US-12618217-B2 - Suction anchor or well support foundation for use in permeable water bottom formations

Abstract

A suction anchor has a skirt open at one end and closed at another end to define an interior volume. At least one conduit nested within or adjacent to the skirt, is open at one end and closed at another end to define an inner volume. A suction line is fluidly connected to the interior volume through a first valve. A second valve is fluidly connected between the inner volume and either the suction line or the interior volume. The first valve and the second valve are operable to cause water flow at respective selected rates along both the skirt and the conduit from a body of water when the interior volume and the inner volume are evacuated and the suction anchor is disposed on the bottom of a body of water.

Inventors

• Wolfgang Mathis
• Ole Kristian Holen

Assignees

• NEODRILL AS

Dates

Publication Date

20260505

Application Date

20230605

Claims (20)

1. 1 . A suction anchor, comprising: a skirt open at one end and closed at another end to define an interior volume; at least one conduit nested within the skirt or disposed adjacent to the skirt, the conduit open at one end and temporarily closed at another end to define an inner volume; a suction line fluidly connected to the interior volume through a first valve; a second valve fluidly connected between the inner volume and either the suction line or the interior volume, wherein the first valve and the second valve are operable to cause water flow along both the skirt and the at least one conduit from a body of water at respective selected rates when the interior volume and the inner volume are evacuated and the suction anchor is disposed on the bottom of a body of water; and a pressure sensor in fluid communication with the inner volume and the interior volume, the pressure sensor arranged to generate signals corresponding to a difference between fluid pressure in the inner volume and fluid pressure in the interior volume.
2. 2 . The suction anchor of claim 1 further comprising a conductor nested within the conduit, the conductor comprising a wellhead housing and a conductor pipe extending from the wellhead housing through the conduit.
3. 3 . The suction anchor of claim 2 wherein the conduit and the conductor pipe are connected at respective longitudinal ends by a conductor anchor.
4. 4 . The suction anchor of claim 2 wherein the inner volume is defined within an interior of the conductor pipe.
5. 5 . The suction anchor of claim 4 further comprising a cap comprising a conductor running tool disposed in the conductor pipe.
6. 6 . The suction anchor of claim 1 wherein the second valve is in fluid communication between the inner volume and the interior volume.
7. 7 . The suction anchor of claim 1 wherein the second valve is in fluid communication between the inner volume and the suction line.
8. 8 . The suction anchor of claim 1 wherein at least one of the first valve and the second valve has a variable orifice.
9. 9 . A method for affixing a suction anchor having at least one conduit nested in or adjacent to a skirt extending to a bottom of a body of water, the method comprising: lowering the suction anchor so that the skirt is in contact with the bottom of the body of water; reducing pressure in an interior volume defined within the skirt and external to the at least one conduit; reducing pressure in an inner volume defined by an interior of the at least on conduit; and wherein the reducing pressure in the inner volume and the reducing pressure in the interior volume are performed at respective rates such that water cross flow between the interior volume and the inner volume is minimized, the reducing pressure comprising measuring a pressure in the inner volume and measuring pressure in the interior volume, and minimizing a difference between the measured pressures is minimized.
10. 10 . The method of claim 9 wherein respective rates of reducing pressure in the inner volume and the interior volume are controlled by operating at least one variable flow valve.
11. 11 . A suction anchor, comprising: a skirt open at one end and closed at another end to define an interior volume; a conduit nested within the skirt or disposed adjacent to the skirt, the conduit open at one end and temporarily closed at another end to define an inner volume; means for evacuating the inner volume and the internal volume, the means for evacuating operable to cause water flow along both the skirt and the conduit from a body of water by separately controlling rates of evacuation from the inner volume and the interior volume when the suction anchor is disposed on a bottom of a body of water, the means for evacuating comprising a pressure sensor in communication with the inner volume and with the interior volume, the pressure sensor generating signals corresponding to a difference in pressure between the inner volume and the interior volume.
12. 12 . The suction anchor of claim 11 further comprising a conductor nested within the conduit, the conductor comprising a wellhead housing and a conductor pipe extending from the wellhead housing through the conduit.
13. 13 . The suction anchor of claim 12 wherein the conduit and the conductor pipe are connected at respective longitudinal ends by a conductor anchor.
14. 14 . The suction anchor of claim 12 wherein the inner volume is defined within an interior of the conductor pipe.
15. 15 . The suction anchor of claim 14 further comprising a cap comprising a conductor running tool disposed in the conductor pipe.
16. 16 . The suction anchor of claim 11 wherein the means for evacuating comprises a pump, a first valve in fluid communication between an inlet of the pump and the internal volume and second valve in fluid communication between the inner volume and the interior volume.
17. 17 . The suction anchor of claim 16 wherein the second valve is in fluid communication between the inner volume and the inlet of the pump.
18. 18 . The suction anchor of claim 16 wherein at least one of the first valve and the second valve has a variable orifice.
19. 19 . The suction anchor of claim 11 wherein the means for evacuating comprises a first pump having an inlet in fluid communication with the inner volume and a second pump having an inlet in fluid communication with the internal volume.
20. 20 . The suction anchor of claim 19 wherein at least one of the first pump and the second pump is a variable speed pump.

