Jack-up drilling unit with tension legs

Abstract

The invention relates generally to a method for supporting non-buoyant offshore drilling units that are anchored to the sea floor and are subject to heavy lateral loads. Specifically, tension tendons are attached to piled foundations to prevent jack-ups from being overturned by the loads. Tension can also be applied to the tendons to provide additional hold down forces to the offshore units.

What is claimed is: 
     
         1 . A method for reinforcing an offshore oil and gas unit that is anchored to the sea floor comprising:
 a) providing an offshore oil and gas unit (OOGU) that is that is anchored to the sea floor with at least one leg;   b) extending a tendon from the OOGU to a foundation on the sea floor; and   c) tensioning said tendon sufficiently to reinforce the OOGU.   
     
     
         2 . The method of  claim 1 , wherein said offshore drilling unit is a jack-up, an ice-worthy jack-up, a conical piled monopod, or a gravity based structure. 
     
     
         3 . A jack-up rig for offshore drilling for hydrocarbons comprising:
 a) a flotation hull having a relatively flat deck at the upper surface thereof;   b) at least three legs that are positioned within a perimeter of the flotation hull wherein the legs are arranged to be i) lifted up off the seafloor so that the jack-up may be towed through shallow water and ii) extend to the sea floor and extend further to lift the hull partially or fully out of the water;   c) a jack-up device associated with each leg to raise and lower said leg; and   d) a plurality of tendons having a top end attached to the jack-up unit and a bottom end configured to be attached to a sea floor foundation.   
     
     
         4 . A jack-up rig as in  claim 3 ), wherein said top end is attached to said hull. 
     
     
         5 . A jack-up rig as in  claim 3 ), wherein said top end is attached to one of said legs. 
     
     
         6 . A jack-up rig as in  claim 3 ), wherein said foundation is a piled foundation. 
     
     
         7 . A jack-up rig as in  claim 4 ), wherein more than one tendon is attached to said piled foundation. 
     
     
         8 . A jack-up rig as in  claim 3 ), wherein said tendons are tubular tendons. 
     
     
         9 . A jack-up rig as in  claim 3 ), wherein said tendons are cable tendons. 
     
     
         10 . A jack-up rig as in  claim 3 ), wherein said tendons comprise a self tensioning tendon. 
     
     
         11 . An improved jack-up rig, jack-up rigs including a buoyant hull, legs traversing said hull, and a jack for each leg such that the buoyant hull can be raised out of the water for use, the improvement comprising tension legs having a top end attached to said jack-up rig and a bottom end attachable to a foundation on the sea floor. 
     
     
         12 . An improved-up rig that includes a buoyant hull, legs traversing each hull and a jack-up device for each leg such that the buoyant hull can be raised out of the water for use, the improvement comprising tension legs having a top end attached to said jack up rig and a bottom end attached to a foundation on the sea floor, said tension legs further having a self-tensioning unit for adjusting the length and thus tension of each tension leg.