The invention relates to a wellhead foundation for 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 low-pressure-barrier pipes extending through the top cover and, at least in the operative position of the suction foundation, beyond the vertical or horizontal extent of the housing. The invention also relates to a method of establishing a subsea wellhead foundation.
The establishment of a subsea well, for example a petroleum well, is conditional on a wellhead, which is arranged on the seabed, being stabilized in such a way that strain, for example lateral forces, to which the wellhead Christmas tree is subjected because of currents in the surrounding water masses is transmitted to the seabed masses surrounding the top part of the wellbore. The stabilization is typically provided by a conductor casing, which defines the top part of the wellbore against the surrounding unconsolidated masses, being cemented against the unconsolidated masses after, for example, the conductor casing has been lowered into a drilled hole or been driven down into the unconsolidated masses by an impacting device. The conductor casing forms a low-pressure barrier in the well and is connected to a low-pressure housing in the wellhead. Through the conductor casing and further through an established bore-hole a well pipe that forms a high-pressure barrier in the well is extended.
An improved stabilization is achieved by the wellhead being provided with a well frame, which is supported on the seabed. The applicant's own suction foundation (Conductor Anchor Node=CAN) as described in NO 313340 B1 and the corresponding US2003029620 A1 provides a larger contact area between the upper part of the conductor casing and the surrounding seabed mass in order thereby to further increase the stability of the wellhead. Preferably, the conductor casing is extended through a supporting pipe, which is typically centered in the suction foundation and secured to the top cover of the suction foundation and to a lower portion of the skirt of the suction foundation.
The establishing of a wellhead is laborious and especially the installation of a conductor casing may result in unconsolidated masses around the conductor casing and well-head foundation being washed out. The risk of such washouts occurring depends on several factors, among them the properties of the unconsolidated masses. Measures are therefore needed in order to reduce the risk of such washouts.
There is also a need to be able to establish several wellheads on the same foundation without this resulting in the foundation having to have a size, which makes the installation unduly demanding because of the dimension and weight.
WO2015054766 discloses the installation of conductor casings, that is to say a low-pressure barrier, in a seabed, with an assembly of one or more suction foundations with one or more integrated pipes extending in the full height of the suction foundation, inside or on the outside of the suction foundation(s) and projecting up above the top of the suction foundation(s). The suction foundation(s) is/are provided with top cover(s) closing the top(s) of the suction foundation(s).
WO2015118348 discloses an apparatus for installing a wellbore in a seabed, in which the upper end of the suction foundation is provided with a wellhead for engagement with a conductor casing, that is to say a low-pressure barrier, extending through the housing of the suction foundation.
The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.
The object is achieved through the features that are specified in the description below and in the claims that follow.
A wellhead foundation is provided for subsea wells for the exploration for or/and production of petroleum, for example, or for the injection of gas or water, for example. The wellhead foundation comprises a suction foundation in which a housing is provided with an open bottom and a top cover, which, at least during the installation of the suction foundation, closes the top of the suction foundation. The ground plan of the housing may be circular, elliptical, oval or polygonal. The wall(s) of the housing is/are tight, so that a negative pressure may be created inside the housing. In the suction foundation, at least one pipe is arranged, which is arranged to form an upper conductor-casing portion for receiving the upper well-pipe portion and form part of a low-pressure barrier in the well. Said pipe extends from the top of the housing and at least over a substantial part of the vertical extent of the housing away from the housing at least in a vertical direction, that is to say beyond the open bottom of the housing and/or outwards from the wall of the housing. An upper portion of said pipe is straight and is preferably standing vertically when the suction foundation is positioned in a seabed, the straight pipe portion lying substantially parallel to the center axis of the suction foundation. A portion of the pipe lying below may be straight or deflected. A deflected pipe may extend through an opening in the wall of the housing. If said pipe extends through the top cover of the housing and/or through the wall of the housing, the top cover and the wall fit tightly around the pipe. Said pipe is braced against the housing. The suction foundation is provided, in a manner known per se, with at least one connection for a suction line, for the internal space of the suction foundation to be evacuated so that surrounding water masses can drive the suction foundation down into unconsolidated masses in a seabed.
