NO345282B1

NO345282B1 - Subsea template structure

Info

Publication number: NO345282B1
Application number: NO20181016A
Authority: NO
Inventors: Brynjulf Spalder; Rolf Barfod Schüller
Original assignee: Aker Solutions As
Priority date: 2018-07-23
Filing date: 2018-07-23
Publication date: 2020-11-30
Also published as: GB201910353D0; GB2576626B; NO20181016A1; GB2576626A

Description

SUBSEA TEMPLATE STRUCTURE

The invention relates to a subsea template structure, and more specifically to a subsea template structure comprising a blowout preventer stabilizing system.

BACKGROUND

Subsea structures are found at any subsea oil or gas field development. They surround various subsea components needed for optimal performance, ensuring efficient operation both during installation and through a field's life. In addition to gathering or distributing subsea infrastructure such as flowlines and umbilicals, they also provide protection to sensitive equipment from the external environment, such as fishing nets of trawlers.

Subsea structures can range from overtrawlable North Sea structures to deepwater cluster systems, and are designed for various water depths, installation methods and seabed conditions in different parts of the world. Such structures are suitable for use in both vertical and horizontal connection systems, and are designed to contain the equipment needed for a specific field development.

One such subsea structure is a subsea template structure, which main function is to provide a protected foundation for subsea trees and manifold, and to be a guide, hang off and support for drilling and the wellhead conductor.

During drilling, completion and work over operations, cyclic loads are transferred through a blowout preventer (BOP) stack and into the well system. A blowout preventer is a valve or similar mechanical device used to seal, control and monitor oil and gas wells to prevent blowouts, uncontrolled release of crude oil or natural gas from a well. During e.g. drilling operations that continue over a long period of time, there is a substantial risk of fatigue fracture in the wellhead due to the rocking back and forth movement of the BOP. This is a common problem in the art of drilling.

Movement of the BOP may be reduced by a BOP stabilizing system that connects and stabilizes the BOP to the subsea template structure. In such a system, the BOP is connected to and supported by the subsea template structure e.g. by means of wires, and thus some of the loads are transferred from the BOP to the subsea template structure. The cyclic bending moments are thus reduced and the fatigue life of the wellhead is increased. When the wires have been pre-tensioned, the BOP stabilizing system provides support to the BOP and relieves the wellhead from cyclic loads.

However, the subsea template structure must also be securely anchored to the seabed in order for the wellhead to be relieved from the cyclic loads of the BOP. When the subsea template structure is positioned on soft soil, suction anchors securely anchor the template structure to the seabed as is known in the art, and such systems efficiently transfer loads from the BOP into the seabed. However, when the seabed consists of hard soil, suction anchors cannot be used. Instead, structures with mudmats may be used on hard soil, but mudmats are not able to transfer loads from the BOP into the seabed efficiently. There is such a need in the art for a subsea template structure comprising a BOP stabilizing system that can be securely anchored to a seabed.

Documents which may be useful for understanding the background include WO 2016/118019 A1; GB 2132669 A; US 9074447 B1; and GB 2279098 A.

SUMMARY

It is an object of the present invention to provide a subsea template structure comprising a blowout preventer stabilizing system with increased anchoring properties. When such a subsea template structure is anchored to the seabed by means of piles, the forces from the blowout preventer will be guided into the seabed, thus limiting fatigue and increasing the lifetime of the wellhead.

In accordance with the present invention, there is provided a subsea template structure comprising a blowout preventer stabilizing system for limiting movement of a blowout preventer on the template structure. A pile is attached to the template structure, for anchoring the subsea template structure to the seabed. The blowout preventer stabilizing system comprises connection means for connecting the blowout preventer to the pile.

According to another embodiment of the invention, the pile is releasably attached to the template structure.

According to another embodiment of the invention, the subsea template structure further comprises a mudmat.

According to another embodiment of the invention, the pile is accomodated in a column on the subsea template structure.

According to another embodiment of the invention, the pile comprises a blowout preventer stabilizing system interface for connecting the connection means to the pile.

According to another embodiment of the invention, the connection means comprises a wire.

According to another embodiment of the invention, the subsea template structure is an integrated template structure.

According to another embodiment of the invention, the blowout preventer stabilizing system is a wellhead load relief system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other characteristics will become clear from the following description of embodiments, given as non-restrictive examples, with reference to the attached schematic figures.

Figure 1 is an exploded perspective view of a subsea template structure comprising mudmats and piles.

Figure 2 is a perspective view of a subsea template structure comprising mudmats, piles, a blowout preventer and a blowout preventer stabilizing system.

DETAILED DESCRIPTION

The following description may use terms such as “horizontal”, “vertical”, “lateral”, ”upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the figures 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.

Referring initially to figure 1, a subsea template structure 1 is illustrated. The subsea template structure 1 may be an integrated template structure, also known as an ITS. The subsea template structure 1 is a structural framework that may comprise tubes and plates that are welded together. The subsea template structure 1 may be a steel structure, and the size of a template structure 1 is dependent on the number of structures attached to it, the number of wells, etc. The top geometry of the subsea template structure 1 may be designed such as to protect the below structure from fishing activities, and such that no protruding features may act as snag points.

The subsea template structure 1 may comprise mudmats 2. A mudmat 2 is a structure that prevents offshore subsea structures from sinking into the seabed, and also prevents horizontal movement of the subsea structure. Mudmats 2 are commonly used on subsea structures in order to increase the footprint of the structure on the seabed. The function of a mudmat 2 is thus to provide adequate area of load distribution to the soil, and support the weight of the structure it supports plus additional loads imposed by environmental conditions. A mudmat 2 may be a plate or grid that enhances friction between a subsea template structure and the seabed. The plate or grid may be horizontally mounted on the template structure, and may be combined with a framework to accommodate soil and stones to settle on the mudmat to further enhance friction.

