Self-supported riser system and method of installing same

Abstract

A self-supported riser system ( 100 ) for an Anticipated Production System (ASP) Test or a Long Duration Production (LDP) Test in a subsea petroleum production system, utilizing an ANM coupled to a wellhead and Floating Production Unit (FPU) is disclosed. The system includes a wellhead at the seabed, connected to an ANM ( 20 ) provided with a preventor (BOP of workover) ( 30 ). The preventor ( 30 ) is connected to a production riser ( 50 ) through a connection tool ( 40 ). The riser ( 50 ), mounted internally within a buoy assembly ( 60 ), is maintained under traction with the aid of a buoy assembly. The upper end of the riser ( 50 ) is provided with a Subsea Intervention Terminal ( 700 ), the Terminal being interlinked to the FPU by a flexible jumper ( 90 ) to carry the oil produced to the FPU. Two methods for installing the self-supported riser system ( 100 ) are also disclosed.

1 . A self-supported riser system for an Anticipated System Production (ASP) Test or a Long Duration Test (LDT) in subsea petroleum production utilizing a WCT coupled to a wellhead and a Floating Production Unit, said system comprising: 
 a) a riser ( 50 ) formed of sections ( 810 ) linked one to another, with the lower end of the riser ( 50 ) being coupled to an ANM ( 20 ) or a manifold and the upper end being coupled to a buoy assembly ( 60 ) with control devices for variable buoyancy, said assembly of buoys ( 60 ) serving to traction a column of said riser ( 50 ), thereby maintaining said riser ( 50 ) erect and in an approximately vertical position;    b) a Subsea Intervention Terminal ( 700 ) for interconnecting a terminal ( 730 ) at the top of riser ( 50 ) and an Intervention rig ( 95 );    c) a flexible jumper ( 90 ) disposed between the top of the riser ( 50 ) and Floating Production Unit (FPU), for production flow;    d) an umbilical ( 80 ) for controlling, monitoring and transmitting electrical and hydraulic energy; said umbilical linking the FPU to the WCT ( 20 ) and supported by the riser ( 50 ) or, alternately in a free catenary mode, wherein; 
 (i) the riser ( 50 ) is installed internally to the buoy assembly ( 60 );  
 (ii) the coupling of the riser ( 50 ) to the Subsea Intervention Unit ( 700 ) with the aid of terminal ( 730 ) permits an access to a well in a vertical direction to perform maintenance operations; and  
 (iii) the riser ( 50 ) is used to lower and install the WCT ( 20 ), wherein a savings in rig time and number of operations is obtained.  
   
   
   
       2 . The System according to the  claim 1 , wherein alternately the buoy assembly ( 60 ) is omitted, and the riser is utilized as a completion riser.  
   
   
       3 . The System in accordance with  claim 1 , wherein the sections ( 810 ) may be connected by threads or mechanical connector.  
   
   
       4 . The System according to the  claim 1 , wherein the unit ( 700 ) is formed with an upper funnel guide ( 710 ), being provided with an internal mandrel ( 711 ) for coupling an intervention tool and a passage ( 715 ), with an intervention valve ( 712 ) being located in a body of the unit ( 700 ) above the Y-shaped divider for a passage of production fluid flow and a production valve ( 713 ) being located in a production flow line and followed by a curved pipe section ( 714 ) in a gooseneck shape to promote production flow, said pipe section ( 714 ) being connected to a flexible jumper ( 90 ) through a connection device ( 720 ).  
   
   
       5 . The System according to the  claim 4 , wherein the mandrel ( 711 ) is linked to a connector ( 717 ), wherein said connector ( 717 ) is provided with a funnel guide ( 718 ), said connector ( 717 ) interconnecting the unit ( 700 ) to the terminal ( 730 ) by the upper-end of the riser ( 50 ), being aided by the mandrel ( 732 ).  
   
   
       6 . The System according to the  claim 5 , wherein a central part of the connector ( 717 ) is provided with a metal sealing ring ( 719 ) adapted to a recess ( 731 ) of complementary shape located in the mandrel ( 732 ) of the terminal ( 730 ), said mandrel ( 732 ) being interconnected to a isolation valve ( 734 ) of the riser ( 50 ) while a connection device ( 735 ) interconnects said valve ( 734 ) to the upper end of the riser ( 50 ).  
   
