Systems and methods for tethering a subsea structure

Abstract

A tethering system includes an adapter configured to couple to an upper end of a subsea anchor, a tensioning system, and a flexible tension member having one end coupled to the tensioning system and the other end coupled to the adapter. The tensioning system is operable to pay in and pay out the flexible tension member relative to the tensioning system. The tensioning system can be mounted to the BOP frame, and tension can be applied via a locally or remotely placed winch assembly. Tension can also be applied by gripping the flexible tension member and pulling on the flexible tension member with a hydraulic cylinder.

1 . A system for tethering a subsea blowout preventer (BOP), the system comprising:
 an anchor disposed about the subsea BOP and secured to the sea floor;   a flexible tension member, wherein the flexible tension member has a first end including a releasable connector engaged to the anchor, wherein the flexible tension member extends horizontally and vertically from the first end to a second end to impart a lateral preload and a vertical preload to the subsea BOP; and   a gripping system mounted on the subsea BOP, wherein the gripping system is configured to selectively engage the flexible tension member to prevent pay out of the flexible tension member.   
     
     
         2 . The system of  claim 1  further comprising:
 a winch reel coupled to the second end of the flexible tension member; and 
 an interface configured for coupling to a remotely operated vehicle (ROV), wherein rotation of the interface causes rotation of the winch reel and paying in or out the flexible tension member. 
 
     
     
         3 . The system of  claim 2  wherein the winch reel is located remotely from the subsea BOP. 
     
     
         4 . The system of  claim 2  wherein the winch reel is mounted to a releasable base connected to a connection point on the subsea BOP. 
     
     
         5 . The system of  claim 2  wherein the gripping system includes a slip. 
     
     
         6 . The system of  claim 2  wherein the gripping system includes a locking ring or a brake mechanism. 
     
     
         7 . The system of  claim 1  further comprising:
 a spool coupled to the second end of the flexible tension member; and 
 a hydraulic cylinder coupled to the gripping system, wherein actuation of the hydraulic cylinder causes paying in or out the flexible tension member. 
 
     
     
         8 . The system of  claim 7  wherein the spool is located remotely from the subsea BOP. 
     
     
         9 . The system of  claim 7  wherein the spool is mounted to a releasable base connected to a connection point on the subsea BOP. 
     
     
         10 . The system of  claim 7  wherein the gripping system includes a slip. 
     
     
         11 . The system of  claim 1  further comprising a winch reel coupled to the second end of the flexible tension member, wherein the winch reel is located on a vessel. 
     
     
         12 . A method for tethering a subsea blowout preventer (BOP) coupled to a subsea wellhead, the subsea BOP including a gripping system connected to a frame of the subsea BOP, the method comprising:
 securing an anchor to the sea floor about the subsea BOP;   extending a first end of a flexible tension member horizontally and vertically;   applying tension to the flexible tension member to impart a lateral preload and a vertical preload to the subsea BOP; and   engaging the flexible tension member with the gripping system to maintain tension in the flexible tension member.   
     
     
         13 . The method of  claim 12 , wherein a second end of the flexible tension member is coupled to a winch reel, and wherein applying tension to the flexible tension member comprises:
 coupling a remotely operated vehicle (ROV) to an interface, and   rotating the winch reel via the interface to cause paying in or out the flexible tension member.   
     
     
         14 . The method of  claim 13  wherein the winch reel is located remotely from the subsea BOP. 
     
     
         15 . The method of  claim 13  wherein the winch reel is mounted to a releasable base connected to a connection point on the frame of the subsea BOP. 
     
     
         16 . The method of  claim 13  comprising engaging the flexible tension member with a slip. 
     
     
         17 . The method of  claim 13  comprising preventing pay out of the flexible tension member using a locking ring or a brake mechanism. 
     
     
         18 . The method of  claim 12  wherein applying tension to the flexible tension member comprises actuating a hydraulic cylinder coupled to the gripping system to cause paying in or out the flexible tension member. 
     
     
         19 . The method of  claim 12 , wherein a second end of the flexible tension member is coupled to a winch reel located on a vessel, and wherein applying tension to the flexible tension member comprises rotating the winch reel to cause paying in or out the flexible tension member.