Tension leg offshore marine apparatus

Claim 2

In a marine structure of high stability and relatively narrow beam adapted for use as a mobile platform for well operations, the combination of: a platform means positionable a selected height above an ocean surface; means supporting said platform means and including submersible buoyant means comprising at least a pair of longitudinally extending horizontally disposed spaced parallel buoyant members, said support means at each end thereof including mooring line restraint means located in the space between said buoyant members; an anchor adapted to be located on the ocean floor beneath each of said restraint means; and a single tensioned mooring means extending vertically between said anchor and said restraint means at each end of said support means; said restraint means providing a location for the center of roll of said platform means at about the depth of said horizontal buoyant members.

Claim 3

In a marine structure as stated in claim 1 wherein said means supporting the platform means includes vertical buoyant column means extending from said longitudinal buoyant members to said platform means and each column means having a selected water plane relative to the buoyancy of the horizontal buoyant members.

Claim 4

In a marine structure as stated in claim 1 wherein said restraint means for said mooring means is located below the center of buoyancy of the marine structure.

Claim 5

In a marine structure as stated in claim 2 wherein said vertical buoyant column means are selectively spaced along the length of said longitudinal horizontal buoyant members a distance related to expected length of ocean waves under a selected condition and said buoyant column means and said horizontal longitudinal buoyant members are so responsive to said waves whereby vertical force components resulting from wave action are virtually cancelled.

Claim 6

In a marine structure the combination of: a platform means positionable in spaced relation to an ocean surface; a pair of longitudinally extending parallel buoyant members disposed Beneath longitudinal side portions of said platform means; transverse submersible buoyant members interconnecting ends of said longitudinal buoyant members; vertical buoyant columns interconnecting said longitudinal buoyant members and said platform means in selected longitudinal spaced relation; said platform means, submersible buoyant means, and vertical column buoyant means having a center of gravity; an anchor adapted to be positioned on an ocean floor beneath each of said submersible transverse buoyant members and in a longitudinal vertical plane normally passing through said center of gravity; a pair of mooring means for said marine structure; restraint means for each mooring means at said transverse buoyant member and at said vertical plane; said mooring means being under selected tension to provide an apparent center of gravity lower than the actual center of gravity; said restraint means providing a center of roll for said marine structure at the approximate depth of said submersible horizontal buoyant members.

Claim 7

In a marine structure the combination of: a platform means positionable in spaced relation to an ocean surface; a pair of longitudinally extending parallel buoyant members disposed Beneath longitudinal side portions of said platform means; transverse submersible buoyant members interconnecting ends of said longitudinal buoyant members; vertical buoyant columns interconnecting said longitudinal buoyant members and said platform means in selected longitudinal spaced relation; said platform means, submersible buoyant means, and vertical column buoyant means having a center of gravity; an anchor adapted to be positioned on an ocean floor beneath each of said submersible transverse buoyant members and in a longitudinal vertical plane normally passing through said center of gravity; a pair of mooring means for said marine structure; restraint means for each mooring means at said transverse buoyant member and at said vertical plane; said mooring means being under selected tension to provide an apparent center of gravity lower than the actual center of gravity; said restraint means providing a center of roll for said marine structure at the approximate depth of said submersible horizontal buoyant members.

Claim 8

In a marine structure of steady stable characteristics, the combination of: a platform means positionable a selected height above an ocean surface; a plurality of anchor means on the ocean floor; a plurality of tensioned mooring line means, each mooring line means being generally vertical and connected at one end to said anchor means and joined at its other end to said structure; means supporting said platform means and including submersible buoyant means, said submersible buoyant means being provided with a positive buoyancy exceeding the weight of the platform and its load to maintain tension in all of said mooring line means above a preselected tension force, said submersible buoyant means comprising: at least two elongated horizontal buoyant cylindrical members extending beneath said platform and a plurality of upstanding vertical buoyant cylindrical columns of uniform diameter throughout their length and providing a water plane at said ocean surface to maintain stability of the structure, said vertical buoyant columns extending between and connecting said horizontal buoyant members to said platform means, said horizontal and vertical members being correlated in size and volume, the total displacement of the horizontal buoyant members with respect to the aggregate displacement of the horizontal and vertical buoyant members being in the ratio of 0.30 to 0.60 whereby action of waves having wave periods from about 8 to 20 seconds in respect of vertical force components is minimal to provide a virtually stable and steady platform means.