   
       7 . The System according to the  claim 6 , wherein the valve ( 734 ) is destined to isolate the content of the riser ( 50 ), thus permitting removal of the unit ( 700 ) for maintenance.  
   
   
       8 . The System according to the  claim 1 , wherein an umbilical ( 80 ) is supported by the riser ( 50 ).  
   
   
       9 . The System according to the  claim 1 , wherein an umbilical ( 80 ) is coupled in a free catenary mode.  
   
   
       10 . The System according to the  claim 1 , wherein said system is configured to facilitate surge production.  
   
   
       11 . The System according to the  claim 1 , wherein alternatively production is effected with the aid of a subsea pumping module coupled to the WCT ( 20 ).  
   
   
       12 . The System according to the  claim 1 , wherein the Floating Production Unit (FPU) is coupled to the said riser system rendering the use of a tower unnecessary.  
   
   
       13 . The System according to the  claim 1 , wherein the FPU utilized is of the type FPSO (Floating Production Storage and Offloading).  
   
   
       14 . The System according to the  claim 13 , wherein the FPSO is anchored.  
   
   
       15 . The System according to the  claim 13 , wherein alternatively the FPSO is of the type DP (Dynamic Positioning).  
   
   
       16 . The System according to the  claim 15 , wherein the FPSO of the type DP requires a presence of an unwinding device (swivel), in order to avoid a twisting of the arrangement of the flexible jumper ( 90 )/riser ( 50 ) due to the possibility of the FPSO executing rotations around its own vertical axis.  
   
   
       17 . The System according to the  claim 1 , wherein the system may be recovered at a low cost after the Anticipated System Production (ASP) Test or a Long Duration Test (LDT).  
   
   
       18 . The System according to the  claim 1 , wherein during a workover operation (intervention), a valve ( 713 ) is closed, and any equipment is lowered or removed via riser ( 50 ) with a valve ( 712 ) in an open position.  
   
   
       19 . An Installation method for the self supported riser system ( 100 ) of  claim 1 , said method comprising the following steps: 
 a) transporting a buoy assembly ( 60 ) fastened to a transportation raft ( 802 ) to a location at which said riser system ( 100 ) is to be installed;    b) proximate a semi-submersible platform ( 804 ) for lowering the riser ( 50 ), connecting said buoy assembly ( 60 ), with the assistance of a cable ( 805 ) to a semi-submersible platform ( 804 ) and connecting said buoy assembly ( 60 ) with the assistance of a cable ( 806 ) to a tug ( 803 ),    c) effecting a partial controlled submersion of one of the ends of the transportation raft ( 802 ) and displacing the buoy assembly ( 60 ) over the raft deck while the tug ( 803 ) tractions the cable to ease the process of displacing the buoy assembly ( 60 );    d) separating and removing the transportation raft ( 802 ) from said location, after the free floating buoy assembly ( 60 ) is successfully connected to the semi-submersible installation platform ( 804 ) by the means of said cable ( 805 ) and to the tug boat ( 803 ) by said cable ( 806 );    e) keel hauling (cargo transfer) said buoy assembly ( 60 ) onto the semi-submersible platform ( 804 ) by appropriately maneuvering the cables ( 805 ) and ( 806 ) and of an auxiliary cable ( 807 ) linked to the tug ( 803 ), which controls an anchor weight ( 808 ) connected to the lower end of the buoy assembly ( 60 ) such that at the completion of the process the buoy assembly ( 60 ) is supported by the platform tower ( 804 ) through the cable ( 805 );    f) bringing the upper end of the buoy assembly ( 60 ) to the moon pool region of the semi-submersible platform ( 804 ) and transferring the weight of the buoy assembly ( 60 ) to steel cables ( 809 ) which form part of the tension system of the platform drilling assembly ( 804 );    g) after the disconnection of the cable ( 805 ), connecting and lowering the sections ( 810 ), whose interconnection forms the riser ( 50 ) assembly, inside the buoy assembly ( 60 ) until the required riser ( 50 ) length is reached;    h) lowering the buoy assembly ( 60 ) to an operational depth by means of a service pipe ( 811 ) of the semi-submersible platform ( 804 ) and making a connection ( 812 ) of the lower end of the riser ( 50 ) to the wellhead ( 10 ) on the seabed;    i) injecting air into the buoy assembly ( 60 ), expelling the water from within said assembly, aided by a remote controlled subsea vehicle ROV ( 813 ) in order to recover a buoyancy of the buoy assembly ( 60 );    j) disconnecting the tubing ( 811 ), utilized for the lowering of the buoy system ( 60 ) and removing the semi-submersible platform ( 804 ) from the location;    k) with the aid of a flexible line launch vessel ( 831 ) installing the production flexible jumper ( 90 ) and the subsea Intervention unit ( 700 ), which is to be coupled to the top of the buoy assembly ( 60 ), with said unit ( 700 ) being supported by a cable ( 833 ) of the launch vessel ( 831 ) during a descent thereof, and further connected to the flexible production jumper ( 90 ) to form an interconnection with the Floating Production Unit (FPU);    l) driving the flexible line launch vessel ( 831 ) to the Floating Production Unit (FPU) while unwinding the stowing spool (B) of the flexible production jumper ( 90 );    m) Transferring the end of the production flexible jumper ( 90 ) to the Floating Production Unit (FPU) utilizing auxiliary cables ( 841 ) and ( 842 ) for the interconnection operation (pull-in);    n) testing the self-supported riser system; and    o) operating the self-supported riser system.    
   
