconsolidated mass, a slightly deflected conductor casing being attached internally in the suction foundation and extending beyond the lower skirt edge of the suction foundation, whereas a greatly deflected conductor casing is attached in the side wall of the suction foundation and extends out from said side wall, and in which a well pipe which extends through one of the conductor casings is indicated in broken lines;

(3) FIG. 2 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;

(4) FIGS. 3 and 4 show simplified plan views of a cylinder-shaped suction foundation with pipes arranged inside and outside the periphery of the suction foundation;

(5) FIG. 5 shows a simplified plan view of an oval suction foundation with pipes arranged inside the periphery of the suction foundation;

(6) FIG. 6 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;

(7) FIGS. 7a-c show principle drawings, in side views, of the deployment of a suction foundation with a projecting portion of a conductor casing, FIG. 7a showing the suction foundation in a horizontal position during transport on a vessel, FIG. 7b showing the suction foundation in an upright position on a framework projecting from the vessel, and FIG. 7c showing the suction foundation hanging from a lifting device, in the process of being lowered into a water mass;

(8) FIGS. 8a-c show principle drawings, in side views, of the deployment of a suction foundation with a telescopically lengthenable portion of the conductor casing, FIG. 8a showing the suction foundation with a retracted conductor casing during transport on the vessel, FIG. 8b showing the suction foundation hanging from the lifting device before the conductor casing has been extended, and FIG. 8c showing the suction foundation after the conductor casing has been extended and the suction foundation is in the process of being lowered into the water mass; and

(9) FIGS. 9a-c show principle drawings, in side views, of the deployment of a suction foundation with a portion of the conductor casing which is lengthened by joining before the suction foundation is lowered into the water mass, FIG. 9a showing a pipe section lying on the vessel and the suction foundation standing on a framework projecting from the vessel, FIG. 9b showings the suction foundation standing on the framework and being connected to the lifting device prepared for lowering into the water mass, the conductor casing having been lengthened with the pipe section, and FIG. 9c showing the suction foundation in the process of being lowered into the water mass.

DETAILED DESCRIPTION OF THE DRAWINGS

(10) 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 pipes 12, 12a, 12b extend downwards from above the top of the suction foundation 1. A straight first pipe 12 is attached to the outside of the housing 11; a slightly deflected second pipe 12a 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 pipe 12a is supported against the wall 111 by means of a pipe mount 15. A greatly deflected third pipe 12b extends through the housing 11 to an opening 111b in the wall 111 where said pipe 12b is attached and fits tightly against the periphery of the wall opening 111b. The top cover 112 fits tightly against the second and third pipes 12a, 12b. All the pipes 12, 12a, 12b have a straight upper pipe portion 121 arranged parallel to the center axis of the housing 11. The deflected pipes 12a, 12b include a curved lower pipe portion 122.

(11) The skirt 111 and pipes 12, 12a, 12b of the suction foundation 1 have substantially been driven down into an unconsolidated mass 4 forming a seabed 31.

(12) 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 a suction-line connection 113. Thereby the suction foundation 1 is driven down into the unconsolidated mass 4 by the pressure from an overlying water mass.

(13) Each of the pipes 12, 12a, 12b forms at least an upper portion of a respective conductor casing 13 projecting with an upper portion 131 up above the suction foundation 1 in order to form a low-pressure wellhead housing in a manner known per se and also a seat for landing the upper portion 141 (indicated in broken lines in the straight pipe 12) of a well pipe 14, that is to say a high-pressure barrier. The conductor casing 13 extends beyond the periphery of the housing 11; that is to say, below the skirt edge 111a of the housing 11 or out from the wall 111 of the housing 11.

(14) The conductor casing 13 forms a stable boundary of a borehole in the top part of the unconsolidated mass 4 in a manner known per se. When establishing a well, the length of the conductor casing 13 is determined according to the properties of the unconsolidated mass 4, especially with a view to preventing washouts during the subsequent drilling through the unconsolidated mass 4 and the installation of a well pipe 14. There is therefore often a need to use conductor casings 13 extending out from the suction foundation 1. In FIG. 1, this is illustrated to different degrees from the three conductor casings 13 shown.

(15) It may be an advantage to form a borehole 41, which can accommodate the lengthened conductor casing 13 before the suction foundation 1 is put down on the seabed 31.

(16) A further extension of the conductor casings 13, may be carried out, for example, by telescopic conductor-casing sections (not shown) being driven down through the integrated portions of the conductor casings 13. The establishing of the complete wellbore by drilling and installing well pipes 14 happens in the ordinary way through the established conductor casings 13.

(17) The installation may be carried out as shown in FIGS. 7a-7c, 8a-8c and 9a-9c.

(18) FIG. 7a shows a suction foundation 1 with a conductor casing 13 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. 7b. 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 where the suction foundation 1 with the conductor casing 13 is driven down into the unconsolidated mass 4, after which the well is established through the suction foundation 1.

(19) FIGS. 8a-8c correspondingly show a suction foundation 1 with a telescopic conductor casing 13 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 123 being released from its retracted position and then secured to the center pipe 12 in its extended position. Alternatively, the telescopic conductor casing 13 may be lengthened while the suction foundation 1 is standing on a framework 21 as shown in FIGS. 9a-9c.

(20) FIGS. 9a-9c show an embodiment in which the center pipe 12 is having a pipe section 124 joined to it, which, during transport of the suction foundation 1, is separate from the suction foundation 1, indicated in FIG. 9a 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.

(21) FIGS. 2-6 show examples of suction foundations 1 having different ground plans and positionings of integrated pipes 12 inside and outside the periphery of the housing 11. In FIG. 3, several pipes 12, 12a, 12b 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.

(22) The suction foundation 1 may be provided with means, not shown, for registering verticality.

(23) 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.

(24) 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.

(25) 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.

(26) 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.