Claim 9

In a marine structure of steady stable characteristics, the combination of: a platform means positionable a selected height above an ocean surface; a plurality of anchor means on the ocean floor; a plurality of tensioned mooring line means, each mooring line means being generally vertical and connected at one end to said anchor means and joined at its other end to said structure; means supporting said platform means and including submersible buoyant means, said submersible buoyant means being provided with a positive buoyancy exceeding the weight of the platform and its load to maintain tension in all of said mooring line means above a preselected tension force, said submersible buoyant means comprising: at least two elongated horizontal buoyant cylindrical members extending beneath said platform and a plurality of upstanding vertical buoyant cylindrical columns of uniform diameter throughout their length and providing a water plane at said ocean surface to maintain stability of the structure, said vertical buoyant columns extending between and connecting said horizontal buoyant members to said platform means, said horizontal and vertical members being correlated in size and volume, the total displacement of the horizontal buoyant members with respect to the aggregate displacement of the horizontal and vertical buoyant members being in the ratio of 0.30 to 0.60 whereby action of waves having wave periods from about 8 to 20 seconds in respect of vertical force components is minimal to provide a virtually stable and steady platform means.

Claim 10

In a structure as stated in claim 6 wherein said plurality of mooring lines consists of two mooring lines, each of said mooring lines being at an opposite end of the platform means.

Claim 11

In a structure as stated in claim 6 wherein said plurality of mooring lines consists of three lines, one of said lines being at one end of said platform means, and two of said lines being at opposite sides of the other end of said platform means.

Claim 12

In a structure as stated in claim 6 wherein said horizontal buoyant members include transversely extending parallel buoyant members.

Claim 13

In a structure as stated in claim 7 including restraining means cooperably engaged with each vertical mooring line adjacent said horizontal buoyant members for lowering and locating the center of roll of said structure at the depth of said horizontal buoyant members.

Claim 14

In a structure as stated in claim 6 including means for resisting roll of said platform means; said roll resisting means including lateral restraint means cooperable with said tension mooring line means for displacing downwardly the normal center of roll of said marine structure to a location at approximately said horizontal buoyant means.

Claim 15

In a structure as stated in claim 11 wherein said lateral restraint means includes boom members extending sidewardly From one end of said platform and connected to said mooring tension lines.

Claim 16

In a marine structure of stable steady characteristics having a platform means adapted to be positioned over a plurality of anchor means on an ocean floor, the combination of: tension leg means substantially vertically disposed and connected to said platform means; means supporting said platform means above the ocean surface and including submersible elongated horizontal buoyant members joined together and of a length and width having a selected displacement volume and adapted to be submerged to a depth within the influence of wave action; vertically disposed buoyant column members of a length and width having a selected displacement volume and joined to said horizontal buoyant members at their bottom ends and to said platform means at their upper ends and having water planes of selected area throughout their height; said horizontal and vertically disposed buoyant members being provided with a positive buoyancy exceeding the weight of the platform and its load to maintain tension in all of said tension leg means above a preselected tension force; the displacement ratio between the horizontal members and the total displacement of said horizontal buoyant members and vertical buoyant members being in the order of 0.30 and 0.60 whereby vertical force components imparted to said submerged horizontal and vertical buoyant members by wave action are virtually offset and cancelled to minimize cyclic stressing of said tension leg means.

Claim 17

In a marine structure of stable steady characteristics having a platform means adapted to be positioned over a plurality of anchor means on an ocean floor, the combination of: tension leg means substantially vertically disposed and connected to said platform means; means supporting said platform means above the ocean surface and including submersible elongated horizontal buoyant members joined together and of a length and width having a selected displacement volume and adapted to be submerged to a depth within the influence of wave action; vertically disposed buoyant column members of a length and width having a selected displacement volume and joined to said horizontal buoyant members at their bottom ends and to said platform means at their upper ends and having water planes of selected area throughout their height; said horizontal and vertically disposed buoyant members being provided with a positive buoyancy exceeding the weight of the platform and its load to maintain tension in all of said tension leg means above a preselected tension force; the displacement ratio between the horizontal members and the total displacement of said horizontal buoyant members and vertical buoyant members being in the order of 0.30 and 0.60 whereby vertical force components imparted to said submerged horizontal and vertical buoyant members by wave action are virtually offset and cancelled to minimize cyclic stressing of said tension leg means.

