Anchor means and method of installing the same

Claim 2

In an anchor means for an offshore flotable structure and including a hole drilled in a subsea formation; the provision of: a drilling casing extending into said hole and above said hole a selected distance; a cable connected at its ends to corresponding ends of said casing; means for prestressing said casing and said cable for combining their strength in tension and for action as a unit under maximum tension forces whereby said casing and said cable will exceed their elastic limits under approximately maximum tension forces; and cement slurry means in said formation hole and in the portions of said casing in said hole for anchoring said casing and cable in said hole; said cement means also filling portions of said casing above said hole to the upper end of said casing, said cement means bonding said cable and said casing together for its entire length whereby said unitary action under maximum tension forces is enhanced and a structurally stiffened anchor portion is provided above said hole.

Claim 3

In a method for anchoring tension mooring lines to offshore platforms and the like, comprising the steps of: drilling a hole in a subsea formation to a selected depth including use of a drill casing; raising the drill casing to a selected height; lowering a cable through said casing; securing the lower cable end at the casing bottom end portion against upward movement of the cable; securing a rotatable means to the upper cable end in seating engagement with an upper casing yoke means connected to said casing; placing said casing and cable under stress by adjustably turning said rotatable means; lowering the prestressed drill casing and cable to the bottom of the hole in said formation by a landing string means; introducing a cement slurry in plastic flowable state through said landing string means between said cable and drill casing and between said casing and walls of the formation hole until the hole is filled; and whereby a prestressed cable and casing embedded in concrete slurry provides a prestressed anchor means cemented to walls of the formation hole.

Claim 4

In a method for anchoring tension mooring lines to offshore platforms and the like, comprising the steps of: drilling a hole in a subsea formation to a selected depth including use of a drill casing; raising the drill casing to a selected height; lowering a cable through said casing; securing the lower cable end at the casing bottom end portion against upward movement of the cable; securing a rotatable means to the upper cable end in seating engagement with an upper casing yoke means connected to said casing; placing said casing and cable under stress by adjustably turning said rotatable means; lowering the prestressed drill casing and cable to the bottom of the hole in said formation by a landing string means; introducing a cement slurry in plastic flowable state through said landing string means between said cable and drill casing and between said casing and walls of the formation hole until the hole is filled; and whereby a prestressed cable and casing embedded in concrete slurry provides a prestressed anchor means cemented to walls of the formation hole.

Claim 5

In a method as stated in claim 2 including the steps of: connecting a subsurface buoy to said casing yoke means; and connecting a mooring line and surface buoy to said subsurface buoy.

Claim 6

In a method for anchoring tension mooring lines to offshore platforms and the like, comprising the steps of: drilling a hole in a subsea formation to a selected depth including the use of a drill casing; raising said drill casing until the bottom end thereof is a selected height above the bottom of the hole; securing the lower end of the cable at the casing bottom end portion against the upper movement of the cable; connecting the upper end of the cable to the upper end of the casing and to a tensioning means; placing said casing and cable under selected stress by said tension means whereby said casing and cable act as a unit under conditions of maximum forces applied thereto; lowering the prestressed drill casing and cable to the bottom of the hole in said formation by a landing string means; introducing a cement slurry in plastic flowable state through said landing string means between said cable and drill casing and between said casing and walls of the formation hole until the hole is filled and the casing is filled; and whereby a prestressed cable and casing embedded in concrete slurry provides a prestressed stiff solid anchor member cemented to walls of the formation hole.

Claim 7

In a method for anchoring tension mooring lines to offshore platforms and the like, comprising the steps of: drilling a hole in a subsea formation to a selected depth including the use of a drill casing; raising said drill casing until the bottom end thereof is a selected height above the bottom of the hole; securing the lower end of the cable at the casing bottom end portion against the upper movement of the cable; connecting the upper end of the cable to the upper end of the casing and to a tensioning means; placing said casing and cable under selected stress by said tension means whereby said casing and cable act as a unit under conditions of maximum forces applied thereto; lowering the prestressed drill casing and cable to the bottom of the hole in said formation by a landing string means; introducing a cement slurry in plastic flowable state through said landing string means between said cable and drill casing and between said casing and walls of the formation hole until the hole is filled and the casing is filled; and whereby a prestressed cable and casing embedded in concrete slurry provides a prestressed stiff solid anchor member cemented to walls of the formation hole.

Claim 8

In the method as stated in claim 20 including the step of: buoyantly supporting the weight of that portion of the anchor member which extends above the surface of the subsea formation.