WO2015044764A1

WO2015044764A1 - Self-burying foundation arrangement

Info

Publication number: WO2015044764A1
Application number: PCT/IB2014/001953
Authority: WO
Inventors: Ole Petter Tomter
Original assignee: Vetco Gray Scandinavia AS
Current assignee: Vetco Gray Scandinavia AS
Priority date: 2013-09-30
Filing date: 2014-09-29
Publication date: 2015-04-02
Anticipated expiration: 2016-03-30
Also published as: NO20131318A1

Abstract

A self-burying foundation arrangement is described being arranged to lower itself into the seabed by removal of seabed material, wherein a pressure source is operable to apply suction to effect transport of seabed material via at least one passageway (12) communicating with suction chambers (14) mouthing in a digging end (4) in operation facing the seabed, characterized in that the suction chambers (14) are separated by baffle walls (15), the lower edges (16) of which defines the mouths of a number of suction chambers adjoining each other in array configuration.

Description

Self-burying foundation arrangement

TECHNICAL FIELD

The present invention relates to a self-burying foundation arrangement arranged to lower itself into the seabed by removal of seabed material. The foundation

arrangement serves as foundation for underwater appliances operating at the bottom of the sea, such as equipment used in subsea processes, including but not limited to appliances used in subsea gas and oil production. BACKGROUND AND PRIOR ART

Equipment used in subsea processes, such as pumps, compressors, power units, transformers etc., are often heavy structures with bulky dimensions requiring correspondingly sized foundations to support the equipment on the seabed. Since the seabed not always presents a firm ground to support gravity based foundation structures, anchoring devices may be needed to tether the foundation structure and the equipment supported thereon.

Self- burying anchoring devices are previously known. Among them is the anchoring device disclosed in US Patent No. 4,086,866. The document discloses a deep burying anchor which in its common form has a generally cylindrical shape and includes a centrally located suction passageway and fluidizing water outlets located in the general region of the lower open end of the suction passageway. This anchor lowers itself into the seabed by moving seabed material from beneath the anchor to above the anchor, successively burying itself under a load of sand, gravel or mud. The anchoring device of US 4,086,866 serves for mooring of surface vessels, e.g.

US 6,371,003 discloses a seabed installation in the general form of a self-burying container. The container has a plurality of passages extending lengthwise of the container. An impeller at the lower end of the container is operable for drawing water through at least one of the passages to form a slurry with the seabed material and for discharging the slurry into the surrounding seawater at an upper end of the container, via another of the passages. The container has inner and outer passageways arranged concentrically about the container, and the impeller has a blade that extends across both inner and outer passageways. The blade has a first portion pitched to draw water down one of the passageways, and a second portion pitched to discharge slurry up the other passageway. The arrangement of US 6,371,003 is intended primarily to carry payloads of moderate dimensions and weight, such as communication and signaling apparatus and systems. However, the impeller, impeller motor and power unit all remain buried as long as the container is not recovered, which turns this solution into an expensive and inconceivable alternative for scaled up implementations.

SUMMARY OF THE INVENTION

A general object of the present invention is to find a non-complex and less expensive alternative to gravity based foundation structures which are

conventionally used for installation of underwater appliances at the bottom of the sea.

Another object of the present invention specifically is to provide a foundation arrangement configured for support of an underwater appliance in a loose or muddy seabed.

These and other objects are met through a self-burying foundation arrangement arranged to lower itself into the seabed by removal of seabed material, wherein a pressure source is operable to apply suction to effect transport of seabed material via at least one passageway communicating with suction chambers mouthing in a digging end in operation facing the seabed, wherein the suction chambers are separated by baffle walls the lower edges of which define the mouths of a number of suction chambers adjoining each other in array configuration. In one embodiment it is foreseen that each radially inner baffle wall extends further at the digging end than the adjacent radially outer baffle wall, the baffle walls producing by their lower edges a stepped, pyramidal or conical digging end to the foundation arrangement. The foundation arrangement provides foundation for an underwater appliance, such as a subsea pump or compressor, a cooler, a separator, a subsea power unit or process control equipment and supplies, etc. In several of these applications the underwater appliance needs protection from the ambient sea and is for this reason often accommodated in a pressurized or pressure compensated container or vessel. In such case the foundation arrangement is arranged to insert the container and its content into the seabed. Underwater appliances may this way, if appropriate, be lowered into the mud to a maximum depth which leaves only a top of the appliance and a service interface accessible above the mud-line. In one embodiment the foundation arrangement provides a protective shell about the underwater appliance to be inserted in the seabed together with the foundation arrangement. The shell comprises a cylinder wall extended from the digging end to an upper end of the foundation arrangement, the shell defining the outer periphery of the foundation arrangement. The shell may have a circular or non-circular cylinder wall.