Description

CROSS REFERENCE TO RELATED APPLICATIONS Continuation of International Application No. PCT/IB2020/061627 filed on Dec. 8, 2020, which application is incorporated herein by reference in its entirety. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not Applicable NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT Not Applicable. BACKGROUND This disclosure relates to the field of water bottom suction anchors. More specifically, the disclosure relates to suction anchors or well supports used in permeable water bottom soils or formations. Suction anchors known in the art have been installed mostly in clay type formations, which have relatively low permeability. More recently, especially motivated by applications connected to offshore wind farming, suction anchors have also been used as foundations in pure sand and mixed (layered clay-sand) formations, which may be relatively permeable. FIG. 1 and FIG. 2 show, respectively, a side cross-section view and a top view of a conventional suction anchor 10. The suction anchor 10 consists of a skirt 12, typically having a circular cross-section, and a top 11 that seals the upper longitudinal end of skirt 12. During installation on the water bottom, the tip 17 of the skirt 12 first penetrates sediments on the water bottom due to the weight of the suction anchor 10, creating a semi permeable seal to the water bottom sediments (formation) 3 at the bottom end of skirt 12. To urge the suction anchor 10 further into the formation 3, a suction pump 18 is connected to a suction line 15 that is fluidly connected to an internal water mass 4 within the skirt 12. In the case wherein the formation 3 consists of sand or mixed sand/clay and is therefore permeable, the under-pressure generated inside the suction anchor 10 by evacuating water from the suction line 15 causes water to be displaced from the surrounding body of water 1 external to the skirt 12 into the internal water mass 4 within the suction anchor 10. This is indicated in FIG. 1 by a flow path shown at 20. The under-pressure also generates a downward force by reason of the greater pressure of the water 1 outside the top 11 that pushes the suction anchor 10 further into the formation 3. Additionally, the water flow around the skirt tip 17 causes fluidization of the sand, which reduces resistance to further penetration of the skirt 12 into the sub-bottom. After reaching the desired penetration depth with the suction anchor 10, it is beneficial if the suction line 15 is sealed, for example using a suction line valve 16 in order to obtain the maximal load capacity of the suction anchor 10. Conventional suction anchors may have an internal structure, for example an internal support member 13, to increase the load capacity of an anchoring point 14 on the skirt 12, where an anchoring chain or the like may be attached. Such internal structures can increase the penetration resistance during deployment of the suction anchor 10. The penetration resistance may be decreased by the installation of a water injection line to the bottom edge of the internal member 13, in order to fluidize the formation 3, e.g., sand, locally, similar to the fluidization that is caused by water flowing along the flow path 20. A well support structure, or Conductor Anchor Node system is based on a suction anchor to form the foundation for subsea oil and gas wells, including water, gas, steam, or other fluid injection wells. One such system is sold under the trademark CAN, which is a registered trademark of Neodrill AS, Stavanger, Norway. The CAN system has some differences with respect to a conventional suction anchor. FIGS. 3 and 4 show, respectively, a side cross-section view and a top view of an example CAN system 30. Because the CAN system 30 is used as a well foundation, a conduit 31 is disposed inside the skirt 12 of the structure of a suction anchor. This conduit 31 is attached to a top 11 disposed on the upper end of the skirt 12 in a pressure tight manner. During the well construction process, a sub-bottom well is established through the conduit 31, which supports well components and acts as a guide for well construction tools. The conduit 31 may in some cases be additionally supported by internal members 32 extending between the conduit 31 and the skirt 12. The CAN system 30 also allows the pre-installation of a conduit known as a conductor (a structural casing) or any other wellbore tubular element as discussed further below. The presence of the conduit 31 causes several complications during the installation process of a CAN system in permeable formation 3, such as sand, sandy clay and interspersed sand and clay. The installation mechanics of a CAN system in permeable formation rely on water being drawn from the surrounding water 1, through the formation 3 along the outer wall of the skirt 12, around the tip 17 of the skirt 12 into the interior of the skirt 12, upward inside the skirt 12 into the internal water mass 4 below the top