Fluid transportation system

Abstract

Method and apparatus for assisting the flow of production fluid from a hydrocarbon well to a remote location in conditions in which gelling or solidification is a problem. The method involves adding dilution fluid ( 60 ) such as water, to production fluid from a wellhead ( 4 ) in a first sub-system ( 8 ) close to the wellhead ( 4 ), conveying the mixture to a second sub-system ( 14 ) where the dilution fluid ( 60 ) is separated from the mixture in a separator chamber ( 38 ) as a consequence of their different specific gravities, recirculating the separated dilution fluid back to the first sub-system ( 8 ) and adding it to further production fluid from the wellhead ( 4 ). The requirements for pipeline heating, chemical injection and conveying large volumes of dilution fluid to a host facility can be avoided by the invention.

1 . A method of assisting flow of production fluid from a subsea wellhead ( 4 ) to a remote subsea location ( 14 ) including the steps of: 
 (a) adding dilution fluid to production fluid at a dilution fluid addition location ( 8 ) close to or at the wellhead ( 4 ) to provide a mixture;    (b) conveying the mixture through a pipe ( 10 ) to the remote location ( 14 );    (c) separating at least some of the dilution fluid from the mixture at the remote location ( 14 );    (d) conveying ( 12 ) the separated dilution fluid from the remote location ( 14 ) to the dilution fluid addition location ( 8 ); and    (e) adding the separated dilution fluid to further production fluid flowing through the wellhead ( 4 ) at the dilution fluid addition location ( 8 ).    
     
     
         2 . The method according to  claim 1  wherein the remote subsea location ( 14 ) is situated close to a host facility ( 2 ).  
     
     
         3 . The method according to claims  1  and  2  wherein prior to step (a) the dilution fluid is supplied from the host facility ( 2 ) to the dilution fluid addition location ( 8 ).  
     
     
         4 . The method according to  claim 2  or  3  comprising the further step of conveying ( 16 ) the separated production fluid to the host facility ( 2 ).  
     
     
         5 . The method according to any preceding claim wherein the dilution fluid essentially comprises water.  
     
     
         6 . The method according to any preceding claim wherein the ratio of dilution fluid to production fluid in the mixture lies in the range 2:1 to 4:1.  
     
     
         7 . The method according to  claim 6  wherein the ratio of dilution fluid to production fluid in the mixture lies in the range 2.5:1 to 3.5:1.  
     
     
         8 . The method according to any preceding claim wherein the step of separating ( 38 ) the dilution fluid ( 60 ) from the mixture involves separating a majority of the dilution fluid ( 60 ) from the mixture.  
     
     
         9 . The method according to  claim 8  wherein the step of separating the dilution fluid ( 60 ) from the mixture involves separating at least 90% of the dilution fluid ( 60 ) therefrom.  
     
     
         10 . The method according to any preceding claim wherein the separation of the dilution fluid from the mixture involves routing the mixture into a separator chamber ( 38 ) of a system ( 14 ) at the remote location where separation of the dilution fluid ( 60 ) from the production fluid ( 63 ) occurs as a consequence of their different specific gravities.  
     
     
         11 . The method according to  claim 10  wherein the system ( 14 ) at the remote location includes a pump ( 62 ) and the conveying of the separated dilution fluid ( 60 ) to the dilution fluid addition location ( 8 ) includes pumping the dilution fluid ( 60 ) with the pump ( 62 ).  
     
     
         12 . The method according to any preceding claim including conveying some of the separated fluid ( 60 ) to a disposal well ( 78 ).  
     
     
         13 . The method according to  claim 12  wherein a pump ( 80 ) is situated at the dilution fluid addition location ( 8 ) and the step of conveying the dilution fluid ( 60 ) to the disposal well ( 78 ) includes pumping it there with the pump ( 80 ).  
     
     
         14 . Apparatus for assisting flow of production fluid from a seabed wellhead ( 4 ) to a remote subsea location ( 14 ) including dilution fluid addition means ( 8 ) situated close to or at the wellhead ( 4 ) for adding dilution fluid to the production fluid to produce a mixture, a pipe ( 10 ) for conveying the mixture to the remote location ( 14 ), separating means ( 38 ) at the remote location ( 14 ) for separating at least some of the dilution fluid ( 60 ) from the mixture and means ( 12 ,  62  . . . ) for conveying the separated dilution fluid ( 60 ) from the remote location ( 14 ) to the dilution fluid addition means ( 8 ) for addition to further production fluid flowing through the wellhead ( 4 ).