The shell is preferably oversized such that a gap is formed between the shell and the underwater appliance accommodated in the shell. The passageways for transport of seabed material run lengthwise through the gap. The one or multiple passageways thus run near the periphery of the foundation arrangement, from the suction chambers in the digging end lengthwise along the shell wall to the opposite, upper end of the foundation arrangement. In one embodiment the transport flows of seabed material in the passageways are arranged to pass via an operation control arrangement before being combined into a singular flow that feeds a pump which generates the necessary sub- pressure/ suction. To this purpose a pressure sensor and a control valve may be installed in the passageways at a position upstream of a collector pipe which combines multiple flows of seabed material into one singular flow. Pressure sensors, control valves, collector pipe and optionally even the pump may be gathered into an operation control arrangement. The operation control assembly is preferably located at the upper end of the foundation arrangement, and may be supported from the rim of the shell wall.

Monitoring and control aiming for a substantially vertical burying of the foundation arrangement may this way be accomplished through pressure sensors arranged to monitor the operating pressure/ suction in each passageway and suction chamber individually, or collectively in a number of distributed suction chambers. For the same purpose of controlling and optionally adjusting the burying direction, control valves may be arranged to control the operating pressure/ suction in each

passageway and suction chamber individually, or collectively in a number of distributed suction chambers. In one embodiment water jet nozzles are installed in the digging end of the foundation arrangement. The water jet nozzles are active for discharge of water to effect dislodging of coarser material and fluidization of finer particles at the mouths of the suction chambers. Water is supplied to the water jet nozzles via a main water pipe and a distributor pipe having branch pipes that extend the water jet nozzles to the mouth area of the suction chambers. Optionally, each suction chamber may this way be equipped with a separate water jet nozzle that effects mixing of water and seabed material into a slurry which can be sucked-in by the suction chamber for further transport via the associated passageway. The water may be seawater which is pressurized by means of a pump that feeds the main water pipe. The pump may be supported from the rim of the shell and may form part of the operation control arrangement. Alternatively, the water jet nozzles may be supplied via separate feed pipes from a manifold arrangement located adjacent to the pump discharge, thereby allowing for individual jetting of each suction chamber.

Water jet nozzles may additionally be arranged to mouth on the exterior of the cylinder wall that forms the protective shell. The external water jets are active for discharge of water that provides lubrication by creating a layer of water or slurry between the shell and the surrounding seabed, reducing friction as the foundation arrangement is lowered into the seabed. Multiple water jet nozzles are for this purpose arranged distributed about the exterior of the shell, and the nozzles are oriented to discharge jets of water substantially upwards in the length direction and along the wall of the shell. The external water jet nozzles may be arranged in rows that encircle the shell at more than one vertical level. The external water jet nozzles may be supplied water via a main water pipe and distributor pipes running on the inner side of the shell wall. The external water jet nozzles may be supplied through a separate pump, or through the pump that supplies the fluidizing water jet nozzles in the digging end of the foundation arrangement.

These and other particulars of the invention will be further explained below. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be discussed below with reference to the accompanying schematic drawings. In the drawings,

Fig. 1 is a side view illustrating a foundation arrangement buried in the seabed together with an underwater appliance in the form of a container,

Fig. 2 is a bottom view illustrating the digging end of the foundation arrangement, Fig. 3 is a bottom view illustrating the digging end of an alternative configuration of the foundation arrangement, and

Fig. 4 is a partially broken away side view illustrating the digging end of the foundation arrangement.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 illustrates a foundation arrangement 1 being buried in the seabed such that a major part of the foundation arrangement is located below the mud line 2 defining the bottom of the sea.

