Sub-sea well intervention vessel and method

Abstract

A sub-sea well intervention vessel includes a dynamically positionable tanker and direct well intervention equipment mounted on the tanker deck. The intervention equipment includes drilling equipment for performing underbalanced drilling and hydrocarbon liquid separation. A separate production riser is provided so that simultaneous drilling and production can be performed via separate risers. The driller riser is selectively disconnectable from the well so that the tanker can be dynamically repositioned over the well. A turret mooring system is provided such that the production riser can remain in operation during repositioning about the turret. The hydrocarbon liquid separator is connected to a separator of the production plant.

1 . A sub-sea well intervention vessel comprising a dynamically positionable tanker and direct well intervention equipment mounted on the deck of the tanker, the direct well intervention equipment including drilling equipment for underbalanced rotating or non-rotating drilling for connection to a drilling riser and a hydrocarbon liquid separator coupled to storage tanks of the tanker such that separated hydrocarbon liquids can be stored in the tanker, wherein there is provided production plant and a coupling arrangement for coupling the plant to at least one production riser that is separate from the drilling riser, the production riser being for connection to a sub-sea manifold associated with the well, thereby allowing simultaneous underbalanced drilling and production via separate risers, the drilling equipment being selectively disconnectable from the well to allow production only via the production riser. 
   
   
       2 . A sub-sea well intervention vessel according to  claim 1 , wherein the production plant comprises a production hydrocarbon separator spaced from the hydrocarbon separator of the drilling equipment, the production hydrocarbon separator being configured to separate hydrocarbon fluids from matter received from the production rise. 
   
   
       3 . A sub-sea well intervention vessel according to  claim 2 , wherein the drilling equipment separator has an outlet for separated hydrocarbon liquids, the outlet being coupled to the production plant. 
   
   
       4 . A sub-sea well intervention vessel according to  claim 3 , wherein the drilling equipment separator outlet is coupled to the production separator. 
   
   
       5 . A sub-sea well intervention vessel according to  claim 2 , wherein the production separator is coupled to storage tanks of the tanker such that hydrocarbon fluids can be stored on the tanker. 
   
   
       6 . A sub-sea well intervention vessel according to any preceding  claim 1 , wherein there is provided a turret mooring system comprising a mooring turret and mooring lines, the vessel being able to rotate about the vertical axis of the mooring turret. 
   
   
       7 . A sub-sea well intervention vessel according to  claim 6 , wherein the mooring turret is mounted in the vessel for rotation and there are a plurality of mooring lines extending therefrom that, in use, are anchored to the sea bed. 
   
   
       8 . A sub-sea well intervention vessel according to  claim 6 , wherein the turret mooring system is spaced from the drilling equipment. 
   
   
       9 . A sub-sea well intervention vessel according to  claim 7 , wherein the vessel is dynamically positionable to hold it in the correct position over the well during drilling. 
   
   
       10 . A sub-sea well intervention vessel according to  claim 6 , wherein the tanker comprises a moonpool for location over the well, and wherein the drilling riser is disconnectable from the well such that the tanker can be dynamically positioned by rotation about a vertical axis of the mooring turret in order to position the moonpool over a desired wellhead. 
   
   
       11 . A sub-sea well intervention vessel according to  claim 10 , wherein the moonpool is spaced from the mooring turret such that it movable in an arc about the vertical axis. 
   
   
       12 . A sub-sea well intervention vessel according  claim 6 , wherein the production riser is connected to the mooring turret such that it can remain operable when the tanker is being dynamically positioned about the mooring turret. 
   
   
       13 . A sub-sea well intervention vessel according to  claim 1 , wherein the tanker is fitted with a plurality of thrusters by which it is dynamically positioned. 
   
   
       14 . A sub-sea well intervention vessel according to  claim 1 , wherein the drilling equipment is located adjacent to a moonpool of the vessel. 
   
   
       15 . A sub-sea well intervention vessel according to  claim 1 , wherein the drilling equipment further comprises a rotating control device (RCD) that, in use, is disposed at or near the surface of the sea. 
   
   
       16 . A sub-sea well intervention vessel according to  claim 15 , wherein a fluid return line is connectable between the drilling riser at a position below the RCD and the drilling separator on the tanker. 
   
   
       17 . A sub-sea well intervention vessel according to  claim 1 , wherein a rotary control device (RCD) is disposed, in use, sub-sea at or adjacent to a Blow Out Preventer (BOP) disposed over the well. 
   
   
       18 . A sub-sea well intervention vessel according to  claim 17 , wherein there is provided a return flow line that is external to the drilling riser and is designed for transporting drilling mud and/or fluid return. 
   
   
       19 . A sub-sea well intervention vessel according to  claim 18 , wherein the return flow line is connectable between a position under the RCD and the drilling separator. 
   
   
       20 . A method for conducting offshore underbalanced drilling, whereby a dynamically positionable tanker having direct well intervention equipment mounted on its deck including underbalanced drilling equipment is dynamically positioned over a well, the drilling equipment is coupled to a drilling riser from said well in order to intervene in said well, a separate production riser is coupled to said vessel from a sub-sea manifold associated with said well and underbalanced drilling is performed simultaneously with production via the separate production riser. 
   
   
       21 . A method according to  claim 20 , wherein the drilling riser is selectively disconnectable from the well to allow production only via the production riser. 
   
   
       22 . A method according to  claim 20 , further comprising the step of using a production plant on the vessel for separating hydrocarbon fluids from the matter delivered from the production riser. 
   
   
       23 . A method according to  claim 20 , wherein hydrocarbon liquids are separated from the mixture delivered from the underbalanced drilling operation and are transferred to the production plant associated with the production riser. 
   
   
       24 . A method according to  claim 23 , wherein the separated hydrocarbon liquids are transferred to a production separator of the production plant. 
   
   
       25 . A method according  claim 20 , further comprising the step of mooring the tanker via a mooring turret such that the tanker is able to rotate around a vertical axis of the turret. 
   
   
       26 . A method according to  claim 25 , further comprising the step of disconnecting the drilling riser from the well, dynamically positioning the vessel by rotation around the turret such that a moonpool of the vessel is positioned over a selected wellhead and then reconnecting the drilling riser. 
   
   
       27 . A method according to  claim 20 , further comprising the step of dynamically positioning the tanker to hold its geo-position stationary over the well whilst performing underbalanced drilling. 
   
   
       28 . A method according to  claim 20 , further comprising the step of disposing a rotating control device (RCD) at the top of the drilling riser at or near the surface of the sea. 
   
   
       29 . A method according to  claim 28 , wherein at least one fluid return conduit is connected between the drilling riser at a position below the RCD and the drilling separator on the tanker and matter from the underbalanced drilling is transported in said conduit from the riser to the separator. 
   
   
       30 . A method according to  claim 20 , further comprising the step of disposing a rotary control device (RCD) sub-sea at or adjacent to a Blow Out Preventer (BOP) disposed over the well. 
   
   
       31 . A method according to  claim 30 , further comprising the step of connecting a return flow conduit external to the drilling riser between the RCD and the drilling separator for transporting drilling mud and/or fluid return.