Riser termination

Abstract

A top termination ( 70 , FIG. 2 ) lies at the top of a riser ( 22 A) that extends vertically from the sea floor into a moon pool of a floating unit, or vessel ( 12 ) that is drilling or servicing a well, wherein the riser transfers fluids such as used drilling fluids up to the vessel. The vessel can move vertically in heave as well as tilt without requiring the top termination to follow such motions. The top termination carries fluid to the vessel through jumper hoses ( 74 ) that bend to take up vessel vertical motion and tilt. The weight of the top termination is carried by the vessel through flexible lines ( 44 A) that extend from near the top termination up to the vessel.

1 . An offshore development system that includes a floating unit that floats at the sea surface, and a riser string that extends from the sea floor to the floating unit, said riser string having an upper portion with a primarily vertical axis, comprising:
 a top termination ( 70 ) lying at the height of the floating unit, said top termination lying at an upper end of the riser string;   at least one fluid collector tank ( 72 ) mounted on said floating unit and spaced from said axis;   at least one jumper hose ( 74 ) that has a first end connected to said riser at said top termination and a second end ( 86 ) connected to said fluid collector tank, said jumper hose having a loop ( 90 ) coupled to said first and second ends of said hose with said loop being flexible so each of said ends is moveable vertically relatively to the other end by bending of the loop;   termination biasing means ( 44 A) for applying an upward force to said top termination to support said top termination at the height of said floating unit while allowing said floating unit to move vertically relative to said top termination.   
     
     
         2 . A system described in  claim 1  wherein:
 said means for applying an upward force includes at least one flexible tension line ( 44 A) that extends at least partially upward from said top termination to said floating unit, said flexible tension line maintaining tension on said top termination when the floating unit undergoes motions; 
 said jumper hose is flexible along said loop, and said jumper hose bends when the floating unit undergoes motions; 
 said top termination is free of connection to said floating unit except through said at least one flexible tension line and said at least one jumper hose, to allow said floating unit to undergo motions without comparable movement of said top termination. 
 
     
     
         3 . A system described in  claim 1  wherein:
 said at least one jumper hose includes a first rigid pipe section ( 76 ) with an inner end connected to an upper end of said riser, a second rigid pipe section ( 84 ) connected to said at least one collector tank ( 72 ), and a flexible hose section ( 90 ) that connects to said first and second rigid pipe sections; 
 said flexible hose section having opposite ends that each extends downward from a corresponding one of said rigid pipe sections and said flexible hose section having a middle portion that extends in primarily a half circle. 
 
     
     
         4 . A system described in  claim 1 , wherein:
 said top termination includes a funnel ( 110 ) with a wide top end and with a narrower lower end that lies in line with said riser string.   
     
     
         5 . A method for coupling the top of a riser through which a string extends, so fluid passes up through a riser annular area around the string and flows to a collecting tank ( 72 ) on a floating unit, wherein the top of the riser is isolated from motion of the vessel, comprising:
 coupling a top termination ( 70 ) that lies at the top of said riser, to said collecting tank, through at least one flexible hose ( 90 ), and supporting said top termination on said floating unit through flexible tension lines ( 44 A) to allow the floating unit to tilt relative to said top termination.   
     
     
         6 . The method described in  claim 5  wherein:
 said step of coupling through at least one flexible hose includes extending said flexible hose in a loop ( 90 ) with opposite upper ends ( 86 ) and connecting said upper ends one to said top termination and one to said collecting tank.