NO20240340A1

NO20240340A1 - Subsea wellhead system

Info

Publication number: NO20240340A1
Application number: NO20240340A
Authority: NO
Inventors: Brynjulf Spalder; Rolf Barfod Schuller
Original assignee: Aker Solutions Subsea As
Priority date: 2021-12-17
Filing date: 2024-04-09
Publication date: 2024-04-09
Also published as: GB2613856A; AU2022408964A1; CA3238402A1; WO2023113613A1; GB2613856B

Description

SUBSEA WELLHEAD SYSTEM

The present invention relates to a subsea wellhead system, and particularly to a subsea wellhead system comprising a template which is secured to the seabed using a plurality of foundation elements such as suction anchors.

BACKGROUND

Wellhead systems for subsea petroleum exploration are traditionally known to comprise a wellhead having a wellhead housing secured to a well casing. It also generally has a valve stack, such as a blowout preventer (hereinafter referred to as BOP) or valve tree, located permanently or temporarily on the wellhead, for example during drilling, work-over operations and various phases of the production.

It is also known to provide the wellhead with a template which comprises a structure which is positioned about the wellhead. The template may also be referred to as a protection frame or protection envelope. The template may be a free-standing frame positionable over the wellhead and its associated components, which acts as a cage around the wellhead to protect the wellhead from damage. In this case, the template may be anchored and mounted on its own dedicated anchoring points and foundations.

When a riser is connected to the valve stack, in some cases high bending moments and/or cyclic forces may be applied on the valve stack from the riser. These forces and moments may then be led onto the wellhead structure. As a result, the wellhead and associated components may be exposed to loads (of a one-off, intermittent and/or cyclic nature) which can cause damage or fatigue and lead to reduced operational lifetime or increasing the risk of component failure.

The risk of such forces causing damage to the wellhead may be reduced by mounting the wellhead on the template or connecting the wellhead to the template.

Publications which may be useful to understand the background include WO 2012/065896; WO 2014/210026; WO 2016/118019; WO2015/118348, WO 2019/103625 A1, and WO2021/091397.

Due to the potentially serious consequences of such damage or fatigue in these safety-critical components, there is a continuous need for improved technology for wellhead systems which may be exposed to such forces or loads, for example from

P348656GB00 a BOP or subsea riser. The present disclosure has the objective to provide such improvements, or at least alternatives to known solutions and techniques.

SUMMARY

According to a first aspect of the disclosed technology we provide a subsea wellhead assembly comprising

a well frame supporting a wellhead,

three foundation elements on which the well frame is supported,

the three foundation elements comprising two larger foundation elements and one smaller foundation element.

By larger foundation element we mean a foundation element which is configured to support a larger load than the smaller foundation element, and by smaller foundation element, we mean a foundation element which is configured to support a smaller load than the larger foundation elements. The larger foundation elements could have a larger diameter than the smaller foundation element. Alternatively, the larger foundation elements could be substantially the same size as the smaller foundation elements, but be configured in such a way, e.g. through the use of thicker structural elements, that they can support a greater load than the smaller foundation element. Advantageously, the smaller foundation element is lighter than the larger foundation elements.

In one embodiment, the wellhead is located between the two larger foundation elements.

In one embodiment, each foundation element has a longitudinal axis, the foundation elements being arranged so that their longitudinal axes are generally parallel and form the corners of an isosceles triangle with the longitudinal axes of the larger foundation elements forming the corners at the base of the triangle.

In one embodiment, each foundation element has a longitudinal axis, the foundation elements being arranged so that their longitudinal axes are generally parallel and form the corners of an equilateral triangle.

In one embodiment, the well frame comprises a plurality of beams which are rigidly interconnected to form a generally planar frame base. In this case, the frame base may comprise two lateral support beams, each of which extends from above one of the larger foundation elements towards the smaller foundation element, and has an end which is rigidly connected to the smaller foundation element.

In one embodiment, the foundation elements are configured to secure the well frame to an area of seabed. In this case, the foundation elements may be at least partially embedded in the seabed.

