Offshore drilling unit and method of maintaining stability of the drilling unit in potential ice conditions

Abstract

An offshore drilling unit includes a main body configured to be bottom supported in shallow water. Also included is an anchoring assembly secured to a sea floor. Further included is a tensioning system operatively coupled to the main body and the anchoring assembly, wherein the tensioning system is configured to apply a downward force on the main body to resist ice loads imposed on the offshore drilling unit.

What is claimed is: 
     
         1 . An offshore drilling unit comprising:
 a main body;   a ballast finable with water to at least partially submerge the unit in a body of water with the unit resting on a sea floor;   an anchoring assembly having a pile secured to the sea floor; and   a tensioning system operatively coupled to the pile and to the main body at a location above the water, wherein the tensioning system is configured to apply a downward force on the main body to resist ice loads imposed on the offshore drilling unit.   
     
     
         2 . The offshore drilling unit of  claim 1 , wherein the tensioning system comprises at least one tension member and a winch configured to adjust tension of the at least one tension member. 
     
     
         3 . The offshore drilling unit of  claim 2 , wherein the at least one tension member comprises a wire cable. 
     
     
         4 . The offshore drilling unit of  claim 2 , wherein the anchoring assembly comprises a plurality of suction piles at least partially embedded in the sea floor. 
     
     
         5 . The offshore drilling unit of  claim 4 , wherein the at least one tension member is directly coupled to the plurality of suction piles. 
     
     
         6 . The offshore drilling unit of  claim 1 , wherein the main body comprises an offshore structure permanently installed at a drilling location. 
     
     
         7 . The offshore drilling unit of  claim 1 , wherein the main body comprises a mobile offshore drilling unit. 
     
     
         8 . The offshore drilling unit of  claim 1 , wherein more than 25 percent of weight for the unit is under the water and spaced from a sea surface toward the sea floor. 
     
     
         9 . A method of maintaining stability of an offshore drilling unit in potential ice conditions, the method comprising:
 positioning the offshore drilling unit in a desired location in a body of water;   filling ballast with water to at least partially submerge the unit until resting on a sea floor of the body of water;   securing an anchoring assembly having a pile to the sea floor; and   imposing a downward force on a main body of the offshore drilling unit at a location above the water with a tensioning system operatively coupled to the main body and the pile.   
     
     
         10 . The method of  claim 9 , further comprising adjusting the downward force with the tensioning system to provide a desired force configured to withstand loads imparted on the offshore drilling unit by contact between ice and the offshore drilling unit. 
     
     
         11 . The method of  claim 9 , wherein the main body is a platform and imposing the downward force on the main body increases the downward force on the platform. 
     
     
         12 . The method of  claim 9 , wherein imposing the downward force on the main body with the tensioning system comprises manipulating a winch configured to adjust a tension of a tension member. 
     
     
         13 . The method of  claim 9 , wherein securing the anchoring assembly to the sea floor comprises partially embedding a plurality of piles within the sea floor. 
     
     
         14 . The method of  claim 13 , wherein securing the anchoring assembly further comprises operatively coupling respective lower ends of a plurality of legs with a plurality of piled sockets operatively coupled to the plurality of piles, wherein the plurality of legs extend downwardly from the main body of the offshore drilling unit. 
     
     
         15 . The method of  claim 9 , wherein the method is performed in bodies of water where ice is present. 
     
     
         16 . A method of extracting hydrocarbons from a well in ice prone waters, the method comprising:
 positioning an offshore drilling unit having a platform in a desired location in a body of water;   filling ballast with water to at least partially submerge the unit until resting on a sea floor;   securing to the sea floor an anchoring assembly having a plurality of piles at least partially embedded in the sea floor;   imposing a downward force on the platform of the offshore drilling unit with a tension member of a tensioning system, the tension member operatively coupled to the platform and the piles; and   extracting hydrocarbons from the well.   
     
     
         17 . The method of  claim 16 , further comprising adjusting the downward force imposed on the platform by manipulating the tension member with a winch.