Purge system

Abstract

A purge system for use with a well intervention system and apparatus is disclosed. The purge system permits well fluids contained in a subsea intervention system to be purged prior to retrieval of the intervention system to the surface. The system comprises a vessel ( 44 ) for storing and deploying wireline tooling, the vessel being exposed to well fluids via the well control package ( 16 ) and first fluid communication means ( 58 ) connected between a purging fluid supply and the well control package, and second fluid communication means ( 60 ) connected between the vessel and the well control package wherein, in use, the purging fluid supply to the vessel via the first fluid communication means displaces fluid from the vessel into a second fluid communication means and into the well control package.

1 . A well intervention system adapted to be coupled to a subsea wellhead assembly including a subsea tree coupled to a wellhead and a well control package coupled to the subsea tree, said system comprising:
 a vessel for use in storing and deploying wireline tooling, the vessel being exposed to well fluids via the well control package; and   first fluid communication means connected between a purging fluid supply and the well control package; and   second fluid communication means connected between the vessel and wherein, in use, the purging fluid supplied to the vessel via the first fluid communication means displaces fluid from the vessel into the second fluid communication means and into the well control package.   
   
   
       2 . A system as claimed in  claim 1  wherein the system, in use, directs the displaced fluid from the vessel towards a production fluid outlet defined in the subsea tree. 
   
   
       3 . A system as claimed in  claim 1  wherein the displaced fluids are directed through a fluid passage within the wellhead assembly to which the vessel is coupled. 
   
   
       4 . A system as claimed in  claim 3  wherein the fluid passage within the wellhead assembly is defined by a production fluid bore which communicates with the production fluid outlet of the subsea tree. 
   
   
       5 . A system as claimed in  claim 3  wherein the fluid passage within the wellhead assembly is defined by a production fluid bore and a subsea tree crossover flow line, wherein the crossover flow line communicates with the production fluid outlet. 
   
   
       6 . A system as claimed in  claim 3  wherein the displaced fluid is directed into the well. 
   
   
       7 . A system as claimed in clam  3  wherein the displaced fluid is flowed to surface via a dedicated flow path. 
   
   
       8 . A system as claimed in  claim 1  wherein the first fluid communication means is adapted to be in fluid communication with a first bore within the well control package, and the second fluid communication means is adapted to be in fluid communication with a second bore within the well control package. 
   
   
       9 . A system as claimed in  claim 8  wherein the first and second bores are laterally offset and aligned parallel with each other. 
   
   
       10 . A system as claimed in  claim 8  wherein the first and second bores may be coaxially aligned wherein the first bore is a central bore of the well control package and the second bore is an annulus. 
   
   
       11 . A system as claimed in  claim 10  wherein the annulus in the well control package is defined by an isolation sleeve extending between the subsea tree and the well control package. 
   
   
       12 . A system as claimed in  claim 11  wherein the isolation sleeve isolates the central bore from the annulus. 
   
   
       13 . A system as claimed in  claim 10  wherein the first bore is aligned with a production bore of the subsea tree of the wellhead assembly, and the second bore is aligned with an annulus bore of said subsea tree. 
   
   
       14 . A system as claimed in  claim 1  wherein the purging fluid supply is a container or vessel located at surface level, and the first fluid communication means may extend from the container at the surface to the vessel. 
   
   
       15 . A system as claimed in  claim 1  wherein the purging fluid supply is a container or vessel located subsea, and preferably adjacent or in close proximity to the vessel and wellhead. 
   
   
       16 . A system as claimed in  claim 15  wherein the purging fluid supply is a Remotely Operated Vehicle (ROV) skid to permit dynamic positioning and control of the location of the purging fluid supply. 
   
   
       17 . A system as claimed in  claim 1  wherein the purging fluid supply is directly or indirectly mounted on the vessel. 
   
   
       18 . A system as claimed in  claim 1  wherein the supply of purging fluid comprises a known volume of purging fluid, which is selected to displace the required volume of fluid from the vessel. 
   
   
       19 . A system as claimed in  claim 1  wherein the purging fluid is glycol or a water and glycol mixture. 
   
   
       20 . A system as claim in  claim 1  wherein the vessel defines a central bore which in use extends towards the wellhead assembly and which is coaxially aligned with a throughbore of the wellhead assembly when the intervention system is coupled thereto. 
   
   
       21 . A system as claimed in  claim 1  wherein the vessel of the intervention system comprises a tool storage chamber. 
   
   
       22 . A system as claimed in  claim 21  wherein the tool storage chamber comprises a plurality of tool storage clamping means capable of retaining a respective tool in a storage position and selectively moving said tool to a deployment position where the tool is coupled and decoupled to a wireline connection tool from above. 
   