In one embodiment, the foundation elements are suction anchors.

Various further embodiments are outlined in the detailed description and claims below, and in the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics will become clear from the following description of illustrative embodiments, given as non-restrictive examples, with reference to the attached drawings, in which:

FIGURE 1 is a perspective view of a subsea wellhead assembly according to the invention,

FIGURE 2 is a side view of the subsea wellhead assembly illustrated in Figure 1 , and

FIGURE 3 is a plan view of the subsea wellhead assembly illustrated in Figure 1 viewed from above.

DETAILED DESCRIPTION

The following description may use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, ’’upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting.

Fig. 1 shows a subsea wellhead assembly 100 having a well frame 101 supporting a wellhead 102. The well frame 101 can be a template or a different type of frame structure which supports the wellhead 102. Whilst, figure 1 illustrates a singlewellhead frame, which supports only one wellhead, as will be clear from the below description, different embodiments may have different number of wellheads 102 supported by the frame 101, for example two, three or four wellheads 102.

Figures 2 and 3 illustrate a top view and a side view of the wellhead assembly 100 as shown in Fig. 1.

In this embodiment, the well frame 101 comprises a plurality of H-beams which are connected to provide a rigid and stable support structure, in this embodiment, a generally planar frame base 110. The wellhead 102 extends through the frame base 110, through a gap between the H-beams, so that the wellhead is surrounded the frame base 110. In this embodiment, the frame base 110 comprises a plurality of beams 110a extending radially outwardly from a receptacle 110b which supports the wellhead 102.

In use, the frame base 110 is supported so that it extends generally parallel to the seabed.

In this embodiment, additional tubular support members 112 are provided, and these extend upwardly from the frame base 110. One or more protective hatches (not shown) may be pivotally mounted on the additional tubular support members 112 or the frame base 110, as is known to persons skilled in the art The protective hatches may be pivotable between an open position and a closed position, and when in the closed position may provide protection for the BOP stack / valve tree / wellhead (either with or without a temporary protective cap) / production flow base and the associated components against damage from trawlers or dropped objects.

It should be appreciated that the disclosed technology may be applied to any configuration of well frame 101, however.

When carrying out certain operations, such as drilling or well intervention, a blowout preventer (BOP) may be arranged on the wellhead 102 but this is not shown in the Figures for clarity. The BOP is conventionally suspended by a riser (not shown) from a vessel or drill rig, and landed on the frame 101. Alternatively or additionally, a valve tree (commonly referred to as a Xmas tree) may be mounted on the wellhead 102. The BOP / valve tree / wellhead 102 may be supported by or connected to the frame 101 , as is known in the art, for example in the prior art document referenced on page 1 above.

A production flow base (not shown) having a plurality of flow control components (such as piping, valves or flow conditioning components) may additionally or alternatively be mounted on the frame 101. The production flow base may be connected to one or more fluid flow line such as production or water injection lines, service lines, hydraulic power lines or mule-purpose lines, as conventional in the art. Where a valve tree is also provided, the valve tree may have fluid connections to components on the production flow base, and may be directly or indirectly supported by the frame structure 101

The frame base 110 and / or the production flow base, where provided, may extend outside a perimeter of the suction anchor wellhead foundation in order to provide sufficient space and appropriate relative positioning of the components on the production flow base.

The well frame 101 is supported on an area of the sea floor 127 (see Figure 2) by three foundation elements 130a, 130b, 130c, which are partially embedded in the seabed 127. In this embodiment, the foundation elements 130a, 130b, 130c are all suction anchors (which may also be referred to as suction piles or suction buckets), of the sort well known to person skilled in the art for securing well templates to the seabed. The frame 101 rests on top of, and is rigidly fixed to, the foundation elements using conventional methods known to persons of skill in the art. Each foundation element 130a, 130b, 130c has a longitudinal axis which extends generally perpendicular to the sea floor 127.

