Storage of Fluids Underwater

Abstract

A subsea fluid storage system comprises: a seabed foundation; a tensile member such as a pipe or a wire extending upwardly from the foundation; and a subsea buoy applying buoyant upthrust to support the tensile member in an upright orientation. At least one fluid storage container is disposed between the foundation and the buoy. The or each container may be disposed around the tensile member, for example with the tensile member extending through the container. The container has at least one inlet or outlet for fluid communication with a source or a consumer of fluid to be stored in the container.

1 . A subsea fluid storage system, comprising:
 a seabed foundation;   a tensile member extending upwardly from the foundation;   a subsea buoy applying buoyant upthrust to support the tensile member in an upright orientation; and   at least one fluid storage container disposed between the foundation and the buoy and mounted to the tensile member, the container having at least one inlet or outlet for fluid communication with a source or a consumer of fluid to be stored in the container;   wherein the tensile member extends from the foundation to the buoy through the container.   
     
     
         2 . The system of  claim 1 , wherein the tensile member comprises at least one of a pipe, a wire or a chain. 
     
     
         3 . The system of  claim 2 , wherein the tensile member serves as a riser pipe for conveying hydrocarbon fluid from a seabed source. 
     
     
         4 . The system of any preceding claim, wherein the buoy is integrated with the container. 
     
     
         5 . The system of any preceding claim, wherein fluid communication between the container and the source or the consumer is effected via at least one flow path at a level beneath the container, beside or within the tensile member. 
     
     
         6 . The system of  claim 5 , wherein the tensile member contains one or more fluid lines that define the or each flow path. 
     
     
         7 . The system of any preceding claim, wherein at least one upward fluid flow path from a subsea source extends through, but does not communicate with, the container. 
     
     
         8 . The system of  claim 7 , wherein the or each upward fluid flow path extends to or through the buoy. 
     
     
         9 . The system of any preceding claim, wherein at least one upward fluid flow path from a subsea source communicates with the container. 
     
     
         10 . The system of  claim 9 , wherein the container has a first compartment that communicates with said upward fluid flow path and a second compartment that communicates with at least one downward fluid flow path toward a subsea consumer. 
     
     
         11 . The system of any preceding claim, wherein the container has at least one filling port arranged for subsea connection with a flexible hose for filling with fluid from or offloading fluid to a surface vessel. 
     
     
         12 . The system of any of  claims 1  to  10 , wherein the container is coupled to a flexible hose that extends to the surface for filling with fluid from or offloading fluid to a surface vessel. 
     
     
         13 . The system of any preceding claim, wherein the container comprises an outer, flooded, rigid-walled housing and at least one inner chamber within the housing, the inner chamber being defined by a flexible-walled envelope. 
     
     
         14 . The system of  claim 13 , wherein the housing has a closed top and/or bottom end defining a trap volume for capturing fluid leaking from the inner chamber. 
     
     
         15 . The system of  claim 13  or  claim 14 , wherein the housing comprises an access opening through which the envelope of the inner chamber can be inserted, subsea, into the housing. 
     
     
         16 . The system of  claim 15 , further comprising a movable or removable closure that is arranged to close the access opening. 
     
     
         17 . The system of  claim 16 , wherein the closure is attached to or supports the envelope of the inner chamber so that the envelope is inserted into the housing when the closure closes the access opening. 
     
     
         18 . The system of  claim 17 , wherein the closure supports at least one fluid coupling that communicates with the envelope to fill the envelope with fluid or to empty fluid from the envelope. 
     
     
         19 . The system of any of  claims 13  to  18 , wherein the or each inner chamber is substantially symmetrical about a central longitudinal axis of the housing. 
     
     
         20 . The system of any of  claims 13  to  19 , wherein the envelope of the or each of said inner chambers is extensible or collapsible longitudinally within the housing. 
     
     
         21 . The system of  claim 20 , wherein the envelope is disposed between end plates, at least one of which plates is movable longitudinally within the housing to guide extension or contraction of the envelope. 
     