   
       23 . A system as claimed in  claim 21  wherein the tool storage chamber defines a portion of the central bore of the vessel. 
   
   
       24 . A system as claimed in  claim 21  wherein a tool when located in the deployment position by a tool storage clamping means is substantially aligned with the central bore of the vessel such that said tool is substantially aligned with the throughbore of the wellhead assembly. 
   
   
       25 . A system as claimed in  claim 1  wherein the vessel of the well intervention system further comprises a wireline winch assembly comprising a winch housing within which a wireline winch drum is located and mounted about the central bore of the vessel. 
   
   
       26 . A system as claimed in  claim 25  wherein the winch assembly is located above the tool storage chamber and the winch housing defines a winch cavity within which the winch drum is located wherein, in use, wireline from the winch drum exits the winch cavity, extends upwardly through a first tube or riser, passes through an upper sheave, and extends downwardly through a second tube or riser and into the central bore of the vessel. 
   
   
       27 . A system as claimed in  claim 25  wherein a crossover fluid conduit is defined between the central bore of the vessel and the winch cavity such that the purging fluid may flow from the central bore and into the winch cavity to displace well fluids therefrom. 
   
   
       28 . A system as claimed in  claim 25  wherein the second fluid communication means is adapted to extend between an upper portion of the vessel, above the tool storage chamber and the winch assembly, and the well control package. 
   
   
       29 . A system as claimed in  claim 28  wherein the second fluid communication means is adapted to extend between the upper sheave of the winch assembly and the wellhead assembly. 
   
   
       30 . A system as claimed in  claim 1  wherein the system comprises a primary isolation means for removing communication with the wellbore. 
   
   
       31 . A system as claimed in  claim 28  wherein the system comprises well fluid isolation means for selectively preventing the flow of well fluid towards the vessel and through the production fluid outlet of the subsea tree. 
   
   
       32 . A system as claimed in  claim 31  wherein the well fluid isolation means is a single valve means, such as a ball valve, gate valve, bore plug or the list which, in use, selectively prevents the flow of well fluid both towards the vessel and through the product fluid outlet of the subsea tree. 
   
   
       33 . A system as claimed in  claim 32  wherein the well fluid isolation means comprises first isolation means for selectively preventing the flow of well fluids towards the vessel, and second isolation means for selectively preventing the flow of well fluids through the production fluid out of the subsea tree. 
   
   
       34 . A system as claimed in  claim 33  wherein the first isolation means is a production master valve and the second isolation; means is a tubing hanger plug. 
   
   
       35 . A system as claimed in  claim 34  wherein the intervention system includes a plug pulling and/or setting tool for setting in place and optionally subsequently removing an isolating plug, for example into and from a bore within the wellhead assembly. 
   
   
       36 . A system as claimed in  claim 1  wherein the system comprises well annulus fluid isolation means adapted to selectively prevent fluid flow into the annulus from the intervention system or wellhead assembly or from the annulus and into the wellhead assembly and/or intervention system. 
   
   
       37 . A system as claimed in  claim 36  wherein the well annulus fluid isolation means may be provided in the wellhead assembly or in the subsea tree. 
   
   
       38 . A system as claimed in  claim 1  wherein the system comprises vessel isolation means for selectively isolating the vessel of the intervention system from the wellhead assembly to which it is coupled. 
   
   
       39 . A system as claimed in  claim 38  wherein the vessel isolation means comprises existing valve means within the wellhead assembly to which the vessel to be purged is coupled. 
   
   
       40 . A system as claimed in  claim 39  wherein the vessel isolation means is provided within the vessel to be purged. 
   
   
       41 . A system as claimed in  claim 1  wherein the system includes closure means for retaining purging fluid within the vessel once purging has taken place, such that the closure means is activated when the intervention system is to be separated from the wellhead assembly and returned to the surface. 
   
   
       42 . A system as claimed in  claim 1  wherein the system includes non-return valve means for preventing the return of purged fluid pack into or towards the vessel. 
   
   
       43 . A system as claimed in  claim 42  wherein the non-return valve means is provided in the second fluid communication means. 
   
   
       44 . A system as claimed in  claim 1  wherein the first fluid communication means comprises a fluid conduit or umbilical, such as coiled tubing, which extends between the purging fluid supply and the well control package. 
   
   
       45 . A system as claimed in  claim 1  wherein the second fluid communication means comprises a fluid conduit or umbilical which extends between the vessel to be purged and the well control package. 
   