The foundation arrangement comprises a shell 3 in the form of a cylinder wall reaching from a digging end 4 to an open upper end 5. The shell 3 may have circular sectional shape as illustrated in Fig. 2, non-circular sectional shape, or polygonal sectional shape as illustrated in Fig. 3. The shell 3 defines the periphery of the foundation arrangement 1 and serves for foundation and protection of an underwater appliance 6 which is mountable in the shell and insertable via the open upper end 5 of the shell. A radial mounting flange 7 resting on the rim of the cylinder wall in the upper end of the shell provides a mounting support for the underwater appliance 6, here in the form of a container, which is mounted suspended from the mounting flange 7. The mounting flange 7 also serves as mounting support for an operation control arrangement, in Fig. 1 shown by reference number 8. The operation control arrangement 8 comprises pressure sensors 9 and control valves 10 effective for performing sub-pressure /suction which is generated by a pump 1 1. Suction is this way applied to the digging end 4 via one or several passageways 12 to cause a flow of seabed material which is inhaled (I) at the digging end for transport via the passageways 12 to be discharged (D) into the sea from the pressure side of the pump. Each passageway 12 may have its own set of pressure sensors and control valves installed upstream of a collector pipe 13 which combines individual flows of seabed material in separate passageways 12 into one singular flow feeding the pump 11. Suction is distributed via the passageway (s) 12 to multiple suction chambers 14 which open in the digging end 4. The suction chambers 14 are defined by baffle walls 15 that run in axial direction towards the digging end wherein the

corresponding lower edges 16 of the baffle walls define the mouths or openings to the suction chambers. The suction chambers are thus separated merely by the baffle walls 15. A completely distributed, substantially full-area suction is this way applied to the seabed material by the multiple suction chambers, closely adjoining each other in the digging end of the foundation arrangement.

In the direction towards the digging end the baffle walls 15 are extended beyond the shell 3 in such way that each radially inner baffle wall extends further in the axial direction of the foundation arrangement than the adjacent radially outer baffle wall, whereby the baffle walls 15 produce by their lower edges 16 a stepped, pyramidal or conical digging end of the foundation arrangement.

The bottom view of Fig. 2 illustrates an embodiment wherein the baffle walls 15 are realized as circular cylinders defining annular mouths to suction chambers 14 which are arranged in array configuration and in concentric relation about the center C of a foundation arrangement having a circular section. In Fig. 2, reference number 12 points to the mouths of a multiplicity of passageways that permit transport of seabed material away from the suction chambers of annular shape.

The bottom view of Fig. 3 illustrates an embodiment wherein the baffle walls 15 are straight plates arranged at right angles, producing rows and columns of rectangular suction chambers arranged in array configuration in a foundation arrangement of rectangular shape. Again, reference number 12 points to the multiple mouths of passageways that permit transport of seabed material away from the suction chambers.

With reference again to Fig. 1 it shall be explained that the passageways 12 run lengthwise, from the digging end to the upper end, near the periphery of the foundation arrangement and close to the shell wall. More precisely, the vertically rising passageways 12 are located in a spatial clearance or gap that is formed by slightly oversizing the diameter of the shell relative to the underwater appliance that is accommodated inside the shell. Although only four passageways are shown in Fig. 1 it should be understood that a multiplicity of suction chambers and passageways can require distribution of passageways 12 along a major portion of the inner periphery, or even about the whole inner periphery of the shell 3.

The foundation arrangement 1 has a length or vertical height which is adapted to the underwater appliance such that a spatial clearance is reserved also underneath the underwater appliance. This space is occupied by horizontal passageway branches 17 that extend the vertically rising passageways 12 to those suction chambers which are located inside of the outermost row or ring of suction

chambers which are located near the periphery of the digging end 4. The embodiment of Fig. 1 further comprises a pump 18 which is operable for supply of seawater to a multiplicity of water jet nozzles 19 which are arranged to open on the exterior of the shell 3. The water is supplied via a main water pipe 20 and branches 21 that encircle the foundation arrangement on the inner side of the shell. The external water jet nozzles 19 are oriented to direct water jets upwards

substantially in the length direction of the shell, providing as previously discussed a layer of water and slurry that aids in lowering the foundation arrangement and its payload in the seabed.

With reference to the drawing of Fig. 4, a water jet nozzle arrangement for

fluidization of seabed material at the digging end will be described. In the illustrated embodiment, seawater is supplied to nozzles 22 via a main water pipe 23 and distributor pipes 24 (only one of which is shown in the drawing). Branch pipes 25 which end substantially flush with the lower edges 16 of the baffle walls 15 extend the water jet nozzles 22 to the mouth area of the suction chambers. Distributor pipes 24 may be arranged to pass through the baffle walls 15 in order to extend the supply of water to those water jet nozzles which are arranged in radially inner suction chambers 14, as illustrated. This way, water jet nozzles may be installed in some or all of the suction chambers. Alternatively, the water jet nozzles may be supplied via separate feed pipes from a manifold arrangement located adjacent to the pump discharge, thereby allowing for individual jetting of each suction chamber.

