Riser apparatus assembly and method of installing same

Abstract

A riser apparatus and method according to which an anchor is installed on the sea bed and a riser conduit is pivotally mounted on the anchor. The riser conduit is provided with end connectors for connection to an upper riser section leading, respectively, to a production platform and a lower riser section leading to a wellhead or subsea storage or export facility. The riser conduit is preformed into a predetermined curved shape and is provided with stiffening webs to safeguard its rigidity, so that it substantially retains its predetermined shape when movements are transmitted through the riser conduit from the upper riser section to the lower riser section, or conversely.

1 . A riser apparatus comprising: 
 an anchor adapted to be installed on the sea bed:    a riser conduit connected to the anchor;    a first riser section located on the sea bed and connected to one end of the riser conduit; and    a second riser section connected to the other end of the riser conduit and extending to the surface of the sea;    the riser conduit being preformed to permit the connections to the first and second riser sections and being substantially rigid such that it substantially retains its preformed shape when changes of the relative positions of the first and second riser sections occurs.    
   
   
       2 . The riser apparatus according to  claim 1 , wherein the riser conduit comprises a curved length of conduit.  
   
   
       3 . The riser apparatus according to  claim 1  or  2 , wherein the riser conduit is provided with at least one stiffening web to contribute to the rigidity of the riser conduit.  
   
   
       4 . The riser apparatus according to  claim 3 , wherein a pair of elongate stiffening webs is secured on the outside surface of the length of conduit, each such web extending in the direction of the flowpath axis of the length of conduit with one web located generally above the flowpath axis and the other web located generally below the flowpath axis.  
   
   
       5 . The riser apparatus according to  claim 1 , wherein the riser conduit is pivotally mounted to the anchor for pivoting about a generally horizontal axis.  
   
   
       6 . The riser apparatus according to  claim 6 , further comprising interlocking shackles for mounting the riser conduit to the anchor.  
   
   
       7 . The riser apparatus according to  claim 1 , wherein the anchor comprises a suction anchor.  
   
   
       8 . The riser apparatus according to  claim 1 , wherein the anchor is designed to be driven into the sea bed by pile driving.  
   
   
       9 . The riser apparatus according to  claim 7 , wherein the suction anchor comprises a rigid top structure with a downwardly depending cylindrical skirt adapted to be driven into the sea bed.  
   
   
       10 . The riser apparatus according to  claim 1 , wherein the riser conduit is provided at its two ends with end flanges for bolting to counterpart flanges on the ends of the first and second riser sections.  
   
   
       11 . The riser apparatus according to  claim 1 , further comprising a pulley wheel mounted on the anchor so that a pulldown line may be passed from the sea surface around the pulley and be attached to the second riser section for pulling the second riser section down so that the riser conduit can be connected to the anchor.  
   
   
       12 . The riser apparatus according to  claim 1  wherein hydrocarbon production fluid may be directed from a sea bed location to the sea surface successively through the first riser section, the riser conduit and the second riser section.  
   
   
       13 . A riser assembly according to  claim 1  wherein at least the first riser section is a flexible conduit and further comprises bend restrictors provided on the first riser section.  
   
   
       14 . A method of installing a riser assembly relative to a sea bed, the method comprising: 
 pre-installing an anchor on the sea bed;    connecting first and second riser sections to the riser conduit;    lowering successively the first riser section and the second riser section so as to place the first riser section on the sea bed and position the riser conduit adjacent the pre-installed anchor; and    connecting the riser conduit to the pre-installed anchor.