   
       20 . The method in accordance with  claim 19 , wherein the test of step (n) is an Anticipated System Production (ASP) Test.  
   
   
       21 . The method in accordance with  claim 19 , wherein the test of step (n) is a Long Duration Test (LDT).  
   
   
       22 . The method in accordance with  claim 19 , wherein alternately the buoy assembly ( 60 ) is located on the transportation raft ( 802 ) using the alternate method of sliding the buoy system over the dock surface.  
   
   
       23 . An installation method of the said self supported riser system ( 100 ) in accordance with  claim 1 , wherein said method alternatively comprises the following steps: 
 a) mounting the WCT ( 20 ), the BOP preventor ( 30 ) and the connection tool ( 40 ) on a temporary support unit ( 901 ) located in the moon pool region ( 902 ) of the installation platform ( 804 );    b) connecting the production riser ( 50 ) constituted of riser sections ( 810 ), to a connection tool ( 40 );    c) connecting and lowering the sections ( 810 ) until the required length for the installation of the first buoy of the buoy assembly ( 60 ) is attained; maneuvering said buoy in the moon pool region ( 902 ) of the installation platform ( 804 ) so as to install the riser section at the center of the buoy aided by the opening ( 903 ), and connecting the buoy ( 60 ) to the riser section ( 810 );    d) connecting new riser section ( 810 ) and repeating the same operation for the remaining buoys;    e) lowering the buoy assembly ( 60 ) to operational depth through a service pipe ( 811 ) of the semi-submersible platform ( 804 ) and then effecting a connection of the lower end of the riser ( 50 ) to the wellhead ( 10 ) at the seabed;    f) injecting air into the buoy assembly ( 60 ) expelling the water within said buoy assembly, aided by a remote controlled subsea vehicle ROV ( 813 );    g) disconnecting the pipe ( 811 ) utilized during the lowering, from the buoy assembly ( 60 ), and removing the semi-submersible platform ( 804 ) from the location;    h) with the aid of a flexible line launch vessel ( 831 ), installing the production flexible jumper ( 90 ) and the subsea intervention unit ( 700 ), which will be coupled to the buoy assembly ( 60 ), said unit ( 700 ) being supported by a cable ( 833 ) of the launch vessel ( 831 ) during a lowering thereof, and said unit ( 700 ) being connected to the production flexible jumper ( 90 ) to form an interconnection to the Floating Production Unit (FPU);    i) driving the flexible line launch vessel ( 831 ) to the Floating Production Unit (FPU) while unwinding the storage spool (B) of the flexible production jumper ( 90 ) from the vessel;    j) transferring the end of the production flexible jumper ( 90 ) to the Floating Production Unit (FPU) utilizing auxiliary cables ( 841 ) and ( 842 ) for the interconnection operation (pull-in);    k) testing the self-supported riser system; and    l) operating the self-supported riser system.    
   
   
       24 . A method in accordance with  claim 23 , wherein the test of step (k) is an Anticipated Production System (APS) Test.  
   
   
       25 . A method in accordance with  claim 23 , wherein the test of step (k) is a Long Duration Production (LDP) Test.