Two of the three foundation elements 130a, 130b are larger than the other foundation element 130c. By larger, we mean that they are capable of supporting a heavier load than the other foundation element 130c. In this embodiment, the larger foundation elements 130a, 130b have a larger outer diameter than the smaller foundation element 130c. The foundation elements will therefore hereinafter be referred to as the larger diameter foundation elements 130a, 130b and the smaller diameter foundation element 130c. It should be appreciated, however, that all three foundation elements 130a, 130b , 130c could be generally the same size, the larger foundation elements 130a, 130b having a greater load-bearing capacity by virtue of the particular way in which they are constructed.

In this embodiment, the wellhead 102 is located directly between the two larger diameter foundation elements 130a, 130b. Advantageously, the wellhead 102 is located centrally between the two larger diameter foundation elements 130a, 130b, with the longitudinal axis of the wellhead 102 lying in the same plane as the longitudinal axes of the two larger diameter foundation elements 130a, 130b.

It will be appreciated that the two larger diameter foundation elements 130a, 130b enable the well frame 101 to provide a good, stable support for the wellhead 102 to resist forces on the wellhead which extend in the same plane as the longitudinal axes of the two larger diameter foundation elements 130a, 130b, including vertically downward forces arising from the weight of any equipment mounted on top of the wellhead 102. The load bearing capacity of the larger foundation elements 130a, 130b is therefore selected to be sufficient to support the maximum anticipated weight of the equipment supported by the well frame 101. The smaller diameter foundation element 130c is provided to support the wellhead 102 to resist forces with a component perpendicular to this plane (hereinafter referred to as “lateral forces”), and can therefore have a lower load bearing capacity, its load bearing capacity being selected based on the maximum anticipated level of the lateral forces acting on the wellhead.

The smaller diameter foundation element 130c is located relative to the large diameter foundation elements 130a, 130b such that the longitudinal axes of the foundation elements 130a, 130b, 130c form an isosceles triangle, with the longitudinal axes of the larger diameter foundation elements 130a, 130b being located on the corners of the base of the triangle. This is best illustrated in Figure 3.

In this embodiment, the distance between the longitudinal axes of the larger diameter foundation elements 130a, 130b is greater than the distance between the longitudinal axis of the smaller diameter foundation element 130c and the longitudinal axis of either of the larger diameter foundation elements 130a, 130b. It should be appreciated, however, that the reverse might be true, or the longitudinal axes could form the corners of an equilateral triangle.

In this embodiment, the base frame 110 comprises two lateral support beams 110c each of which extends from above one of the larger diameter foundation elements 130a, 130b towards the smaller diameter foundation element 130c. One end of each lateral support beam 110c is connected to the top of the smaller diameter foundation element 130c.

In this embodiment, one end of each lateral support beam 110c is connected to the top of the smaller diameter foundation element 130c via a connection structure. The lateral support beams 110c therefore assist in transferring lateral forces on the wellhead 102 to sea floor via the smaller diameter foundation element 130c, thus stabilising the wellhead 102 when acted on by such lateral forces.

In this embodiment, the connection structure comprises four connection beams 110d arranged in a generally square array. In this embodiment, two of the four connection beams 110d extend generally parallel to a line connecting the longitudinal axes of the larger diameter foundation elements 130a, 130b.

In order to provide sufficient area for the frame base 110 to support the required equipment as described above, in this embodiment, one of the four connection beams 110d which extends generally parallel to a line connecting the longitudinal axes of the larger diameter foundation elements 130a, 130b extends beyond the top of the smaller diameter foundation element 130c, so that its ends form two corners of the base frame 110. Beams connected to the larger diameter foundation elements 130a, 130b form two further corners of the base frame 110, the four corners being arranged in a generally rectangular array.

The foundation elements 130a, 130b, 130c may, alternatively, be of a different type than a suction anchor foundation as described above. They may, for example, be a piled foundation having one or more mud mats and piles securing the frame 101 to the sea floor. This foundation may, for example, be advantageous for harder ground conditions.

