Mid water gas lift

Abstract

Methods and apparatuses for the production of hydrocarbons from an offshore reservoir are disclosed. The hydrocarbons are produced using at least one spur (or flowline), and at least one riser conduit to transport said hydrocarbons from the seafloor to a point at or near the sea surface, wherein an artificial lift method, such as the injection of a lifting gas, is used to help transport said hydrocarbons from the reservoir to said point at or near the surface, and wherein said artificial lift method is applied to said hydrocarbons at a point along the at least one riser conduit, substantially above said seafloor.

1 . A method of production of hydrocarbons from an offshore reservoir using at least one spur or flowline to transport hydrocarbon wellfluid from a wellhead to the bottom of at least one riser conduit, and using said at least one riser conduit to transport said hydrocarbon wellfluid from the seafloor to a point at or near the sea surface, wherein an artificial lift method is used to help transport said hydrocarbon from the reservoir to said point at or near the surface, and wherein said artificial lift method is applied to said hydrocarbon wellfluid at a point along the at least one riser conduit, substantially above said seafloor. 
     
     
         2 . A method as claimed in  claim 1  wherein the hydrocarbon wellfluid comprises crude oil. 
     
     
         3 . A method as claimed in claim I wherein the hydrocarbon well fluid comprises a mixture of crude oil, water and natural gas. 
     
     
         4 . A method as claimed in any  claim 1  wherein said at least one riser conduit forms part of a riser tower having a top, said riser tower comprising one or more rigid conduits supported in a tower structure and extending in use from a foundation connecting structure on the seabed to a point below the sea surface and wherein there are provided one or more flexible conduits extending from said tower structure to connect said tower structure to a surface structure, and wherein there is further provided a buoyancy device attached to said top of said tower structure, such that in use said buoyancy device is located above and exerts an uplift buoyancy force on said riser tower. 
     
     
         5 . A method as claimed in  claim 1  wherein said artificial lift method comprises a gas lift method, where gas is injected into the hydrocarbon wellfluid to be recovered, at a point on said riser conduit substantially above the seafloor, so as to reduce its density. 
     
     
         6 . A method as claimed in  claim 5  wherein said injection is made at a point where hydrostatic pressure is below a cricondenbar of the hydrocarbon wellfluid. 
     
     
         7 . A method as claimed in  claim 6  wherein said injection is made at a point where pressure in the riser conduit is below a bubble point pressure of the hydrocarbon wellfluid. 
     
     
         8 . A method as claimed in  claim 5  wherein said gas for injection is transported from the surface to the injection point by a dedicated pipe. 
     
     
         9 . A method as claimed in  claim 5  wherein said gas for injection is transported from the surface to the injection point at least partly in an annulus of a pipe-in-pipe structure, a central pipe comprising a main conduit for transporting said hydrocarbon wellfluid. 
     
     
         10 . A riser apparatus for the production of hydrocarbons from an offshore well comprising at least one riser conduit adapted to transport hydrocarbon wellfluid from a spur on the seafloor to a point at or near the sea surface, and an artificial lift recovery mechanism to help transport said hydrocarbon wellfluid from the well to said point at or near the surface, wherein said artificial lift recovery mechanism operates on said hydrocarbon wellfluid at a point along the at least one riser conduit disposed in use to be substantially above the seafloor. 
     
     
         11 . A riser apparatus as claimed in  claim 10 , said apparatus comprising a riser tower having a top comprising one or more rigid conduits supported in a tower structure and adapted in use to extending from a connecting structure on the seabed to a point below the sea surface and wherein there are provided one or more flexible conduits extending from said tower structure to connect said tower structure to a surface structure, and wherein there is further provided a buoyancy device attached to the top of said tower structure, such that in use said buoyancy device is located above and exerts an uplift force on said riser tower. 
     
     
         12 . A riser apparatus as claimed in  claim 11 , wherein the artificial lift recovery mechanism comprises for at least one of said rigid conduits, at least one inlet for the injection of gas, in use, at a point substantially above said seabed. 
     
     
         13 . A riser apparatus as claimed in  claim 12  adapted such that in use said injection is made at a point where the hydrostatic pressure is below a cricondenbar of the hydrocarbon wellfluid. 
     
     
         14 . A riser apparatus as claimed in  claim 13  adapted such that in use said injection is made at a point where pressure in the riser conduit is below a bubble point pressure of the hydrocarbon wellfluid. 
     
     
         15 . A riser apparatus as claimed in  claim 12  comprising a dedicated pipe for carrying from the surface the gas for injection at the injection point. 
     
     
         16 . A riser apparatus as claimed in  claim 12  wherein at least one of said one or more rigid conduits comprises a pipe-in-pipe structure for at least a portion of its length, an annulus of said pipe-in-pipe structure being adapted for carrying from the surface the gas for injection at the injection point, a central pipe of said pipe-in-pipe structure comprising a main conduit for transporting said hydrocarbon wellfluid.