GB2342112A

GB2342112A - Apparatus for installing a suction pile

Info

Publication number: GB2342112A
Application number: GB9920511A
Authority: GB
Inventors: John Stephen Baross; Robin Stuart Colquhoun
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-02
Filing date: 1999-09-01
Publication date: 2000-04-05
Also published as: GB9920511D0; GB9819451D0; GB9818995D0

Abstract

Apparatus for driving a suction pile 1 into the bottom of a body of water comprises a hollow vessel 4, a pipe 3 for connecting the interior of the vessel to the interior of the suction pile, and a valve 5 for opening and closing the connection pipe. During installation of the suction pile 1, the pressure in the interior of the pile is reduced by opening valve 5 to allow water to be vented into the vessel 4, the interior of the vessel being at atmospheric pressure.

Description

1 2342112 Deepwater Suction Pile Installable Without Pump A traditional

suction pile is an open-bottomed flat-topped can, typically but not necessarily made of fabricated steel plate or rolled section, which is inserted into the clay or sand seabed by pumping out the internal water to create an internal underpressure ("suction") which lowers the can until the can top is approximately level with the seabed. The pile mobilises the passive pressure of the seabed soil to resist the lateral forces and moments applied to it and mobilises pile-soil friction to resist vertical loads either upwards or downwards. A suction pile is normally referred to as such when it has a high aspect ratio reminiscent of a pile. At lower aspect ratios it may be referred to as a suction anchor. Suction piles may be used as pin piles for subsea manifolds and other subsea structures or as piles for platform jacket foundations or as mooring anchors.

Standard suction piles and suction anchors are being used increasingly in the offshore oil and gas industry. Standard suction anchors are the subject of one or more patents held by others and such patents are neither challenged nor claimed by the present application. A person or company wishing to exploit the present invention may be liable for royalty to the patent holder of standard suction piles and suction anchors in addition to any royalty for use of the present invention.

The present invention describes devices to enable a subsea suction pile or suction caisson anchor or the suction caisson foundations of a subsea structure to be installed in the seabed without the aid of a pump.

The invention is characterised by the fact that no pump is required, since the water is evacuated from the suction pile or caisson anchor during installation into the seabed by allowing A to pass to a tank filled with air, initially at atmospheric pressure, under the influence of the differential between the ambient water pressure and the pressure in the tank. This obviates the need for a pump or umbilical other than the umbilical of the WROV (Working Remotely Operated vehicle). The tank may be the upper part of the pile or anchor (i.e. from seabed level to pile head) formed by a diametral diaphragm in the pile at seabed level. In this case, unless the water depth is modest, the preferred cross- section shape of the pile, or at least of the upper part of the pile which constitutes the tank, will be circular in order to provide the required resistance to collapse under nett external pressure without necessitating an unduly thick wall. Alternatively the tank may be separate from the pile and connected to it by hose. In this case the tank may have a circular cross section while the suction pile has a cross section which is square or rectangular or some other suitable shape. When the tank is separate, a diaphragm within the pile is not essential. In the case of the suction caisson foundations of a subsea structure, the one atmosphere chamber may be provided by members of the structure being anchored.

2 A specific embodiment of the invention with will now be described by way of an example (a suction embedded pile) with reference to the accompanying drawings in which:

Figl Shows the general arrangement of the invention when the tank is integral with the pile.

Fig 2 Shows the pile penetrating the seabed under its self weight.

Fig 3 Shows the pile embedded by suction ( by evacuation of water into the one atmosphere chamber).

Fig 4 Shows the pile in situ and the one atmosphere chamber being recovered.

The pile (1) typically, though not necessarily, has a circular cross section. it is divided into a lower open-bottomed chamber (2) and an upper closed chamber (3) by a diametral diaphragm (4). The upper and lower chambers are connected by an external pipe (5) or a partially internal pipe (6) which carries an external valve (7) or (8). This valve is designed to be actuated by a WROV (Working Remotely Operated Vehicle). There is a seacock (9) on the pile head connected by internal pipe to the lower chamber (2) and another seacock (10) on the pile head connecting directly into the upper chamber (3). These seacocks are likewise designed to be actuated by a WROV. There is also a padeye (11) on the pile head.