It should be appreciated that the well frame 101 described above could be used to support more than one wellhead 102. For example, the well frame 101 could be used to support two or more wellheads, with all the wellheads being located directly between the two larger diameter foundation elements (130a, 130b). In this case, the wellheads could be arranged in a row, with their longitudinal axes arranged in the same plane as the longitudinal axes of the larger diameter foundation elements (130a, 130b). Alternatively, where more than one wellhead 102 is supported by the well frame 101, the longitudinal axes of one or more of the wellheads 102 may be offset relative to the plane in which the longitudinal axes of the larger diameter foundation elements (130a, 130b) lie. For example, the well frame 101 may support two wellheads which are arranged, one on either side of the plane in which the longitudinal axes of the larger diameter foundation elements (130a, 130b) lie, the two wellheads being equidistant from that plane, and equidistant from both of the larger diameter foundation elements (130a, 130b). Similarly, the well frame 101 may support three wellheads, one of which is located with its longitudinal axis lying on the plane in which the longitudinal axes of the larger diameter foundation elements (130a, 130b) lie, and the other two being arranged, one on either side of the plane in which the longitudinal axes of the larger diameter foundation elements (130a, 130b) lie and equidistant from that plane. Further alternatively, the well frame (101) may support four or more wellheads 102 which are arranged in a rectangular or square array having an axis of symmetry which lies in the plane in which the longitudinal axes of the larger diameter foundation elements (130a, 130b) lie.

Foundation elements which have a lower load bearing capacity are generally lighter and / or less expensive than foundation elements with a greater load bearing capacity. As such, by virtue of the disclosed arrangement of foundation elements, and tailoring the load bearing capacities of the larger and smaller foundation elements according to the anticipated downward and lateral forces respectively, the weight, cost and size of the wellhead support system may be reduced without compromising the support provided to the wellhead, to avoid damage or fatigue to the wellhead and associated components.

Claims

1. A subsea wellhead assembly (100) comprising

a well frame (101) supporting a wellhead (102),

three foundation elements (130a, 130b, 130c) on which the well frame (101) is supported,

the three foundation elements comprising two larger foundation elements (130a, 130b) and one smaller foundation element (130c), the larger foundation elements (130a, 130b) having a larger load bearing capacity than the smaller foundation element (130c).

2. A subsea wellhead assembly (100) according to claim 1 wherein the wellhead is located between the two larger foundation elements.

3. A subsea wellhead assembly (100) according to any preceding claim, wherein each foundation element has a longitudinal axis, the foundation elements being arranged so that their longitudinal axes are generally parallel and form the corners of an isosceles triangle with the longitudinal axes of the larger foundation elements forming the corners at the base of the triangle.

4. A subsea wellhead assembly (100) according to claim 1 or 2, wherein each foundation element has a longitudinal axis, the foundation elements being arranged so that their longitudinal axes are generally parallel and form the corners of an equilateral triangle.

5. A subsea wellhead assembly (100) according to any preceding claim, wherein the well frame (101) comprises a plurality of beams which are rigidly interconnected to form a generally planar frame base (110).

6. A subsea wellhead assembly (100) according to claim 5, wherein the frame base comprises two lateral support beams (110c) each of which extends from above one of the larger foundation elements (130a, 130b) towards the smaller foundation element (130c), and has an end which is rigidly connected to the smaller foundation element (130c).

7. A subsea wellhead assembly (100) according to any preceding claim, wherein the foundation elements (130a, 130b, 130c) are configured to secure the well frame (101) to an area of seabed (127).

8. A subsea wellhead assembly (100) according to claim 7 wherein the foundation elements (130a, 130b, 130c) are at least partially embedded in the seabed (127).

9. A subsea wellhead assembly (100) according to claim 8, wherein the foundation elements (130a, 130b, 130c) are suction anchors.

10. A subsea wellhead assembly (100) according to any preceding claim wherein the larger foundation elements (130a, 130b) have a larger diameter than the smaller foundation element (130c).