In the operative state of the suction foundation, said pipe has a length, which is adapted to the properties of the unconsolidated masses into which the suction foundation is going to be set. If said pipe does not extend beyond the open lower end of the housing during transport, the transport and deployment of the suction foundation may be simplified, as, in this embodiment, the suction foundation may be transported upright on a vessel deck. Since, in an operative state, said pipe is going to have a length extending beyond the horizontal and/or vertical extent(s) of the suction foundation, said pipe may be formed in various ways. In one embodiment, said pipe may be manufactured with the desired, fixed length and be attached to the housing. In this embodiment it is the most obvious to transport the suction foundation lying down. In another embodiment said pipe may be formed as a telescopic pipe which is extended while or after the suction foundation is being/has been put down, for example while the suction foundation is hanging from a lifting device on an installation vessel or by the use of an underwater hammer after the suction foundation has been driven into the unconsolidated masses. A further way of providing a lengthened pipe is to join an extension to the pipe while the suction foundation is placed in an upright position, hanging from a lifting device on an installation vessel, possibly standing on a frame-work projecting from the hull of the vessel or across a moon pool of the vessel.
When installing a suction foundation with one or more lengthened pipes, it is an advantage if boreholes that can accommodate at least some of the straight pipes have been established in the unconsolidated masses. In unconsolidated masses having the right properties, the pipes may be driven down into the unconsolidated masses by the weight of the suction foundation and the water pressure on the evacuated suction foundation. This may also apply to deflected pipes.
An advantage of the present invention is that several wellheads may be established on a suction foundation in that several well pipes may be placed with good spacing near and within the periphery of the suction foundation, possibly also outside the periphery of the suction foundation, and the well pipes may be given a deflection even before they leave the suction foundation. In addition, the connection between the upper portion of the conductor casing and the suction foundation may be optimized, as there is easy access to the connecting portions while the wellhead foundation is being made.
When a pipe extends down below the skirt of the suction foundation or outwards from the wall of the suction foundation, the pipe may be provided with a weakening inside the portion that is inside or at the periphery of the suction foundation to simplify a shutting down and abandoning of the well(s). Such a weakening may result in the suction foundation being easier to pull up and recover.
The invention is defined by the independent claims. The dependent claims define advantageous embodiments of the invention.
In a first aspect, the invention relates more specifically to 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, characterized by
The straight upper pipe portion of said pipe may be arranged eccentrically in the suction foundation.
A deflected pipe may extend through the top cover and through a wall opening in the housing, the wall opening fitting tightly against the periphery of the deflected pipe.
Alternatively, a deflected pipe may extend through the top cover and beyond a skirt edge of the housing.
The pipe may be lengthenable.
The pipe may be telescopingly lengthenable by means of one or more telescope sections. Alternatively, the pipe may be joinably lengthenable by means of one or more pipe sections.
Several pipes may be distributed inside and/or outside the periphery of the housing.
At least one straight or deflected pipe may be arranged outside of the periphery of the housing.
The housing may be provided with several internal walls that form several separate chambers, which are each provided with a suction-line connection.
In a second aspect, the invention relates more specifically to a method of establishing a subsea wellhead foundation, the method comprising the steps of
The method may include the further step of
The method may include the further step of
The method may include the further step steps of
In what follows, examples of preferred embodiments are described, which are illustrated in the accompanying drawings, in which:
Reference is first made to
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.
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.
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.
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
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.
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.
The installation may be carried out as shown in
The suction foundation 1 may be provided with means, not shown, for registering verticality.
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.
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.
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.
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.
Number | Date | Country | Kind |
---|---|---|---|
20151608 | Nov 2015 | NO | national |
20161083 | Jun 2016 | NO | national |
20161815 | Nov 2016 | NO | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/NO2016/050237 | 11/24/2016 | WO | 00 |