In an alternative embodiment the installation of fluidizing water jet nozzles is restricted to nozzles located in the radially outermost suction chambers, near the periphery, whereby these peripheral nozzles are oriented to direct their water jets angularly inwards, towards a point below the mouth of the centrally located suction chamber. The fluidizing water jet nozzles may be supplied by a separate pump or by the same pump 18 that supplies the external water jet nozzles. In both cases the pump or pumps may be supported on the mounting flange 7, and may form part of the operation control arrangement 8. If appropriate, the operation control arrangement 8 may alternatively be provided with a coupling interface for releasable connection to the pump or pumps, which can this way be retrieved after use.

It serves to notice that the foundation arrangement is not limited to use in connection with container- shaped payloads. The shell 3 constitutes itself a container which can be modified into a pressure vessel wherein underwater equipment can be installed in a pressurized or pressure compensated environment.

It is also possible to use the foundation arrangement as a self-burying extension of an underwater appliance, which in such case will be connected in the upper or trailing end of the self-burying foundation arrangement.

Another modification foresees the provision of a coupling interface by which the operation control arrangement 8, comprising sensors, valves, pumps etc., can be disconnected and shifted to another foundation arrangement leaving only passive structural components buried in the seabed.

Still another modification foresees that the one or more passageways may alternatively be connected to a distributor pipe located in the lower end of the foundation arrangement, together with the appropriate valves and pressure sensors.

These and other obvious modifications of the disclosed embodiments are all aimed to be covered within the scope of the invention as claimed.

Claims

1. A self- burying foundation arrangement arranged to lower itself into the seabed by removal of seabed material, wherein a pressure source is operable to apply suction to effect transport of seabed material via at least one passageway (12)

communicating with suction chambers (14) mouthing in a digging end (4) in operation facing the seabed, characterized in that the suction chambers (14) are separated by baffle walls (15), the lower edges (16) of which defines the mouths of a number of suction chambers adjoining each other in array configuration.

2. The foundation arrangement of claim 1, wherein the baffle walls (15) are circular cylinders arranged about a common axis (C), defining annular mouths to

concentrically arranged suction chambers.

3. The foundation arrangement of claim 1 or 2, wherein each radially inner baffle wall (15) extends further than the adjacent radially outer baffle wall (15), the baffle walls producing by their lower edges (16) a stepped, pyramidal or conical digging end.

4. The foundation arrangement of any previous claim, wherein the outer periphery of the foundation arrangement is defined by the wall of a shell (3) reaching from the digging end (4) to an upper end (5) of the foundation arrangement.

5. The foundation arrangement of claim 4, wherein one or multiple passageways (12) run near the periphery of the foundation arrangement, from the suction chambers (14) in the digging end (4) lengthwise along the shell wall (3) to the opposite, upper end (5) of the foundation arrangement.

6. The foundation arrangement of any previous claim, wherein the flows of seabed material in multiple passageways (12) are arranged to pass via an operation control arrangement (8) located at the upper end of the foundation arrangement.

7. The foundation arrangement of claim 6, wherein pressure sensors (9) and control valves (10) are installed in the passageways (12) at a position upstream of a collector pipe (13) which combines the multiple flows of seabed material into a singular flow.

8. The foundation arrangement of claim 7, wherein pressure sensors (9) are arranged to monitor the operating pressure in each passageway (12) and suction chamber (14) individually.

9. The foundation arrangement of claim 7 or 8, wherein control valves (10) are arranged to control the operating pressure in each passageway (12) and suction chamber (14) individually.

10. The foundation arrangement of any previous claim, wherein water jet nozzles (22) are installed in the digging end.

11. The foundation arrangement of claim 10, wherein water is supplied to the water jet nozzles (22) via a main water pipe (23) and a distributor pipe (24) having branch pipes (25) that extend the water jet nozzles to the mouth area of the suction chambers.

12. The foundation arrangement of claim 10, wherein the water jet nozzle(s) (22) are supplied by a separate water line from a distributor at the pump discharge, fitted with valves to allow for individual jetting of suction chambers.

13. The foundation arrangement of any of claims 10- 12, wherein each suction chamber is equipped with a separate water jet nozzle.

14. The foundation arrangement of any of claims 4- 13, wherein multiple water jet nozzles (19) are distributed about the exterior of the shell (3), the exterior nozzles oriented to discharge jets of water substantially upwards in the length direction of the shell wall.

15. The foundation arrangement of claim 14, wherein external water jet nozzles (19) are arranged in rows that encircle the shell (3) at more than one vertical level.