Prior to overboarding of the pile from the deployment vessel the seacock (9) is opened and the seacock (10) and pipe valve (7) or (8) are closed with the upper chamber full of air at atmospheric pressure. The deployment winch line is attached to the padeye (11) and the pile (1) is deployed to the seabed. On arrival at the seabed the pile is inserted into the structure (if any) or pile guide (if any) or stood with its foot on the seabed and still supported by the winch line. The winch line is then lowered or released and the pile (1) descends into the seabed under its own weight until this weight is in equilibrium with the resisting frictional force from the soil. The WROV then closes the seacock (9) and opens the valve (7) or (8) on the connectiong pipe (5) or (6). This causes the remaining water in the lower chamber (2) to be forced through the pipe (5) or (6) into the upper 0 chamber (3) under the influence of the differential between ambient water pressure in the lower chamber (2) and the lower pressure in the upper chamber (3) thus driving the pile dovrn%%,ards into the soil. The WROV monitors this process with the aid of external depth markings on the pile. When the pile has reached the intended depth, the WROV closes the valve (7) or (S) in order to ensure that soil is not also forced up through the pipe with the result that the pile is driven too far. The WROV then opens seacock (10) to allow the upper chamber (3) to stabillse at ambient pressure and prevent any subsequent further descent of the pile due to, low bleeding past the valve (7) or (8) F nall, the NIROV disconnects the deployment line shackle from the padeye (11) and the line is recovered to the vessel.

The general arrangement of the second alternative of the present invention (i.e. when the tank is separate from the pile) is shown in Fig. X. et seq. The pile (12) typically, though not necessarily, has a square or rectangular cross section. It is open at the bottom and closed at the top. An intermediate diaphragm is not essential. The pile head is fitted with a QCDC (Quick Connect DisConnect) (13). A hose (14) designed to withstand high nett external pressure runs from the QCDC to a separate tank (15). This line is fitted with a valve (16). This valve is designed to be actuated by a WROV. There is a seacock (17) on the pile head. This seacock is likewise designed to be actuated by a WROV. There is also a padeye (18) on the pile head. There is a seacock (19) on the tank (15).

Prior to overboarding of the pile from the deployment vessel the seacock (18) is opened. Prior to overboarding of the tank the valve (16) is closed with the tank full of air at atmospheric pressure. The deployment winch line is attached to the padeye (18) and the pile (12) is deployed to the seabed. The tank (15) may be connected to the pile (12) by the hose (14) prior to deployment or may be deployed separately to the seabed and connected by WROV thereafter. On arrival at the seabed the pile is inserted into the structure (if any) or pile guide (if any) or stood with its foot on the seabed and still supported by the winch line. The winch line is then lowered or released and the pile (1) descends into the seabed under its own weight until this weight is in equilibrium with the resisting frictional force from the soil. The WROV then closes the seacock (18) and opens the valve (16) on the connectiong hose (14). This causes the remaining water in the lower pile (12) to be forced through the hose (14) into the tank (15) under the influence of the differential between ambient water pressure in the pile (12) and the lower pressure in the tank (15) thus driving the pile downwards into the soil. The WROV monitors this process with the aid of external depth markings on the pile. When the pile has reached the intended depth, the WROV closes the valve (16) in order to ensure that soil is not also forced up through the pipe with the result that the pile is driven too far. The WROV disconnects the QCDC (13) to release the hose (14) from the pile (12). The WROV then opens seacock (19) to allow the tank (15) to fill with water and minimise the content of pressurised air recovered to the surface. Finally the WROV disconnects the deployment line shackle from the padeye (18) and the line is recovered to the vessel. The tank may be rigged for simultaneous recovery with the line or may be recovered separately. When the tank (15) has been recovered on deck the valve (16) and seacock (19) are opened to void the water and closed again once the tank is full of air at atmospheric pressure. The tank (15) is not ready for re-use with the next pile.

4

Claims

CLAIMS (1) Devices to enable a tubular subsea pile or caisson anchor or

the caisson foundations of a subsea structure to be installed in the seabed without the aid of a pump.

(2) Devices as claimed in Claim I wherein the evacuation of water from the pile or caisson is accomplished by venting it into a bottle or chamber or tubular member whose contents are air or nitrogen at atmospheric pressure prior to such venting.

(3) Devices as claimed in Claim I or Claim 2 wherein the bottle or chamber or tubular member into which the water is vented is attached to or is a part of the structure being installed.

(4) Devices as claimed in Claim 1 or Claim 2 wherein the bottle or chamber or tubular member is a part of a recoverable deployment unit.

(5) Devices as claimed in Claim 1 or Claim 2 or Claim 3 or Claim 4 wherein the venting is achieved via valves actuated by diver or by WROV (Working Remotely Operated Vehicle) or by other means.

(6) Devices as claimed in Claim I or Claim 2 or Claim 3 or Claim 4 or Claim 5 wherein a part of the penetration into the seabed is due to the self weight of the structure and any additional ballast before the venting is activated to complete the penetration.

(7) Devices as claimed in Claim I or Claim 2 or Claim 3 or Claim 4 or Claim 5 or Claim 6 wherein the depth of penetration or the tilt or heel of the structure are accurately controlled by the opening and closing of the valves.