     
         22 . The system of  claim 21 , wherein at least one of the end plates comprises material with positive buoyancy. 
     
     
         23 . The system of any of  claims 13  to  22 , comprising two or more of said inner chambers disposed end-to-end within a common outer housing. 
     
     
         24 . The system of any of  claims 13  to  23 , wherein the envelope comprises a slot that extends from a centre of the envelope to open to an outer edge of the envelope, the slot accommodating the tensile member when the envelope is within the housing. 
     
     
         25 . The system of  claim 24 , wherein the slot follows a path that is curved from the centre to the outer edge. 
     
     
         26 . The system of any of  claims 13  to  25 , wherein the housing comprises at least one port for inward or outward flow of seawater. 
     
     
         27 . The system of any preceding claim, wherein the container comprises a plurality of interengaged modules, each defining a respective storage compartment. 
     
     
         28 . A subsea installation comprising at least one subsea fluid storage system of any preceding claim. 
     
     
         29 . The installation of  claim 28 , comprising at least one subsea consumer of fluid stored by the system, in fluid communication with the container of the system for supply of that stored fluid to the consumer. 
     
     
         30 . The installation of  claim 28  or  claim 29 , comprising at least one subsea source of hydrocarbon fluid, in fluid communication with the container of the system or with a riser serving as the tensile member of the system. 
     
     
         31 . A method of storing a fluid underwater, the method comprising:
 conveying the fluid into at least one subsea storage container mounted to a tensile member that extends between a seabed foundation and a subsea buoy, the buoy supporting the tensile member in an upright orientation; and   dispensing the fluid from the container to a subsea consumer or offloading the fluid from the container to a surface vessel.   
     
     
         32 . The method of  claim 31 , wherein the fluid is a hydrocarbon fluid that is conveyed into the container from a subsea source. 
     
     
         33 . The method of  claim 31 , wherein the fluid is a chemical for subsea processing or for injection into a subsea well that is conveyed into the container from a surface vessel or underwater vehicle. 
     
     
         34 . The method of  claim 33 , wherein the tensile member is a riser up which hydrocarbon fluid flows toward a surface vessel without entering the container. 
     
     
         35 . The method of any of  claims 31  to  34 , comprising conveying fluid into the container or dispensing fluid from the container via a flow path beside or within the tensile member. 
     
     
         36 . The method of any of  claims 31  to  35 , comprising: effecting fluid connection, subsea, of a flexible hose of a surface vessel with a port of the container; and filling the container with fluid, or offloading fluid from the container, through the hose. 
     
     
         37 . The method of any of  claims 31  to  35 , comprising: effecting fluid connection, at the surface, of a surface vessel to a flexible hose in fluid communication with the container; and filling the container with fluid, or offloading fluid from the container, through the hose. 
     
     
         38 . The method of any of  claims 31  to  37 , comprising holding the fluid in an inner chamber defined by a flexible-walled envelope within an outer, flooded, rigid-walled housing of the container. 
     
     
         39 . The method of  claim 38 , comprising inserting the envelope into the housing through an access opening of the housing, when underwater. 
     
     
         40 . The method of  claim 39 , comprising closing the access opening with a closure that supports the envelope, such that the envelope is inserted into the housing when the closure closes the access opening. 
     
     
         41 . The method of  claim 40 , preceded by lowering the envelope from the surface to the access opening. 
     
     
         42 . The method of  claim 41 , comprising: lowering the envelope and the closure from the surface together; attaching the closure to the housing; and inserting the envelope into the housing by closing the closure across the access opening. 
     
     
         43 . The method of any of  claims 39  to  42 , comprising accommodating the tensile member within a slot of the envelope when the envelope is inserted into the housing. 
     
     
         44 . The method of any of  claims 38  to  43 , comprising extending and contracting the envelope longitudinally within the housing in accordance with variations in volume of the fluid held within the envelope.