   
       46 . A system as claimed in  claim 1  wherein the well control package forms part of the well intervention system, and well control package having a plurality of well control valve means, and said first and second fluid communication means being adapted to be coupled to the well control package at a location below at least one of the well control valve means. 
   
   
       47 . A system for use in purging fluid from a vessel adapted to be coupled to a subsea wellhead assembly including a subsea tree coupled to a wellhead and a well control package coupled to the subsea tree, said system comprising:
 first fluid communication means adapted to extend between a purging fluid supply and the well control package; and   second fluid communication means adapted to extend between the vessel to be purged and the well control package;   wherein, in use, purging fluid supplied to the well control package via the first fluid communication means displaces fluid from the vessel into the second fluid communication means and into the well control package.   
   
   
       48 . A method of purging fluid from a vessel when coupled to a subsea wellhead assembly including a subsea tree coupled to a wellhead and a well control package coupled to the subsea tree, said method comprising the steps of:
 providing a first fluid communication means extending between a purging fluid supply and the well control package;   providing a second fluid communication means extending between the vessel and the well control package; and   passing purging fluid from the purging fluid supply to the well control package via the first fluid communication means to displace fluid within the vessel therefrom, wherein the displaced fluid flows from the vessel and back into the well control package via the second fluid communication means.   
   
   
       49 . A method as claimed in  claim 48  wherein the method further involves the step of flowing the displaced fluids to a production fluid outlet of the subsea tree and subsequently to surface level via a production riser. 
   
   
       50 . A method as claimed in  claim 48  wherein the displaced fluid may be directed into the well or flowed to surface via a dedicated flow path. 
   
   
       51 . A method as claimed in  claim 48  wherein this step may be achieved by closing a sub-surface safety vessel (SSSV) and a production master valve within the wellhead and wellhead assembly. 
   
   
       52 . A method as claimed in  claim 48  wherein the vessel is isolated from the wellhead assembly by setting in place a suitable plug such as a tubing hanger plug. 
   
   
       53 . A method as claimed in  claim 52  including the step of re-opening the sub-surface safety valve and exposing the plug to well fluid pressure to ensure adequate sealing integrity of the plug has been achieved. 
   
   
       54 . A method as claimed in  claim 48  including the step of further comprising the step of isolating the vessel from annulus fluids through the wellhead assembly by closing one or more valves within the wellhead assembly. 
   
   
       55 . A method as claimed in  claim 48  including the step of the purging fluid is flowed into the vessel at a rate selected to prevent or at least minimise any mixing between the purging fluid and well fluids within the vessel. 
   
   
       56 . A method as claimed in  claim 48  including the step of setting a sealing plug within the wellhead assembly and isolating the purging fluid within the vessel such that the intervention system may be detached from the wellhead and returned to surface, and the wellhead can continue to produce well fluids to surface through the production fluid outlet and via a production marine riser. 
   
   
       57 . A method of performing a well intervention, said method comprising the steps of:
 providing a vessel for storing and deploying wireline tooling and coupling said vessel to a subsea wellhead assembly including a subsea tree coupled to a wellhead and a well control package coupled to the subsea tree;   selecting and running wireline tooling into the well from the vessel to perform an intervention operation;   retrieving all wireline tooling from the well and into a stored position within the vessel;   providing a first fluid communication means extending between a purging fluid supply and the well control package;   providing a second fluid communication means extending between the vessel and the well control package;   passing purging fluid from the purging fluid supply to the well control package via the first fluid communication means to displace fluid within the vessel therefrom, wherein the displaced fluid flows from the vessel and into the well control package via the second fluid communication means; and   detaching the vessel from the wellhead assembly and retrieving the vessel to surface.   
   
   
       58 . A method as claimed in  claim 57  wherein the well control package comprises a plurality of well control valve means and the second fluid communication means is provided to extend between the vessel and the well control package at a position below at least one of the well control valve means. 
   
   
       59 . A well intervention system adapted to be coupled to a subsea wellhead assembly, said system comprising:
 a vessel for use in storing and deploying wireline tooling, said vessel adapted to be exposed to well fluids via the wellhead assembly when in use;   first fluid communication means adapted to extend between a purging fluid supply and the wellhead assembly; and   second fluid communication means adapted to extend between the vessel and the wellhead assembly;   wherein, in use, purging fluid supplied to the wellhead assembly via the first fluid communication means and displaces fluid from the vessel into the second fluid communication means and back into the wellhead assembly.   
   
   
       60 . A method as claimed in  claim 59  wherein the wellhead assembly comprises a subsea tree coupled to a wellhead, and a well control package coupled to the subsea tree, wherein the first and second fluid communication means is adapted to be in fluid communication with the well control package.