Claim 18

In a tension leg marine structure, the combination of: a platform means adapted to be positioned in spaced relation to a water surface; anchor means and tension mooring line means anchoring said platform means at a selected site, said tension mooring line means being connected at one end with said platform means; said submersible buoyant means disposed below and supporting said platform means; said submersible buoyant means being provided positive buoyancy exceeding the weight of the platform and its load to maintain tension in all of said mooring line means above a preselected tension force, said submersible buoyant means including interjoined elongated horizontal cylindrical buoyant members parallel to said platform means and upstanding cylindrical buoyant members interconnecting said horizontal buoyant members and said platform means, said upstanding buoyant members being spaced apart a selected distance along said horizontal members; said upstanding buoyant members having a water plane area at the water surface for maintaining a stability of said marine structure under towing, submergence, and moored conditions thereof; said horizontal members having effective horizontal surface component areas reactive to motion of water particles to develop vertical force components; the displacement of said horizontal buoyant members with respect to the total displacement of the marine structure being in the order of 0.30 to 0.60 for waves having periods ranging from about 8 to 20 seconds.

Claim 19

In a tension leg marine structure, the combination of: a platform means adapted to be positioned in spaced relation to a water surface; anchor means and tension mooring line means anchoring said platform means at a selected site, said tension mooring line means being connected at one end with said platform means; said submersible buoyant means disposed below and supporting said platform means; said submersible buoyant means being provided positive buoyancy exceeding the weight of the platform and its load to maintain tension in all of said mooring line means above a preselected tension force, said submersible buoyant means including interjoined elongated horizontal cylindrical buoyant members parallel to said platform means and upstanding cylindrical buoyant members interconnecting said horizontal buoyant members and said platform means, said upstanding buoyant members being spaced apart a selected distance along said horizontal members; said upstanding buoyant members having a water plane area at the water surface for maintaining a stability of said marine structure under towing, submergence, and moored conditions thereof; said horizontal members having effective horizontal surface component areas reactive to motion of water particles to develop vertical force components; the displacement of said horizontal buoyant members with respect to the total displacement of the marine structure being in the order of 0.30 to 0.60 for waves having periods ranging from about 8 to 20 seconds.

Claim 20

A tension leg marine apparatus comprising: a floatable structure including a platform adapted to be supported above a water surface in a horizontal planar zone; a submersible buoyant means supporting said platform and comprising a plurality of submersible elongated horizontal buoyant members, each horizontal buoyant member being joined with an adjacent horizontal buoyant member, said joined horizontal buoyant members providing a configuration in plan generally corresponding to the configuration of the platform; a plurality of upstanding buoyant members in spaced relation around the configuration of the horizontal buoyant members and joined at their lower ends to said horizontal buoyant members extending through the water surface, and connected at their upper ends to said platform; a plurality of anchor means in the ocean floor; a tensioned moorinG line for each anchor means, each line extending generally vertically between its anchor means and said floatable structure, all of said mooring lines being held in tension above a selected tension force imparted thereto by positive buoyancy of the submersible buoyant means, the positive buoyant forces exceeding total weight of the platform and loading thereof; the displacement of the horizontal buoyant members and horizontal portions thereof joining the lower ends of the upstanding buoyant members having a displacement ratio of 0.30 to 0.60 of the total displacement of the floatable structure whereby for wave periods of from about 8 to 20 vertical forces due to wave action are substantially neutralized by the variable buoyancy of said upstanding members and the acceleration of water particles acting on said horizontal and upstanding members.

Claim 21

A tension leg marine apparatus comprising: a floatable structure including a platform adapted to be supported above a water surface in a horizontal planar zone; a submersible buoyant means supporting said platform and comprising a plurality of submersible elongated horizontal buoyant members, each horizontal buoyant member being joined with an adjacent horizontal buoyant member, said joined horizontal buoyant members providing a configuration in plan generally corresponding to the configuration of the platform; a plurality of upstanding buoyant members in spaced relation around the configuration of the horizontal buoyant members and joined at their lower ends to said horizontal buoyant members extending through the water surface, and connected at their upper ends to said platform; a plurality of anchor means in the ocean floor; a tensioned moorinG line for each anchor means, each line extending generally vertically between its anchor means and said floatable structure, all of said mooring lines being held in tension above a selected tension force imparted thereto by positive buoyancy of the submersible buoyant means, the positive buoyant forces exceeding total weight of the platform and loading thereof; the displacement of the horizontal buoyant members and horizontal portions thereof joining the lower ends of the upstanding buoyant members having a displacement ratio of 0.30 to 0.60 of the total displacement of the floatable structure whereby for wave periods of from about 8 to 20 vertical forces due to wave action are substantially neutralized by the variable buoyancy of said upstanding members and the acceleration of water particles acting on said horizontal and upstanding members.