In the illustrated embodiment, the template structure 1 comprises four mudmats 2 positioned at each respective corner of the template structure 1, but any number of mudmats 2 could be utilized, positioned anywhere on the template structure 1.

Alternatively, one large mudmat could also be utilized. If the footprint area of the template structure 1 is adequately large, or the seabed is adequately compact, the template structure 1 may not need a dedicated mudmat at all.

The subsea template structure 1 comprises in the illustrated embodiment four wellheads 9, and four wells can as such be drilled from the subsea template structure 1. The number of wellheads 9 in a subsea template structure 1 can range from one up to eight or more.

The template structure 1 may comprise one or more columns 3 that are hollow and provided to accommodate a pile 4. The template structure 1 in the illustrated embodiment comprises four such columns 3, and the columns 3 may be provided at the corners of the template structure 1. The columns 3 could be posts or similar tubular members that may be structural members of the template structure 1.

A pile 4 is adapted to be inserted into the seabed and be releasably attached to the subsea template structure 1. The piles 4 thus anchor the subsea template structure 1 to the seabed. The pile 4 can be inserted into the seabed through the column 3, and the pile 4 can be releasably attached to a corresponding column 3.

Alternatively, the piles 4 can also be releasably attached to the subsea template structure 1 by a corresponding framework, through plates with corresponding holes, etc. A pile 4 may be a pipe which is approximately 30-50 meter long and made of steel. The piles 4 can be installed into the template structure 1 after it has been installed on the seabed. The piles 4 may comprise a blowout preventer (BOP) stabilizing system interface 5 that may be located at a distal end of the pile 4, this is described further with reference to figure 2. This distal end may be the top end of the pile 4.

Referring now to figure 2, a template structure 1 with piles 4 installed is illustrated. The piles 4 extend through the columns 3 and are driven into the seabed. The piles 4 can be releasably fixed to the template structure 1, and thus securely anchor the template structure 1 to the seabed. The piles 4 may also be permanently fixed to the subsea template structure 1, either as part of the framework or structure, or as a separate assembly fixed to the subsea template structure 1. The piles 4 may even be e.g. hingedly connected to the subsea template structure 1, in order to secure an adjustable and rigid connection between the piles and the structure.

The template structure 1 comprises a BOP stabilizing system 6 that may connect a BOP 7 to the piles 4 by means of the BOP stabilizing system interface 5 and connection means 8. The BOP stabilizing system interface 5 provides for an easy connection between the BOP stabilizing system 6 and a pile or a subsea template structure. Loads from the BOP 7 are thus led through the BOP stabilizing system 6 and transferred through the piles 4 into the seabed. The BOP stabilizing system interface 5 may designed such that it does not protrude significantly upwards nor sideways, and it will thus not be exposed to risk from being damaged by trawling, nor will it act as a snag point.

The BOP stabilizing system 6 may be a wellhead load relief, also known as a WLR system, and the connection means 8 may be wires, chains, cables or other means suitable for connecting a BOP 7 to a pile 4. The connection means 8 are firmly

Claims

tensioned and limit both movement and rotation of the BOP 7 in the horizontal plane. If the connection means 8 are wires, the BOP stabilizing system interface 5 may be a wire connection interface. The BOP stabilizing system 6 may also be a stiff frame, and the connection means 8 may thus be bars, rods or similar elements of a stiff framework. Loads from the BOP 7 are transferred into the seabed by the BOP stabilizing system 6 and piles 4, thus relieving the wellhead 9 from cyclic loads and fatigue.

In the illustrated embodiment, the BOP stabilizing system 6 connects the BOP 7 to four piles 4 located at the corners of the template structure 1, but any number of piles 4, and any number of BOP stabilizing system interfaces 5, may be utilized. Alternatively, one or more BOP stabilizing system interfaces 5 may be positioned on the subsea template structure 1 itself, such that the BOP stabilizing system 6 connects the BOP 7 directly to the subsea template structure 1. The BOP 7 is thus connected to the subsea template structure 1, which is anchored to the seabed by means of piles 4.

1. A subsea template structure (1), comprising:

a blowout preventer stabilizing system (6) for limiting movement of a blowout preventer (7) on the template structure (1), characterized by

a pile (4) attached to the template structure (1), for anchoring the subsea template structure (1) to the seabed; and

the blowout preventer stabilizing system (6) comprising connection means (8) for connecting the blowout preventer (7) to the pile (4).
2. The subsea template structure (1) according to claim 1, where the pile (4) is releasably attached to the template structure (1).
3. The subsea template structure (1) according to claim 1 or 2, further comprising a mudmat (2).
4. The subsea template structure (1) according to any one of the previous claims, where the pile (4) is accomodated in a column (3) on the subsea template structure (1).
5. The subsea template structure (1) according to any one of the previous claims, where the pile (4) comprises a blowout preventer stabilizing system interface (5) for connecting the connection means (8) to the pile (4).
6. The subsea template structure (1) according to any one of the previous claims, where the connection means (8) comprises a wire.
7. The subsea template structure (1) according to any one of the previous claims, where the subsea template structure (1) is an integrated template structure.
8. The subsea template structure (1) according to any one of the previous claims, where the blowout preventer stabilizing system (6) is a wellhead load relief system.