Modular island drilling system

A set of modular structural units of coordinated and cooperatively related configuration and arrangement assemblable in selected numbers and arrangements to define one of a series of possible mobile gravity structures for marine use in a selected range of water depths within a wider range of water depths pertinent to the series, the set comprising at least one of each of the following modular structural units:

• a. a deck unit of selected height, length and width fabricated of steel and arranged to define an upper deck of a mobile gravity structure,
• b. a first base unit of selected height, length and width and having vertical essentially flat outer walls extending between top and bottom surfaces, and
• c. a second base unit of selected height different from the height of the first base unit and having length and width essentially equal to that of the first base unit and vertical essentially flat outer walls extending between top and bottom surfaces,
• each modular structural unit being floatable and including ballast means operable for controllably ballasting and deballasting the unit between positively and substantial negatively buoyant states.

A set of modular structural units of coordinated and cooperatively related configuration and arrangement assemblable in selected numbers and arrangements to define one of a series of possible mobile gravity structures for marine use in a selected range of water depths within a wider range of water depths pertinent to the series, the set comprising at least the following modular groups of structural units:

• (a) two substantially similar deck units of selected height, length and width fabricated of steel and arranged to define an upper deck of a mobile gravity structure,
• (b) first and second similar base units of selected height, length and width and having vertical essentially flat outer walls extending between top and bottom surfaces, and
• (c) third and fourth similar base units of selected height, which may differ from the height of the first and second base units, and having length and width essentially equal to that of the first and second base units and vertical essentially flat outer walls extending between top and bottom surfaces,
• each modular structural unit being floatable and including ballast means operable for controllably ballasting and deballasting the unit between positively and substantial negatively buoyant states, and base units having lengths greater than their widths, and each deck unit having a bottom surface having length and width dimensions essentially equal respectively to the base unit lengths and widths, and connection means releasably cooperable between the first and second base units, between the third and fourth base units, and between the deck units for connecting such units in side-by-side relation.

An armor panel for use with an offshore structure supported on a sea floor and extending through the surface of water on which ice may float, the structure having a flat vertical outer wall to which the panel is mountable at a location on the offshore structure which extends from substantially below to above the water surface, the panel comprising a substantially uniformly thick constructed member of selected height and width for covering a substantial area of the outer wall of the offshore structure, the panel member having front and rear surfaces and a thickness therebetween adequate in combination with the construction of the panel member for distributing over said area of the offshore structure outer wall via the panel member a load applied laterally to the offshore structure as by an ice floe contacting the panel member, and mounting means carried by the panel operable for mounting the panel to the structure outer wall in cooperation with cooperating means carried by the structure, the panel mounting means including a first socket in the panel at a selected location in the height of the panel substantially centrally of the width thereof and open through the panel rear surface for receipt of a round panel support member adequate to support the entire weight of the panel member, a second socket in the panel in substantial spaced relation to the first socket and open through the panel rear surface for receipt of an elongate torque resisting member, and a plurality of passages through the panel from the front to the rear surfaces thereof for receipt of tension members operable for holding the panel against the structure outer wall.

A method for assembling and installing at a selected offshore site a surface-piercing, bottom-supported multi-tier offshore structure comprising the steps of

• a. providing each of the tiers of the structure as floatable constructions capable of being ballasted between positively and negatively buoyant states,
• b. at an assembly location in waters deeper than the sum of the light draft of a first and upper tier and the height of a second and lower tier, and shallower than the sum of said height and a deep draft floating state of the first tier construction,
• (1) ballasting the second tier construction to its negatively buoyant state to place it on the sea floor,
• (2) positioning the first tier in a floating state over the second tier construction in a selected orientation relative to the second tier construction,
• (3) ballasting the first tier construction toward its deep draft floating state thereby to move it into engagement with the second tier construction,
• (4) securing the engaged constructions from lateral relative movement,
• (5) and deballasting at least the second tier construction adequately to render the combination of the first and second tier constructions positively buoyant and free floating with the first tier loading the second tier,
• c. repeating in water of suitable depth the operations described in step b., as necessary, mutatis mutandis, with each additional tier construction proceeding downwardly through additional tier constructions and with each combination of engaged tier constructions above each additional tier construction, thereby to fully assemble all tier constructions of the offshore structure as a group,
• d. deballasting the group of fully assembled tier constructions to a draft less than the water depth at the selected site in such manner that each tier construction is loaded by the tier constructions thereabove,
• e. moving the group of assembled tier constructions to the selected site,
• f. ballasting the group of assembled tier constructions in such manner to maintain said loading and to sink into a condition of support by a sea floor at the site, and
• g. further ballasting the tier constructions to establish a desired effective mass of the group of tier constructions.

An arctic offshore structure of the gravity type movable buoyantly to and from a position over a site of use located on a sea floor under waters in a selected range of depths, the structure when installed at the site extending from a lower end substantially at the sea floor through and above the water surface to an upper operations end of the structure which is adapted to carry a selected operations facility, the structure through a portion thereof between (a) a first location adjacent its lower end and below the water surface and (b) a second location in the structure a substantial distance above the water surface being comprised of at least one base unit, each base unit being floatable, the structure being reversibly ballastable adequately to impart to the structure sufficient negative buoyancy, in combination with the nature of the sea floor, to maintain a desired position at the site under environmental forces applied horizontally to the structure, the structure in said portion being composed of at least a single tier of components of the structure, each tier being composed of a pair of base units of equal height, each base unit in each said tier having a sidewall arranged to face the sidewall of another base unit of the same tier in the structure, the facing sidewalls of the base units having registrable features operative upon registration for securing the base units from selected movements relative to each other.

An arctic offshore structure of the gravity type movable buoyantly to and from a position over a site of use located on a sea floor under waters in a selected range of depths, the structure when installed at the site extending from a lower end substantially at the sea floor through and above the water surface to an upper operations end of the structure which is adapted to carry a selected operations facility, the structure through a portion thereof between (a) a first location adjacent its lower end and below the water surface and (b) a second location in the structure a substantial distance above the water surface being comprised of at least one unitary base unit, each base unit being floatable and being reversibly ballastable adequately to impart to the structure sufficient negative buoyancy, in combination with the nature of the sea floor, to maintain a desired position at the site under environmental forces applied horizontally to the structure, an environmental armor belt of selected height carried by the structure about its circumference in said portion of the structure, the armor belt extending vertically on the structure from above the water surface to below the water surface, the armor belt being comprised of a plurality of discrete armor panels each of the selected height, panel connection means releasably connectible between each panel and the adjacent base unit for securely connecting the panel to the base unit, the connection means including, for each panel, first connection means for carrying shear loads between the panel and the adjacent base unit, second connection means operative for carrying torque loads between the panel and the base unit, and third connection means for carying loads urging the panel away from the base unit.